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Repair and maintenance of Computer Monitors / CRTs, 200 Page Manual

Sunday, 13 August 2006

I used this manual when
I owned my computer/laptop
repair business

It is a very comprehensive
piece of work taht goes into
great detail on the
repair and upkeep of monitors

\n This email address is being protected from spam bots, you need Javascript enabled to view it at URL: --> \n This email address is being protected from spam bots, you need Javascript enabled to view it "> http-equiv=Reply-to content=" This email address is being protected from spam bots, you need Javascript enabled to view it (Filip Gieszczykiewicz)" content="Filip M. Gieszczykiewicz" name=author --> [Mirrors]

Notes on the Troubleshooting and Repair of Computer and Video Monitors

Contents:

[Document Version: 2.73] [Last Updated: 05/25/1998]

Chapter 1) About the Author & Copyright

Notes on the Troubleshooting and Repair of Computer and Video Monitors

Author: Samuel M. Goldwasser
Corrections/suggestions: | Email

Reproduction of this document in whole or in part is permitted if both of the following conditions are satisfied:

This notice is included in its entirety at the beginning.
There is no charge except to cover the costs of copying.

Chapter 2) Introduction

2.1) Monitors, monitors, and more monitors

	In the early days of small computers, a 110 baud teletype with a personal

	paper tape reader was the 'preferred' input-output device (meaning that

	this was a great improvement over punched cards and having to deal with

	the bozos in the computer room.  Small here, also meant something that

	would comfortably fit into a couple of 6 foot electronics racks!)

	

	The earliest personal computers didn't come with a display - you connected

	them to the family TV.  You and your kids shared the single TV and the

	Flintstones often won out.  The Commodore 64 would never have been as

	successful as it was if an expensive monitor were required rather than

	an option.

	

	However, as computer performance improved, it quickly became clear that

	a dedicated display was essential.  Even for simple text, a TV can only

	display 40 characters across the screen with any degree of clarity.

	

	When the IBM PC was introduced, it came with a nice 80x25 green monochrome

	text display.  It was bright, crisp, and stable.  Mono graphics (MGA or MDA)

	was added at 720x350, CGA at a range of resolutions from 160x200 to 640x200 

	at 2 to 16 colors, and EGA extended this up to a spectacular resolution of

	640x350.  This was really fine until the introduction of Windows (well, at

	least once Windows stayed up long enough for you to care).

	

	All of these displays used digital video - TTL signals which coded for a

	specific discrete number of possible colors and intensities.  Both the video

	adapter and the monitor were limited to 2, 4, or 16 colors depending on the

	graphics standard.  The video signals were logic bits - 0s and 1s.

	

	With the introduction of the VGA standard, personal computer graphics

	became 'real'.  VGA and its successors - PGA, XGA, and all of the SVGA

	(non) standards use analog video - each of the R, G, and B signals is

	a continuous voltage which can represent a continuous range of intensities

	for each color.  In principle, an analog monitor is capable of an unlimited

	number of possible colors and intensities.  (In practice, unavoidable noise

	and limitations of the CRT restricts the actual number to order of 64-256

	distinguishable intensities for each channel.)

	 

	Note that analog video was only new to the PC world.  TVs and other video

	equipment, workstations, and image analysis systems had utilized analog

	signals for many years prior to the PC's 'discovery' of this approach.  In

	all fairness, both the display adapter and monitor are more expensive so

	it is not surprising that early PCs did not use analog video.

	

	Most of the information in the document applies to color computer video

	monitors and TV studio monitors as well as the display portions of television

	sets.  Black and white, gray scale, and monochrome monitors use a subset

	of the circuitry (and generally at lower power levels) in color monitors so

	much of it applies to these as well.

	

	For most descriptions of symptoms, testing, diagnosis, and repair, an

	auto-scan PC SVGA monitor is assumed.  For a fixed frequency workstation

	monitor, studio video monitor, or closed circuit TV monitor, only a subset

	of the possible faults and procedures will apply.

	

	Note: we use the term 'auto-scan' to describe a monitor which accepts a wide

	(and possibly continuous) range of scan rates.  Usually, this refers mostly

	to the horizontal frequency as the vertical refresh rate is quite flexible on

	many monitors of all types.  Fixed scan or fixed frequency monitors are

	designed to work with a single scan rate (though a 5% or so variation may

	actually be accepted).  Multi-scan monitors sync at two or more distinct

	scan rates.  While not very common anymore, multi-scan monitors may still

	be found in some specific applications.

2.2) Related Information

	See the manuals on "Troubleshooting and Repair of Small Switchmode Power

	Supplies" and "Troubleshooting and Repair of Television Sets" for additional

	useful pointers.  Since a monitor must perform a subset of the functions

	of a TV, many of the problems and solutions are similar.  For power related

	problems the info on SMPSs may be useful as well.  If you are considering

	purchasing a monitor or have one that you would like to evaluate, see

	the companion document: "Performance Testing of Computer and Video Monitors".

2.3) Monitor fundamentals

	Note: throughout this document, we use the term 'raster' to refer to the

	entire extent of the scanned portion of the screen and the terms 'picture',

	'image'. or 'display', to refer to the actual presentation content.

	

	Monitors designed for PCs, workstations, and studio video have many

	characteristics in common.  Modern computer monitors share many

	similarities with TVs but the auto-scan and high scan rate deflection

	circuitry and more sophisticated power supplies complicates their servicing.

	

	Currently, most computer monitors are still based on the Cathode

	Ray Tube (CRT) as the display device.  However, handheld equipment,

	laptop computers, and the screens inside video projectors now use flat

	panel technology, mostly Liquid Crystal Displays - LCDs.  These are

	a lot less bulky than CRTs, use less power, and have better geometry - but

	suffer from certain flaws.

	

	First, the picture quality in terms of gray scale and color is generally

	inferior to a decent analog monitor.  The number of distinct shades of

	gray or distinct colors is a lot more limited.  They are generally not as

	responsive as CRTs when it comes to real-time video which is becoming

	increasingly important with multimedia computers.  Brightness is generally

	not as good as a decent CRT display.  And last but not least, the cost

	is still much much higher due both to the increased complexity of flat

	panel technology and lower production volumes (though this is certainly

	increasing dramatically).  It is really hard to beat the simplicity of the

	shadow mask CRT.  For example, a decent quality active matrix color LCD

	panel may add $1000 to the cost of a notebook computer compared to $200

	for a VGA monitor.  More of these panels go into the dumpster than make it

	to product due to manufacturing imperfections.

	

	However, a variety of technologies are currently competing for use in

	the flat panel displays of the future.  Among these are advanced LCD,

	plasma discharge, and field emission displays.  Only time will tell which, if

	any survives to become **the** picture-on-the-wall or notepad display - at

	reasonable cost.

	

	Projection - large screen - TVs and monitors, on the other hand, may be able

	to take advantage of a novel development in integrated micromachining - the

	Texas Instruments Inc. Digital Micromirror Device (DMD).  This is basically

	an integrated circuit with a tiltable micromirror for each pixel fabricated

	on top of a static memory - RAM - cell.  This technology would

	permit nearly any size projection display to be produced and would

	therefore be applicable to high resolution computer monitors as well as HDTV.

	Since it is a reflective device, the light source can be as bright as needed.

	This is still not a commercial product but stay on line.

2.4) Monitor characteristics

	The following describe the capabilities which characterize a display:

	

	1. Resolution - the number of resolvable pixels on each line and the

	   number of scanning lines.  Bandwidth of the video source, cable, and

	   monitor video amplifiers as well as CRT focus spot size are all critical.

	   However, maximum resolution on a color CRT is limited by the dot/slot/line

	   pitch of the CRT shadow/slot mask or aperture grille.  

	

	2. Refresh rate - the number of complete images 'painted' on the screen

	   each second.  Non-interlaced or progressive scanning posts the entire

	   frame during each sweep from top to bottom.  Interlaced scanning posts

	   1/2 of the frame called a field - first the even field and then the

	   odd field.  This interleaving reduces the apparent flicker for a given

	   display bandwidth when displaying smooth imagery such as for TV.  It is

	   usually not acceptable for computer graphics, however, as thin horizontal

	   lines tend to flicker at 1/2 the vertical scan rate.  Refresh rate is the

	   predominant factor that affects the flicker of the display though the

	   persistence of the CRT phosphors are also a consideration.  Long persistence

	   phosphors decrease flicker at the expense of smearing when the picture

	   changes or moves.  Vertical scan rate is equal to the refresh rate for

	   non-interlaced monitors but is the twice the refresh rate for interlaced

	   monitors (1 frame equals 2 fields).  Non-interlaced vertical refresh rates

	   of 70-75 Hz are considered desirable for computer displays.  Television

	   uses 25 or 30 Hz (frame rate) interlaced scanning in most countries.

	

	3. Horizontal scan rate - the frequency at which the electron beam(s) move

	   across the screen.  The horizontal scan rate is often the limiting factor

	   in supporting high refresh rate high resolution displays.  It is what may

	   cause failure if scan rate speed limits are exceeded due to the component

	   stress levels in high performance deflection systems.

	

	4. Color or monochrome - a color monitor has a CRT with three electron

	   guns each associated with a primary color - red, green, or blue.

	   Nearly all visible colors can be created from a mix of primaries

	   with suitable spectral characteristics using this additive color

	   system.

	

	   A monochrome monitor has a CRT with a single electron gun.  However,

	   the actual color of the display may be white, amber, green, or whatever

	   single color is desired as determined by the phosphor of the CRT selected.

	

	5. Digital or analog signal - a digital input can only assume a discrete

	   number of states depending on how many bits are provided.  A single bit

	   input can only produce two levels - usually black or white (or amber,

	   green, etc.).  Four bit EGA can display up to 16 colors (with a color

	   monitor) or 16 shades of gray (with a monochrome monitor).

	

	   Analog inputs allow for a theoretically unlimited number of possible gray

	   levels or colors.  However, the actual storage and digital-to-analog

	   convertors in any display adapter or frame store and/or unavoidable

	   noise and other characteristics of the CRT - and ultimately, limitations

	   in the psychovisual eye-brain system will limit this to a practical

	   maximum of 64-256 discernible levels for a gray scale display or for

	   each color channel.

	

	   However, very high performance digital video sources may have RAMDACs (D/A

	   convertors with video lookup tables) of up to 10 or more bits of intensity

	   resolution.  While it is not possible to perceive this many distinct gray

	   levels or colors (per color channel), this does permit more accurate tone

	   scale ('gamma') correction to be applied (via a lookup table in the RAMDAC)

	   to compensate for the unavoidable non-linearity of the CRT phosphor

	   response curve or to match specific photometric requirements.

2.5) Types of monitors

	Monitors can be classified into three general categories:

	

	1. Studio video monitors - Fixed scanning rate for the TV standards

	   in the country in which they are used.  High quality, often high

	   cost, utilitarian case (read: ugly), underscan option.  Small

	   closed circuit TV monitors fall into the class.  Input is usually

	   composite (i.e., NTSC or PAL) although RGB types are available.

	

	2. Fixed frequency RGB - High resolution, fixed scan rate.  High quality,

	   high cost, very stable display.  Inputs are analog RGB using either

	   separate BNC connectors or a 13W3 (Sun) connector.  These often have

	   multiple sync options.  The BNC variety permit multiple monitors to

	   be driven off of the same source by daisychaining.  Generally used

	   underscanned for computer workstation (e.g., X-windows) applications

	   so that entire frame buffer is visible.  There are also fixed frequency

	   monochrome monitors which may be digital or analog input using a BNC,

	   13W3, or special connector.

	

	3. Multi-scan or auto-scan - Support multiple resolutions and scan rates

	   or multiple ranges of resolutions and scan rates.  The quality and

	   cost of these monitors ranges all over the map.  While cost is not

	   a strict measure of picture quality and reliability, there is a

	   strong correlation.  Input is most often analog RGB but some older

	   monitors of this type (e.g., Mitsubishi AUM1381) support a variety

	   of digital (TTL) modes as well.  A full complement of user controls

	   permits adjustment of brightness, contrast, position, size, etc. to

	   taste.  Circuitry in the monitor identifies the video scan rate

	   automatically and sets up the appropriate circuitry.  With more

	   sophisticated (and expensive) designs, the monitor automatically

	   sets the appropriate parameters for user preferences from memory as well.

	   The DB15 high density VGA connector is most common though BNCs may be

	   used or may be present as an auxiliary (and better quality) input.

2.6) Why auto-scan?

	Thank IBM.  Since the PC has evolved over a period of 15 years, display

	adapters have changed and improved a number of times.  With an open system,

	vendors with more vision (and willing to take more risks) than IBM were

	continuously coming up with improved higher resolution display adapters.

	With workstations and the Apple MacIntosh, the primary vendor can control

	most aspects of the hardware and software of the computer system.  Not so

	with PCs.  New improved hardware adapters were being introduced regularly

	which were not following any standards for the high resolution modes (but

	attempted to be backward compatible with the original VGA as well as EGA

	and CGA (at least in terms of software)).  Vast numbers of programs were

	written that were designed to directly control the CGA, EGA, and VGA

	hardware.  Adapter cards could be designed to emulate these older

	modes on a fixed frequency high resolution monitor (and these exist to

	permit high quality fixed scan rate workstation monitors to be used on PCs)

	However, these would be (and are) much more expensive than basic display

	adapters that simply switch scan rates based on mode.  Thus, auto-scan

	monitors evolved to accommodate the multiple resolutions that different

	programs required.

	

	Note: we will use the generic term 'auto-scan' to refer to a monitor which

	automatically senses the input video scan rate and selects the appropriate

	horizontal and vertical deflection circuitry and power supply voltages to

	display this video.  Multi-scan monitors, while simpler than true auto-scan

	monitors, will still have much of the same scan rate detection and selection

	circuitry.  Manufacturers use various buzz words to describe their versions

	of these monitors including 'multisync', 'autosync','panasync', 'omnisync',

	as well as 'autoscan' and 'multiscan'.

	

	Ultimately, the fixed scan rate monitor may reappear for PCs.  Consider

	one simple fact: it is becoming cheaper to design and manufacture complex

	digital processing hardware than to produce the reliable high quality

	analog and power electronics needed for an auto-scan monitor.  This is

	being done in the specialty market now.  Eventually, the development

	of accelerated chipsets for graphics mode emulation may be forced by

	the increasing popularity of flat panel displays - which are basically

	similar to fixed scan rate monitors in terms of their interfacing

	requirements.

2.7) Analog vs. digital monitors

	There are two aspects of monitor design that can be described in terms

	of analog or digital characteristics:

	

	1. The video inputs.  Early PC monitors, video display terminal

	   monitors, and mono workstation monitors use digital input signals

	   which are usually TTL but some very high resolution monitors may

	   use ECL instead.

	

	2. The monitor control and user interface.  Originally, monitors all

	   used knobs - sometimes quite a number of them - to control all

	   functions like brightness, contrast, position, size, linearity,

	   pincushion, convergence, etc.  However, as the costs of digital

	   circuitry came down - and the need to remember settings for multiple

	   scan rates and resolutions arose, digital - microprocessor

	   control - became an attractive alternative in terms of design,

	   manufacturing costs, and user convenience.  Now, most better quality

	   monitors use digital controls - buttons and menus - for almost all

	   adjustments except possibly brightness and contrast where knobs are

	   still more convenient.

	

	Since monitors with digital signal inputs are almost extinct today except for

	specialized applications, it is usually safe to assume that 'digital' monitor

	refers to the user interface and microprocessor control.

2.8) Interlacing

	Whether a monitor runs interlaced or non-interlaced is almost always

	strictly a function of the video source timing.  The vertical sync

	pulse is offset an amount equal to 1/2 the line time on alternate fields

	(vertical scans - two fields make up a frame when interlaced scanning is

	used).

	

	Generally, a monitor that runs at a given resolution non-interlaced can run

	at a resolution with roughly twice the number of pixels interlaced at the

	same horizontal scan rate.  For example, a monitor that will run 1024x768

	non-interlaced at 70 Hz will run 1280x1024 interlaced at a 40 Hz frame rate.

	Whether the image is usable at the higher resolution of course also depends

	on many other factors including the dot pitch of the CRT and video bandwidth

	of the video card and monitor video amplifiers, as well as cable quality

	and termination.  The flicker of fine horizontal lines may also be

	objectionable.

2.9) Monitor performance

The ultimate perceived quality of your display is influenced by many aspects

of the total video source/computer-cable-monitor system. Among them are:

1. Resolution of the video source. For a computer display, this is determined

by the number of pixels on each visible scan line and the number of visible

scan lines on the entire picture.

2. The pitch of the shadow mask or aperture grille of the CRT. The smallest

color element on the face of the CRT is determined by the spacing of the

groups of R, G, and B colors phosphors. The actual conversion from

dot or line pitch to resolution differs slightly among dot or slot mask

and aperture grille CRTs but in general, the finer, the better - and

more expensive.

Typical television CRTs are rather coarse - .75 mm might be a reasonable

specification for a 20 inch set. High resolution computer monitors

may have dot pitches as small as .22 mm for a similar size screen.

A rough indication of the maximum possible resolution of the CRT can be

found by determining how many complete phosphor dot groups can fit across

the visible part of the screen.

Running at too high a resolution for a given CRT may result in Moire - an

interference pattern that will manifest itself as contour lines in smooth

bright areas of the picture. However, many factors influence to what

extent this may be a problem. See the section: "Contour lines on high resolution monitors - Moire".

3. Bandwidth of the video source or display card - use of high performance

video amplifiers or digital to analog convertors.

4. Signal quality of the video source or display card - properly designed

circuitry with adequate power supply filtering and high quality components.

5. High quality cables with correct termination and of minimal acceptable

length without extensions or switch boxes unless designed specifically

for high bandwidth video.

6. Sharpness of focus - even if the CRT dot pitch is very fine, a fuzzy

scanning beam will result in a poor quality picture.

7. Stability of the monitor electronics - well regulated power supplies

and low noise shielded electronics contribute to a rock solid image.

2.10) Performance testing of monitors

	WARNING: No monitor is perfect.  Running comprehensive tests on your

	monitor or one you are considering may make you aware of deficiencies you

	never realized were even possible.  You may never be happy with any monitor

	for the rest of your life!

	

	Note: the intent of these tests is **not** to evaluate or calibrate a monitor

	for photometric accuracy.  Rather they are for functional testing of the

	monitor's performance.

	

	Obviously, the ideal situation is to be able to perform these sorts of

	tests before purchase.  With a small customer oriented store, this may

	be possible.  However, the best that can be done when ordering by mail

	is to examine a similar model in a store for gross characteristics and

	then do a thorough test when your monitor arrives.  The following should

	be evaluated:

	

	        * Screen size and general appearance.

	        * Brightness and screen uniformity, purity and color saturation.

	        * Stability.

	        * Convergence.

	        * Edge geometry.

	        * Linearity.

	        * Tilt.

	        * Size and position control range.

	        * Ghosting or trailing streaks.

	        * Sharpness.

	        * Moire.

	        * Scan rate switching.

	        * Acoustic noise.

	

	The companion document: "Performance Testing of Computer and Video Monitors"

	provides detailed procedures for the evaluation of each of these criteria.

	

	CAUTION: since there is no risk free way of evaluating the actual scan

	rate limits of a monitor, this is not an objective of these tests.  It

	is assumed that the specifications of both the video source/card and the

	monitor are known and that supported scan rates are not exceeded.  Some

	monitors will operate perfectly happily at well beyond the specified range

	or will shut down without damage.  Others will simply blow up instantly and

	require expensive repairs.

2.11) Monitor repair

	Unlike PC system boards where any disasters are likely to only affect

	your pocketbook, monitors can be very dangerous.  Read, understand, and

	follow the set of safety guidelines provided later in this document

	whenever working on TVs, monitors, or other similar high voltage equipment.

	

	If you do go inside, beware: line voltage (on large caps) and high voltage

	(on CRT) for long after the plug is pulled.  There is the added danger of

	CRT implosion for carelessly dropped tools and often sharp sheetmetal

	shields which can injure if you should have a reflex reaction upon touching

	something you should not touch.  In inside of a TV or monitor is no place

	for the careless or naive.

	

	Having said that, a basic knowledge of how a monitor works and what can

	go wrong can be of great value even if you do not attempt the repair yourself. 

	It will enable you to intelligently deal with the service technician.  You

	will be more likely to be able to recognize if you are being taken for a ride

	by a dishonest or just plain incompetent repair center.  For example, a

	faulty picture tube CANNOT be the cause of a color monitor only displaying

	in black-and-white (this is probably a software or compatibility problem).

	The majority of consumers - and computer professionals - may not know even

	this simple fact.

	

	This document will provide you with the knowledge to deal with a large

	percentage of the problems you are likely to encounter with your monitors.

	It will enable you to diagnose problems and in many cases, correct them

	as well.  With minor exceptions, specific manufacturers and models

	will not be covered as there are so many variations that such a treatment would

	require a huge and very detailed text.  Rather, the most common problems

	will be addressed and enough basic principles of operation will be provided

	to enable you to narrow the problem down and likely determine a course of

	action for repair.  In many cases, you will be able to do what is required

	for a fraction of the cost that would be charged by a repair center.

	

	Should you still not be able to find a solution, you will have learned a great

	deal and be able to ask appropriate questions and supply relevant information

	if you decide to post to sci.electronics.repair.  It will also be easier to do

	further research using a repair text such as the ones listed at the end of

	this document.  In any case, you will have the satisfaction of knowing you

	did as much as you could before taking it in for professional repair.

	With your new-found knowledge, you will have the upper hand and will not

	easily be snowed by a dishonest or incompetent technician.

2.12) Most Common Problems

	The following probably account for 95% or more of the common monitor ailments:

	

	* Intermittent changes in color, brightness, size, or position - bad

	  connections inside the monitor or at the cable connection to the computer

	  or or video source.

	

	* Ghosts, shadows, or streaks adjacent to vertical edges in the picture -

	  problems with input signal termination including use of cable extensions,

	  excessively long cables, cheap or improperly made video cables, improper

	  daisychaining of monitors, or problems in the video source or monitor

	  circuitry.

	

	* Magnetization of CRT causing color blotches or other color or distortion

	  problems - locate and eliminate sources of magnetic fields if relevant

	  and degauss the CRT.

	

	* Electromagnetic Interference (EMI) - nearby equipment (including and

	  especially other monitors), power lines, or electrical wiring behind walls,

	  may produce electromagnetic fields strong enough to cause noticeable

	  wiggling, rippling, or other effects.  Relocate the monitor or offending

	  equipment.  Shielding is difficult and expensive.

	

	* Wiring transmitted interference - noisy AC power possibly due to other

	  equipment using electric motors (e.g., vacuum cleaners), lamp dimmers or

	  motor speed controls (shop tools), fluorescent lamps, and other high power

	  devices, may result in a variety of effects.  The source is likely local - in

	  your house - but could be several miles away.  Symptoms might include bars of

	  noise moving up or down the screen or diagonally.  The effects may be barely

	  visible as a couple of jiggling scan lines or be broad bars of salt and

	  pepper noise, snow, or distorted video.  Plugging the monitor into another

	  outlet or the use of a line filter may help.  If possible, replace or repair

	  the offending device.

	

	* Monitor not locking on one or more video scan ranges - settings of

	  video adapter are incorrect.  Use software setup program to set these.

	  This could also be a fault in the video source or monitor dealing with

	  the sync signals.

	

	* Adjustments needed for background brightness or focus - aging CRT reduces

	  brightness.  Other components may affect focus.  Easy internal (or sometimes

	  external) adjustments.

	

	* Dead monitor due to power supply problems - very often the causes are

	  simple such as bad connections, blown fuse or other component.

2.13) Repair or replace

	If you need to send or take the monitor to a service center, the repair

	could easily exceed half the cost of a new monitor.  Service centers

	may charge up to $50 or more for providing an initial estimate of repair

	costs but this will usually be credited toward the total cost of the repair

	(of course, they may just jack this up to compensate for their bench time).

	

	Some places offer attractive flat rates for repairs involving anything but

	the CRT, yoke, and flyback.  Such offers are attractive if the repair center

	is reputable.  However, if by mail, you will be stuck with a tough decision

	if they find that one of these expensive components is actually bad.

	

	Monitors become obsolete at a somewhat slower rate than most other electronic

	equipment.  Therefore, unless you need the higher resolution and scan rates

	that newer monitors provide, repairing an older one may make sense as long as

	the CRT is in good condition (adequate brightness, no burn marks, good focus).

	However, it may just be a good excuse to upgrade.

	

	If you can do the repairs yourself, the equation changes dramatically as

	your parts costs will be 1/2 to 1/4 of what a professional will charge

	and of course your time is free.  The educational aspects may also be

	appealing.  You will learn a lot in the process.  Thus, it may make sense

	to repair that old clunker for your 2nd PC (or your 3rd or your 4th or....).

Chapter 3) Monitors 101

3.1) Subsystems of a monitor

	A computer or video monitor includes the following functional blocks:

	

	1.  Low voltage power supply (some may also be part of (2)).  Most of the lower

	    voltages used in the TV may be derived from the horizontal deflection

	    circuits, a separate switching power supply, or a combination of the two. 

	    Rectifier/filter capacitor/regulator from AC line provides the B+ to the

	    switching power supply or horizontal deflection system.  Auto-scan

	    monitors may have multiple outputs from the low voltage power supply

	    which are selectively switched or enabled depending on the scan rate.

	

	    Degauss operates off of the line whenever power is turned on (after

	    having been off for a few minutes) to demagnetize the CRT.  Better

	    monitors will have a degauss button which activates this circuitry

	    as well since even rotating the monitor on its tilt-swivel base can

	    require degauss.

	

	2.  Horizontal deflection.  These circuits provide the waveforms needed to

	    sweep the electron beam in the CRT across and back at anywhere from

	    15 KHz to over 100 KHz depending on scan rate and resolution.  The

	    horizontal sync pulse from the sync separator or the horizontal sync

	    input locks the horizontal deflection to the video signal.  Auto-scan

	    monitors have sophisticated circuitry to permit scanning range of

	    horizontal deflection to be automatically varied over a wide range.

	

	3.  Vertical deflection.  These circuits provide the waveforms needed to

	    sweep the electron beam in the CRT from top to bottom and back at

	    anywhere from 50 - 120 or more times per second.  The vertical sync

	    pulse from the sync separator or vertical sync input locks the vertical

	    deflection to the video signal.  Auto-scan monitors have additional

	    circuitry to lock to a wide range of vertical scan rates.

	

	4.  CRT high voltage (also part of (2)).  A modern color CRT requires

	    up to 30 KV for a crisp bright picture.  Rather than having a totally

	    separate power supply, most monitors derive the high voltage (as well

	    as many other voltages) from the horizontal deflection using a special

	    transformer called a 'flyback' or 'Line OutPut Transformer (LOPT) for

	    those of you on the other side of the lake.  Some high performance

	    monitors use a separate high voltage board or module which is a self

	    contained high frequency inverter.

	

	5.  Video amplifiers.  These buffer the low level inputs from the computer

	    or video source.  On monitors with TTL inputs (MGA, CGA, EGA), a resistor

	    network also combines the intensity and color signals in a kind of poor

	    man's D/A.  Analog video amplifiers will usually also include DC restore

	    (black level retention, back porch clamping) circuitry stabilize the

	    black level on AC coupled video systems.

	

	6.  Video drivers (RGB).  These are almost always located on a little

	    circuit board plugged directly onto the neck of the CRT.  They boost

	    the output of the video amplifiers to the hundred volts or so needed

	    to drive the cathodes (usually) of the CRT.

	

	7.  Sync separator.  Where input is composite rather than separate H and

	    V syncs, this circuit extracts the individual sync signals.  Output is

	    horizontal and vertical sync pulses to control the deflection circuits.

	    This is not needed on a monitor that only uses separate sync inputs.

	

	8.  System control.  Most higher quality monitors use a microcontroller

	    to perform all user interface and control functions from the front panel

	    (and sometimes even from a remote control).  So called 'digital monitors'

	    meaning digital controls not digital inputs, use buttons for everything

	    except possibly user brightness and contrast.  Settings for horizontal

	    and vertical size and position, pincushion, and color balance for each

	    scan rate may be stored in non-volatile memory.  The microprocessor

	    also analyzes the input video timing and selects the appropriate scan

	    range and components for the detected resolution.  While these circuits

	    rarely fail, if they do, debugging can be quite a treat.

	

	Most problems occur in the horizontal deflection and power supply sections.

	These run at relatively high power levels and some components run hot.

	This results in both wear and tear on the components as well as increased

	likelihood of bad connections developing from repeated thermal cycles.

	The high voltage section is prone to breakdown and arcing as a result

	of hairline cracks, humidity, dirt, etc.

	

	The video circuitry is generally quite reliable.  However, it seems that

	even after 15+ years, manufacturers still cannot reliably turn out circuit

	boards that are free of bad solder connections or that do not develop them

	with time and use.

3.2) For more information on monitor technology

	The books listed in the section: "Suggested references" include additional

	information on the theory and implementation of the technology of monitors

	and TV sets.

3.3) On-line tech-tips databases

	A number of organizations have compiled databases covering thousands of common

	problems with VCRs, TVs, computer monitors, and other electronics equipment.

	Most charge for their information but a few, accessible via the Internet, are

	either free or have a very minimal monthly or per-case fee.  In other cases, a

	limited but still useful subset of the for-fee database is freely available.

	

	A tech-tips database is a collection of problems and solutions accumulated by

	the organization providing the information or other sources based on actual

	repair experiences and case histories.  Since the identical failures often

	occur at some point in a large percentage of a given model or product line,

	checking out a tech-tips database may quickly identify your problem and

	solution.

	

	In that case, you can greatly simplify your troubleshooting or at least

	confirm a diagnosis before ordering parts.  My only reservation with respect

	to tech-tips databases in general - this has nothing to do with any one in

	particular - is that symptoms can sometimes be deceiving and a solution that

	works in one instance may not apply to your specific problem.  Therefore,

	an understanding of the hows and whys of the equipment along with some good

	old fashioned testing is highly desirable to minimize the risk of replacing

	parts that turn out not to be bad.

	

	The other disadvantage - at least from one point of view - is that you do not

	learn much by just following a procedure developed by others.  There is no

	explanation of how the original diagnosis was determined or what may have

	caused the failure in the first place.  Nor is there likely to be any list

	of other components that may have been affected by overstress and may fail

	in the future.  Replacing Q701 and C725 may get your equipment going again

	but this will not help you to repair a different model in the future.

	

	Having said that, here are three tech-tips sites for computer monitors, TVs,

	and VCRs:

	

	* http://www.anatekcorp.com/techforum.htm            (Free).

	* http://www.repairworld.com/                        ($8/month).

	* http://elmswood.guernsey.net/                      (Free, somewhat limited).

	

	The following is just for monitors.  Some portions are free but others require

	a $5 charge.  However, this may include a personal reply from a technician

	experienced with your monitor so it could be well worth it.

	

	* http://www.netis.com/members/bcollins/monitor.htm

	

	Some free monitor repair tips:

	

	* http://www.kmrtech.com/

	

	Tech-tips of the month and 'ask a wizard' options:

	

	* http://members.tripod.com/~ADCC/          (Home page)

	* http://members.tripod.com/~ADCC/tips.htm  (Tech-tips of the month)

	

	The Resolve Monitor Tech-Tips database is a diskette that is priced out of

	the reach of most hobbyists.  However, a reduced shareware version may be

	downloaded from a number of web sites.  Go to http://www.filez.com/ and look

	for res16sw.zip.

Chapter 4) CRT Basics

	Note: Most of the information on TV and monitor CRT construction, operation,

	interference and other problems. has been moved to the document: "TV and Monitor CRT (Picture Tube) Information".  The following is just a brief

	introduction with instructions on degaussing.

4.1) Color CRTs - shadow masks and aperture grills

	All color CRTs utilize a shadow mask or aperture grill a fraction of an inch

	(1/2" typical) behind the phosphor screen to direct the electron beams 

	for the red, green, and blue video signals to the proper phosphor dots.

	Since the electron beams for the R, G, and B phosphors originate from

	slightly different positions (individual electron guns for each)

	and thus arrive at slightly different angles, only the proper phosphors

	are excited when the purity is properly adjusted and the necessary

	magnetic field free region is maintained inside the CRT.  Note that

	purity determines that the correct video signal excites the

	proper color while convergence determines the geometric

	alignment of the 3 colors.  Both are affected by magnetic fields.

	Bad purity results in mottled or incorrect colors.  Bad convergence

	results in color fringing at edges of characters or graphics.

	

	The shadow mask consists of a thin steel or InVar (a ferrous alloy)

	with a fine array of holes - one for each trio of phosphor

	dots - positioned about 1/2 inch behind the surface of the phosphor

	screen.  With some CRTs, the phosphors are arranged in triangular

	formations called triads with each of the color dots at the apex

	of the triangle.  With many TVs and some monitors, they are

	arranged as vertical slots with the phosphors for the 3 colors

	next to one another.

	

	An aperture grille, used exclusively in Sony Trinitrons (and now

	their clones as well), replaces the shadow mask with an array of finely

	tensioned vertical wires.  Along with other characteristics of the

	aperture grille approach, this permits a somewhat higher possible

	brightness to be achieved and is more immune to other problems like

	line induced moire and purity changes due to local heating causing

	distortion of the shadow mask.

	

	However, there are some disadvantages of the aperture grille design:

	

	* weight - a heavy support structure must be provided for the tensioned

	  wires (like a piano frame).

	

	* price (proportional to weight).

	

	* always a cylindrical screen (this may be considered an advantage

	  depending on your preference.

	

	* visible stabilizing wires which may be objectionable or unacceptable

	  for certain applications.

	

	Apparently, there is no known way around the need to keep the fine

	wires from vibrating or changing position due to mechanical shock

	in high resolution tubes and thus all Trinitron monitors require

	1, 2, or 3 stabilizing wires (depending on tube size) across the 

	screen which can be see as very fine lines on bright images.  Some

	people find these wires to be objectionable and for some critical

	applications, they may be unacceptable (e.g., medical diagnosis).

4.2) Degaussing (demagnetizing) a CRT

	Degaussing may be required if there are color purity problems with the

	display.  On rare occasions, there may be geometric distortion caused

	by magnetic fields as well without color problems.  The CRT can get

	magnetized:

	

	* if the TV or monitor is moved or even just rotated.

	

	* if there has been a lightning strike nearby.  A friend of mine

	  had a lightning strike near his house which produced all of the

	  effects of the EMP from a nuclear bomb.

	

	* If a permanent magnet was brought near the screen (e.g., kid's

	  magnet or megawatt stereo speakers).

	

	* If some piece of electrical or electronic equipment with unshielded

	  magnetic fields is in the vicinity of the TV or monitor.  

	

	Degaussing should be the first thing attempted whenever color

	purity problems are detected.  As noted below, first try the

	internal degauss circuits of the TV or monitor by power cycling a few

	times (on for a minute, off for 30 minutes, on for a minute, etc.)

	If this does not help or does not completely cure the problem,

	then you can try manually degaussing.

	

	Commercial CRT Degaussers are available from parts distributors

	like MCM Electronics and consist of a hundred or so turns of magnet wire

	in a 6-12 inch coil.  They include a line cord and momentary switch. You 

	flip on the switch, and bring the coil to within several inches of the 

	screen face. Then you slowly draw the center of the coil toward one edge 

	of the screen and trace the perimeter of the screen face. Then return to 

	the original position of the coil being flat against the center of the 

	screen.  Next, slowly decrease the field to zero by backing straight up 

	across the room as you hold the coil. When you are farther than 5 feet 

	away you can release the line switch. 

	

	The key word here is ** slow **.  Go too fast and you will freeze the

	instantaneous intensity of the 50/60 Hz AC magnetic field variation

	into the ferrous components of the CRT and may make the problem worse.

	

	It looks really cool to do this while the CRT is powered.  The kids will

	love the color effects.

	

	Bulk tape erasers, tape head degaussers, open frame transformers, and the

	"ass-end" of a weller soldering gun can be used as CRT demagnetizers but

	it just takes a little longer. (Be careful not to scratch the screen

	face with anything sharp.) It is imperative to have the CRT running when

	using these whimpier approaches, so that you can see where there are 

	still impurities. Never release the power switch until you're 4 or 5 

	feet away from the screen or you'll have to start over.

	

	I've never known of anything being damaged by excess manual degaussing

	though I would recommend keeping really powerful bulk tape erasers turned

	degaussers a couple of inches from the CRT.

	

	If an AC degaussing coil or substitute is unavailable, I have even done

	degaussed with a permanent magnet but this is not recommended since it is more

	likely to make the problem worse than better.  However, if the display

	is unusable as is, then using a small magnet can do no harm. (Don't use

	a 20 pound speaker or magnetron magnet as you may rip the shadow mask right

	out of the CRT - well at least distort it beyond repair.  What I have in

	mind is something about as powerful as a refrigerator magnet.)

	

	Keep degaussing fields away from magnetic media.  It is a good idea to

	avoid degaussing in a room with floppies or back-up tapes.  When removing

	media from a room  remember to check desk drawers and manuals for stray

	floppies, too. 

	

	It is unlikely that you could actually affect magnetic media but better

	safe than sorry.  Of the devices mentioned above, only a bulk eraser or

	strong permanent magnet are likely to have any effect - and then only when

	at extremely close range (direct contact with media container).

	

	All color CRTs include a built-in degaussing coil wrapped around the 

	perimeter of the CRT face. These are activated each time the CRT is 

	powered up cold by a 3 terminal thermister device or other control

	circuitry.  This is why it is often suggested that color purity problems

	may go away "in a few days".  It isn't a matter of time; it's the number

	of cold power ups that causes it.  It takes about 15 minutes of the power

	being off for each cool down cycle. These built-in coils with thermal

	control are never as effective as external coils.

	

	See the document: " TV and Monitor CRT (Picture Tube) Information" for

	some additional discussion of degaussing tools, techniques, and cautions.

4.3) How often to degauss

	Some monitor manufacturers specifically warn about excessive use of degauss,

	most likely as a result of overstressing components in the degauss circuitry

	which are designed (cheaply) for only infrequent use.  In particular,

	there is often a thermister that dissipates significant power for the second

	or two that the degauss is active.  Also, the large coil around the CRT

	is not rated for continuous operation and may overheat.

	

	If one or two activations of the degauss button do not clear up the color

	problems, manual degaussing using an external coil may be needed

	or the monitor may need internal purity/color adjustments.  Or, you may have

	just installed your megawatt stereo speakers next to the monitor!

	

	You should only need to degauss if you see color purity problems

	on your CRT.  Otherwise it is unnecessary.  The reasons it only works the

	first time is that the degauss timing is controlled by a termister

	which heats up and cuts off the current.  If you push the button

	twice in a row, that thermister is still hot and so little happens.

	

	One word of clarification:  In order for the degauss operation to be

	effective, the AC current in the coil must approach zero before the

	circuit cuts out.  The circuit to accomplish this often involves a 

	thermister to gradually decrease the current (over a matter of several

	seconds), and in better monitors, a relay to totally cut off the current

	after a certain delay.  If the current was turned off suddenly, you would

	likely be left with a more magnetized CRT.  There are time delay elements

	involved which prevent multiple degauss operations in succession.  Whether

	this is by design or accident, it does prevent the degauss coil - which is

	usually grossly undersized for continuous operation - to cool.

4.4) Why are there fine lines across my Trinitron monitor or TV?

	These are not a defect - they are a 'feature'.

	

	All Trinitron (or clone) CRTs - tubes that use an aperture grille - require

	1, 2, or 3 very fine wires across the screen to stabilize the array of

	vertical wires in the aperture grille.  Without these, the display would

	be very sensitive to any shock or vibration and result in visible shimmering

	or rippling.  (In fact, even with these stabilizing wires, you can usually

	see this shimmering if you whack a Trinitron monitor.)  The lines you see

	are the shadows cast by these fine wires.

	

	The number of wires depends on the size of the screen.  Below 15" there

	is usually a single wire; between 15" and 21" there are usually 2 wires;

	above 21" there may be 3 wires.

	

	Only you can decide if this deficiency is serious enough to avoid the

	use of a Trinitron based monitor.  Some people never get used to the fine

	lines but many really like the generally high quality of Trinitron based

	displays and eventually totally ignore them.

Chapter 5) Monitor Placement and Preventive Maintenance

5.1) General monitor placement considerations

	Proper care of a monitor does not require much.  Following the recommendations

	below will assure long life and minimize repairs:

	

	* Subdued lighting is preferred for best viewing conditions.  Avoid direct

	  overhead light falling on the screen or coming from behind the monitor

	  if possible.

	

	* Locate the monitor away from extremes of hot and cold.  Avoid damp or dusty

	  locations if possible.  (Right you say, keep dreaming!)  This will help

	  keep your PC happy as well.

	

	* Allow adequate ventilation - monitors use a fair amount of power - from

	  60 watts for a 12 inch monochrome monitor to over 200 W for a 21 inch

	  high resolution color monitor.  Heat is one major enemy of electronics.

	

	* Do not put anything on top of the monitor that might block the ventilation

	  grill in the rear or top of the cover.  This is the major avenue for

	  the convection needed to cool internal components.

	

	* Do not place two monitors close to one another.  The magnetic fields

	  may cause either or both to suffer from wiggling or shimmering images.

	  Likewise, do not place a monitor next to a TV if possible.

	

	* Locate loudspeakers and other sources of magnetic fields at least a couple

	  of feet from the monitor.  This will minimize the possibility of color purity

	  or geometry problems.  The exception is with respect to good quality shielded

	  multimedia speakers which are designed to avoid magnetic interference

	  problems.

	

	  Other devices which may cause interference include anything with power

	  transformers including audio equipment, AC or DC wall adapters, and laptop

	  power supplies; fluorescent lamps with magnetic ballasts; and motorized

	  or heavy duty appliances.

	

	* Situate monitors away from power lines - even electric wiring behind

	  or on the other side of walls - and heavy equipment which may cause

	  noticeable interference like rippling, wiggling, or swimming of the

	  picture.  Shielding is difficult and expensive.

	

	* Make sure all video connections are secure (tighten the thumbscrews)

	  to minimize the possibility of intermittent or noisy colors.  Keep the

	  cables as short as possible.  Do not add extension cables if at all

	  possible as these almost always result in a reduction in image crispness

	  and introduce ghosting, smearing, and other termination problems.

	  If you must add an extension, use proper high quality cable only long

	  enough to make connections conveniently.  Follow the termination 

	  recommendations elsewhere in this document.

	

	* Finally, store magnetic media well away from all electronic equipment

	  including and especially monitors and loudspeakers.  Heat and magnetic

	  fields will rapidly turn your diskettes and tapes into so much trash.  The

	  operation of the monitor depends on magnetic fields for beam deflection. 

	  Enough said.

5.2) Non-standard monitor mounting considerations

Monitors normally are positioned horizontally or via the limits of their tilt

swivel bases out in the open on a table or desktop. However, for use in

exhibits or for custom installations, it may be desirable to mount a monitor

in a non-standard position and/or inside an enclosure.

(From: Bob Myers (
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)).

Your mileage may vary, but (and please take the following for what it is, a

very general answer)...

There are basically two potential problems here; one is cooling, and the other

is the fact that the monitor has no doubt been set up by the factory assuming

standard magnetic conditions, which probably DIDN'T involve the monitor

tilting at much of an angle. If you're happy with the image quality when it's

installed in the cabinet, that leaves just the first concern. THAT one can be

addressed by simply making sure the cabinet provides adequate ventilation (and

preferably adding a fan for a bit of forced-air cooling), and making sure that

the whole installation isn't going to be exposed to high ambient temperatures.

(Most monitors are speced to a 40 deg. C ambient in their normal orientation;

adding forced-air cooling will usually let you keep that rating in positions

somewhat beyond the normal.) Under no circumstances should you block the

cabinet's vents, and - depending on the installation - it may be preferable to

remove the rear case parts of the monitor (but NOT the metal covers beneath

the plastic skin) in order to improve air circulation.

Your best bet is to simply contact the service/support people of the monitor

manufacturer, and get their input on the installation. Failing to get the

manufacturer's blessing on something like this most often voids the warranty,

and can probably lead to some liability problems. (Note - I'm not a lawyer,

and I'm not about to start playing one on the net.)

5.3) Preventive maintenance - care and cleaning

Preventive maintenance for a monitor is pretty simple - just keep the case

clean and free of obstructions. Clean the CRT screen with a soft cloth just

dampened with water and mild detergent or isopropyl alcohol. This will

avoid damage to normal as well as antireflection coated glass. DO NOT use

anything so wet that liquid may seep inside of the monitor around the edge

of the CRT. You could end up with a very expensive repair bill when the

liquid decides to short out the main circuit board lurking just below.

Then dry thoroughly. Use the CRT sprays sold in computer stores if you

like but again, make sure none can seep inside. If you have not cleaned

the screen for quite a while, you will be amazed at the amount of black

grime that collects due to the static buildup from the CRT high voltage

supply.

In really dusty situations, periodically vacuuming inside the case and the use

of contact cleaner for the controls might be a good idea but realistically,

you will not do this so don't worry about it.

(From: Tom Watson (
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)).

If you are maintaining a site, consider periodic cleaning of the monitors.

Depending on the location, they can accumulate quite a bit of dust. In normal

operation there is a electrostatic charge on the face of the crt (larger

screens have bigger charges) which act as 'dust magnets'. If the operator

smokes (thankfully decreasing), it is even worse. At one site I helped out

with, most of the operators smoked, and the screens slowly got covered with a

film of both dust and smoke particles. A little bit of glass cleaner applied

with reasonable caution and the decree of "adjustments" to make the screen

better (these were character monochrome terminals), and lo and behold, "what

an improvement!". Yes, even in my dusty house, the TVs get a coating of

film/goo which needs to be cleaned, and the picture quality (BayWatch viewers

beware) improves quite a bit. Try this on your home TV to see what comes off,

then show everyone else. You will be surprised what a little bit of cleaning

does.

(From: Bob Myers (
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)).

1. Don't block the vents; make sure the monitor has adequate ventilation,

and don't operate it more than necessary at high ambient temperatures.

2. If the monitor is used in particularly dusty environments, it's probably

a good idea to have a qualified service tech open it up every so often

(perhaps once a year, or more often depending on just how dirty it gets)

and clean out the dust.

3. The usual sorts of common-sense things - don't subject the monitor to

mechanical shock and vibration, clean up spills, etc., promptly, and

so forth. And if you're having repeated power-supply problems with your

equipment, it may be time to get suspicious of the quality of your AC

power (are you getting noise on the line, sags, surges, spikes, brownouts,

that sort of thing?).

And most importantly:

4. Turn the monitor OFF when it's not going to be used for an extended

period (such as overnight, or if you'll be away from your desk for the

afternoon, etc.). Heat is the enemy of all electronic components, and

screen-savers do NOTHING in this regard. Many screen-savers don't even

do a particularly good job of going easy on the CRT. With modern

power-management software, there's really no reason to be leaving a

monitor up and running all the time.

These won't guarantee long life, of course - nothing can do that, as there

will always be the possibility of the random component failure. But these

are the best that the user can do to make sure the monitor goes as long as

it can.

5.4) Monitor tuneup?

	(From: Bob Myers (
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 )).

	

	Most manufacturers will quote an MTBF (Mean Time Before Failure) of

	somewhere in the 30,000 to 60,000 hour range, EXCLUSIVE OF the CRT.  The

	typical CRT, without an extended-life cathode, is usually good for 

	10,000 to 15,000 hours before it reaches half of its initial brightness.

	Note that, if you leave your monitor on all the time, a year is just about

	8,000 hours.

	

	The only "tuneup" that a monitor should need, exclusive of adjustments

	needed following replacement of a failed component, would be video amplifier

	and/or CRT biasing adjustments to compensate for the aging of the tube.

	These are usually done only if you're using the thing in an application where

	exact color/brightness matching is important.  Regular degaussing of the

	unit may be needed, of course, but I'm not considering that a "tuneup" or

	adjustment.

Chapter 6) Monitor Troubleshooting

6.1) SAFETY

	TVs and computer or video monitors are among the more dangerous of consumer

	electronics equipment when it comes to servicing.  (Microwave ovens are

	probably the most hazardous due to high voltage at flesh frying and cardiac

	arresting high power.)

	

	There are two areas which have particularly nasty electrical dangers: the

	non-isolated line power supply and the CRT high voltage.

	

	Major parts of nearly all modern TVs and many computer monitors are directly

	connected to the AC line - there is no power transformer to provide the

	essential barrier for safety and to minimize the risk of equipment damage.

	In the majority of designs, the live parts of the TV or monitor are limited

	to the AC input and line filter, degauss circuit, bridge rectifier and main

	filter capacitor(s), low voltage (B+) regulator (if any), horizontal output

	transistor and primary side of the flyback (LOPT) transformer, and parts

	of the startup circuit and standby power supply.  The flyback generates most

	of the other voltages used in the unit and provides an isolation barrier so

	that the signal circuits are not line connected and safer.

	

	Since a bridge rectifier is generally used in the power supply, both

	directions of the polarized plug result in dangerous conditions and an

	isolation transformer really should be used - to protect you, your test

	equipment, and the TV, from serious damage.  Some TVs do not have any

	isolation barrier whatsoever - the entire chassis is live.  These are

	particularly nasty.

	

	The high voltage to the CRT, while 200 times greater than the line input,

	is not nearly as dangerous for several reasons.  First, it is present in a

	very limited area of the TV or monitor - from the output of the flyback

	to the CRT anode via the fat red wire and suction cup connector.  If you

	don't need to remove the mainboard or replace the flyback or CRT, then

	leave it alone and it should not bite.  Furthermore, while the shock from

	the HV can be quite painful due to the capacitance of the CRT envelope, it

	is not nearly as likely to be lethal since the current available from the

	line connected power supply is much greater.

6.2) Safety Guidelines

	These guidelines are to protect you from potentially deadly electrical shock

	hazards as well as the equipment from accidental damage.

	

	Note that the danger to you is not only in your body providing a conducting

	path, particularly through your heart.  Any involuntary muscle contractions

	caused by a shock, while perhaps harmless in themselves, may cause collateral

	damage - there are many sharp edges inside this type of equipment as well as

	other electrically live parts you may contact accidentally.

	

	The purpose of this set of guidelines is not to frighten you but rather to

	make you aware of the appropriate precautions.  Repair of TVs, monitors,

	microwave ovens, and other consumer and industrial equipment can be both

	rewarding and economical.  Just be sure that it is also safe!

	

	* Don't work alone - in the event of an emergency another person's presence

	  may be essential.

	

	* Always keep one hand in your pocket when anywhere around a powered

	  line-connected or high voltage system.

	

	* Wear rubber bottom shoes or sneakers.

	

	* Don't wear any jewelry or other articles that could accidentally contact

	  circuitry and conduct current, or get caught in moving parts.

	

	* Set up your work area away from possible grounds that you may accidentally

	  contact.

	

	* Know your equipment: TVs and monitors may use parts of the metal chassis

	  as ground return yet the chassis may be electrically live with respect to the

	  earth ground of the AC line.  Microwave ovens use the chassis as ground

	  return for the high voltage.  In addition, do not assume that the chassis

	  is a suitable ground for your test equipment!

	

	* If circuit boards need to be removed from their mountings, put insulating

	  material between the boards and anything they may short to.  Hold them in

	  place with string or electrical tape.  Prop them up with insulation sticks -

	  plastic or wood.

	

	* If you need to probe, solder, or otherwise touch circuits with power off,

	  discharge (across) large power supply filter capacitors with a 2 W or greater

	  resistor of 100 to 500 ohms/V approximate value (e.g., for a 200 V capacitor,

	  use a 20K to 100K ohm resistor).  Monitor while discharging and verify that

	  there is no residual charge with a suitable voltmeter.  In a TV or monitor,

	  if you are removing the high voltage connection to the CRT (to replace the

	  flyback transformer for example) first discharge the CRT contact (under the

	  insulating cup at the end of the fat red wire).  Use a 1M to 10M ohm 5 W or

	  greater wattage (for its voltage holdoff capability, not power dissipation)

	  resistor on the end of an insulating stick or the probe of a high voltage

	  meter.  Discharge to the metal frame which is connected to the outside of

	  the CRT.

	

	* For TVs and monitors in particular, there is the additional danger of

	  CRT implosion - take care not to bang the CRT envelope with your tools.

	  An implosion will scatter shards of glass at high velocity in every

	  direction.  There are several tons of force attempting to crush the typical

	  CRT.  While implosion is not really likely even with modest abuse, why take

	  chances?  However, the CRT neck is relatively thin and fragile and breaking

	  it would be very embarrassing and costly.  Always wear eye protection when

	  working around the back side of a CRT.

	

	* Connect/disconnect any test leads with the equipment unpowered and

	  unplugged. Use clip leads or solder temporary wires to reach cramped

	  locations or difficult to access locations.

	

	* If you must probe live, put electrical tape over all but the last 1/16"

	  of the test probes to avoid the possibility of an accidental short which

	  could cause damage to various components.  Clip the reference end of the

	  meter or scope to the appropriate ground return so that you need to only

	  probe with one hand.

	

	* Perform as many tests as possible with power off and the equipment unplugged.

	  For example, the semiconductors in the power supply section of a TV or

	  monitor can be tested for short circuits with an ohmmeter.

	

	* Use an isolation transformer if there is any chance of contacting line

	  connected circuits.  A Variac(tm) is not an isolation transformer!

	  The use of a GFCI (Ground Fault Circuit Interrupter) protected outlet is a

	  good idea but will not protect you from shock from many points in a line

	  connected TV or monitor, or the high voltage side of a microwave oven, for

	  example.  (Note however, that, a GFCI may nuisanse trip at power-on or at

	  other random times due to leakage paths (like your scope probe ground) or

	  the highly capacitive or inductive input characteristics of line powered

	  equipment.)  A fuse or circuit breaker is too slow and insensitive to provide

	  any protection for you or in many cases, your equipment.  However, these

	  devices may save your scope probe ground wire should you accidentally connect

	  it to a live chassis.

	

	* Don't attempt repair work when you are tired.  Not only will you be more

	  careless, but your primary diagnostic tool - deductive reasoning - will

	  not be operating at full capacity.

	

	* Finally, never assume anything without checking it out for yourself!

	  Don't take shortcuts!

6.3) Troubleshooting tips

Many problems have simple solutions. Don't immediately assume that

your problem is some combination of esoteric complex convoluted

failures. For a monitor, it may just be a bad connection or blown fuse.

Remember that the problems with the most catastrophic impact on operation

like a dead monitor usually have the simplest solutions. The kind of

problems we would like to avoid at all costs are the ones that are

intermittent or difficult to reproduce: the occasional jitter or a monitor

that blows its horizontal output transistor every six months.

If you get stuck, sleep on it. Sometimes, just letting the problem

bounce around in your head will lead to a different more successful

approach or solution. Don't work when you are really tired - it is both

dangerous (especially with respect to monitors) and mostly non-productive

(or possibly destructive).

Whenever working on complex equipment, make copious notes and diagrams.

You will be eternally grateful when the time comes to reassemble the unit.

Most connectors are keyed against incorrect insertion or interchange

of cables, but not always. Apparently identical screws may be of differing

lengths or have slightly different thread types. Little parts may fit in

more than one place or orientation. Etc. Etc.

Pill bottles, film canisters, and plastic ice cube trays come in handy for

sorting and storing screws and other small parts after disassembly. This

is particularly true if you have repairs on multiple pieces of equipment

under way simultaneously.

Select a work area which is wide open, well lighted, and where dropped

parts can be located - not on a deep pile shag rug. The best location will

also be relatively dust free and allow you to suspend your troubleshooting

to eat or sleep or think without having to pile everything into a cardboard

box for storage.

Another consideration is ESD - Electro-Static Discharge. Some components

(like ICs) in a TV are vulnerable to ESD. There is no need to go overboard

but taking reasonable precautions such as getting into the habit of touching

a **safe** ground point first.

WARNING: even with an isolation transformer, a live chassis should **not** be

considered a safe ground point. When the monitor is unplugged, the shields

or other signal ground points should be safe and effective.

A basic set of precision hand tools will be all you need to disassemble

a monitor and perform most adjustments. These do not need to be really

expensive but poor quality tools are worse than useless and can cause

damage. Needed tools include a selection of Philips and straight blade

screwdrivers, socket drivers, needlenose pliers, wire cutters, tweezers,

and dental picks. For adjustments, a miniature (1/16" blade) screwdriver

with a non-metallic tip is desirable both to prevent the presence of

metal from altering the electrical properties of the circuit and to

minimize the possibility of shorting something from accidental contact

with the circuitry. A set of plastic alignment tools will be useful for

making adjustments to coils (though you can forgo these until the (rare)

need arises.

A low power (e.g., 25 W) fine tip soldering iron and fine rosin core solder

will be needed if you should need to disconnect any soldered wires (on purpose

or by accident) or replace soldered components. A higher power iron or small

soldering gun will be needed for dealing with larger components. Never use

acid core solder or the type used for sweating copper pipes!

See the document: "Troubleshooting and Repair of Consumer Electronics Equipment" for additional info on soldering and rework techniques.

For thermal or warmup problems, a can of 'cold spray' or 'circuit chiller'

(they are the same) and a heat gun or blow dryer come in handy to identify

components whose characteristics may be drifting with temperature. Using the

extension tube of the spray can or making a cardboard nozzle for the heat

gun can provide very precise control of which components you are affecting.

For info on useful chemicals, adhesives, and lubricants, see "Repair Briefs,

an Introduction" as well as other documents available at this site.

6.4) Test equipment

	Don't start with the electronic test equipment, start with some analytical

	thinking.  Your powers of observation (and a little experience) will make

	a good start.   Your built in senses and that stuff between

	your ears represents the most important test equipment you have.

	

	However, some test equipment will be needed:

	

	* Multitester (DMM or VOM) - This is essential for checking of power supply

	  voltages and voltages on the pins of ICs or other components - service

	  literature like the SAMs Photofacts described elsewhere in this document

	  include voltage measurements at nearly every circuit tie point for properly

	  functioning equipment.  The multitester will also be used to check 

	  components like transistors, resistors, and capacitors for correct value

	  and for shorts or opens.  You do not need a fancy instrument.  A basic 

	  DMM - as long as it is reliable - will suffice for most troubleshooting.

	  If you want one that will last for many years, go with a Fluke.  However,

	  even the mid range DMMs from Radio Shack have proven to be reliable and

	  of acceptable accuracy.  For some kinds of measurements - to deduce trends

	  for example - an analog VOM is preferred (though some DMMs have a bar graph

	  scale which almost as good).

	

	* Oscilloscope - While many problems can be dealt with using just a multimeter,

	  a 'scope will be essential as you get more into advanced troubleshooting.

	  Basic requirements are: dual trace, 10-20 MHz minimum vertical bandwidth,

	  delayed sweep desirable but not essential.  A good set of proper 10x/1x

	  probes.  Higher vertical bandwidth is desirable but most consumer electronics

	  work can be done with a 10 MHz scope.  A storage scope or digital scope

	  might be desirable for certain tasks but is by no means essential for basic

	  troubleshooting.

	

	  I would recommend a good used Tektronix or HP scope over a new

	  scope of almost any other brand.  You will usually get more scope

	  for your money and these things last almost forever.  My 'good' scope

	  is the militarized version (AN/USM-281A) of the HP180 lab scope.  This

	  has a dual channel 50 MHz vertical plugin and a delayed sweep horizontal

	  plugin.  I have seen these going for under $300 from surplus outfits.

	  For a little more money, you can get a Tek 465 100 Mhz scope ($400-700)

	  which will suffice for all but the most demanding (read: RF or high

	  speed digital) repairs.

	

	* A video signal source - depending on what type of monitor you are repairing,

	  you may need both computer and television signals.

	

	  Computer Monitors - a test PC is useful as a video source.  Of course,

	  it will need to support whatever scan rates and video types the

	  monitor is designed to accept.  Software programs are available to

	  display purity, convergence, focus, color, and other test patterns.

	  Or create your own test patterns using a program like Windows Paint.

	  See the section: "Using a PC as a monitor test pattern generator".

	

	  Studio monitors - a baseband video source like a VCR or camcorder

	  is useful in lieu of a test pattern generator.  These will allow you to

	  you to control the program material.  In fact, making some test tapes

	  using a camcorder or video camera to record static test patterns will

	  allow you full control of what is being displayed and for how long.

	

	* Color bar/dot/crosshatch signal generator.  This is a useful piece

	  of equipment if you are doing a lot of TV or studio monitor repair and

	  need to perform CRT convergence and chroma adjustments.  However, there

	  are alternatives that are almost as good: a VHS recording of these

	  test patterns will work for TVs.  A PC programmed to output a suitable

	  set of test patterns will be fine for monitors (and TVs if you can set

	  up the video card to produce an NTSC/PAL signal.  This can be put

	  through a VCR to generate the RF (Channel 3/4) input to your TV if

	  it does not have direct video inputs (RCA jacks).

	

	  Sophisticated (and expensive) universal test pattern generators are available

	  that will handle any possible monitor scan rate.

6.5) Incredibly handy widgets

	These are the little gadgets and homemade testers that are useful for many

	repair situations.  Here are just a few of the most basic:

	

	* Series light bulb for current limiting during the testing of TVs,

	  monitors, switching power supplies, audio power amplifiers, etc. I built

	  a dual outlet box with the outlets wired in series so that a lamp

	  can be plugged into one outlet and the device under test into the other.

	  For added versatility, add a regular outlet and 'kill' switch using a

	  quad box instead.  The use of a series load will prevent your expensive

	  replacement part like a horizontal output transistor from blowing if

	  there is still some fault in the circuit you have failed to locate.

	

	* A Variac.  It doesn't need to be large - a 2 A Variac mounted with

	  a switch, outlet and fuse will suffice for most tasks.  However,

	  a 5 amp or larger Variac is desirable.  If you will be troubleshooting

	  220 VAC equipment in the US, there are Variacs that will output 0-240 VAC

	  from a 115 VAC line (just make sure you don't forget that this can easily

	  fry your 115 VAC equipment.)  By varying the line voltage, not only can

	  you bring up a newly repaired monitor gradually to make sure there are no

	  problems; you can also evaluate behavior at low and high line voltage.

	  This can greatly aid in troubleshooting power supply problems.  Warning:

	  a Variac is not an isolation transformer and does not help with respect

	  to safety.  You need an isolation transformer as well.

	

	* Isolation transformer.  This is very important for safely working on

	  live chassis equipment.  Since nearly all modern monitors utilize line

	  connected switchmode power supply or line connected deflection circuits,

	  it is essential.  You can build one from a pair of similar

	  power transformers back-to-back (with their highest rated secondaries

	  connected together.  I built mine from a couple of similar old

	  tube type TV power transformers mounted on a board with an outlet box

	  including a fuse.  Their high voltage windings were connected together.

	  The unused low voltage windings can be put in series with the primary

	  or output windings to adjust voltage.  Alternatively, commercial line

	  isolation transformers suitable for TV troubleshooting are available

	  for less than $100 - well worth every penny.

	

	* Variable isolation transformer.  You don't need to buy a fancy combination

	  unit.  A Variac can be followed by a normal isolation transformer.  (The

	  opposite order also works.  There may be some subtle differences in

	  load capacity.).

	

	* Degaussing coil.  Make or buy.  The internal degaussing coil salvaged

	  from a defunct color TV or monitor doubled over to half it original diameter

	  to increase its strength in series with a 200 W light bulb for current

	  limiting will work just fine.  Or, buy one from a place like MCM Electronics

	  for about $15-$30 that will be suitable for all but the largest TVs and

	  monitors.   Also, see the section:  "Degaussing (demagnetizing) a CRT".

6.6) Safe discharging of capacitors in TVs and video monitors

	It is essential - for your safety and to prevent damage to the device under

	test as well as your test equipment - that large or high voltage capacitors

	be fully discharged before measurements are made, soldering is attempted,

	or the circuitry is touched in any way.  Some of the large filter capacitors

	commonly found in line operated equipment store a potentially lethal charge.

	

	This doesn't mean that every one of the 250 capacitors in your TV need to be

	discharged every time you power off and want to make a measurement.  However,

	the large main filter capacitors and other capacitors in the power supplies

	should be checked and discharged if any significant voltage is found after

	powering off (or before any testing - some capacitors (like the high voltage

	of the CRT in a TV or video monitor) will retain a dangerous or at least

	painful charge for days or longer!)

	

	The technique I recommend is to use a high wattage resistor of about

	100 ohms/V of the working voltage of the capacitor.  This will

	prevent the arc-welding associated with screwdriver discharge but will

	have a short enough time constant so that the capacitor will drop to

	a low voltage in at most a few seconds (dependent of course on the

	RC time constant and its original voltage).

	

	Then check with a voltmeter to be double sure.  Better yet, monitor

	while discharging (not needed for the CRT - discharge is nearly

	instantaneous even with multi-M ohm resistor).

	

	Obviously, make sure that you are well insulated!

	

	* For the main capacitors in a switching power supply which might be

	  100 uF at 350 V this would mean a 5K 10W resistor.  RC=.5 second.

	  5RC=2.5 seconds.  A lower wattage resistor can be used since the total

	  energy in not that great.   If you want to be more high tech, you can

	  build the capacitor discharge circuit outlined in the companion

	  document: "Testing capacitors with a multimeter and safe discharge".

	  This provides a visible indication of remaining charge and polarity.

	

	* For the CRT, use a high wattage (not for power but to hold off the high

	  voltage which could jump across a tiny 1/4 watt job) resistor of a few

	  M ohms discharged to the chassis ground connected to the outside of the

	  CRT - NOT SIGNAL GROUND ON THE MAIN BOARD as you may damage sensitive

	  circuitry.  The time constant is very short - a ms or so.  However, repeat

	  a few times to be sure.  (Using a shorting clip lead may not be a bad idea

	  as well while working on the equipment - there have been too many stories

	  of painful experiences from charge developing for whatever reasons ready

	  to bite when the HV lead is reconnected.)  Note that if you are touching the

	  little board on the neck of the CRT, you may want to discharge the HV

	  even if you are not disconnecting the fat red wire - the focus and screen

	  (G2) voltages on that board are derived from the CRT HV.

	

	  WARNING: Most common resistors - even 5 W jobs - are rated for only a few

	  hundred volts and are not suitable for the 25KV or more found in modern

	  TVs and monitors.  Alternatives to a long string of regular resistors are

	  a high voltage probe or a known good focus/screen divider network.  However,

	  note that the discharge time constant with these may be a few seconds.  Also

	  see the section: "Additional information on discharging CRTs".

	

	  If you are not going to be removing the CRT anode connection, replacing

	  the flyback, or going near the components on the little board on the neck

	  of the CRT, I would just stay away from the fat red wire and what it is

	  connected to including the focus and screen wires.  Repeatedly shoving

	  a screwdriver under the anode cap risks scratching the CRT envelope which

	  is something you really do not want to do.

	

	Again, always double check with a reliable voltmeter!

	

	Reasons to use a resistor and not a screwdriver to discharge capacitors:

	

	1. It will not destroy screwdrivers and capacitor terminals.

	

	2. It will not damage the capacitor (due to the current pulse).

	

	3. It will reduce your spouse's stress level in not having to hear those

	   scary snaps and crackles.

6.7) Additional information on discharging CRTs

	You may hear that it is only safe to discharge from the Ultor to the Dag.

	So, what the @#$% are they talking about? :-).

	

	(From: Asimov (
 This email address is being protected from spam bots, you need Javascript enabled to view it
 )).

	

	'Dag' is short for Aquadag. It is a type of paint made of a graphite pigment

	which is conductive. It is painted onto the inside and outside of picture

	tubes to form the 2 plates of a high voltage filter capacitor using the glass

	in between as dielectric. This capacitor is between .005uF and .01uF in

	value. This seems like very little capacity but it can store a substantial

	charge with 25,000 volts applied.

	

	The outside "dag" is always connected to the circuit chassis ground via a

	series of springs, clips, and wires around the picture tube. The high voltage

	or "Ultor" terminal must be discharged to chassis ground before working on the

	circuit especially with older TV's which didn't use a voltage divider to

	derive the focus potential or newer TV's with a defective open divider.

	

	For more details, see the document: "TV and Monitor CRT (Picture Tube)

	Information.

6.8) The series light bulb trick

	When powering up a monitor (or any other modern electronic devices with

	expensive power semiconductors) that has had work done on any power circuits,

	it is desirable to minimize the chance of blowing your newly installed parts

	should there still be a fault.  There are two ways of doing this: use of a

	Variac to bring up the AC line voltage gradually and the use of a series load

	to limit current to power semiconductors.

	

	Actually using a series load - a light bulb is just a readily available

	cheap load - is better than a Variac (well both might be better still) since

	it will limit current to (hopefully) non-destructive levels.

	

	What you want to do is limit current to the critical parts - usually the

	horizontal output transistor (HOT).  Most of the time you will get away with

	putting it in series with the AC line.  However, sometimes, putting a light

	bulb directly in the B+ circuit will provide better protection as it will

	limit the current out of the main filter capacitors to the HOT.  Actually,

	an actual power resistor is probably better as its resistance is constant

	as opposed to a light bulb which will vary by 1:10 from cold to hot.  The

	light bulb, however, provides a nice visual indication of the current drawn

	by the circuit under test.  For example:

	

	* Full brightness: short circuit or extremely heavy load - a fault probably

	  is still present.

	

	* Initially bright but then settles at reduced brightness: filter capacitors

	  charge, then lower current to rest of circuit.  This is what is expected

	  when the equipment is operating normally.  There could still be a problem

	  with the power circuits but it will probably not result in an immediate

	  catastrophic failure.

	

	* Pulsating: power supply is trying to come up but shutting down due to

	  overcurrent or overvoltage condition.  This could be due to a continuing

	  fault or the light bulb may be too small for the equipment.

	

	Note: for a TV or monitor, it may be necessary (and desirable) to unplug the

	degauss coil as this represents a heavy initial load which may prevent the unit

	from starting up with the light bulb in the circuit.

	

	The following are suggested starting wattages:

	

	* 40 W bulb for VCR or laptop computer switching power supplies.

	* 100 W bulb for small (i.e., B/W or 13 inch color) monitors or TVs.

	* 150-200 W bulb for large color monitors or projection TVs.

	

	A 50/100/150 W (or similar) 3-way bulb in an appropriate socket comes in

	handy for this but mark the switch so that you know which setting is which!

	

	Depending on the power rating of the equipment, these wattages may need to be

	increased.  I have had to go to a 300 W light bulb for some computer monitors.

	However, start low.  If the bulb lights at full brightness, you know there is

	still a major fault.  If it flickers or the TV (or other device) does not quite

	come fully up, then it should be safe to go to a larger bulb.  Resist the

	temptation to immediately remove the bulb at this point - I have been screwed

	by doing this.  Try a larger one first.  The behavior should improve.  If it

	does not, there is still a fault present.

	

	Note that some TVs and monitors simply will not power up at all with any kind

	of series load - at least not with one small enough (in terms of wattage) to

	provide any real protection.  The microcontroller apparently senses the drop

	in voltage and shuts the unit down or continuously cycles power.  Fortunately,

	these seem to be the exceptions.

6.9) Getting inside a monitor

	You will void the warranty - at least in principle.  There are usually no

	warranty seals on a monitor so unless you cause visible damage or mangle the

	screws or plastic, it is unlikely that this would be detected.  You need to

	decide.  A monitor still under warranty should probably be returned for

	warranty service for any covered problems except those with the most obvious

	and easy solutions.  Another advantage of using warranty service is that

	should your problem actually be covered by a design change, this will be

	performed free of charge.  And, you cannot generally fix a problem which

	is due to poor design!

	

	Getting into a monitor is usually quite simple requiring the removal of 2-10

	Philips or 1/4" hex head screws - most around the edge of the cabinet or

	underneath, a couple perhaps in the rear.  Disconnect the input and power

	cables first as it they stay with catch on the rear cover you are detaching.

	Reconnect whatever is needed for testing after the cover is removed.  Set

	the screws aside and make notes if they are not all of the same length

	and thread type - putting a too long screw in the wrong place can short out

	a circuit board or break something else, for example.  A screw that is

	too short may not be secure.

	

	Once all visible screws are out, try to remove the cover.  There still

	may be hidden catches or snaps around the edges or seam or hidden beneath

	little plastic or rubber cosmetic covers.  Sometimes, the tilt-swivel base

	will need to be removed first.  If no snaps or catches are in evidence,

	the cover may just need a bit of persuasion in the form of a carefully

	placed screwdriver blade (but be careful not to damage the soft plastic).

	A 'splitting' tool is actually sold for this purpose.

	

	As you pull the cover straight back (usually) and off, make sure that no

	other wires are still attached.  Often, the main circuit board rests on

	the bottom of the cover in some slots.  Go slow as this circuit board may

	try to come along with the back.  Once the back is off, you may need to prop

	the circuit board up with a block of wood to prevent stress damage and contact

	with the work surface.

	

	Most - but not all - monitors can be safely and stably positioned either

	still on the tilt-swivel base or on the bottom of the frame.  However, some

	will require care as the circuit board will be vulnerable.

	

	Larger monitors are quite heavy and bulky.  Get someone to help and take

	precautions if yours is one of the unstable variety.  If need be, the monitor

	can usually safely be positioned on the CRT face if it is supported by

	foam or a folded blanket.

	

	Once the cover is off, you will find anywhere from none to a frustratingly

	large number of sheetmetal (perforated or solid) shields.  Depending on which

	circuit boards need to be accessed, one or more of these shields may need

	to be removed.  Make notes of which screws go where and store in a safe

	place.  However, manufacturers often place holes at strategic locations

	in order to access adjustments - check for these before going to a lot

	of unnecessary bother.  Note: sheetmetal usually has sharp edges.  Take care.

	

	Reassemble in reverse order.  Getting the circuit board to slide smoothly

	into its slots may take a couple of attempts but otherwise there should

	be no surprises.

6.10) Specific considerations before poking around inside a TV or monitor

	Both electrical and mechanical dangers lurk:

	

	* Main filter capacitor(s).  This is the most dangerous (not the HV as you

	  would expect).  Fortunately, these capacitors will normally discharge in

	  a few minutes or less especially if the unit is basically working as the

	  load will normally discharge the capacitors nearly fully as power is

	  turned off.  With TVs, the main filter capacitor is nearly always on the

	  mainboard.  Monitors are more likely to have a separate power supply

	  module.

	

	  However, you should check across this capacitor - usually only one and by

	  far the largest in the unit - with a voltmeter and discharge as suggested

	  in the section: "Safe discharging of capacitors in TVs and video monitors"

	  if it holds more than a few volts (or wait longer) before touching anything.

	

	  Some of these are as large as 1,000 uF charged to 160 V - about 13 w-s or

	  a similar amount of energy as that stored in an electronic flash.  This is

	  enough to be potentially lethal under the wrong circumstances.

	   

	* High Voltage capacitor formed by the envelope of the CRT.  It is connected

	  to the flyback transformer by the fat (usually red) wire at the suction cup

	  (well, it looks like one anyhow) attached to the CRT.  This capacitor can

	  hold a charge for quite a while - weeks in the case of an old tube type TV!

	

	  If you want to be doubly sure, discharge this also.  However, unless you

	  are going to be removing the HV connector/flyback, it should not bother you.

	

	  The energy stored is about 1 w-s but if you touch it or come near to an

	  exposed terminal, due to the high voltage, you will likely be handed *all*

	  the energy and you *will* feel it.  The danger is probably more in the

	  collateral damage when you jump ripping flesh and smashing your head against

	  the ceiling.

	

	  Some people calibrate their jump based on voltage - about 1 inch/V. :-).

	

	  There will be some HV on the back of the circuit board on the neck of the

	  CRT but although you might receive a tingle but accidentally touching the

	  focus or screen (G2) pins, it is not likely to be dangerous.

	

	* CRT implosion risk.  Don't hammer on it.  However, it is more likely that

	  you will break the neck off the tube since the neck is relatively weak.  This

	  will ruin your whole day and the TV or monitor but will likely not result in

	  flying glass everywhere.  Just, don't go out of your way to find out.

	

	* Sharp sheet metal and so forth.  This is not in itself dangerous but

	  a reflex reaction can send your flesh into it with nasty consequences.

6.11) Dusting out the inside of a monitor

	The first thing you will notice when you remove the cover is how super

	dusty everything is.  Complements to the maid.  You never dreamed there

	was that much dust, dirt, and grime, in the entire house or office building!

	

	Use a soft brush (like a new paintbrush) and a vacuum cleaner to carefully

	remove the built up dust.  Blowing off the dust will likely not hurt the unit

	unless it gets redeposited inside various controls or switches but will

	be bad for your lungs - and will spread dirt all over the room.  Don't turn

	anything - many critical adjustments masquerade as screws that just beg to

	be tightened.  Resist the impulse for being neat and tidy until you know

	exactly what you are doing.  Be especially careful around the components on

	the neck of the CRT - picture tube - as some of these are easily shifted

	in position and control the most dreaded of adjustments - for color purity

	and convergence.  In particular, there will be a series of adjustable ring

	magnets.  It is a good idea to mark their position in any case with

	some white paint, 'white out', or a Magic Marker so that if they do get

	moved - or you move them deliberately, you will know where you started.

6.12) Troubleshooting a monitor with the mainboard disconnected

	There are times when it is desirable to remove the chassis or mainboard and

	work on it in a convenient location without having to worry about the

	attachments to the CRT and cabinet circuitry.

	

	My approach is usually to do as much work as possible without removing the

	main board and not attempt to power it up when disconnected since there are

	too many unknowns.  Professionals will plug the chassis into a piece of

	equipment which will simulate the critical functions but this is rarely

	an option for the doit-yourselfer.

	

	Note that if you have a failure of the power supply - blown fuse, startup,

	etc., then it should be fine to disconnect the CRT since these problems

	are usually totally unrelated.  Tests should be valid.

	

	However, if you really want to do live testing with the main board removed,

	here are some considerations.  There are usually several connections to the

	CRT and cabinet:

	

	* Deflection yoke - since the horizontal coils are part of the horizontal

	  flyback circuit, there could be problems running without a yoke.  This

	  could be anything from it appearing totally dead to an overheating or

	  blown horizontal output transistor.  There may be no problems.  Vertical

	  and any convergence coils may or may not be problems as well.

	

	* CRT video Driver board - pulling this should not usually affect anything

	  except possibly video output and bias voltages.

	

	* CRT 2nd anode - without the CRT, there will be no capacitor to filter

	  the high voltage and you would certaily want to insulate the HV connector

	  **real** well.  I do not know whether there are cases where damage to

	  flyback could result from running in thie manner, however.

	

	* Front panel controls - disconnecting these may result in inability to

	  even turn the unit on, erratic operation, and other unexpected behavior.

	

	* Degauss - you just won't have this function when disconnected.  But who

	  cares - you are not going to be looking at the screen anyhow.

	

	* Remote sensor - no remote control but I doubt that the floating

	  signals will cause problems.

	

	* Speakers - there will be no audio but this should not cause damage.

	

	If you do disconnect everything, make sure to label any connectors whose

	location or orientation may be ambiguous.  Most of the time, these will

	only fit one way but not always.

Chapter 7) Monitor Adjustments

7.1) User picture adjustment

	For general viewing, subdued lighting is preferred.  Avoid backlighting

	and direct overhead lighting if possible.

	

	Display an image with a variety of colors and the full range of brightness

	from deep shadows to strong highlights.  For PCs, a Windows desktop is

	generally satisfactory.  An outdoor scene on a sunny day is excellent for

	studio monitors.  Alternatively, use a test pattern specially designed

	for this purpose.

	

	Turn the BRIGHTNESS and CONTRAST controls (or use the buttons) all the way

	down.

	

	Increase the BRIGHTNESS until a raster is just visible in the darkest

	(shadow) areas of the picture.

	

	Increase the CONTRAST until the desired intensity of highlights is obtained.

	

	Since BRIGHTNESS and CONTRAST are not always independent, go back and forth

	until you get the best picture.

	

	On monitors with a color balance adjustment, you may want to set this but

	unless you are doing photorealistic work, using the manufacturer's defaults

	will be fine unless you need to match the characteristics of multiple

	monitors located side-by-side.

7.2) Focus adjustment

	One of the most common complaints is that the monitor is not as crisp as

	it used to be - or just not as sharp as expected.

	

	Assuming that the focus has just been gradually getting worse over time,

	tweaking the internal focus control may be all that is needed.

	

	Some monitors have the focus adjustment accessible through a (possibly

	unmarked) hole in the side or rear of the case.  If there is a single

	hole, it is almost certainly for overall focus.  If there are two holes,

	one may be the screen (G2 - master brightness) or the two adjustments may

	be for different aspects of focus (e.g., horizontal and vertical).  Just

	carefully observe what happens when each adjustment is moved a little so

	that you can return it to its original setting if you turned the wrong one.

	Use a thin insulated screwdriver - preferably with a plastic blade.  As

	a extra precaution, determine of the screwdriver will mate easily with the

	adjustment with the monitor **off** (don't turn anything, however).

	

	Where there are two adjustment knobs on the flyback transformer, the top one

	is generally for focus and the bottom one is for G2.

	

	Most inexpensive monitors have only what is known as static focus - a constant

	voltage derived from the HV power supply is applied to the focus grid of the

	CRT.  This does not allow for optimal focus across the screen and any setting

	is just a compromise between central and edge sharpness.

	

	Better monitors will have (in addition) H and V focus controls.  These are

	for dynamic focus adjustments.  There may be some interaction between the

	static and dynamic adjustments.  If either of these controls has no effect or

	insufficient range, then there may be a fault in the circuitry for that

	particular adjustment -  a fault with the driver, waveform source, power

	supply, etc.  The most sophisticated schemes use a microprocessor (or at least

	digital logic) to specify the waveform for each section of the screen with a

	map of correction values stored in non-volatile memory.  It would be virtually

	impossible to troubleshoot these systems without detailed service information

	and an oscilloscope - and even then you might need a custom adapter cable and

	PC software to adjust values!

	

	Also see the section: "About the quality of monitor focus".

	

	If you need to go inside to tweak focus pots:

	 

	Safety: as long as you do not go near anything else inside the monitor while

	it is on AND keep one hand in you pocket, you should be able to do this without

	a shocking experience.

	

	Plug it in, turn it on and let it warm up for a half hour or so.  Set your

	PC (or other video source) to display in the resolution you use most often.

	First turn the user brightness and contrast fully counterclockwise.  Turn

	brightness up until the raster lines in a totally black area appear, then

	back a hair until they disappear.  Then, turn the contrast control up until

	you get a fairly bright picture.  Fullly clockwise is probably ok.  Adjust

	FOCUS for generally best focus.  You will not be able to get it razor sharp

	all over the screen - start at the center and then try to get the

	edges and corners as good as you can without messing up the center too much.

	Double check that the focus is ok at your normal settings of brightness and

	contrast and at other resolutions that you normally use.

	

	The focus pot is usually located on the flyback transformer or on an

	auxiliary panel nearby.  The focus wire usually comes from the flyback or

	the general area or from a terminal on a voltage the multiplier module

	(if used).  It is usually a wire by itself going to the little board

	on the neck of the CRT.

	

	The SCREEN control adjusts background brightness.  If the two controls are

	not marked, you will not do any damage by turning the wrong one - it will

	be immediately obvious as the brightness will change rather than focus

	and you can then return it to its original position (or refer to the section

	on brightness adjustments to optimize its setting).

	

	On a decent monitor, you should be able to make out the individual scanning

	lines at all resolutions though it will be toughest at the highest scan rates.

	If they lines are fuzzy, especially in bright areas, then focus may need

	to be adjusted or there may be an actual fault in the focus circuitry or

	a defective or just marginal CRT.

7.3) Brightness and color balance adjustment

	A monitor which has a picture that is very dark and cannot be adequately

	set with the user brightness and contrast controls may need

	internal adjustment of the SCREEN (the term, screen, here refers to a

	particular electrode inside the CRT, not really the brightness of the screen

	you see, though it applies here), MASTER BRIGHTNESS, or BACKGROUND level

	controls.  As components age, including the CRT, the brightness will

	change, usually decrease.  The following procedure will not rejuvenate

	an old CRT but may get just enough brightness back to provide useful

	functionality for a few months or longer.  If the problem is not with the age

	of the CRT, then it may return the monitor to full brightness.  The assumption

	here is that there is a picture but the dark areas are totally black and

	the light areas are not bright enough even with the user brightness control

	turned all the way up.

	

	Note that circuit problems can also cause similar symptoms.  These are

	particularly likely if the brightness descresed suddenly - CRT emission

	problems will result in a gradual decrease in brightness over time.

	

	In most cases, the cover will need to be removed.  The controls we

	are looking for may be located in various places.  Rarely, there will

	be access holes on the back or side.  However, if there are unmarked

	holes, then the FOCUS and SCREEN controls are the most likely possibilities.

	

	The controls may be located on the:

	

	* Flyback (LOPT) transformer.  Usually there is a master screen control

	  along with a focus control on the flyback transformer.

	

	* A little board on the neck of the CRT.  There may be a master screen

	  control. a master brightness control, a master background level control,

	  or individual controls for red, green, and blue background level.  Other

	  variations are possible.  There may also be individual gain/contrast

	  controls.

	

	* Main video board is less common, but the background level controls may

	  be located here.

	

	Display a picture at the video resolution you consider most important

	which includes both totally black and full white areas which also

	includes sharp vertical edges.

	

	Set the user brightness control to its midpoint and the user contrast

	control as low as it will go - counterclockwise.

	

	Let the monitor warm up for at least 15 minutes so that components can

	stabilize.

	

	If there is a MASTER BRIGHTNESS or BACKGROUND level control, use this to

	make the black areas of the picture just barely disappear.  Them, increase

	it until the raster lines just appear.  (They should be a neutral gray.

	If there is a color tint, then the individual color background controls will

	need to be adjusted to obtain a neutral gray.)  If there is no

	such control, use the master screen control on the flyback.  If it is unmarked,

	then try both of the controls on the flyback - one will be the screen control

	and the other will be focus - the effects will be obvious.  If you did touch

	focus, set it for best overall focus and then get back to the section on focus

	once you are done here.

	

	If there are individual controls for each color, you may use these but be

	careful as you will be effecting the color balance.  Adjust so that the

	raster lines in a black area are just visible and dark neutral gray.

	

	If there is a 'service switch' you may prefer to make the adjustment

	with this in the service position.  The raster will collapse to a single

	horizontal line and the video input will be disabled and forced to black.

	The BACKGROUND or SCREEN control can then be adjusted as above.

	

	Now for the gain controls.   On the little board on the neck of the CRT

	or on the video or main board there will be controls for R, G, and B DRIVE

	(also may be called GAIN, or CONTRAST - they are the same).  The knobs or

	slots may even be color coded as to which primary (R,G,B) it affects.

	If there are only two then the third color is fixed and if the color balance

	in the highlights of the picture was ok, then there is nothing more you can

	do here.

	

	Set the user contrast control as high as it will go - clockwise.

	

	Now adjust each internal color DRIVE control as high as you can without

	that particular color 'blooming' at very bright vertical edges.  Blooming

	means that the focus deteriorates for that color and you get a big blotch

	of color trailing off to the right of the edge.  You may need to go back

	and forth among the 3 DRIVE controls since the color that blooms first

	will limit the amount that you can increase the contrast settings.  Set

	them so that you get the brightest neutral whites possible without any

	single color blooming.

	

	Note that this is ignoring the effects of any beam current or brightness

	limiter circuitry.  Any recommendations in the service manual should be

	followed to minimize the chance of excess X-ray emissions as well as to

	avoid burn-in of the phosphor screen.

	

	Now check out the range of the user controls and adjust the appropriate

	internal controls where necessary.  You may need to touch up the background

	levels or other settings.  Check at the other resolutions and refresh rates

	that you normally use.

	

	If none of this provides acceptable brightness, then either your CRT

	is in its twilight years or there is something actually broken in the

	monitor.  If the decrease in brightness has been a gradual process over the

	course of years, then it is most likely the CRT.  As a last resort you can

	try increasing the filament current to the CRT the way CRT boosters that

	used to be sold for TVs worked.  See the section: "Brightening an old CRT".

7.4) Optimal procedure for setting brightness/background and screen adjustments

For slight tweaks, the following is not necessary. However, if someone

turned all the internal controls, if you are making significant changes

that affect G2 (screen), or you are setting up a new or replacement CRT for

the first time, then following the procedure below is desirable to achieve

best performance and maximize life of the CRT.

The typical user controls - brightness and contrast can, of course, be set

arbitrarily, depending on video content and ambient lighting conditions.

Set the user brightness and contrast controls in the middle for the following

adjustments and let the monitor warm up for 20 minutes or so.

(From: Jeroen Stessen (
This email address is being protected from spam bots, you need Javascript enabled to view it
)).

Now the screen control, that's another matter. It sets the voltage

on the second grid of the electron guns, typically between +500 and

+1000 V. You will want to use a well-isolated screwdriver for that

if it is a naked potentiometer. In the old days there used to be 3

separate potentiometers for 3 G2s, now there is generally only one.

Its purpose is to set the cutoff voltage for the guns, i.e. the

voltage between K and G1 at which the beam is just off. The higher

you set the VG2, the higher VK - VG1 must be to cut off the beam.

If you set VG2 too low then your picture will be dark. You can

compensate for that with the brightness control, which in effect will

lower the VKs. A disadvantage is that you will not get optimum

sharpness and peak brightness from your picture tube.

If you set VG2 too high then your picture will be bright. You can

compensate for that with the brightness control, which in effect will

raise the VKs. You might even get retrace lines which can usually

not be made to disappear with the brightness control. Another

disadvantage is that you will not get optimum LIFETIME from your

picture tube. With a too high cutoff voltage the cathode (electron

emitting surface) will wear out too soon.

You will need to see the picture tube specifications (or possibly

the service manual for the monitor --- sam) in order to find the correct

setting for the cutoff voltage. This is measured as VK - VG1 (for each

channel RGB) and is typically 130-160 V max. There will be spread between

the 3 channels, typically the highest of the 3 measured values will be set

against the upper limit.

The usual adjustment procedure is as follows:

* Use any low-level adjustments to set a black picture with all 3

cathode voltages at the specified level (e.g. 130 V) above

the VG1 voltage (may be 0 V or 12 V or 20 V ?). (These are typically

called RGB brightness, bias, or background level and are often on the

little board on the neck of the CRT but not always --- sam).

* Adjust VG2 (screen) until one colour just starts too light up,

turn it back down until the screen is just black again.

* Now adjust 2 of the 3 low-level black controls until the

other 2 colours just light up, and then back to black again.

* Select a white picture and use 2 low-level white (RGB drive or gain, also

generally on the neck board --- sam) controls to set the proper colour

temperature for white to your own taste.

* Check your black calibration again, may have to iterate a bit.

7.5) Position, size, and linearity adjustment

	Position and size are usually user controls on computer and video monitors

	but not on TVs.  On monitors with digital controls, they may usually be set

	for each resolution and (automatically) stored in non-volatile memory so they

	will be retained when the monitor is turned off.  On cheaper monitors, there

	may be a knobs on the front or back panel and may need to readjusted whenever

	the scan rate/resolution is changed.  Sometimes, there are located internally.

	There may be separate adjustments for each scan range and may or may not be

	accessible through holes in the back panel.

	

	There may also be an adjustment called 'horizontal phase' which controls the

	relative timing of the horizontal sync pulse with respect to retrace.  Its

	effect is subtly different than horizontal position which actually moves the

	raster.  If possible, center the raster and then use H Phase to center the

	picture.

	

	In monochrome monitors (mostly), position may be set via a pair of rings on the

	neck of the CRT.

	

	Size can be set to your preference for each scan rate (if they are

	independent).  For computer work, slight underscan is often preferred as

	all of the frame buffer is visible.  However, any slight geometric problems

	with the raster will be all too visible when compared with the straight

	sides of the CRT bezel.

	

	Note that resolutions like 640 x 480, 800 x 600, and 1024 x 768 all have a

	4:3 aspect ratio.  The edge of the image will line up with the bezel on most

	if not all monitors since CRTs are made to a 4:3 aspect ratio.  However,

	resolutions like 1280 x 1024 and 1600 x 1280 have a 5:4 aspect ratio.  With

	these, in order to get (highly desireably) square pixels, the horizontal size

	must be adjusted slightly smaller than that required to fill the screen.

	

	For normal viewing of video (television) monitors, raster size should be set

	so that there is about 10-15 percent overscan all around.  This will allow

	ample margin for power line voltage fluctuations, component aging, and the

	reduction in raster size that may occur with some VCR special effects (CUE and

	REV) modes.  However, for studio use, underscan is often preferred or at least

	an option to permit the entire raster to be inspected.

	

	Modern color monitors may not have any horizontal linearity control but you

	may find this on older models.  There may be an internal vertical linearity

	adjustment.  I am not aware of any that have user accessible linearity

	controls.   If there are internal pots or coils, you will need to go back

	and forth between size and linearity as these adjustments are usually not

	independent.

	

	Of course, parameters controlling your video card also affect position and

	size.  There is no best approach to reconciling the effects of monitor and

	video card position adjustments.  But, in general, start with the monitor

	controls centered within their range or use the memory defaults as

	appropriate.  Then, use the video card setup program to optimize the

	settings.  Only if these do not have enough range should you use the

	monitor controls.

7.6) Pincushion adjustments

	Horizontal pincushion refers to any bowing in or out on the vertical sides of

	the raster.  There is not usually any explicit vertical pincushion adjustment.

	Adjustment usually uses two controls - amplitude and phase.  Pincushion

	amplitude as its name implies, controls the size of the correction.  Pincushion

	phase affects where on the sides it is applied.  Don't expect perfection.

	

	If the controls have no effect, there is probably a fault in the pincushion

	correction circuitry.

	

	It is best to make these adjustments with a crosshatch or dot test pattern

7.7) Geometry adjustment

	This refers to imperfections in the shape of the picture not handled

	by the pincushion and size adjustments.  These types of defects include a

	trapezoidal or keystone shaped raster and jogs or wiggles around the periphery

	of the raster.  Unfortunately, one way these are handled at the factory is to

	glue little magnets to strategic locations on the CRT and/or rotate little

	magnets mounted on the yoke frame.  Unless you really cannot live with the

	way it is (assuming there isn't something actually broken), leave these

	alone!  You can end up with worse problems.  In any case, carefully mark the

	position AND orientation of every magnet so that if this happens, you can

	get back to where you started.  If the magnets are on little swivels, some

	experimenting with them one at a time may result in some improvement.  Of

	course it is best to obtain a service manual and follow its instructions.

	However, this may not be possible at reasonable cost or at all for many

	computer monitors.

7.8) Why is the convergence on my monitor bad near the edges

	Very simple - nothing is quite perfect.  Perfect convergence is not

	even necessarily possible in theory with the set of adjustments available

	on a typical monitor.  It is all a matter of compromises.  Consider what

	you are trying to do: get three electron beams which originate from

	different electron guns to meet at a single point within a fraction

	of a mm everywhere on the screen.  This while the beams are scanning

	at an typical effective writing rate of 50,000 mph across the face of a 17"

	CRT (assumed resolution: 1024x768 at 75 Hz) in a variable magnetic environment

	manufactured at a price you can afford without a second mortgage!

	

	The specifications for misconvergence have two parts: a center error and a

	corner error.  The acceptable center error is always the smaller of the

	two - possibly .1-.2 mm. compared to .3-.5 mm in the corners.  Very often,

	you will find that what you are complaining about is well within this

	specification.

7.9) CRT purity and convergence problems

	Purity assures that each of the beams for the 3 primary colors - R, G, B, -

	red, green, and blue - strikes only the proper phosphor for that color.  A

	totally red scene will appear pure red and so forth.  Symptoms of poor purity

	are blotches of discoloration on the screen.  Objects will change shades of

	color when the move from one part of the screen to another.  There may even be

	excess non-uniformity of pure white or gray images.

	

	Convergence refers to the control of the instantaneous positions of the red,

	green, and blue spots as they scan across the face of the CRT so that they are

	as nearly coincident as possible.  Symptoms of poor convergence are colored

	borders on solid objects or visible separate R, G, and B images of fine lines

	or images,

	

	Note: It is probably best to face the monitor East-West (front-to-back) when

	performing any purity and convergence adjustments.  Since you probably do not

	know what orientation will eventually be used, this is the best compromise as

	the earth's magnetic field will be aligned mostly across the CRT.  This will

	minimize the possible rotation of the picture when the unit is moved to its

	final position but there may be a position shift.  Neither of these is that

	significant so it probably doesn't really matter that much unless you are

	super fussy.  Of course, if you know the final orientation of the monitor use

	that instead.  Or, plan to do the final tilt and position adjustments after

	the monitor is in position - but this will probably require access to the

	inside!

	

	First, make sure no sources of strong magnetic fields are in the vicinity of

	the monitor - loudspeakers, refrigerator magnets, MRI scanners, etc.  A nearby

	lightning strike or EMP from a nuclear explosion can also affect purity

	so try to avoid these.

	

	Cycle power a couple of times to degauss the CRT (1 minute on, 20 minutes

	off) - see the section: "Degaussing (demagnetizing) a CRT".  If the built

	in degaussing circuits have no effect, use an external manual degaussing coil

	to be sure that your problems are not simply due to residual magnetism.

	

	Assuming this doesn't help, you will need to set the internal purity

	and/or convergence adjustments on the CRT.

	

	First, mark the positions of all adjustments - use white paint, 'White out',

	or a Magic Marker on the ring magnets on the neck of the CRT, the position

	and tilt of the deflection yoke, and any other controls that you may touch

	deliberately or by accident.

	

	Note: if your monitor is still of the type with a drawer or panel of knobs

	for these adjustments, don't even think about doing anything without a

	service manual and follow it to the letter unless the functions of all

	the knobs is clearly marked (some manufacturers actually do a pretty good

	job of this).

7.10) CRT purity adjustment

	Purity on modern CRTs is usually set by a combination of a set of ring

	magnets just behind the deflection yoke on the neck of the CRT and the

	position of the yoke fore-aft.  As always, mark the starting position of

	all the rings and make sure you are adjusting the correct set if rings!

	

	Use the following purity adjustment procedure as a general guide only.

	Depending on the particular model monitor, your procedure may substitute

	green for red depending on the arrangement of guns in the CRT.  The procedures

	for dot-mask, slot mask, and Trinitron (aperture grille) CRTs will vary

	slightly.  See you service manual!

	

	Obtain a white raster (sometimes there is a test point that can be grounded

	to force this).  Then, turn down the bias controls for blue and green so

	that you have a pure red raster.  Let the monitor warm up for a minimum of

	15 minutes.

	

	Loosen the deflection yoke clamp and move the yoke as far back as it will go,

	

	Adjust the purity magnets to center the red vertical raster on the screen.

	

	Now, move the yoke forward until you have the best overall red purity.

	Tighten the clamp securely and reinstall the rubber wedges (if your CRT

	has these) to stabilize the yoke position.  Reset the video adjustments

	you touched to get a red raster.

7.11) CRT convergence adjustment

	In the good old days when monitors were monitors (and not just a mass

	produced commodity item) there were literally drawers or panels full of

	knobs for setting convergence.  One could spend hours and still end up

	with a less than satisfactory picture.  As the technology progressed,

	the number of electronic adjustments went down drastically so that today

	there are very few if any.  However, some high end monitors do have user

	accessible controls for minor adjustment of static (center) convergence.

	

	Unless you want a lot of frustration, I would recommend not messing with

	convergence.  You could end up a lot worse.  I have no idea what is used

	for convergence on your set but convergence adjustments are never

	quite independent of one another.  You could find an adjustment that

	fixes the problem you think you have only to discover some other area

	of the screen is totally screwed.  In addition, there are adjustments

	for geometry and purity and maybe others that you may accidentally move

	without even knowing it until you have buttoned up the set.

	

	Warning: Accurately mark the original positions - sometimes you will change

	something that will not have an obvious effect but will be noticeable

	later on.  So it is extremely important to be able to get back to where

	you started.  If only red/green vertical lines are offset, then it is

	likely that only a single ring needs to be moved - and by just a hair.

	But, you may accidentally move something else!

	

	If you really cannot live with it, make sure you mark everything very

	carefully so you can get back to your current state.  A service manual is

	essential!

	

	Convergence is set using a white crosshatch or dot test pattern.  For PCs

	(a similar approach applies to workstations) If you do not have a test

	pattern generator, use a program like Windows Paint to create a facsimile

	of a crosshatch pattern and use this for your convergence adjustments.

	For a studio video monitor, any static scene (from a camcorder

	or previously recorded tape, for example) with a lot of fine detail will

	suffice.

	

	Static convergence sets the beams to be coincident in the exact center of

	the screen.  This is done using a set of ring magnets behind the purity

	magnets on the CRT neck.  (Set any user convergence controls to their

	center position).

	

	Adjust the center set of magnets on the CRT neck to converge blue to green

	at the center of the screen.  Adjust the rear set of magnets to converge

	red to green at the center of the screen."  Your monitor may have a slightly

	different procedure.

	

	Dynamic convergence adjusts for coincidence at the edges and corners.

	

	On old tube, hybrid, and early solid state monitors, dynamic convergence was

	accomplished with electronic adjustments of which there may have been

	a dozen or more that were not independent.  With modern monitors, convergence

	is done with magnet rings on the neck of the CRT, magnets glued to the CRT,

	and by tilting the deflection yoke.  The clamp in conjunction with rubber

	wedges or set screws assures that the yoke remains in position.

	

	Remove the rubber wedges.

	

	Loosen the deflection yoke clamp just enough so that it can be tilted but

	will remain in the position you leave it.  Rock the yoke up and down to

	converge the right and left sides of the screen.  Rock the yoke from side

	to side to converge the top and bottom of the screen.  The rubber wedges

	can be used as pivots to minimize the interaction between the two axes but

	you may need to go back and forth to optimize convergence on all sides.

	Reinstall the wedges firmly and tape them to the CRT securely.  Tighten the

	yoke clamp enough to prevent accidental movement.

	

	Some monitors may use a plastic frame and set screws instead of just a clamp

	and rubber wedges but the procedure is similar.

	

	Refer to your service manual.  (Is this beginning to sound repetitious?)

	

	For additional comments on convergence adjustments, see the section: "Tony's notes on setting convergence on older delta gun CRTs".

7.12) Tilted picture

	You have just noticed that the picture on your fancy (or cheap) monitor is not

	quite horizontal - not aligned with the front bezel.  Note that often there is

	some keystoning or other geometric distortion as well where the top and bottom

	or left and right edges of the picture are not quite parallel - which you may

	never have noticed until now.  Since this may not be correctable (at least,

	not without a lot of hassle), adjusting tilt may represent a compromise at

	best between top/bottom or left/right alignment of the picture edges.   You

	may never sleep again knowing that your monitor picture is not perfect!  BTW,

	I can sympathize with your unhappiness.  Few things are more annoying than a

	just noticeable imperfection such as this.

	

	This is probably one reason why older monitors tended not to be able to expand

	the picture to totally fill the screen - it is easier to overlook imperfect

	picture geometry if there is black space between the edges of the picture and

	the bezel!

	

	There are several possible causes for a tilted picture:

	

	1. Monitor orientation.  The horizontal component of the earth's magnetic field

	   affects this slightly.  Therefore, if you rotate the unit you may be able

	   to correct the tilt.  Of course, it will probably want to face the wall!

	

	   Other external magnetic fields can sometimes cause a rotation without any

	   other obvious effects - have you changed the TV's location?  Did an MRI

	   scanner move in next door?

	

	2. Need for degaussing.  Most of the time, magnetization of the CRT will

	   result in color problems which will be far more obvious than a slight

	   rotation.  However, internal or external shields or other metal parts in

	   the monitor could become magnetized resulting a tilt.  More extensive

	   treatment than provided by the built-in degaussing coil may be needed.

	   Even, the normal manual degaussing procedure may not be enough to get close

	   enough to all the affected parts.

	

	3. You just became aware of it but nothing has changed.  Don't dismiss this

	   offhand.  It is amazing how much we ignore unless it is brought to our

	   attention.  Are you a perfectionist?  Did your friend just visit boasting

	   about his P8-1000 screamer and point the tilt out to you?

	

	4. There is an external tilt control which may be misadjusted.  Newer Sony 

	   monitors have this (don't know about TVs) - a most wonderful addition.

	   Too bad about the stabilizing wires on Trinitron CRTs.  A digital control

	   may have lost its memory accidentally.  The circuitry could have a problem.

	

	   For example, on the Sony CPD1730, you press the left arrow button and blue

	   '+' button at the same time.  Then adjust the tilt with the red buttons.

	

	5. There is an internal tilt control that is misadjusted or not functioning.

	   The existence of such a control is becoming more common.

	

	6. The deflection yoke on the CRT has gotten rotated or was not oriented

	   correctly at the time of the set's manufacture.  Sometimes, the entire yoke

	   is glued in place in addition to being clamped adding another complication.

	

	   If the monitor was recently bumped or handled roughly, the yoke may have

	   been knocked out of position.  But in most cases, the amount of abuse

	   required to do this with the yoke firmly clamped and/or glued would have

	   totally destroyed it in the process.

	

	   There is a risk (in addition to the risk of frying yourself on the various

	   voltages present inside as operating TV) of messing up the convergence

	   or purity when fiddling with the yoke or anything around it since the yoke

	   position on the neck of the tube and its tilt may affect purity and

	   convergence.  Tape any rubber wedges under the yoke securely in place

	   as these will maintain the proper position and tilt of the yoke while you

	   are messing with it.  (Don't assume the existing tape will hold - the

	   adhesive is probably dry and brittle).

	

	7. The CRT may have rotated slightly with respect to the front bezel.

	   Irrespective of the cause of the tilt, sometimes it is possible to

	   loosen the 4 (typical) CRT mounting screws and correct the tilt by

	   slightly rotating the CRT.  This may be easier than rotating the yoke.

	   Just make sure to take proper safety precautions when reaching inside!

7.13) Monchrome monitor size, position, and geometry adjustments

	These tend to be a lot simpler and less critical than for color monitors

	or TV sets.

	

	On a monochrome (B/W) monitor you will probably see some of the following

	adjustments:

	

	1. Position - a pair of rings with tabs on the neck of the CRT.

	   There may be electronic position adjustements as well.

	

	2. Width and height (possibly linearity as well) controls.  There may be

	   some interaction between size and linearity - a crosshatch test pattern

	   is best for this.  Vertical adjustments are almost always pots while

	   horizontal (if they exist) may be pots and/or coils.  Where desired,

	   set sizes for 5-10% overscan to account for line voltage fluctuations and

	   component drift.  Confirm aspect ratio with test pattern which includes

	   square boxes.

	

	3. Geometry - some little magnets either on swivels around the yoke or

	   glued to the CRT.  If these shifted, the the edges may have gotten

	   messed up - wiggles, dips, concave or convex shapes.  There may be

	   a doxen or more each mostly affecting a region around the edge of the

	   raster.  However, they will not be totally independent.

	

	Check at extremes of brightness/contrast as there may be some slight

	changes in size and position due to imperfect HV regulation.

	

	There may be others as well but without a service manual, there is no

	way of knowing for sure.

	

	Just mark everything carefully before changing - then you will be able to

	get back where you started.

Chapter 8) Low Voltage Power Supply Problems

8.1) Low voltage power supply fundamentals

Monitors require a variety of voltages (at various power levels) to function.

The function of the low voltage power supply is to take the AC line input

of either 115 VAC 60 Hz (220 VAC 50 Hz or other AC power in Europe and

elsewhere) and produce some of these DC voltages. In all cases, the power

to the horizontal output transistor of the horizontal deflection system (B+)

is obtained directly from the low voltage power supply. In some cases,

a variety of other DC voltages are derived directly from the AC line by

rectification, filtering, and regulation. In other designs, however, most

of the low voltages are derived from secondary windings on the flyback

(LOPT) transformer of the horizontal deflection system. In still other

designs, there is a separate switchmode power supply that provides some or

all of these voltages. There are also various (and sometimes convoluted)

combinations of any or all of the above.

Note: we will often use the term 'B+' to denote the main DC voltage that

powers the horizontal deflection system of most monitors.

The following are a couple of the typical arrangements found in color monitors:

1. All low voltages except for the B+ to the horizontal output transistor

(HOT) are derived from the horizontal deflection (flyback). This

is the scheme used in the majority of TVs. Some kind of startup circuit

gets the HOT booted but then all internal logic and video amplifier

power is obtained from various windings on the flyback transformer.

The B+ of anywhere from 60 to 130 V (higher for countries using 220 VAC

line voltage) is likely to be regulated and its value selected based

on the scan rate detected. High voltage is obtained from the flyback.

2. Some or all of the low voltages are provided by a switchmode power supply

(SMPS) independent of the horizontal deflection. Additional voltages may

be provided from flyback windings as in (1). Sometimes, this SMPS is

a self contained and easily tested, swapped, and repaired unit. In

other cases, it is built onto the mainboard making it more difficult

to trace the circuit and troubleshoot. High voltage may be obtained

from the flyback or a separate HV module.

For auto-scan monitors, the low voltage power supplies can get to be

quite complex as varying voltages are required for at least the horizontal

deflection based on scan range. Separate regulators may be used for each

range which are switched by the microprocessor or a single regulator

may be programmed for the required voltages. This is one area where

a typical PC monitor departs significantly in design compared to a TV

or fixed scan rate studio or workstation monitor.

There will always be:

1. A power switch, relay, or triac to enable main power.

2. A set of rectifiers - usually in a bridge configuration - to turn the

AC into DC. Small ceramic capacitors are normally placed across the

diodes to reduce RF interference.

3. One or more large filter capacitors to smooth the unregulated DC. In

the U.S., this is most often a voltage around 150-160 V DC. In countries

with 220 VAC power, it will typically be around 300-320 V DC.

4. A discrete, hybrid, or IC regulator to provide stable DC to the horizontal

deflection system. Sometimes feedback from a secondary output of the

flyback or even the high voltage is used. This regulator may be either

a linear or switching type. In some cases, there is no regulator.

Alternatively, an entire switchmode power supply may be used to provide

one or more stable voltages to the horizontal deflection and other

circuitry.

Items (1) to (4) may be part of a separate low voltage power supply module

or located on the mainboard.

5. Zero or more voltage dividers and/or regulators to produce additional

voltages directly from the line power. This relatively rare except for

startup circuits. These voltages will not be isolated from the line.

6. A degauss control circuit usually including a thermistor or Posistor

(a combination of a heater disk and Positive Temperature Coefficient (PTC)

thermistor in a single package). When power is turned on, a relatively

high AC current is applied to the degauss coil wrapped around the periphery

of the CRT. The PTC thermister heats up, increases in resistance, and

smoothly decreases the current to nearly zero over a couple of seconds.

Alternative schemes including RC delays and relays are often used in

monitors which have degaussing buttons.

7. A startup circuit for booting the horizontal deflection if various voltages

to run the monitor are derived from the flyback. This may be an IC or

discrete multivibrator or something else running off a non-isolated

voltage or the standby power supply. Some monitors simply take the

video input and use this via some simple logic or amplifier circuitry

to drive the HOT. With these, there will be no action of any kind if

there is no input signal. (Remember the old IBM PC monitors? Unplug

the video cable and the raster collapsed to a vertical line and then

disappeared.)

8. A standby power supply for the microcontroller and remote sensor. Usually,

this is a separate low voltage power supply using a small power transformer

for line isolation. If the monitor does not have digital controls and/or

has a hard on/off switch (not s soft touch button), this section is not

neeeded.

Always use an isolation transformer when working on a monitor but this is

especially important - for your safety - when dealing with the non-isolated

line operated power supply section. Read and follow the safety guidelines.

Also see the document: "Notes on the Troubleshooting and Repair of Small Switchmode Power Supplies" for additional tips and techniques when diagnosing

and testing switchmode power supplies.

8.2) Monitor deflection derived power supply faults

	Monitors use a variety of switching supply techniques and it would be

	difficult to cover every possibility but here are some comments for

	those that use deflection derived approaches:

	

	Horizontal output transistor (usually a TO3 metal or TOP3 plastic case

	shorts out.  This will usually blow a fuse or fusable resistor as well.

	

	Horizontal drive chain - horizontal oscillator, driver, or driver transformer.

	Newer monitors may use an IC for the oscillator and this can fail.

	

	Startup - There may be some kind of startup circuit which gets the whole

	thing going until the auxiliary voltages are available.  This could be

	as simple as a multivibrator or transistor regulator to provide

	initial voltage to the horizontal oscillator chip or circuit.

	

	Output rectifier diodes can fail shorted and load down the outputs to

	the point of shutting down.

	

	Some load could be shorted or a capacitor could be shorted leading to

	overload and shutdown.

	

	Flyback transformer can have shorted windings which load down the output.

	These (primary shorts in particular) may cause the horizontal output

	transistor to fail as well.  Common problem with older MacIntosh computers

	and video terminals.  Some secondary faults may not be instantly destructive

	but result in little or no high voltage and overheating.

	

	Also, look for cold solder joints - monitors tend to have these as a

	result of temperature cycling and bad manufacturing.  (Is this sounding

	repetitive yet?)

	

	Sometimes there is a series regulator after the filter cap and this could

	be bad as well.

	

	Without a schematic, I would attempt to trace the circuit from the main

	filter cap or output of the line operated switchmode power supply assuming

	that has the proper (approx. 60-120 VDC depending on scan range) voltage.

	

	If you can locate the horizontal output transistor, see if there is voltage

	on its collector, should be the same.  If there is, then there is probably

	a drive problem.  If you have an ECG or similar semi cross reference,

	that will help you identify the ICs and transistors and locate the relevant

	portions of the circuitry.

	

	If there is no voltage at the horizontal output transistor, then there

	is probably a blown fuse or bad connection somewhere or a fault in the

	line operated SMPS if there is one.  However, the fuse may have blown

	due to a fault in the SMPS or horizontal deflection.

8.3) Power button on monitor is flakey

	If the on/off (or other button) on the monitor itself behaves erratically

	then the most likely cause is the obvious - the button or switch is dirty

	or worn.  On a momentary pushbutton, if you can get at it, some contact

	cleaner may help.

	

	If power is controlled by a hard switch - a mechanical push-push latching

	switch and this has become erratic due to worn contacts or just plain broken,

	replacements may be available but often only directly from the original

	manufacturer to physically fit.  As an alternative, consider mounting a small

	toggle switch on the side of the cabinet to substitute for the defective one.

	This will almost certainly be easier and cheaper - and quite possibly, more

	reliable.

8.4) Monitor blows fuse

	If the fuse really blows absolutely instantly with no indication that the

	circuits are functioning (no high pitched horizontal deflection whine (if

	your dog hides under the couch whenever the monitor is turned on, deflection

	is probably working)), then this points to a short somewhere quite near

	the AC power input.  The most common places would be:

	

	        * Degauss Posistor - very likely.

	        * MOV or other surge suppressor.

	        * Horizontal output transistor (if deflection derived power supply)

	        * Power supply regulator if there is one.

	        * Switchmode power transistor if there is a line operated SMPS.

	        * Diode(s) in main bridge

	        * Main filter capacitor(s).

	

	You should be able to eliminate these one by one.

	

	Unplug the degauss coil as this will show up as a low resistance.

	

	First, measure across the input to the main power rectifiers - it

	should not be that low.  A reading of only a few ohms may mean a

	shorted rectifier or two, a shorted Posistor, or a fried MOV.

	

	* Test the rectifiers individually or remove and retest the resistance.

	

	* Some monitors use a Posistor for degauss control.  This is a little cubical

	  (about 1/2" x 3/4" x 1") component with 3 legs.  It includes a line

	  operated heater disk (which often shorts out) and a PTC thermister to

	  control current to the degauss coil.  Remove the posistor and try power.

	  If the monitor now works, obtain a replacement but in the meantime you

	  just won't have the automatic degauss.

	

	If these test good, use an ohmmeter with the monitor unplugged to measure

	the horizontal output transistor or SMPS switchmode transistor.  Even

	better to remove it and measure it.

	

	* C-E should be high in at least one direction.  (Both directions should be

	  high if the transistor does not have an internal damper diode).

	

	* B-E should be high in one direction and not shorted in the other or around

	  50 ohms in both directions (typical for transistors with internal damper

	  diodes) but should not be near 0.

	

	If any readings are under 5 or 10 ohms, the transistor is bad.  The parts

	sources listed at the end of this document will have suitable replacements.

	

	If this tests bad, try powering the monitor first with your light bulb and if

	it just flashes once when the capacitor is charging, put a proper fuse in

	and try it.  The fuse should not blow with the transistor removed.

	

	Of course, not much else will work either.

	

	Install a new transistor and power the monitor using your series light bulb.

	If the bulb now flashes once and then settles down to a low brightness level,

	the monitor may be fine.  See if there is an indication of deflection and

	HV - look for the glow of the CRT filaments and turn up the brightness to

	see if there is any indication of a raster.  With the light bulb, not

	everything will be normal but some life would be a good sign.  Even a

	pulsating light bulb may just mean that the light bulb is too small for

	the monitor power requirements.  It may be safe to try a higher wattage bulb.

	

	If the bulb glows at close to full brightness, there is probably still some

	fault elsewhere.  Don't be tempted to remove the light bulb just yet.

	There could be problems with the driving circuits, flyback, secondary loads,

	or with the feedback from the voltages derived from the horizontal not

	regulating properly.

	

	See if you can locate any other large power transistors in metal (TO3) cans

	or large plastic (TOP3) cases.  There may be a separate power transistor

	that does the low voltage regulation or a separate regulator IC or hybrid.

	As noted, some monitors have a switchmode power supply that runs off

	a different transistor than the HOT.  There is a chance that one of these

	may be bad.

	

	If it is a simple transistor, the same ohmmeter check should be performed.

	

	If none of this proves fruitful, it may be time to try to locate a schematic.

	

	A blown fuse is a very common type of fault due to poor design very often

	triggered by power surges due to outages or lightning storms.  However,

	the most likely parts to short are easily tested, usually in-circuit, with

	an ohmmeter and then easily removed to confirm.

	

	Occasionally, fuses simply tire of life and just replacing the fuse will

	be all that is needed.

	

	Even if it is more involved than this, if you find the problem and repair

	it yourself, the cost is likely to be under $25.

8.5) Internal fuse blew during lightning storm (or elephant hit power pole)

	Power surges or nearby lightning strikes can destroy electronic equipment.

	However, most of the time, damage is minimal or at least easily repaired.

	With a direct hit, you may not recognize what is left of it!

	

	Ideally, electronic equipment should be unplugged (both AC line and phone

	line!) during electrical storms if possible.  Modern TVs, VCRs, microwave

	ovens, and even stereo equipment is particularly susceptible to lightning and

	surge damage because some parts of the circuitry are always alive and therefore

	have a connection to the AC line.  Telephones, modems, and faxes are directly

	connected to the phone lines.  Better designs include filtering and surge

	suppression components built in.  With a near-miss, the only thing that may

	happen is for the internal fuse to blow or for the microcontroller to go

	bonkers and just require power cycling.  There is no possible protection

	against a direct strike.  However, devices with power switches that totally

	break the line connection are more robust since it takes much more voltage

	to jump the gap in the switch than to fry electronic parts.  Monitors and

	TVs may also have their CRTs magnetized due to the electromagnetic fields

	associated with a lightning strike - similar but on a smaller scale to

	the EMP of a nuclear detonation.

	

	Was the monitor operating or on standby at the time?  If it was switched

	off using an actual power switch (not a logic pushbutton), then either

	a component in front of the switch has blown, the surge was enough to

	jump the gap between the switch contacts, or it was just a

	coincidence (yeh, right).

	

	If it was operating or on standby or has no actual power switch, then

	a number of parts could be fried.

	

	Monitors usually have their own internal surge protection devices like MOVs

	(Metal Oxide Varistors) after the fuse.  So it is possible that all that is

	wrong is that the line fuse has blown.  Remove the case (unplug it first!) and

	start at the line connector.  If you find a blown fuse, remove it and measure

	across the in-board side of fuse holder and the other (should be the neutral)

	side of the line.  The ohmmeter reading should be fairly high - more than 100

	ohms in at least one direction.  You may need to unplug the degaussing coil

	to get a reasonable reading as its resistance may be less than 30 ohms.  If

	the reading is really low, there are other problems.  If the resistance checks

	out, replace the fuse and try powering the monitor.  There will be three

	possibilities:

	 

	1. It will work fine, problem solved.

	

	2. It will immediately blow the fuse.  This means there is at least one

	   component shorted - possibilities include an MOV, line rectifiers, main

	   filter cap, regulator transistor, horizontal output transistor, etc.  You

	   will need to check with your ohmmeter for shorted semiconductors.  Remove

	   any that are suspect and see of the fuse now survives (use the series

	   light bulb to cut your losses - see the section: "The series light bulb trick".

	

	3. It will not work properly or appear dead.  This could mean there are

	   open fusable resistors other defective parts in the power supply or

	   elsewhere.  In this case further testing will be required and at some

	   point you may need the schematic.

	

	If the reading is very low or the fuse blows again, see the section:

	"Monitor blows fuse".

8.6) Fuse replaced but monitor clicks with power-on but no other action

	The click probably means that the power relay is working, though there could

	be bad contacts.

	

	Since the fuse doesn't blow now (you did replace it with one of the same

	ratings, right?), you need to check for:

	

	* Other blown fuses - occasionally there are more than one in a TV.

	

	Replace with one of exactly the same ratings.

	

	* Open fusable resistors.  These sometimes blow at the same time or in

	  place of the fuses.  They are usually low values like 2 ohms and are in

	  big rectangular ceramic power resistor cases or smaller blue or gray

	  colored cylindrical power resistors.  They are supposed to protect

	  expensive parts like the HOT but often blow at the same time (or the

	  pricey HOT sacrifices itself to save the resistor.)

	

	If any of these are bad, they will need to be replaced with flameproof

	resistors of the same ratings (though you can substitute an ordinary

	resistor for testing purposes).  Before applying power, check: Rectifier

	diodes, horizontal output transistor, regulator pass or chopper transistor

	(if present), and main filter capacitor for shorts.

	

	An initial test with an ohmmeter can be done while in-circuit.  The

	resistance across each diode and the collector to emitter of the

	transistors should be relatively high - a few hundred ohms at lest -

	in at least one direction (in-circuit).  If there is a question, unsolder

	one side of each diode and check - should be in the Megohms or higher in

	one direction.  Removed from the circuit, the collector-emitter resistance

	should be very high in one direction at least.  Depending on the type,

	the base-emitter resistance may be high in one direction or around 50 ohms.

	If any reading on a semiconductor device is under 10 ohms - then the device

	most likely bad.  Assuming that you do not have a schematic, you should

	be able to locate the rectifiers near where the line cord is connected and

	trace the circuit.  The transistors will be either in a TO3 large metal can

	or a TOP3 plastic package - on heat sinks.  The filter capacitor should

	eventually measure high in one direction (it will take a while to charge

	from your ohmmeter).   It could still be failing at full voltage, however.

	

	If you find one bad part, still check everything else as more than one part

	may fail and just replacing one may cause it to fail again.

	

	Assuming nothing tests faulty so far, clip a voltmeter set on its 500 V or

	higher scale across the horizontal output transistor and turn the power on.

	Warning - never measure this point if the horizontal deflection is operating.

	It is ok now since the monitor is dead.  If the voltage here is 100-150, then

	there is a problem in the drive to the horizontal output circuit.  If it

	is low or 0, then there are still problems in the power supply or with the

	winding on the flyback transformer or one of its outputs.

	

	Other possible problems: bad hybrid voltage regulator, bad startup circuit,

	bad relay contacts as mentioned above.

8.7) Power-on tick-tick-tick or click-click-click but no other action

	A variety of power supply or startup problems can result in this or

	similar behavior.  Possibilities include:

	

	* Lack of startup horizontal drive (see the section: "Startup problems - nothing happens, click, or tick-tick-tick sound".)  The main regulator is

	  cycling on overvoltage due to lack of load.

	

	* Excessive load or faulty power supply cycling on its overcurrent

	  protection circuit.

	

	* HV shutdown, or some other system detecting an out of regulation condition.

	  However, in this case, there should be some indication that the deflection

	  and HV is attempting to come up like momentary high pitched deflection whine,

	  static on the screen, etc.

	

	* A dried up main filter capacitor or other filter capacitor in the low

	  voltage power supply that is producing an out-of-regulation condition

	  A bad filter capacitor on the output of a series regulator may also

	  result in excessive voltage and shutdown.

	

	* A problem with the microcontroller, relay or its driver, or standby

	  power supply.

	

	One possible test would be to vary the line voltage and observe the

	set's behavior.  It may work fine at one extreme (usually low) or the

	other.  This might give clues as to what is wrong.

	

	Also see the section: "Dead monitor with periodic tweet-tweet-tweet or

	flub-flub-flub, low-low voltage".

8.8) No picture but indications of power

	The screen is blank with no raster at all.  There are indications that the

	power is alive - the status LEDs are lit and you can hear the normal

	relay clicking sounds when you change video modes.  This indicates that some

	of the low voltages are present but these may be derived from the standby

	supply.

	

	Assuming there is no deflection and no HV, you either have a low

	voltage power supply problem, bad startup circuit, or bad horizontal

	output transistor (HOT)/bad parts in the horizontal deflection.

	

	Check for bad fuses.

	

	(If you have HV as indicated by static electricity on the front of the

	screen and you hear the high pitched whine of the horizontal deflection

	when it is turned on, then the following does not apply).

	

	1. Use an ohmmeter to test the HOT for shorts.  If it is bad, look for

	   open fusable resistors or other fuses you did not catch.

	

	2. Assuming it is good, measure the voltage on the collector-emitter

	   of the HOT (this is safe if there is no deflection).  You should see

	   the B+ of between 60 and 150 V (typical) depending on mode (for a

	   auto-scan monitor).

	

	3. If there is no voltage, you have a low voltage power supply problem

	   and/or you have not found all the bad/open parts.  The flyback primary

	   winding may be open as well.

	

	4. If there is voltage and no deflection, you probably have a startup

	   problem - all TVs need some kind of circuit to kick start the horizontal

	   deflection until the auxiliary power outputs of the flyback are available.

	   Some designs use a simple multivibrator for this - a couple of transistors.

	   Others power the horizontal oscillator IC from a special line-derived

	   voltage.

	

	   Look for pulses at the HOT base.  If there are none, trace back to the 

	   driver and oscillator.  Most likely: the power for startup is missing.

	

	   Test the transistors if it is that type with an ohmmeter.  If one is

	   shorted, you have a problem.  The usual way a TV service person would

	   test for startup problems is to inject a signal to the base of the HOT

	   of about 15.75 KHz.  If the TV then starts and runs once this signal

	   is removed, the diagnosis is confirmed.  This is very risky for monitors

	   and I would not recommend it - you can all too easily blow things up if

	   not careful (including yourself).

	

	If you hear the high pitched whine of the deflection (probably not for

	workstation or SVGA computer monitors unless you are a bat) and/or feel

	some static on the scree, confirm that the horizontal deflection and high

	voltage are working by adjusting the SCREEN control (probably on the flyback).

	If you can get a raster then your problem is probably in the video (or chroma)

	circuits, not the deflection or high voltage.

8.9) Monitor mostly dead, possible whine from power supply

Note that this may be perfectly normal for your monitor if there is no video

input - confirm that there is a signal that is compatible with the monitor's

scan rate(s) and sync. Make sure the sync selection is set appropriately

as well.

This may indicate an overloaded low voltage switching power supply.

The whine is caused by the switching power supply's chopper frequency

dropping down due to the overload.

Test the B+ to the horizontal deflection circuits (B+ input to the flyback).

If it is near zero, test the HOT for shorts and replace but continue

testing with a series light bulb and/or Variac. There may be something

causing the HOT to go bad like a shorted flyback or bad damper diode or

snubber cap.

If the voltage is not zero but is low (e.g., it should be 120 V but is

only 60 V), there may be a problem with:

1. Defective low voltage power supply. Test with a substitute load like

a 40 W light bulb or power resistor. If the supply now outputs full

voltage, it is probably fine. For a power resistor, select a value such

that the load at the expected voltage will be about 1/2 to 2/3 of the

nameplate power rating of the monitor. Make sure the resistor can handle

this power dissipation!

2. Flyback (LOPT) transformer - shorted windings. See the section:

"Testing of Flyback (LOPT) Transformers".

3. Deflection yoke - shorted turns in the horizontal or geometry correction

windings. Unplug the yoke if possible and very slowly bring up the

monitor on a Variac. Be careful - if you now get high voltage, you

may get a very bright spot in the center of the screen which will

quickly turn to a very dark spot in the center of the screen - turn

the screen (G2) control down and don't run in this state for more than a

few seconds. The problem may not be in the yoke but in the circuitry

around it. Quickly test the B+. It will probably now be normal.

With the yoke connected, use an oscilloscope to monitor the collector

of the HOT using a Variac to bring up the voltage slowly. This is safe

since you will not be going to full B+ - just enough to look at the

signal shape (don't let the collector signal go over a couple hundred

volts). The waveform should be a clean pulse during retrace and nearly

zero during active video. Ideally it will look like a sinusoidal positive

half cycle. If there are dips, serious ringing, or other uglies, then

there is likely a fault in the flyback, horizontal deflection coils, or

associated circuitry. Pull off the yoke connector and repeat. If it is

now clean, suspect the yoke or other components directly connected to it

(geometry correction coils, caps, etc.).

If you suspect the yoke perform a 'ring test'. See the section: "Testing of Flyback (LOPT) Transformers" since similar techniques may be used.

4. Excess load on one of the flyback's secondaries. Disconnect all secondary

output pins from the flyback if possible and see if your B+ returns to

normal. Of course, much of the monitor will not work without these

power supplies. You will then need to test the components in each of

these supplies and/or reconnected them one by one.

5. Improper drive to HOT. Inspect with an oscilloscope. The drive should

match the video input - its frequency should match the horizontal rate

with a high time equal to the active video - typically 75-85% of the

total line time. If it is on for too long, or of incorrect frequency,

the output will not be correct and there may be excessive load on the

low voltage power supply.

8.10) Reduced width picture and/or hum bars in picture

	The most likely cause is a dried up main filter capacitor.  Once the

	effective capacitance drops low enough, 120 Hz (or 100 Hz in countries with

	50 Hz power) ripple will make its way into the regulated DC supply

	(assuming full wave rectification).

	

	Another likely cause of similar symptoms is a defective low voltage

	regulator allowing excessive ripple.  The regulator IC could be bad

	or filter capacitor following the IC could be dried up.

	

	Either of these faults may cause:

	

	1. A pair of wiggles and/or hum bars in the picture which will float up

	   the screen.  For NTSC where the power line is 60 Hz but the frame rate

	   is 59.94 Hz, it will take about 8 seconds for each bar to pass a given

	   point on the screen.  (On some sets, a half wave recitifier is used

	   resulting in a single wiggle or hum bar).

	

	   For high scan rate computer monitors, the this may result in horizontal

	   hum bars, wiggles, or other distortions that will drift up or down

	   the screen based on the difference frequency between the power line

	   and video refresh rate being supplied by the PC or workstation.  A

	   confirmation can be obtained by varying the scan rate and seeing if

	   the rate of drift changes predictably.

	

	2. Possible regulation problems resulting in HV or total shutdown or power

	   cycling on and off.

	

	The best approach to testing the capacitors is to clip a good capacitor of

	approximately the same uF rating and at least the same voltage rating across

	the suspect capacitor (with the power off).  A capacitor meter can also

	be used but the capacitor may need to be removed from the circuit.

	

	Once the capacitors have been confirmed to be good, voltage measurements

	on the regulator should be able to narrow down the problem to a bad IC

	or other component.

8.11) Dead monitor with periodic tweet-tweet-tweet, flub-flub-flub, low-low voltage

	A monitor which appears to be dead except for a once a second or so tweet or

	flub usually indicates an overload fault in the power supply or a short in one

	of its load circuits.  In some cases, the low voltage (including B+) will just

	be reduced to a fraction of their normal value as a result of an overload on

	one of the outputs - usually the main B+.

	

	Shorted rectifiers in the switching supply or secondary supplies running off

	the flyback common.  The HFR854s (one popular type in monitors) or other high

	speed high efficiency rectifiers in the output side of the switching power

	supply or flyback seem to like to turn into short circuits.  (I had a couple

	of DOA monitors where this was the problem. so much for quality control!)

	

	After unplugging the monitor and waiting a few minutes for the filter

	capacitors to discharge (check with a voltmeter but stay away from the

	CRT HV connector as it may retain a dangerous and painful charge for a long

	time), use an ohmmeter across the various diodes in the power supply.

	These appear commonly as black cylinders about 3/8" long by 1/4 diameter.

	(Kind of like 1N400Xs on steroids).  The resistance of the diodes

	in at least one direction should be greater than 100 ohms.

	If it is much less (like 0 or 5 ohms), then the diode is probably bad.

	Unsolder and check again - it should test infinite (greater than 1M ohms) in

	one direction.  If it now tests good, there may be something else that

	is shorted.

	

	Replacements are available for about $.25 from places like MCM Electronics.

	

	Check other power semiconductors as well, in particular, the horizontal

	output transistor.

	

	Sometimes this is an indication of an *overvoltage shutdown* due to a faulty

	regulator or open load.

	

	Summary of possible causes:

	

	        * Bad solder connections.

	        * Other shorted components like capacitors.

	        * Other problems in the power supply or its controller like bad caps.

	        * Bad flyback.

	        * Short or excessive load on secondary supplies fed from flyback.

	        * Short in horizontal yoke windings.

	        * Problem with startup drive (cycling on overvoltage).

8.12) Monitor power cycling on and off

	The power light may be flashing or if you are runing with a series light bulb

	it may be cycling on and off continuously.  There may be a chirping or clicking

	sound from inside the set.  (Note: using too small a light bulb for the size of

	the monitor may also result in this condition.)

	

	If there is a low voltage regulator or separate switching supply, it could be

	cycling on and off if the horizontal output, flyback, or one of its secondary

	loads were defective.

	

	Does this monitor have a separate low voltage regulator and/or switching power

	supply or is it all part of the flyback circuit?  For the following, I assume

	it is all in one.

	

	Some simple things to try first:

	

	Verify that the main filter capacitor is doing its job.  Excessive ripple

	on the rectified line voltage bus can cause various forms of shutdown

	behavior.  An easy test is to jumper across the capacitor with one of

	at least equal voltage rating and similar capacitance (make connections

	with power off!).

	

	Use a Variac, if possible, to bring up the input voltage slowly and see if

	the monitor  works at any point without shutting down.  If it does, this

	could be an indication of X-ray protection circuit kicking in, though this

	will usually latch and keep the set shut off if excessive HV were detected.

	

	Since the monitor is not totally dead - there are some signs of life - the 

	once a second or so tweet or flup - this often means that the switching

	power supply has a short in one of its load circuits, very often a shorted

	rectifier.  It could also be the flyback, but check the the loads first.

	Wait a few minutes for the filter caps to discharge (but stay away from the

	CRT HV connector as it may retain a dangerous and painful charge for a long

	time), use an ohmmeter across the various diodes in the power supply.

	Using an ohmmeter on the  rectifier diodes, the resistance in at least one

	direction should be greater than 100 ohms.  If it is much less (like 0 or 5

	ohms), then the diode is probably bad.  Unsolder and check again - it should

	test infinite (greater than 1M ohms) in one direction.

	

	Other possible causes:

	

	        * Bad solder connections.

	        * Other shorted components like capacitors.

	        * Other problems in the power supply.

	        * Bad flyback.

	        * Short or excessive load on secondary supplies fed from flyback.

	        * Problem with startup drive (cycling on overvoltage).

8.13) Shorted Components

	A failure of the horizontal output transistor or power supply switchmode

	transistor will blow a fuse or fusable resistor.

	

	Look for blown fuses and test for open fusable resistors in the power circuits.

	If you find one, then test the HOT and/or switchmode transistor for shorts.

	

	Other possibilities: rectifier diodes or main filter capacitor.

	

	While you are at it, check for bad connections - prod the circuit board with an

	insulated stick when the problem reoccurs - as these can cause parts to

	fail.

8.14) Startup problems - nothing happens, click, or tick-tick-tick sound

	TVs and monitors usually incorporate some kind of startup circuit to provide

	drive to the horizontal output transistor (HOT) until the flyback power supply

	is running.  Yes, TVs and monitors boot just like computers.

	

	There are two typical kinds of symptoms: power on click but nothing else

	happens or a tick-tick-tick sound indicating cycling of the low voltage

	(line regulator) but lack of startup horizontal drive.

	

	Check the voltage on the horizontal output transistor (HOT).  If no voltage

	is present, there may be a blown fuse or open fusable resistor - and

	probably a shorted HOT.

	

	However, if the voltage is normal (or high) - usually 60-150 V depending

	on scan rate (for an auto-scan monitor), then there is likely a problem with

	the startup circuit not providing initial base drive to the HOT.

	

	The startup circuits may take several forms:

	

	1. Discrete multivibrator or other simple transistor circuit to provide

	   base drive to the HOT.

	

	2. IC which is part of deflection chain powered off of a voltage divider

	   or transformer.

	

	3. Other type of circuit which operates off of the line which provides

	   some kind of drive to the HOT.

	

	The startup circuit may operate off of the standby power supply or

	voltage derived from non-isolated input.  Be careful - of course, use

	an isolation transformer whenever working on TVs and especially for power

	supply problems.

	

	Note that one common way of verifying that this is a startup problem is

	to inject a 15 KHz signal directly into the HOT base or driver circuit

	(just for a second or two).  If the TV then starts up and continues to run,

	you know that it is a startup problem.

	

	Caution: be careful if you do this.  The HOT circuit may be line-connected

	and it is possible to destroy the HOT and related components if this is not

	done properly.  I once managed to kill not only the HOT but the chopper

	transistor as well while working in this area.  An expensive lesson.

	

	I have also seen startup circuits that were designed to fail.  Turning

	the TV on and off multiple times would exceed the power ratings of the

	components in the startup circuit.  Some Zenith models have this 'feature'.

	

	When this situation exists, it could be that the circuit is not providing

	the proper drive or that due to some other circuit condition, the drive

	is not always sufficient to get the secondary supplies going to the point

	that the normal circuits take over.

	

	I would still check for bad connections - prod the circuit board with an

	insulated stick when the problem reoccurs.

8.15) Monitor turns off after warming up

	If you can turn it back on with the s momentary key or power button:

	

	When it shuts off, do you need to push the power button once or twice

	to get it back on?  Also, does anything else about the picture or sound

	change as it warms up?

	

	1. If once, then the controller is shutting the TV down either as a result of

	   a (thermally induced) fault in the controller or it sensing some other

	   problem.  Monitoring the voltage on the relay coil (assuming these

	   is one) could help determine what is happening.  The controller thinks

	   it is in charge.

	

	2. If twice, then the power supply is shutting down as the controller still

	   thinks it is on and you are resetting it.  A couple of possibilities

	   here would be low voltage or high voltage regulation error (excessive

	   high voltage is sensed and causes shutdown to prevent dangerous X-ray

	   emission).  A partially dried up main filter capacitor could also cause a

	   shutdown but there might be other symptoms like hum bars in the picture just

	   before this happened.  Clipping a good capacitor across the suspect (with

	   power off!) would confirm or eliminate this possibility.

	

	If it uses a hard on/off switch, then this may be like pulling the plug

	and would reset any abnormal condition.

8.16) Monitor doesn't power up immediately

	The monitor may do nothing, cycle on and off for a while, power up and then

	shutdown in an endless cycle - or at least for a while.  Then it comes

	on and operates normally until it is turned off.

	

	A couple of possibilities:

	

	1. The main filter capacitor or other filter capacitors in the low voltage

	   power supply is dried up and this can cause all kinds of regulation

	   problems.

	

	2. The power supply regulator is defective (or marginal) allowing excessive

	   voltage on its output and then the X-ray protection circuitry shuts

	   you down.

	

	If you can get access to a Variac, it would be worth bringing up the input

	voltage slowly and seeing if there is some point at which it would stay on.

	

	If there is, then if the picture has serious hum bars in it the main filter

	cap could be bad.  If more or less a decent picture with minor hum bars then

	it could be the regulator.

8.17) Old monitor requires warmup period

	So, what else is new?  In the old days, a TV or monitor was expected to take

	a few minutes (at least) to warm up.  We are all spoiled today.  Of course,

	you usually maintained a full time technician or engineer to fiddle with the

	convergence adjustments!

	

	If it just takes a while for the picture to become as bright as you like,

	this is probably just a result of an old tired CRT (see the section: Monitor

	life and the care and feeding of CRTs" and "Brightening an old CRT".  If,

	however, nothing happens for a few minutes, then some component needs to be

	powered for a while before it starts cooperatings.  This is probably a dried

	up capacitor in the power supply since that is drifting with temperature and

	needs to be located with cold spray or a heat gun.

8.18) Monitor shuts down with bright picture or when brightness is turned up

	This is probably a protection circuit kicking in especially if turning power

	off or pulling the plug is required to restore operation.

	

	The detection circuit could be in the power supply or horizontal deflection

	output circuit.  It may be defective or the current may be too high for some

	other reason.  A couple of tests can be performed to confirm that it is due

	to beam current:

	

	* Determine if behavior is similar when adjusting the user brightness control

	  and the screen (G2) pot (on the flyback) or master brightness control.  If

	  the monitor quits at about the same brightness level, overcurrent protection

	  is likely.

	

	* Disconnect the filaments to the CRT (unsolder a pin on the CRT socket) and

	  see if it still shuts down under the same conditions.  If it is overcurrent

	  protection, shut down should now *not* take place since there is no beam

	  current.

8.19) Power supply interactions

	This describes problems like turning up the brightness causes a loss

	of sync or adjusting height also affects width.

	

	These may be caused by poor regulation in one or more low voltage power

	supplies or and interaction between the high voltage and low voltage

	power supplies - possibly a dried up capacitor if it is relatively old,

	bad connections, or another faulty component.  Measure the B+ to the

	horizontal deflection (to the flyback, not the horizontal output transistor).

	If it is changing with the problem, then a regulation problem is confirmed.

	If this voltage is solid, you will need to check the others to see which

	one is actually changing.

8.20) Relays in the Power Circuitry of monitors

	What exactly is the purpose of such a relay ... i.e., why doesn't the power

	switch on the monitor just apply power directly instead of through a relay?

	

	On a TV, the usual reason for a relay instead of a knob switch is to permit

	a remote control to turn power on and off.  If your TV does not have a remote,

	then it is simply the same chassis minus 24 cents worth of circuitry to do the

	remote function.  Isn't marketing wonderful?

	

	On a monitor without any remote control, there can be two likely reasons:

	

	1. Reduce the needed capacity of the on/off switch.  High resolution

	   monitors do consume a fair amount of power.  A soft touch button may

	   be more elegant or cheaper.

	

	2. Allow for automatic power saving 'green' operation.

	

	When replacing a relay, only unknown is the coil voltage.  It is probably

	somewhere in the 6-12 volt range.  You should be able to measure this on

	the coil terminals in operation.  It will be a DC coil.

	 

	However, the relay controls the 125 VAC (or 220) which you should treat

	with respect - it is a lot more dangerous than the 25KV+ on the CRT!

	

	Almost certainly, the relay will have 4 connections - 2 for power and 2

	for the coil.  If it is not marked then, it should be pretty easy to

	locate the power connection.  One end will go to stuff near the AC line

	and the other end will go to the rectifier or maybe a fusable resistor

	or something like that.  These will likely be beefier than the coil

	connections which will go between a transistor and GND or some low voltage,

	or maybe directly into a big microcontroller chip.

	

	Of course, the best thing would be to get the schematic but with monitors

	this may not be easy.

	

	Once you are sure of the AC connections - measure across them while it is

	off and also while it is on.  While off, you should get 110-125 VAC.

	While on and working - 0.  While on and not working either 110-125 VAC

	if the relay is not pulling in or 0 if it is and the problem is elsewhere.

	We can deal with the latter case if needed later on.  Note the even if the

	relay contacts are not working, the problem could still be in the control

	circuitry not providing the correct coil voltage/current, though not likely.

	

	It may be expensive and/or difficult to obtain an exact replacement, but

	these are pretty vanilla flavored as relays go.  Any good electronics

	distributor should be able to supply a suitable electrical replacement

	though you may need to be creative in mounting it.

8.21) What is a posistor?

	A posistor is a combination of a PTC (positive temperature coefficient)

	resistor and another resistor-element to heat it up and keep it hot.

	Sometimes, these will go by the name posister or thermister.  The heater

	is a disk shaped resistor across the power line and the themister

	is a disk shaped device in series with the degauss coil.  They are in

	clamped together to be in close contact thermally.  You can pry off the

	lid and see for yourself.

	

	The most common failure mode is for the part to short across the line.

	

	Its function is to control degauss, so the only thing you lose when you

	remove one of these is the degauss function on power-on.  When you turn

	the TV or monitor on, the PTC resistor is cold and low resistance.  When

	heated, it becomes very high resistance and turns off the degauss coil

	but gradually - the current ramps down to zero rather than being abruptly

	cut off..

	

	Computer Component Source stocks a wide variety, I believe but it may be

	cheaper to go direct to the manufacturer if they will sell you one.

8.22) Flameproof Resistors

	Flameproof Resistor or Fusable Resistor are often designated by the

	symbol 'FR'. They are the same.

	

	You may see these in the switchmode power supplies used in TVs and monitors.

	They will look like power resistors but will be colored blue or gray, or may

	be rectangular ceramic blocks.  They should only be replaced with flameproof

	resistors with identical ratings.  They serve a very important safety function.

	

	These usually serve as fuses in addition to any other fuses that may be

	present (and in addition to their function as a resistor, though this isn't

	always needed).  Since your FR has blown, you probably have shorted

	semiconductors that will need to be replaced as well.  I would check

	all the transistors and diodes in the power supply with an ohmmeter.

	You may find that the main switch mode transistor has decided to turn into

	a blob of solder - dead short.  Check everything out even if you find one

	bad part - many components can fail or cause other components to fail

	if you don't locate them all.  Check resistors as well, even if they look ok.

	

	Since they function as fuses, flameproof resistors should not be replaced

	with higher wattage types unless specifically allowed by the manufacturer.

	These would not blow at the same level of overload possibly resulting in

	damage to other parts of the circuitry and increasing the risk of fire.

	

	Then, with a load on the output of the power supply use a Variac to bring

	up the voltage slowly and observe what happens.  At 50 VAC or less, the

	switcher should kick in and produce some output though correct regulation

	may not occur until 80 VAC or more.  The outputs voltages may even be

	greater than spec'd with a small load before regulation is correct.

Chapter 9) Deflection Problems

9.1) Deflection fundamentals

Note: the following is just a brief introduction. For more detailed deflection

system theory of operationo and sample circuits, see the document: "TV and Monitor Deflection Systems".

The electron beams in the CRT need to be scanned horizontally and vertically

in a very precise manner to produce a raster - and a picture.

For NTSC and PAL, the horizontal scan rates are 15,734 and 15,625 Hz

respectively, the vertical scan rates are 60 and 50 Hz (approximately)

respectively.

For PCs and workstation monitors, a wide range of scan rates are used.

For example:

Standard Horizontal, KHz Vertical, Hz

------------------------------------------------

MDA 18.43 50

CGA 15.75 60

EGA 15.75-21.85 60

VGA 31.4 60-70

SVGA (800x600) 35-40 50-75+

SVGA (1024x768) 43-52+ 43-75+

SVGA (1280x1024) 64-72+ 60-75+

Workstations 64-102+ 60-76+

Even in high resolution fixed frequency monitors, these high horizontal

(in particular) scan rates necessitate some fancy circuit design. All

components are running under stressful conditions and it is amazing that

failures are not more common.

With auto-scan monitors, the complexity of the circuits increases dramatically

to accommodate the wide range of horizontal scan rates. Relays or electronic

switches are used to select power supply voltages, tuning components, and

to make other alternations in the deflection circuits to handle DOS VGA

one minute and Autocad 1280x1024 the next. It comes as no surprise that

the most stressful time for a monitor is when switching scan rates.

Unfortunately, successfully diagnosing problems dealing with the scan

switching logic and circuitry is virtually impossible without a schematic.

The deflection yoke includes sets of coils for horizontal and vertical

scanning oriented at 90 degrees with respect to each other. Additional

coils are needed to correct for pincushion and other geometric defects.

The deflection circuits must be synchronized and phase locked to the

incoming video signal.

Therefore, we have the following functions:

1. Sync separator to obtain horizontal and vertical synchronization pulses

for monitors with composite video or sync inputs. Input sync detectors

and auto polarity switching circuits as needed for separate horizontal

and vertical sync inputs.

2. Horizontal oscillator which locks to horizontal sync pulses.

3. Horizontal drive followed by horizontal output which feeds deflection

yoke (and flyback for HV and other voltages), Yoke requires a sawtooth

current waveform for linear horizontal deflection. Horizontal output

in all but the smaller TVs or monitors is a large discrete power

transistor, most often an NPN bipolar type.

4. Vertical oscillator which locks to vertical sync pulses. Yoke requires

sawtooth waveform for linear vertical deflection.

5. Vertical drive/output which feeds vertical deflection yoke. Newer TVs

and monitors use ICs for vertical drive and output.

6. Various additional deflection signals to correct for the imperfections

in the geometry of large angle deflection CRTs. These may be fed into

the normal deflection coils and/or there may be separate coils mounted

on the neck of the CRT.

7. Auto-scan deflection control and selection circuitry (auto-scan monitors

only), probably controlled by a microprocessor which stores scan

parameters for each scan rate and automatically detects the appropriate

settings to use by analyzing the input video. For horizontal deflection,

the usual way of size constant regardless of scan rate is to scale the

B+ to the HOT with horizontal frequency. Thus, VGA resolution may us

60 V B+ while 1280x1024 at 75 Hz may require 150 V. Various other

components may need to be selected based on scan rate. Relays are often

used for this selection since they are easy to control and can handle the

voltages and currents in the various deflection circuits reliably.

9.2) Monitor display is off-center

	These sorts of problems usually relate to the picture shifting when switching

	between applications or between DOS and Windows.

	

	A couple things to check if you have a setup program for your video card

	(1-3 are software adjustments in the DOS setup program):

	

	1. Make sure you are running well withing the accepted scan rates for each

	   resolution.

	

	2. Toggle sync polarity and see if this makes any difference.

	

	3. Adjust H position or phase and see what this does.

	

	4. Make sure your cables are secure.  While a bad connection would likely

	   messed things up worse, it won't hurt to check.

	

	Your monitor may have a problem though it is not likely to be major (in

	a relative way).  If you still like the monitor, repair may be worth the

	money.  However, not doing anything now may lead to more serious (and

	costly monitor damage.

9.3) Gross problems in size or position at certain scan rates

	First, make sure you are not specifying incorrect scan rate for your monitor.

	Check your video card setup and/or monitor selection in Win95.

	

	Assuming you are not violating the scan rate specifications but have a

	picture that is twice the height of the screen and one half the width,

	for example, this could indicate a failure in the scan rate switching

	circuitry of an auto-scan monitor.  Either the logic is faulty and ordering

	the wrong selections for power supply voltage and tuning components or the

	relays or the relevant parts are faulty.  This could be due to bad connections

	as well - quite likely in fact.  Also, try to reset the afflicted parameters

	using the digital controls (if relevant) and confirm that your video card

	is putting out the correct scan rate - try another monitor or examine the

	video signals with an oscilloscope.

	

	Try prodding the circuit boards with an insulated stick - this may identify

	bad connections or unstick a sticky relay.

	

	A schematics will likely be needed to proceed further with these sorts of

	problems.

9.4) Reduced width

Complaints about the picture not filling the screen with computer monitors

are common but may not indicate problems (except with your expectations).

Older monitors, in particular, often did not allow a full screen display

at certain resolutions. There may be underscan modes/switches as well.

Keep in mind that advertizing a large diagonal CRT does not necessarily

imply that you can fill it!

However, if this problem just happened with no changes to your computer system

(video card, scan rates, O/S), then the following are possibilities:

* The B+ to the horizontal output is lower than normal. The way width control

functions is that as you increase the horizontal scan rate, the B+ to the

HOT must increase to keep the width constant. It could be that yours is

low to start with and not tracking scan rate changes either.

* A bad capacitor might also result in reduced width but I would expect

non-linearity as well.

* As noted in the section: "Gross problems in size or position at certain scan rates", there could be problems in the scan rate switching circuitry

selecting incorrect components for certain scan rates.

* There might be a bad (low value or high ESR) decoupling capacitor.

Scope the rail after the low-value decoupling R for H-rate stuff.

There shouldn't be anything significant. If there is, the ESR of the

decoupling capacitor is too high or its value is too low. Seen it

often where it also cooks the decoupling R, because the efficiency of

the H-out becomes poor. (
This email address is being protected from spam bots, you need Javascript enabled to view it
(Gary Woods)).

* A more unlikely possibility is a open yoke winding. The horizontal

deflection yoke consists of multiple windings in parallel so it is

theoretically possible for one or more of these to open up. I don't

know what effects the associated detuning of the horizontal output

circuit would have in this case.

9.5) Can incorrect or missing video damage my monitor?

	The short answer is - quite possibly.  Don't push your luck.

	

	Mostly, there are problems at scan rates which exceed the monitor's

	specifications.  However, some poorly designed monitors or just a

	particular combination of events can blow a monitor with too low a

	scan rate or an absent or corrupted signal input.  There was one case

	where a very expensive high performance monitor would consistently blow

	its horizontal deflection circuits when driven by a particular ATI

	video card.  It turned out that during the power-on self test of the ATI

	BIOS, just the wrong video timing was being generated for a fraction of

	a second - but that was enough.

	

	As far as scan rate limits, there is no way of knowing - it really all

	depends on the quality of the design of your monitor.  Some will happily

	run continuously at 25% above specifications.  Other will blow out totally

	at the first excuse.

	

	The specification that is likely to be more critical is the horizontal rate

	as it probably puts more stress on the components than the vertical rate.

	I have found that as you approach the upper limits, there is a good chance

	that the geometric accuracy of the raster near the top of the screen may

	start to deteriorate due to lock in problems as well.  However, it would be 

	foolhardy to depend on this sort of behavior as an indication of going over

	the edge.

	

	It will be much too late when you find out.  If the manual says 75 Hz V and

	64 KHz H, stay below **both** of these.  If you exceed the safe ratings and

	the design isn't really good, there is the possibility of blowing components

	in the horizontal deflection and high voltage sections which will result in

	expensive repair bills.  You will likely get no warning of impending failure.

	In addition, even if the monitor does not immediately turn into a pile

	of smoking silicon and plastic, components may be under more stress and

	running at higher levels of power dissipation.  Total failure may be just

	around the corner.  More subtle degradation in performance may occur over

	time as well.

	

	You won't see the difference anyhow beyond 75 Hz and your programs may

	run slightly faster at lower refresh rates since the video is not using

	as much bandwidth (however, the difference here may be very slight or

	non-existent depending on your board, computer, applications, etc..

9.6) Picture squeezed in then died

	You were happily playing 'Doom' when the sides of the picture squeezed in two

	inches or so when the entire monitor went dead - has remained like this since.

	Sound is fine, but no activity at all from the tube.  Has it died?  How

	much time, effort, and expense to fix?

	

	No, it's not dead, at least it certainly is not the picture tube.

	

	Your probably shot the monitor instead of the bad guys!

	

	Is there any indication of light on the screen?  Any indication of the

	horizontal deflection running at all as evidenced by static on the screen?

	

	In any case, there is a problem in the horizontal deflection and you probably

	have no high voltage as well assuming no light on the screen.

	

	The fact that it squeezed in first indicates that a partial short or other

	fault may have developed in the horizontal deflection circuits - possibly

	the deflection yoke or flyback transformer.  It could also have been a bad

	connection letting loose.  Once it failed completely, the horizontal output

	transistor may have bought the farm or blown a fuse.

9.7) Horizontal deflection shutting down

	Confirm that the horizontal deflection is shutting down (along with the

	high voltage since it is derived from horizontal deflection: listen

	for the high pitched deflection whine (NTSC/PAL/CGA), test for static on

	the screen, see if the CRT filaments are lit, turn up the brightness and/or

	screen control to see if you can get a raster) and then why:

	

	1) Power is failing to the horizontal output transistor - this could be

	   due to a low voltage power supply problem, bad connection, etc.

	

	2) Base drive to the horizontal output transistor is failing - could be a

	   fault in the horizontal oscillator or bad connection.

	

	3) Problem with the flyback transformer or its secondary loads (flyback

	   may provide other power voltages).

	

	4. X-ray protection is activating - either due to excess HV or due to a

	   fault in the X-ray protection circuitry.

	

	If the problem comes and goes erratically it sounds like a bad connection,

	especially if whacking has an effect.  If it comes and goes periodically,

	then a component could be heating up and failing, then cooling, etc.

9.8) Horizontal squashed

	A very narrow picture may indicate problems with the power supply to the

	horizontal deflection circuits, incorrect scan rate selection or defective

	components, faulty deflection yoke, or bad connections.

	

	If the size is erratic and/or gently whacking the monitor makes the width

	change, bad connections are likely.  See the section: "Monitor manufacturing quality and cold solder joints".

	

	Confirm that your video card is running at the proper scan rate - particularly

	that it is not violating the monitor's specifications.  An excessive horizontal

	scan rate is a common cause of a reduced width raster.  Try its software

	setup adjustments as these may have been lost.

	

	Beyond this, a schematic will probably be needed to isolate the fault.

9.9) Monitor non-linearity

	Most modern monitors are nearly perfect with respect to non-linearity.

	There almost never any user adjustments and there may not even be an

	internal adjustments.  See the section: "Position, size, and linearity adjustment".

	

	A sudden change in linearity or a monitor that requires a warmup period

	before linearity becomes acceptable may have a bad component - probably

	a capacitor in the horizontal deflection circuits.  For the latter, try

	some cold spray or a heatgun to see if you can locate the bad part.

	

	(From: helio (
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 )).

	

	You should likely begin in the area immediately around the HOT, perhaps

	there might be a high frequency NP (non polarized) electrolytic just

	starting to go. Some larger monochrome monitors actually have working H-lin

	adjustment coils (believe it or not) especially if they are older ones. But

	most are glued/potted down or fixed value. If you locate it (the coil) the

	problem should be nearby.

9.10) Picture squeezed on both left and right side of screen

	"I'm trying to repair a Target DN-1564 monitor with a problem in the

	 horizontal deflection: on both the left and right side of the screen

	 the picture gets squeezed together, regardless of H-width and other

	 settings. I've checked most semiconductors in this part, but I can't

	 find anything wrong there."

	

	This sounds like an S-correction capacitor may have too small a value or

	failed open.  Check the capacitors in the vicinity of the deflection yoke

	connector and HOT.  It could be due to bad connections as well.

	

	S-correction is needed to linearize the horizontal scan (and vertical as well

	scan but that is a separate circuit).  Without S-correction, the scan current

	would be nearly linear.  This would result in greater coverage in a given

	time near the edges of high deflection angle CRTs.  The picture would appear

	stretched near the edges  In this case, the correction appears excessive.

	

	(From: David Henniker (
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 )).

	

	I had a similar problem with a monitor (here in Edinburgh Scotland).

	The S-correction cap was open-circuit altogether. Other caps in parallel

	allowed the distorted scan. If it had been a TV there wouldn't have been

	other caps in parallel and the result would have been no line scan, maybe

	a vertical line (line collapse) or nothing at all.

9.11) Vertical squashed

	This means the vertical size is reduced with or without distortion.

	

	Before attacking the circuitry, make sure your vertical scan rate is within

	the monitor's capabilities and that the user vertical size control is adjusted

	properly.  If there is no distortion, this is likely as many (but not all)

	circuit problems would result in non-linearity or cutoff of the top or bottom

	portions of the picture.  All you may need to do is change your computer's

	video settings!  Swap the monitor or computer to be sure it is not a problem

	with the video card.

	

	However, if failure happened suddenly and the vertical is squashed at all scan

	rates, this is likely a vertical deflection problem - possibly a bad capacitor,

	bad connection, bad flyback/pumpup diode, or other component.  None of these

	should be very expensive (in a relative sort of way).

	

	If the symptoms change - particularly if they become less severe - as the unit

	warms up, a dried up electrolytic capacitor is most likely.  If they get

	worse, it could be a bad semiconductor.  Freeze spray or a heat gun may be

	useful in identifying the defective component.

	

	It is often easiest to substitute a good capacitor for each electrolytic in

	the vertical output circuit.  Look for bad connections (particularly to the

	deflection yoke), then consider replacing the vertical output IC or

	transistor(s).

	

	A defective deflection yoke is also possible or in rare cases, a bad yoke

	damping resistor (e.g., 500 ohms, may be mounted on the yoke assembly itself).

	

	The following are NOT possible: CRT or flyback.  I am just trying to think of

	really expensive parts that cannot possibly be at fault :-).

9.12) Keystone shaped picture

This means that the size of the picture is not constant from top to bottom

(width changes) or left to right (height changes). Note that some slight

amount of this is probably just within the manufacturing tolerance of the

deflection yoke and factory setup (geometry magnet placement, if any). With

a monitor, such defects are more noticeable than with a TV since much of the

display is of rectangular boxes - i.e., windows, lines of text, graphics, etc.

Furthermore, the monitor is usually run just barely underscanned to maximize

the viewing area without cutting anything off. Any deviations from perfection

show up in relation to the CRT bezel.

However, a sudden increase may indicate a problem with the deflection yoke.

An open or short in a winding (or any associated components mounted on the yoke

assembly) will result in the beam being deflected less strongly on the side

where that winding is located. However, with a high scan rate monitor, there

may be many individual windings connected in parallel in the yoke so the effect

of only one opening up may not be as dramatic as with a TV where there may only

be a single pair of windings for the horizontal and another for the vertical.

A simple test of the yoke in this case can be performed by simply swapping

the connections to the yoke for the affected direction (i.e., if the width

changes from top to bottom, interchange the connections to the vertical

windings).

* If the keystone shape remains the same (but of course the picture flips),

it is likely the yoke.

* If the keystone shape flips, it is a circuit problem (see below).

See the section: "Deflection yoke testing".

If the monitor has been dropped off a 20 story building, the yoke may have

shifted its position on the neck, of the CRT resulting in all sorts of

geometry and convergence problems (at the very least).

(From: James Poore (
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)).

I have seen the 'reverse keystoning' in several monitors and the fix is

usually the same. In the horizontal leg of the pincushion transformer are 1

or more electrolytics to ground. The caps have + going to transformer and -

to ground. Anyway when they start loosing capacitance and/or become leaky the

reverse keystoning effects become more pronounced.

9.13) Picture size changing

	If the picture area is expanding or contracting without any changes to your

	video card settings or other software. then there is a problem with the power

	supplies in the monitor.  This would be confirmed if the change is (1) gradual

	over the course of say, an hour, and/or (2) gently whacking the monitor has

	some effect indicating bad internal connections.  Software problems would not

	result in either of these characteristics.

	

	Note that if the change is very small - say, less than 1 or 2%, then it may

	simply be normal for your monitor due to poor design or the use of inferior

	components - some parts associated with power supply regulation may be

	changing value as the monitors warms up.

	

	A way to confirm that something is drifting due to thermal problems would

	be the monitor from another computer and see if the same thing happens.

	Just powering the monitor by itself (but not in any power saving mode) might

	also work for this test.

	

	One possible cause could be that the high voltage is drifting gradually

	due to a faulty component - increasing and making the beam 'stiffer' or

	vice-versa.  If this is the case there might also be a gradual change in

	brightness as well (decreasing image size -> increase in brightness).

	Alternatively, the HV may be stable but the power to both H and V deflection

	is gradually changing.

	

	Excess high voltage can increase the X-ray emissions and any kind of power

	supply problems may ultimately result in total failure and an expensive

	repair.  Therefore, these symptoms should not be ignored.  See the sections

	on low voltage and high voltage power supply problems.

9.14) Monitor will not sync

	For monitors using BNC cables, first make sure that the cable connections

	are correct - interchange of H and V sync or G with one of the other video

	signals (sync-on-gree setups) can result in all kinds of weird sync problems.

	

	There are a wide variety of causes for a monitor that will not display

	a stable or properly configured image.  Among the symptoms are:

	

	* Lack of sync horizontal - drifts smoothly horizontally.  This may mean

	  that the horizontal sync signal is missing due to a bent, pushed in,

	  or broken connector pin (pin 13) or other bad connection or a fault

	  in the sync processing circuitry.

	

	* Incorrect lock horizontal - torn picture (like a TV with the horizontal

	  hold control misadjusted - if you remember these).  This means that the

	  sync signal is reaching the monitor but that it is having problem locking

	  to it.  Check the rate specifications - you may be exceeding them.

	

	* Lack of sync vertical - rolls smoothly vertically.  This may mean

	  that the vertical sync signal is missing due to a bent, pushed in,

	  or broken connector pin (pin 14) or other bad connection or a fault

	  in the sync processing circuitry.

	

	* Lock not stable vertical - jumps or vibrates vertically.  This may be

	  due to scan rate problems or a fault in the vertical sync circuitry of

	  the monitor.

	

	* Multiple or repeated images horizontally or vertically.  There may be

	  multiple images side-by-side, on top of each other, or interleaved.

	  Most likely cause is driving the monitor with an incorrect scan rate.

	  However, faulty circuitry could also be to blame.

	

	Additional comments on some of these problems follow in the next few

	sections.

9.15) Horizontal lock lost

	A monitor which loses horizontal lock when changing resolutions, momentarily

	losing the signal, or switching inputs may have a horizontal oscillator

	that is way out of adjustment or has drifted in frequency due to aging

	components.  Alternatively, you may be running at scan rates that are not

	supported by your monitor.  Check its user manual (yeh, right, like you 

	have it!).  Use the setup program that came with your video card to adjust

	the default scan rates to match the monitor.  Not only will it lock better,

	you are less likely to damage the monitor by feeding it improper scan rates.

	

	Note that the characteristics of this are distinctly different than

	for total loss of sync.  In the latter case, the picture will drift sideways

	and/or up and down while with an off frequency oscillator, the torn up

	picture will try at least to remain stationary.

	

	Assuming you are have your video card set up properly - double check anyhow -

	this could be a capacitor or other similar part.  Or, the oscillator

	frequency may just need to be tweaked (particularly with older monitors).

	There may be an internal horizontal frequency adjustment - either a pot

	or a coil - which may need a slight tweak.  If a coil, use a plastic

	alignment tool, not metal to avoid cracking the fragile core.  There may

	be several adjustments for auto-scan monitors - one for each major scan

	range.

	

	A schematic will be useful to locate the adjustment if any or to identify

	possible defective parts.  If it is a heat related problem try cold spray

	or a heat gun in an effort localize the offending part.

9.16) Insufficient width (without hum bars)

	If there are hum bars or wiggles in the picture, see the section: "Reduced width picture and/or hum bars in picture".

	

	If both width and height are affected, the cause is likely something common:

	low, low voltage power supply voltages or excessive high voltage (resulting

	in a 'stiffer' beam).

	

	(From: Jerry G. (
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 )).

	

	Lack of width is usually caused by defective power supply, low horizontal

	drive to the yoke and flyback, defective circuits in the pincushioning

	amplifier section, excessive high-voltage caused by defective voltage

	regulation, and or excessive loading on the secondary side of the flyback.

9.17) Loss of horizontal sync (also applies to vertical) after warmup

	The problem lies either in the horizontal oscillator or in the sync system.

	If it really is a problem with sync pulses not reaching the oscillator,

	the picture will move around horizontally and can be brought to hold

	momentarily with the hold control. If the picture breaks up into strips,

	there is a problem in the horizontal oscillator.  If there is an accessible

	hold control try rotating it: if the frequency is too far off, the picture

	will not settle into place at any adjustment of the hold control. Look

	around the horizontal oscillator circuit: all of the oscillator parts will

	be right there, or check on the horizontal oscillator module.  If only

	one resolution on a auto-scan monitor is affected, the there could be a

	separate oscillator circuit for each range.

9.18) Replicated or offset multiple images

	Multiple images on the screen horizontally or vertically indicate that

	the scan rate is way off (by a factor equal to the number of complete

	pictures.)  This could be a fault in the monitor or you could be running

	way outside of the monitor's specifications.  Even slightly exceeding

	these for the horizontal or vertical may confuse the scan rate selection

	logic and result in the monitor setting itself with incorrect scan rate

	settings.

	

	A situation where successive sweeps alternate position slightly resulting

	in double or triple images may be caused by a incorrect or out of range

	video timing, a bad component, or improper sync signals.

	

	Check the settings of the video card and any sync termination or selection

	on the monitor.  Beyond this, a schematic will be required.

9.19) Part of picture cut off

	The following applies if the part of the picture is missing but not

	otherwise squashed or distorted.  For example, 85% is missing but the

	portion still visible is normal size.

	

	Wow! That's an interesting one, more so than the typical run-of-the-mill

	"my TV just up and died on me".  Or, "my pet orangutan just put a hole

	in the CRT, what should I do"?

	

	With a monitor, this is more likely than a TV.  But the cause is probably

	not in the monitor (though not impossible).  Check that your video parameters

	are set up correctly (particularly if you have full control of them as with

	Linux).  You may have set the active too short or blanking too long.

	

	If your video is confirmed to be ok (looking at it with an oscilloscope would

	be best), then with the size of the picture fragment correct but 85% missing,

	check waveforms going into the vertical output stage.  The supply voltage is

	probably correct since that often determines the size.  It almost sounds like

	the waveform rather than being mostly on (active video) and off for the short

	blanking period is somehow only on during the last part of the active video

	thus giving you just the bottom of the picture. If there is a vertical output

	IC, it may be defective or the blanking input to it may be corrupted.  The

	problem may be as far back as the sync separator.  Then again who knows,

	schematics would be really handy.

9.20) Bright or dark bars on edge of picture (horizontal or vertical)

	These may be sharp-edged or blurry.  The latter could result when a portion

	of the active video is unblanked during retrace.

	

	* Where the entire picture is present, the problem is one of the video

	  blanking not occurring properly beyond the picture boundary.

	

	* Where part of the picture is cut off with a bright horizontal or vertical

	  line at that point, it is either a video timing problem or a fault in the

	  deflection circuitry preventing the beam from being where it is supposed to

	  scan in enough time.

	

	  You may be seeing part of the active video during retrace or as the beam

	  reverses direction at the start or end of retrace.  Horizontal timing

	  problems would produce vertical bars on the right or left edge; vertical

	  timing problems would produce horizontal bars at the top or bottom edge.

	

	* If your video card permits control of video timing parameters, try reducing

	  the relevant active time relative to the blanking period.  The relevant

	  software settings might be horizontal position, phase, size, and sync

	  polarity.  If this does not work, your video card may be incompatible with

	  the monitor.

	

	* If the problem just happened without any changes to the video source, the

	  monitor may have a problem:

	

	  - Deflection circuits - coil or capacitor, a power supply fault, position or

	    size settings or control, or deflection yoke.

	

	  - Video amplifier or drive (CRT neck board), or blanking circuits - chip

	    decoupling capacitors or filter capacitors in scan derived power supplies.

	    If the bars are significantly colored - not just shades of gray - then

	    a video problem is likely.

	

	An oscilloscope would help greatly in identifying the source of the problem.

9.21) Single Vertical Line

	CAUTION: To prevent damage to the CRT phosphors, immediately turn down the

	brightness so the line is just barely visible.  If the user controls do not

	have enough range, you will have to locate and adjust the master brightness or

	screen/G2 pots.

	

	Since you have high voltage, the horizontal deflection circuits are almost

	certainly working (unless there is a separate high voltage power supply -

	almost unheard of in modern TVs and very uncommon in all but the most

	expensive monitors).

	

	Check for bad solder connections between the main board and the deflection

	yoke.  Could also be a bad horizontal coil in the yoke, linearity coil, etc.

	There is not that much to go bad based on these symptoms assuming the high 

	voltage and the horizontal deflection use the same flyback. It is almost

	certainly not an IC or transistor that is bad.

9.22) Single Horizontal Line

	CAUTION: To prevent damage to the CRT phosphors, immediately turn down the

	brightness so the line is just barely visible.  If the user controls do not

	have enough range, you will have to locate and adjust the master brightness or

	screen/G2 pots.

	

	A single horizontal line means that you have lost vertical deflection.

	High voltage is most likely fine since there is something on the screen.

	

	This could be due to:

	

	1. Dirty service switch contacts.  There is often a small switch on the

	   located inside on the main board or perhaps accessible from the back.  This

	   is used during setup to set the color background levels.  When flipped

	   to the 'service' position, it kills vertical deflection and video to the

	   CRT.  If the switch somehow changed position or got dirty or corroded

	   contacts, you will have this symptom.  Flip the switch back and forth

	   a couple of times.  If there is some change, then replace, clean, resolder,

	   or even bypass it as appropriate.

	

	2. Bad connection to deflection yoke or other parts in vertical output

	   circuit.  Bad connections are common in TVs and monitors.  Check

	   around the pins of large components like transformers, power transistors

	   and resistors, or connectors for hairline cracks in the solder.  Reseat

	   internal connectors. Check particularly around the connector to the

	   deflection yoke on the CRT.

	

	3. Bad vertical deflection IC or transistor. You will probably need

	   the service manual for this and the following.  However, if the

	   vertical deflection is done with an IC, the ECG Semiconductor

	   Master Substitution guide may have its pinout which may be enough to

	   test it with a scope.

	

	4. Other bad parts in vertical deflection circuit though there are not

	   that many parts that would kill the deflection entirely.

	

	5. Loss of power to vertical deflection circuits.  Check for blown

	   fusable resistors/fuses and bad connections.

	

	6. Loss of vertical oscillator or vertical drive signals.

	

	The most likely possibilities are in the deflection output stage or

	bad connections to the yoke.  To locate the vertical output circuitry without

	a service manual, trace back from the deflection yoke connector.  The vertical

	coils will be the ones with the higher resistance if they are not marked.

9.23) Intermittent jumping or jittering of picture or other random behavior

	This has all the classic symptoms of a loose connection internal to the

	TV or monitor - probably where the deflection yoke plugs into the main PCB or

	at the base of the flyback transformer.  TVs and monitors are notorious for

	both poor quality soldering and bad connections near high wattage components

	which just develop over time from temperature cycling.

	

	The following is not very scientific, but it works:  Have you tried whacking

	the TV when this happened and did it have any effect?  If yes, this would

	be further confirmation of loose connections.

	

	What you need to do is examine the solder connections on the PCBs in the

	monitor, particularly in the area of the deflection circuits and power supply.

	Look for hairline cracks between the solder and the component pins - mostly

	the fat pins of transformers, connectors, and high wattage resistors.  Any

	that are found will need to be reflowed with a medium wattage (like 40W) or

	temperature controlled soldering iron.

	

	It could also be a component momentarily breaking down in the power supply

	or deflection circuits.

	

	Another possibility is that there is arcing or corona as a result of humid

	weather.  This could trigger the power supply to shut down perhaps

	with a squeak, but there would probably be additional symptoms including

	possibly partial loss of brightness or focus before it shut down.  You may

	also hear a sizzling sound accompanied by noise or snow in the picture,

	static in the sounds, and/or a smell of ozone.

	

	If your AC power fluctuates, an inexpensive monitor may not be well enough

	regulated and may pass the fluctuations on as jitter.  The video card is

	unlikely to be the cause of this jitter unless it correlates with computer

	(software) activity.

9.24) Horizontal output transistors keep blowing (or excessively hot)

	Unfortunately, these sorts of problems are often difficult to definitively

	diagnose and repair and will often involve expensive component swapping.

	

	You have just replaced an obviously blown (shorted) horizontal output

	transistor (HOT) and an hour (or a minute) later the same symptoms

	appear.  Or, you notice that the new HOT is hotter than expected:

	

	Would the next logical step be a new flyback (LOPT)?  Not necessarily.

	

	If the monitor performed normally until it died, there are other possible

	causes.  However, it could be the flyback failing under load or when it

	warms up.  I would expect some warning though  - like the picture shrinks

	for a few seconds before the poof.

	

	Other possible causes:

	

	1. Improper drive to horizontal output transistor (HOT).  A weak drive might

	   cause the HOT to turn on or (more likely) shut off too slowly (greatly

	   increasing heat dissipation.  Check driver and HOT base circuit components.

	   Dried up capacitors, open resistors or chokes, bad connections, or a driver

	   transformer with shorted windings can all affect drive waveforms.

	

	2. Excessive voltage on HOT collector - check LV regulator (and line

	   voltage if this is a field repair), if any.

	

	3. Defective safety capacitors or damper diode around HOT.  (Though

	   this usually results in instant destruction with little heating).

	

	4. New transistor not mounted properly to heat sink - probably needs mica

	   washer and heat sink compound.

	

	5. Replacement transistor not correct or inferior cross reference.

	   Sometimes, the horizontal deflection is designed based on the quirks

	   of a particular transistor.  Substitutes may not work reliably.

	

	The HOT should not run hot if properly mounted to the heat sink (using

	heatsink compound).  It should not be too hot to touch (CAREFUL - don't

	touch with power on - it is at over a hundred volts with nasty multihundred

	volt spikes and line connected - discharge power supply filter caps first

	after unplugging).  If it is scorching hot after a few minutes, then you

	need to check the other possibilities.

	

	It is also possible that a defective flyback - perhaps one shorted turn - would

	not cause an immediate failure and only affect the picture slightly.  This

	would be unusual, however.  See the section: "Testing of Flyback (LOPT) Transformers".

	

	Note that running the monitor with a series light bulb may allow the HOT

	to survive long enough for you to gather some of the information needed

	to identify the bad component.

9.25) Horizontal output transistors blowing at random intervals

	The HOT may last a few minutes, days, months or years but then blow again.

	

	These are among the hardest problems to locate. It could even be some peculiar

	combination of user cockpit error - customer abuse - that you will never

	identify.  Yes, this should not happen with a properly designed monitor.

	However, a combination of mode switching, loss of sync during bootup, running

	on the edge of acceptable scan rates, and frequent power cycles, could test

	the monitor in ways never dreamed of by the designers.  It may take only one

	scan line that is too long to blow the HOT.

9.26) Vertical foldover

	The picture is squashed vertically and a part of it may be flipped over and

	distorted.

	

	This usually indicates a fault in the vertical output circuit.  If it uses

	an IC for this, then the chip could be bad.  It could also be a bad capacitor

	or other component in this circuit.  It is probably caused by a fault in 

	the flyback portion of the vertical deflection circuit - a charge pump that

	generates a high voltage spike to return the beam to the top of the screen.

	

	Test components in the vertical output stage or substitute for good ones.

9.27) Excessive width/pincushioning problems

	This would mean that the left and right sides of the picture are 'bowed' and

	the screen looks something like the diagram below (or the opposite - barrel

	distortion).

	

	However, the obvious symptoms may just be excess width as the curved sides may

	be cut off by the CRT bezel.

	

	 ============================================

	 \                                          /

	  \                                        /

	   \                                      /

	    \                                    /

	     \                                  /

	      \                               /

	       |                              |

	       |                              |

	       |                              |

	      /                                \

	     /                                  \

	    /                                    \

	   /                                      \

	  /                                        \

	 /                                          \

	==============================================

	

	In particular, this sounds like a pincushion problem - to correct for

	pincushion, a signal from the vertical deflection that looks something

	like a rectified sinewave is used to modify width based on vertical position.

	There is usually a control to adjust the magnitude of this signal and also

	often, its phase.  It would seem that this circuit has ceased to function.

	

	If you have the schematics, check them for 'pincushion' adjustments and

	check signals and voltages.  If not, try to find the 'pincushion' magnitude

	and phase adjustments and look for bad parts or bad connections in in the

	general area.  Even if there are no adjustment pots, there may still be

	pincushion correction circuitry.

	

	If the internal controls have absolutely no effect, then the circuit

	is faulty.  With modern digital setup adjustments, then it is even tougher

	to diagnose since these control a D/A somewhere linked via a microprocessor.

	

	Pincushion adjustment adds a signal to the horizontal deflection

	to compensate for the geometry of the CRT/deflection yoke.  If you have

	knobs, then tracing the circuitry may be possible.  With luck, you have

	a bad part that can be identified with an ohmmeter - shorted or open.

	For example, if the pincushion correction driver transistor is shorted,

	it will have no effect and the picture will be too wide and distorted as

	shown above.

	

	However, without a schematic even this will be difficult.  If the adjustments

	are digital this is especially difficult to diagnose since you don't even

	have any idea of where the circuitry would be located.

	

	Faulty capacitors in the horizontal deflection power supplies often cause

	a similar set of symptoms.

9.28) Uncorrectable pincushion distortion with new monitor

"I just bought a new Sony 200SX 17" monitor and I just can't get the

pin-cushion control to work right. If I get the outer edges straight

then any window an inch or so from the edge will curve like crazy. The

only way around this is to shrink my screen size so I'll have 3/4 in or

so of black space. This is very irritating since I am not getting the

15.9" viewable size as advertised. Is this normal?"

(From: Jeroen H. Stessen (
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)).

The distortion that you describe is called 'inside pincushion'. Normally it

can be corrected by a dynamic S-correction circuit. Maybe Sony didn't do a

too good job on this, or none at all. It may also be that the correction is

optimized for certain horizontal scan frequencies only, as dynamic S-correction

is a resonant circuit. You might want to test at another frequency.

(From:
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)).

You may have a monitor that is at the edge of the acceptance tolerance, (which

is a defined acceptable variation for cost and production yield reasons). A

typical worse case tolerance may be up to 3mm of a deviation from a straight

line for the edges. This applies for all monitors and all manufacturers. Of

course some companies actually control the variation better than others, (and

some just say they do).

For reference; try using the "Recall" function which will set the adjustments

to the original factory settings. (This assumes that your video timing matches

the preset timing used in the factory). Check the infamous user manual.

9.29) Deflection yoke testing

	A faulty deflection yoke can affect the geometry (size and shape) of the

	raster, result in insufficient high voltage and/or other auxiliary power

	problems, and blow various components in the low voltage power supply or

	elsewhere.

	

	* A simple test to determine if the yoke is at fault for a major geometry

	  problem (e.g., a keystone shaped picture) is to interchange the connections

	  to the yoke for the axis that is not affected (i.e., the vertical coils if

	  the width is varying from top to bottom).  If the raster/picture flips

	  (indicating that you swapped the proper connections) but the shape of the

	  raster remains the same - the geometry is unchanged, the problem is almost

	  certainly in the deflection yoke.

	

	* Where high voltage (and other flyback derived voltages) are reduced and

	  other problems have been ruled out, unplugging the deflection yoke (assuming

	  no interlock) may reveal whether it is likely at fault.  If this results in

	  high voltage and a relatively clean deflection waveform or returns the power

	  supply or deflection chip load to something reasonable, a defective yoke is

	  quite possible.

	

	  CAUTION: powering a TV or monitor with a disconnected yoke must be done with

	  care for several reasons:

	

	  - The CRT electron beam(s) will not be deflected.  If it turns out that the

	    yoke is the problem, this may result in a very bright spot in the center

	    of the screen (which will turn into a very dark permanent spot quite

	    quickly) :-(.  Disconnecting only the winding that is suspect is better.

	    Then, the other direction will still scan resulting in a very bright line

	    instead of a super bright spot.  In any case, make sure the brightness is

	    turned all the way down (using the screen/G2 control on the flyback if

	    necessary).  Keep an eye on the front of the screen ready to kill power at

	    the first sign of a spot or line.  Disconnecting the CRT heater as an

	    added precaution would be even better unless you need to determine if

	    there is a beam.

	

	  - Removing the yoke (which is effectively in parallel with the flyback)

	    increases the inductance and the peak flyback voltage on the HOT.  In the

	    extreme, this may blow the HOT if run at full line voltage/normal B+.  It

	    is better to perform these tests using a Variac at reduced line voltage if

	    possible.

	

	  - The deflection system will be detuned since the yoke inductance plays a

	    very significant role in setting the resonance point in most designs.

	    Don't expect to see totally normal behavior with respect to high voltage.

	    However, it should be much better than with the faulty yoke.

	

	* If possible, compare all measurements with a known good identical deflection

	  yoke.  Of course, if you have one, swapping is the fastest surest test of

	  all!  In many cases, even a not quite identical yoke will be close enough to

	  provide useful information for testing.  However, it must be from a similar

	  piece of equipment with similar specifications - size and scan range.  Don't

	  expect a color TV yoke to work in a high performance SVGA monitor!

	

	  Note: the substitute yoke doesn't have to be mounted on the CRT which would

	  disturb purity and convergence adjustments but see the caution above about

	  drilling holes in the CRT face plate!

	

	The deflection yoke consists of the horizontal coils and vertical coils (wound

	on a ferrite core), and mounting structure.  Little magnets or rubber/ferrite

	strips may be glued in strategic locations.  DO NOT disturb them!  In rare

	instances, there may be additional coils or other components mounted on the

	same assembly.  The following deals only with the actual deflection coils

	themselves - the other components (if any) can be tested in a similar manner.

	

	Where the test procedure below requires removal of the yoke, see the section:

	"Removing and replacing the deflection yoke" first.

	

	* Horizontal - the horizontal section consists of an even number of windings

	  hooked up in parallel/interleaved with half of the windings on each of the

	  two ferrite core pieces.

	

	  The horizontal windings will be oriented with the coil's axis vertical and

	  mounted on the inside of the yoke (against the CRT neck/funnel).  It may be

	  wound with thicker wire than that used for the vertical windings.

	

	  - Resistance check - This may be possible without removing the yoke from

	    the CRT if the terminal block is accessible.  Disconnect the individual

	    windings from each another and determine if the resistances are nearly

	    equal.  Check for shorts between windings and between the horizontal and

	    vertical windings as well.

	

	    Typical resistance of the intact windings (at the yoke connector assuming

	    no other components): TV or NTSC/PAL monitor - a few ohms (3 ohms typical),

	    SVGA monitor - less than an ohm (.5 ohms typical).

	

	  - Inspection - Look for charring or other evidence of insulation breakdown

	    due to arcing or overheating.  For the horizontal windings, this will

	    require removing the yoke from the CRT since little if any of the windings

	    are visible from the outside.  However, even then, most of the windings

	    are hidden under layers of wire or behind the ferrite core.

	

	  - Ring test.  See the document "Testing of Flyback (LOPT) Transformers".

	    This deals with flyback transformers but the principles are the same.

	    Disconnecting the windings may help isolate the location of a fault.

	    However, for windings wound on the same core, the inductive coupling

	    will result in a short anywhere on that core reducing the Q.

	

	* Vertical - The vertical section is usually manufactured as a pair of windings

	  wired in parallel (or maybe in series) though for high vertical scan rate

	  monitors, multiple parallel/interleaved windings are also possible.

	

	  The vertical windings will be oriented with the coil's axis horizontal and

	  wound on the outside of the yoke.  The wire used for the vertical winding

	  may be thinner than that used for the horizontal windings.

	

	  - Resistance check - This may be possible without removing the yoke from

	    the CRT if the terminal block is accessible.  Disconnect the individual

	    windings from each other and determine if the resistances are nearly

	    equal.  Check for shorts between windings and between the horizontal

	    and vertical windings as well.

	

	    Typical resistance of the intact windings (at the yoke connector assuming

	    no other components): TV or NTSC/PAL monitor - more than 10 ohms (15 ohms

	    typical), SVGA monitor - at least a few ohms (5 ohms typical).

	

	  - Inspection - Look for charring or other evidence of insulation breakdown

	    due to arcing or overheating.  The accessible portions of the vertical

	    windings are mostly visible without removing the yoke from the CRT.

	    However, most of the windings are hidden under layers of wire or behind

	    the ferrite core.

	

	  - Ring test - Since the vertical windings have significant resistance and

	    very low Q, a ring test may be of limited value.

9.30) Deflection yoke repair

	So you found a big black charred area in/on one of the yoke windings.  What

	can be done?  Is it possible to repair it?  What about using it for testing

	to confirm that there are no other problems before ordering a new yoke?

	

	If the damage is minor - only a few wires are involved, it may be possible to

	separate them from each other and the rest of the winding, thoroughly clean

	the area, and then insulate the wires with high temperature varnish.  Then,

	check the resistances of each of the parallel/interleaved windings to make

	sure that you caught all the damage.

	

	Simple plastic electrical tape can probably be used for as insulation for

	testing purposes - it has worked for me - but would not likely survive very

	long as a permanent repair due to the possible high temperatures involved.

	A new yoke will almost certainly be needed.

9.31) Testing of flyback (LOPT) transformers

	How and why do flyback transformers fail?

	

	Flybacks fail in several ways:

	

	1. Overheating leading to cracks in the plastic and external arcing.  These

	   can often be fixed by cleaning and coating with multiple layers of high

	   voltage sealer, corona dope, or even plastic electrical tape (as a 

	   temporary repair in a pinch).

	

	2. Cracked or otherwise damaged core will effect the flyback characteristics

	   to the point where it may not work correctly or even blow the horizontal

	   output transistor.

	

	3. Internal shorts in the FOCUS/SCREEN divider network, if present.  One sign

	   of this may be arcover of the FOCUS or SCREEN sparkgaps on the PCB on the

	   neck of the CRT.

	

	4. Internal short circuits in the windings.

	

	5. Open windings.

	

	More than one of these may apply in any given case.

	

	First, perform a careful visual inspection with power off.  Look for cracks,

	bulging or melted plastic, and discoloration,  Look for bad solder connections

	at the pins of the flyback as well.  If the TV or monitor can be powered

	safely, check for arcing or corona around the flyback and in its vicinity,

	

	Next, perform ohmmeter tests for obvious short circuits between windings,

	much reduced winding resistances, and open windings.

	

	For the low voltage windings, service manuals may provide the expected

	DC resistance (SAMs PhotoFact, for example).  Sometimes, this will change

	enough to be detected - if you have an ohmmeter with a low enough scale.

	These are usually a fraction of an ohm.  It is difficult or impossible to

	measure the DC resistance of the HV winding since the rectifiers are usually

	built in.  The value is not published either.

	

	Caution: make sure you have the TV or monitor unplugged and confirm that

	the main filter capacitor is discharged before touching anything!  If you

	are going to remove or touch the CRT HV, focus, or screen wires, discharge

	the HV first using a well insulated high value resistor (e.g., several

	M ohms, 5 W) to the CRT ground strap (NOT signal ground.  See the section:

	"Safe discharging of capacitors in TVs and video monitors".

	

	Partially short circuited windings (perhaps, just a couple of turns)

	and sometimes shorts in the focus/screen divider will drastically lower

	the Q and increase the load the flyback puts on its driving source with

	no outputs connected.  Commercial flyback testers measure the Q by

	monitoring the decay time of a resonant circuit formed by a capacitor and

	a winding on the flyback under test after it is excited by a pulse

	waveform.  It is possible to easily construct testers that perform a

	well.  See the companion document "Testing of Flyback (LOPT) Transformers"

	for further information.

9.32) Picture size suddenly becomes larger (or smaller)

	You are playing your favorite game (read: addiction) and suddenly, the

	picture size increases by 20% and the brightness may have changed as

	well.  What part should I replace?  I only used my phasers on the #3

	setting!

	

	Unfortunately, I do not have a crystal ball.  There are a number of parts

	that could be faulty and no way of know for your monitor and your symptoms

	which it is.  Sorry, you will almost certainly have to have it professionally

	repaired or replaced.

	

	What it sounds like is happening is that the circuitry that selects internal

	components depending on scan rate have failed in some way.  They could be

	making an incorrect selection or the power supply could be faulty and applying

	an incorrect voltage to the horizontal and vertical deflection circuits.  The

	brightness changes since it is not compensated for properly.

9.33) Burning up of various size or centering resistors

	Check the capacitors that couple the yoke to to ground.  If they become

	reduced in value or develop a high ESR, the current will be diverted to other

	components with unfortunate and rapid consequences.

9.34) Picture shifted horizontally

	The first thing to determine is if this is a position or phase problem:

	

	* A fault with horizontal position means that the entire raster is shifted

	  left or right.  This is almost certainly a monitor problem.  If you turn

	  up the brightness control, the edges of the scan lines will probably be

	  visible on one side.

	

	  - Assuming the position or centering controls do not work at or or have

	    insufficient range, check for a defective centering pot and bad centering

	    diodes and other components in their vicinity.  If digitally controlled,

	    you will probably need a schematic to find the cause.

	

	  - If the monitor was dropped, the yoke or other assembly on the CRT neck

	    may have shifted (though there would probably be other symptoms as well).

	

	  - Monochrome monitors have centering rings on the CRT neck which may have

	    be knocked out of adjustment.  Color monitors adjust the centering

	    electronically since magnetic rings would mess up the purity and/or

	    convergence.

	

	* A fault with horizontal phase means that the raster is still centered on

	  the screen but the picture itself is shifted (and may have some wrap-around)

	  within the raster.  This could be a fault in the monitor or video card or

	  incorrect settings in the software setup for the video card.

	

	  - If this happened while trying out this monitor on a different or modified

	    computer, just after you have done a software upgrade, or just after

	    something strange happened (like your PC's CMOS settings got corrupted -

	    monitor settings are generally not in the CMOS setup but may have been

	    affected at the same time), reset the monitor's controls to their default

	    or middle position and then use the software setup or install program that

	    came with your video card to set scan rates, size, position, and sync

	    polarity.

	

	  - Some monitors have a user accessible horizontal phase control in addition

	    to horizontal position.  This adjusts the delay in the sync circuits so

	    check that area of the electronics if the control doesn't work or have

	    enough range.

	

	* There could also be a problem with base drive to the HOT.  This may result

	  in position, phase, size, and linearity errors as the scan being initiated

	  too soon or too late.

	

	  - Weak drive to the HOT due to faulty components in the base circuit or

	    driver stage might result in the HOT coming out of saturation early.  The

	    picture would be shifted to the right and the HOT might run excessively

	    hot and blow.

	

	    WARNING: The case of the HOT has >1,000 V spikes and B+ when off - don't

	    touch with power on or until you confirm no voltage is present after

	    pulling plug.

	

	  - If marginal, a drift of position, phase, size, and linearity with warmup

	    is also likely.  Check for dried up electrolytic capacitors and use cold

	    spray to isolate other bad components.  If the drive becomes too weak,

	    the HOT may blow after after being on for a while.

Chapter 10) High Voltage Power Supply Problems

10.1) HV power supply fundamentals

	Most, monitors derive the high voltage for the CRT second anode (THE high

	voltage, focus, and (sometimes) screen (G2) from the horizontal deflection

	system.  This technique was developed quite early in the history of commercial

	TV and has stuck for a very simple reason - it is very cost effective.  A

	side effect is that if the horizontal deflection fails and threatens to

	burn a (vertical) line into the CRT phosphors, the high voltage dies as well.

	Of course, if the vertical deflection dies....

	

	Some high end monitors utilize a separate high voltage supply.  One reason

	for this approach is to decouple the horizontal deflection from the HV

	in auto-scan monitors thus simplifying the design.

	

	Usually it is a self contained inverter module.  It if can be opened, then

	repair may be possible.  With a separate HV supply, there is no need for a

	HV flyback transformer on the mainboard.  Some designs may use a separate HV

	supply including a flyback which is part of the mainboard but is self

	contained and independent of the horizontal deflection system.

	

	Most TV and monitor (flyback) high voltage supplies operate as follows:

	

	1. Horizontal output transistor (HOT) turns on during scan.  Current increases

	   linearly in primary of flyback transformer since it appears as an

	   inductor.  Magnetic field also increases linearly.  Note: flyback is

	   constructed with air gap in core.  This makes it behave more like an

	   inductor than transformer as far as the primary drive is concerned.

	

	2. HOT shuts off at end of scan.  Current decreases rapidly.  Magnetic field

	   collapses inductively coupling to secondary and generates HV pulse.

	   Inductance and capacitance of flyback, snubber capacitors, and parasitic

	   capacitance of circuitry and yoke form a resonant circuit.  Ideally,

	   voltage waveform across HOT during flyback (retrace) period will be a

	   single half cycle and is clamped by damper diode across HOT to prevent

	   undershoot.

	

	3. Secondary of flyback is either a single large HV winding with HV rectifiers

	   built in (most often) or an intermediate voltage winding and a voltage

	   multiplier (see the section: "What is a tripler".)  The output will be

	   DC HV pulses.

	

	4, The capacitance of the CRT envelope provides the needed filtering to

	   adequately smooth the HV pulses into a DC voltage.  Sometimes there is

	   a separate HV capacitor as well.

	

	5, A high resistance voltage divider provides the several KV focus voltage

	   and sometimes the several hundred volt screen (G2) voltage as well.

	   Often, the adjustments for these voltages are built into the flyback.

	   The focus and screen are generally the top and bottom knobs, respectively.

	   Sometimes they are mounted separately.  This or a similar divider may

	   also provide feedback to control high voltage regulation.

10.2) What is a tripler?

	In some TVs and monitors, the flyback transformer only generates about 6-10 KV

	AC which is then boosted by a capacitor-diode ladder to the 18-30 KV needed

	for modern color CRTs.  The unit that does this is commonly called a tripler

	since it multiplies the flyback output by about 3 times.  Some TVs use a

	quadrupler instead.  However, many TVs and monitors generate the required

	HV directly with a winding with the required number of turns inside the

	flyback transformer.

	

	Triplers use a diode-capacitor ladder to multiply the 6-10 KV AC to 18-30 KV

	DC.  Many triplers are separate units, roughly cubical, and are not repairable.

	Some triplers are built in to the flyback - it is probably cheaper to

	manufacture the HV diodes and capacitors than to wind a direct high voltage

	secondary on the flyback core.  In either case, failure requires replacement 

	of the entire unit.

	

	For external multipliers, the terminals are typically marked:

	

	        * IN - from flyback (6-10 KV AC).

	        * OUT - HV to CRT (20-30 KV DC).

	        * F - focus to CRT (2-8 KV).

	        * CTL - focus pot (many megohm to ground).

	        * G, GND, or COM - ground.

	

	Symptoms of tripler failure are: lack of high voltage or insufficient high

	voltage, arcing at focus protection spark gap, incorrect focus voltage, other

	arcing, overload of HOT and/or flyback, or focus adjustment affecting

	brightness (screen) setting or vice-versa.

10.3) High voltage shutdown due to X-ray protection circuits

	A monitor that runs for a while or starts to come on but then shuts down may

	have a problem with the X-ray protection circuitry correctly or incorrectly

	determining that the high voltage (HV) is too great (risking excessive

	X-ray emission) and shutting everything down.

	

	A side effect of activation of this circuitry is that resetting may require

	pulling the plug or turning off the real (hard) power switch.

	

	Is there anything else unusual about the picture lately that would indicate

	an actual problem with the HV?  For example, has it suddenly gotten brighter

	than normal or has the size decreased? If this is the case, then there may be

	some problem with the HV regulation.  If not, the shutdown circuit may

	be overly sensitive or one of its components may be defective - a bad

	connection of leaky cap (or zener).

	

	If the horizontal frequency is not correct (probably low) due to a faulty

	horizontal oscillator or sync circuit or bad horizontal hold control (should

	one exist!), HV may increase and trigger shutdown.  Of course, the picture

	won't be worth much either!  With a multiscan monitor, this could happen if the

	mode switching is faulty resulting in incorrect component settings for a

	given scan rate.  A symptom might be HV shutdown when switching into scan

	ranges.

	

	The HV shutdown circuit usually monitors a winding off of the flyback

	for voltage exceeding some reference and then sets a flip flop shutting

	the horizontal drive off.

	

	On some Sony models, a HV resistive divider performs this function and these

	do fail - quite often.  The red block called a 'HV capacitor' is a common

	cause of immediate or delayed shutdown on certain Sony monitors and TVs.

	See the section: "Apple/Sony monitor dies after variable length of time".

10.4) Low or no high voltage

	Most of these problems are due to faults in the horizontal deflection

	system - shorted HOT, shorted windings or HV rectifiers in the flyback,

	defective tripler, or other bad parts on the primary side of the flyback.

	

	In addition, with auto-scan monitors, the incorrect voltage or other

	component could be selected due to a logic fault or a problem with the

	selection relay or other circuitry.

	

	However, if you discover an inch layer of filth inside the monitor, the HV

	could simply be shorting out - clean it first.

	

	In most cases, these sorts of faults will put an excessive load on the

	horizontal output circuits so there may be excessive heating of the HOT

	or other components.  You may hear an audible arcing or sizzling sound from

	internal shorts in the flyback or tripler.  Either of these may bet hot,

	crack, bulge, or exhibit visible damage if left on with the fault present.

	

	Many modern monitors do not regulate HV directly but rather set it via

	control of the low voltage power supply to the HOT (B+), by snubber

	capacitors across the HOT, and the turns ratio of the flyback.  The

	HV is directly related to the B+ so if this is low, the HV will be low

	as well.  Faulty snubber capacitors will generally do the opposite - increase

	the HV and the X-ray protection circuits may kick in.  However, low HV

	is also a possibility.  The only way the turns ratio of the flyback can

	change is from a short which will manifest its presence in other ways as

	well - excessive heating and load on the horizontal output circuits.

	

	While a shorted second anode connection to the CRT is theoretically

	possible, this is quite unlikely (except, as noted, due to dirt).

10.5) Excessive high voltage

	Any significant increase in HV should cause the X-ray protection circuits

	to kick in and either shut down the set or modify the deflection in such

	a way as to render it harmless.

	

	Symptoms include arcing/sparking of HV, smaller than normal picture, and

	under certain scenarios, possible excessive brightness.

	

	Causes of the HV being too high are:

	

	1. Excess B+ voltage to the HOT.  The likely cause is to a low voltage

	   regulator failure.

	

	2. Open snubber capacitors across the HOT.  These are under a lot of

	   stress and are located near hot components so failure is possible.

	

	3. Incorrect excessively long scan drive to HOT caused by failure of

	   horizontal oscillator/sync circuits.  However, other things like the

	   HOT will probably blow up first.  The picture will definitely be

	   messed up.  This is more likely with auto-scan monitors than TVs

	   since what is too long for one scan range may be correct for another

	   and the selection circuitry is confused or broken.

	

	4. Failure of HV regulator.  Actual HV regulators are uncommon today but

	   the HV may controlled by a feedback voltage from a divider (focus or

	   screen, or its own) or a secondary winding on the flyback setting the

	   B+ or drive timing.  This may result in an underscanned (smaller than

	   normal) picture if only the HV and not the deflection voltages as well

	   are derived from the same supply.

	

	In one example of (4), a arcing of the HV in a Conrac studio monitor resulted

	in the destruction of the HV switchmode inverter transistor (this used

	a separate HV supply) and a fusable resistor.  The cause was an open HV

	feedback resistor divider allowing the HV to increase drastically.

10.6) Snaps, crackles, and other HV breakdown

	Various problems can result in occasional or sustained sparking or arcing

	sounds from inside the monitor.  Note that a static electricity buildup

	is common on the front of the screen.  It is harmless and there iss nothing

	you can do about it anyhow.

	

	The following may result in occasional or sustained sounds not commonly

	associated with a properly working TV or monitor.  There may or may not be

	flashes or blanking of the screen at the same time as the audible noise.

	See the same-named sections that follow for details.

	

	* Arcing, sparking, or corona from CRT HV anode (red wire/suction cup).

	

	* Arcing at CRT sparkgaps.

	

	* Arcing from flyback or vicinity.

	

	* Arcing due to bad connections to or disconnected CRT return.

	

	* Flashovers inside the CRT.

10.7) Arcing, sparking, or corona from CRT HV anode (red wire/suction cup)

	Symptoms could include a sizzling corona or more likely, an occasional

	or rapid series of sharp snaps - possibly quite loud and quite visible - from

	the anode cap on the CRT to the grounded coating on the outside of the CRT or

	a chassis ground point (or any other conductor nearby).  Corona is a high

	resistance leakage through the air without total breakdown.  The snapping

	is caused by the sudden and nearly complete discharge of the CRT anode

	capacitance through a low resistance ionized path similar to lightning.

	

	There are two likely causes:

	

	1. Dirt, dust, grime, around and under the suction cup on the CRT are

	   providing a discharge path.  This may be more severe in humid weather.

	   Safely discharge the HV and then remove and thoroughly clean the HV

	   suction cup and the area under it and on the CRT for several inches

	   around the HV connection.  Make sure there are no loose wires or other

	   possible places for the HV to discharge to in the vicinity.

	

	2. The high voltage has gone through the roof.  Usually, the X-ray protection

	   circuitry should kick in but it can fail.  If cleaning does not help,

	   this is a likely possibility.  See the sections: "High voltage shutdown due to X-ray protection circuits" and "Excessive high voltage".

10.8) Arcing at spark gaps and gas discharge tubes on CRT neck board or elsewhere

	These are protective devices intended to breakdown and divert excessive voltage

	away from the CRT (usually).

	

	This is rarely due to a defective sparkgap or gas discharge tube but rather is

	a safety mechanism like a fuse designed to protect the internal electrodes of

	the CRT if the focus or screen voltage should become excessive.  The sparkgap

	breaks down first and prevents internal arcing in the CRT.  These sparkgaps

	may be built into the CRT socket as well.

	

	Arcing at a sparkgap or a glowing or flashing discharge tube may be accompanied

	by total loss of picture or bad focus, brightness or focus fluctuations, or

	any of a number of similar symptoms.  A common cause is a breakdown inside the

	focus divider (usually part of the flyback or tripler) but could also be due to

	excessive uncontrolled high voltage due to a failure of the B+ regulator or HOT

	snubber capacitor, or (ironically) even a short inside the CRT.

	

	* Spark gaps may be actual two or three pin devices with seemingly no insides,

	  part of the CRT socket, or printed on the circuit board itself.

	

	* Gas discharge tubes look like small neon lamps (e.g., NE2) but could be

	  filled with some other gas mixture to provide a controlled higher breakdown

	  voltage.

	

	Therefore, like a fuse, don't just replace or disable these devices, locate and

	correct underlying problem.  The CRT makes an expensive fuse!

10.9) Arcing from flyback or vicinity

Arcing may be visible or audible and result in readily detectable levels

of ozone. Note that very slight traces of ozone may not indicate anything

significant but if the TV smells like an office copier, there is probably

some discharge taking place.

WARNING: It is possible for arcing to develop as a result of excessive high

voltage. Symptoms might be a smaller than normal excessively bright picture

but this may not be able to be confirmed until the flyback is repaired or

replaced. See the section: "Excessive high voltage".

* On the HV output, it will probably be a loud snapping sound (due to the

capacitance of the CRT) with associated blue/white sparks up to an inch or

more in length. If the arc length is short enough, this may turn into a

nearly continuous sizzling sound with yellow/orange arc and melting/burning

plastic.

* Prior to the HV rectifier, it will likely be a continuous sizzle with

orange/yellow/white arc and melting/burning plastic or circuit board

material.

* Internal arcing in the flyback may be audible and eventually result in

a bulging and/or cracked case (if some other component doesn't fail first

as this would take some time to develop).

* A corona discharge without actual sparks or a visible well defined arc

is also possible. This may be visible in a totally dark room, possibly

more likely when the humidity is high. A thorough cleaning to remove all

dust and grime may be all that is needed in this case.

* If the arc is coming from a specific point on the flyback - a crack or

pinhole - this may be patched well enough to confirm that the rest of the

monitor is operational and a new flyback is worth the money. Otherwise,

there is no way of knowing if the arcing may have damaged other circuitry

until a replacement flyback - possibly money wasted - arrives.

To attempt a repair, scrape off any dirt or carbon that is present along the

path of the arcing and its vicinity. Then, clean the area thoroughly with

alcohol and dry completely. Otherwise, the dirt and carbon will just act as

a good conductor and the arcing will continue under your repair! Several

layers of plastic electrical tape may be adequate for testing. Multiple

coats of high voltage sealer or non-corroding RTV silicone (if it smells like

viniger - acetic acid - as it cures, this may get in and affect the windings)

would be better if the objective is an actual repair. This may prove to be

a permanent fix although starting the search for a source for a new flyback

would not hurt just in case. The arc most likely did damage the insulation

internally which may or may not be a problem in the future.

Also see the section: "Dave's complete procedure for repair of an arcing flyback".

* In some cases, the pinhole or crack is an indication of a more serious

problem - overheating due to shorted windings in the flyback or excessive

secondary load.

* If the arc is from one of the sparkgaps around the CRT or the CRT socket,

this could also be a flyback problem indicating internal shorts in the

focus/screen network.

* If the arcing is inside the CRT, this could indicate a bad CRT or a problem

with the flyback focus/screen network and no or inadequate sparkgap

protection.

Where repair seems possible, first, clean the areas around the arc thoroughly

and then try several layers of plastic electrical tape. If the TV works

normally for say, an hour, then there is probably nothing else wrong and you

can try for a proper sealing job or hope that tape holds out (put a few more

layers on - each is good for about 8-10 KV theoretically).

Once I had a TV where the main problem was a cracked flyback arcing

but this took out one of the fusable resistors for the power supply to

the *vertical* output so the symptoms included a single horizontal line.

Don't ask me to explain - replacing that resistor and the flyback (the

flyback tested good, but this was for someone else) fixed the TV.

In another case, a pinhole developed in the flyback casing probably

due to poor plastic molding at the time of manufacture. This resulted in

a most spectacular case of sparking to a nearby bracket. A few layers of

electrical tape was all that was needed to affect a permanent repair.

However, replacement is really the best long term solution both for reliability

as well as fire risk.

(From: Bert Christensen (
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)).

It may well last a long time. The insulation breakdown was probably in the

area of the rectifier section rather than the flyback section. I have repaired

several units in the same way but I have generally replaced the flyback before

sending back to the customer. I am worried that the repair will not hold and

that a fire could start. I have no desire whatsoever to be sued by some fire

insurance company.

I am always reminded by the experience that Zenith had with its System 3

chassis a few years ago. They burned and caused many house fires including

one in the governor's mansion in Texas. Zenith spent mega bucks on that one.

They also spent mega-bucks on their 'safety capacitor' mess a few years

before that.

10.10) Dave's complete procedure for repair of an arcing flyback

	(From: Dave Moore (
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 ).

	

	First I clean the afflicted area with Electromotive spray from Autozone. It's

	for cleaning alternators.  On Z-line I remove the focus control and wash with

	the alternator cleaner and a tooth brush until all dirt and carbon deposits

	are removed. Then I take an xacto knife and carve out the carbonized hole

	where the arcing broke through. Then take your soldering iron and close the

	hole by melting adjacent plastic into it. (clean any solder off your iron with

	solder-wick first). Then cut some plastic off of some other part off the

	flyback where it wont be needed and use this to plastic weld (with your iron)

	a hump of a patch into and over the arc hole. Smooth and seal with iron. Next

	apply as thick a layer of silicone rubber as you can and let dry overnight.

10.11) Spark gaps and gas discharge bulbs on CRT neck board or elsewhere

	These are protective devices intended to breakdown and divert excessive voltage

	away from the CRT (usually).

	

	* Spark gaps may be actual two or three pin devices with seemingly no insides

	  or printed on the circuit board itself.

	

	* Gas discharge bulbs look like small neon lamps (e.g., NE2) but could be

	  filled with some other gas mixture to provide a controlled higher breakdown

	  voltage.

	

	Arcing at a spark gap or a flashing or glowing gas discharge tube may indicate

	excessive high voltage, a short in the focus/screen divider network of the

	flyback, a short in the CRT, or some other fault resulting in abnormally high

	voltage on its terminals.

10.12) Arcing due to bad connections to or disconnected CRT return

	The Aquadag coating on the outside of the CRT is the negative plate of the HV

	filter capacitor.  If this is not solidly connected to the HV return, you will

	have your 25 KV+ trying to go where it should not be.  There should be a wire

	solidly attached to the CRT neck board or chassis.  Without this, voltage will

	build up until it is able to take some other path - possibly resulting in

	damage to sensitive solid state components in the process.  Therefore, is is

	important to rectify the situation.

	

	Warning: If you find this disconnected, don't just attach it anywhere.  You

	may instantly kill ICs or other solid state components.  It must be connected

	to the proper return point on the CRT neck board or chassis.

10.13) Flashovers inside the CRT

	Due to sharp edges on the electron gun electrodes, impurities, and other

	manufacturing defects, there can be occasional arcing internal to the

	CRT.  Properly designed HV, deflection, and power supply circuits can

	deal with these without failing but not all monitors are designed well.

	

	There is nothing you can do about flashovers assuming your HV is not

	excessive (see the section: "Excessive high voltage".  If these persist

	and/or become more frequent, a new CRT or new monitor will be needed.

10.14) Ozone smell and/or smoke from monitor

	Smoking is just as bad for monitors as for people and usually more quickly

	terminal (no pun....).

	

	White acrid smoke may indicate a failed electrolytic capacitor in the

	power supply probably in conjunction with a shorted rectifier.  Needless to

	say, pull the plug at once.

	

	A visual inspection should be able to easily confirm the bad capacitor as it

	will probably be bulging and have condensed residue nearby.  Check the

	rectifier diodes or bridge rectifier with an ohmmeter.  Resistance across

	any pair of leads should be more than a few ohms in at least one direction.

	Remove from the circuit to confirm.  Both the faulty diode(s) and capacitor

	should be replaced (though the capacitor may work well enough to test

	with new diode(s).

	

	If a visual inspection fails to identify the smoking part, you can probably

	plug the monitor in for a few seconds until the source of the smoke is obvious

	but be prepared to pull the plug in a real hurry.

	

	If the smell/smoke is coming from the flyback, then it has probably gone

	belly up.  You may be able to see a crack or bulge in the case.  While

	the flyback will definitely need to be replaced, it is likely that nothing

	else is wrong.  However, it might be prudent to use a Variac when performing

	initial testing with the replacement just in case there is a secondary

	short circuit or excess HV problem.

10.15) X-ray and other EM emission from my monitor?

X-ray radiation is produced when a high velocity electron beam strikes

a target containing heavy metals. In a modern monitor, this can only

take place at the shadow mask/aperture grille and phosphor screen of the CRT.

For X-rays, the amount of radiation (if any) will be proportional to

brightness. The energy (determined by the CRT high voltage, called KVP

in the medical imaging field) is not affected. This is one reason many

monitors and TVs are designed with brightness limiting circuits.

In any case, there will be virtually no X-ray emissions from the front of

the CRT as the glass is greater than an inch thick and probably contains

some lead for added shielding. Also see the section: "Should I be worried about X-ray exposure while servicing a TV or monitor?".

Electromagnetic radiation (EM) is produced mostly from the deflection yoke

and to a lesser extent from some of the other magnetic components like

transformers and inductors. Depending on monitor design (some are

specifically designed to reduce this), EM emissions can vary quite a bit.

Frequencies range from the 50/60 Hz of the power line or vertical scan rate

to several hundred KHz in the AM broadcast band. The intensity and spectral

distribution will vary depending on horizontal and vertical scan rate.

A totally black screen will reduce X-ray emission to zero. It will not

affect EM emissions significantly as most of this comes from the magnetic

parts, particularly the deflection yoke.

There is no measurable microwave, IR, or UV radiation.

I refuse to get into the discussion of what, if any, health problems result

from low level EM emissions. There is simply not enough data.

10.16) Should I be worried about X-ray exposure while servicing a TV or monitor?

	The only source of X-rays in a modern TV or monitor is from the CRT.  X-rays

	are generated when a high velocity electron beam strikes a heavy metal target.

	For anything you are likely to encounter, this can only happen in a vacuum -

	thus inside the CRT.  The higher the voltage, the greater the velocity and

	potential danger.  Really old TVs (prior to around 1975) may still have HV

	rectifier and regulator tubes - other sources of X-rays.  However, modern TVs

	and monitors implement these functions with solid state components.

	

	The thick front CRT faceplate protects users adequately but there may be some

	emission from the thinner sides.  At 25-30 KV (quite low as X-ray energies go)

	X-rays will be stopped by almost any metal so what you have to worry about

	is where there are no shields.  In addition, the CRT glass usually contains

	some lead compounds to block X-ray emissions.

	

	However, realistically, there is very little danger.  I would not worry about

	exposure unless you plan to be sitting for hours on the sides, behind, or

	under the TV or monitor - with a picture (there will be none if the screen is

	black).

	

	It is interesting that even those 1.5" Watchman and .5" camcorder viewfinder

	CRTs have X-ray warning labels even though the high voltage used with these

	isn't anywhere near high enough to be of any concern!

10.17) Flyback got wet

	You put your can of Coke where????

	

	Who says these FAQs cannot be funny?

	

	Needless to say, unplug the monitor immediately.  Inspect around the target

	area for obviously blown or damaged components.  Test fuses and fusable

	resistors.  Remove all traces of liquid - especially sugary or corrosive

	liquid.  Use water first and then alcohol to promote drying.

	Repair burnt solder connections and circuit board traces.

	Once the monitor is entirely dried out, power it up - preferably through a

	series light bulb and/or Variac until you are sure nothing else will

	let loose.  Look, listen, and smell for any unusual behavior.  If it

	now works, then consider yourself lucky.  If not, there may be damage

	to transistors, ICs, or other components.

	

	Another cause of this is using spray cleaner or a too wet rag on the front

	of the CRT (other parts of the monitor, for that matter).  Any liquid

	which drips inside (all too likely) may short out circuitry on the mainboard

	with very expensive consequences.

10.18) Blooming or breathing problems

	There are several symptoms that are basically similar:

	

	* Blooming is defined as an expansion of the raster or horizontal sections of

	  the raster with bright material.  For example, switching between dark and

	  light picture causes the size of the picture to expand by 10%.  A slight

	  change in size is unavoidable but if it is greater than 1 or 2 percent from

	  a totally black image to a full white one, this is either an indication of a

	  defective monitor or one that is badly designed.  The cause is poor low or

	  high voltage regulation.

	

	  Check the B+ to the horizontal deflection.  This is usually well regulated.

	  If it is varying in sympathy to the size changes, trace back to determine

	  why the low voltage regulator is not doing its job.  The reason for the size

	  change is that the high voltage is dropping and reducing the stiffness of

	  the electron beam.

	

	* Expansion of the raster width in areas of bright imagery is an indication 

	  of short term regulation problems.  The video drive may be interacting

	  with the other power supplies.  Check for ripple - this would be

	  at the vertical scan rate - in the various regulated power supplies.

	  The cause may be a dried up electrolytic capacitor - once you locate the

	  offending voltage, test or substitute capacitors in that supply.

	

	In both these cases, if this just started after some work was done to the

	monitor, the brightness limiter and/or video drive may simply be set so

	high that the monitor cannot supply enough current to the high voltage.

	If the brightness is acceptable with these turned down slightly and still

	have acceptable brightness, then there may be nothing wrong.

	

	* Breathing is defined as a periodic change in the size of the raster which

	  may be independent of what is displayed or its severity or frequency may

	  be related to the brightness or darkness of the image.  This is another type

	  of regulation problem and may be caused by bad electrolytic capacitors or

	  other components in the low voltage power supplies.

	

	  If the monitor uses a switchmode power supply or low voltage regulator

	  separate from the horizontal deflection, first check its output(s) for a

	  variation in voltage at the breathing rate.  Test with a light bulb or

	  resistor load to confirm that the problem is here and not the deflection

	  or remainder of the monitor.

	

	* A condition with somewhat similar symptoms is bad focus - fuzzy picture - but

	  only with bright (high beam current) scenes.  This could be just a matter of

	  adjusting the focus control but may also indicate sub-optimal filament

	  voltage due to bad connections or components in the filament circuit, or a

	  tired worn CRT.  You won't get high beam current without some serious spot

	  blooming (a fat beam because too much cathode area is used) and you will get

	  cathode 'poisoning' after prolonged use.

	

	  Visually inspect the neck of the CRT for the normal orange glow of the

	  filaments and check for bad connections and bad parts.

10.19) Erratic focus or screen (G2) voltage and/or controls on flyback

	Symptoms may include fluctuating focus or brightness.  In extreme cases,

	the result may be a too bright or dark picture or other behavior caused

	by breakdown in the Focus/Screen(G2) divider network.

	

	Usually, this will require flyback replacement to repair reliably.  Sometimes,

	the section with the controls can be snapped apart and cleaned but this is not

	common.

	

	First, just try rotating the screen (G2) control back and forth a few times.

	This may clean up the contacts and eliminate the erratic behavior.  Possibly,

	positioning it a bit to one side of the original location will help.  Then,

	use the individual or other master background/bias adjustments to compensate

	for the improper brightness.

	

	If this doesn't help, here is a 'well it's going in the dumpster anyhow'

	procedure to try:

	

	After discharging the CRT (so you don't get zapped) drill a tiny hole in

	the plastic cover near the bad control.  Be careful you don't damage anything

	inside - you just want access to the contacts of the controls.  Use a hand

	drill with, say, a 1/16" bit.  Don't drill more than about 1/8" deep which

	should enter the airspace.  Then spray some contact cleaner through the

	hole and work the controls.  Wait sufficient time for the everything to dry

	COMPLETELY and see if behavior changes (or it works at all).

	

	This is a 'you have got to be kidding' type of repair so no guarantees :-).

	

	If by some miracle it does work, fill the hole with a drop of RTV or just

	put a couple of layers of electrical tape over it.

10.20) Focus/Screen divider bypass surgery

This is kludge number 41256 but may be the difference between a bit more life

and the dumpster.

If the previous extreme measures don't help, then it may be possible to simply

substitute a good divider network externally.

Note that if there is evidence of internal breakdown in the divider of the

original flyback (hissing, cracks, overheating, bulging case, etc.), this will

not work unless you can disconnect it from its HV connection.

There are two issues:

1. Is this a stable situation? Even if you provide an external substitute,

the parts inside the flyback may continue to deteriorate eventually

resulting in other more total failure of the flyback or worse.

2. If you provide an external focus/screen divider, it must be done is such a

manner (including proper mounting and super insulation) such that it cannot

be called into question should there be a fire where the monitor is even

the slightest bit suspect.

Various size external focus/screen divider networks can be purchased but

whether this is truly a cost effective solution is not obvious.

(From: Larry Sabo (
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)).

I just ordered a 'bleeder resistor' from Data Display Ltd (Canadian sub of

CCS) to use as a cure for flybacks with flaky focus/screen pots. It contains

focus and screen pots, and costs Cdn$ 16.99, which is a lot less than a

complete flyback, that's for sure. I expect it will be compatible with quite a

wide range of flybacks.

I have used bleeder resistor assemblies from duff flybacks a couple of times

with good success. You connect the HV lead into the HV cap of the original

flyback, ground all pins of the sub flyback, and use the focus and screen

leads from the sub bleeder assembly in place of the originals.

Looks like hell but works fine. Mounting (and securing) the substitute is a

challenge given the limited space available. I only use this approach on what

would otherwise be uneconomical to repair, and always advise the owner or

customer of the cobbling job. It also enables you to verify whether it is

the flyback that needs replacement, versus the CRT.

10.21) Decaying or erratic focus or screen (G2) voltages

	The following applies to both CRT focus voltage (which should be a few KV)

	and screen or G2 voltage (which should be several hundred V).

	

	"The screen voltage will come up to normal after sitting over night, 400 V or

	 so. After approximately 5 minutes or slightly longer, I hear a slight arcing.

	 From that point on, the screen voltage will wander anywhere from 75 V up to

	 maybe 150 V. Adjustment of the screen control on the flyback has only a small

	

	 effect and is not permanent. Removing the CRT pcb results in the screen

	 voltage returning to normal."

	

	This is very likely a short between electrodes inside the CRT unless there

	is something on the neck board that is breaking down as a result of some

	connection to the CRT.  The flyback should largely not know the difference

	with the socket plugged into the CRT.

	

	One possibility is that glue used to hold components down on some circuit

	boards has deteriorated and turned conductive.  Check for tan to brown

	stuff shorting traces on the CRT neck board.  If this is present on the

	focus or screen traces or wires, it may just be your problem.  Scrape off

	all of the old glue and then clean thoroughly.  Repair any damaged traces.

	

	What happens to the HV?  A HV breakdown possibly inside the CRT would result

	in all the voltages being dragged down.

	

	What happens to the picture?

	

	If you connect a charged HV capacitor (guessing a couple hundred volts,

	a couple microfarads) between G2 and G1 or focus, you **will** know if

	tapping the neck results in a momentary short!  I cannot predict whether

	this will be a temporary cure or permanent killer.  See the section:

	"Rescuing a shorted CRT".

	

	Here is another thing to try: put a 100 M ohm or so resistor between SCREEN

	and the CRT socket.  This should not affect the behavior much until the

	failure occurs.  Then, check the voltage on both sides with a high impedance

	voltmeter (1000 M).  If the CRT is arcing, it will be much lower on the CRT 

	side and will probably fluctuate.  You can play similar games with focus

	voltage.

10.22) Disconnecting focus wire from CRT driver board

	In some cases, the focus wire - the not-so-fat wire from the flyback or focus

	divider - may terminate directly in the CRT socket with no obvious means of

	freeing it should flyback replacement be needed.

	

	One alternative is simply to cut the wire in a location that is well away from

	any place to short out, solder, and then do a  most excellent job of insulating

	the splice.

	

	However, you may find that the cap on the CRT socket snaps off using a thin

	knife blade or screwdriver.  The wire may be soldered or just pressed in place

	in such a way that pulling it out is difficult or impossible without removing

	the cover.

	

	(From: Raymond Carlsen (
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 )).

	

	The last one I worked on puzzled me for a few moments. See if you can see a

	space between the little cup (where the wire enters the socket) and the socket

	itself.  Pry up on the cap with a knife and it should pop right off. The wire

	is soldered to a pin under it. Don't apply heat for very long... you may melt

	the socket.

10.23) Focus or screen voltage drifts after warmup only when CRT is connected

	"I have a 3-5 yr old monitor that loses screen voltage.  I believe that the

	 problem is specific to the CRT or the flyback, either one is a guess I'd

	 rather be sure of prior to ordering a part. 

	

	 The screen voltage will come up to normal after sitting over night, 400 V or

	 so. After approximately 5 minutes or slightly longer, I hear a slight arcing.

	 From that point on, the screen voltage will wander anywhere from 75 V up to

	 maybe 150 V.  Adjustment of the screen control on the flyback has only a

	 small effect and is not permanent. Removing the CRT pcb results in the screen

	 voltage returning to normal. 

	

	 I cannot find the source of the arcing, as it happens quickly and I have

	 always been on the other side of the set when it happens. I have replaced

	 the crt socket, thinking the spark gap was arcing. I have checked the CRT

	 for G1 and HK shorts on a sencore crt checker, it checks good, but I am aware

	 that since it is an intermittent problem, that the checker probably will not

	 catch it."

	

	This sounds like a CRT short unless there is something on the neck board

	that is breaking down.  The Sencore may not provide the same high voltages

	as normal screen (several hundred volts) or focus (several thousand volts).

	The flyback should largely not know the difference whether the screen or

	focus electrode of the CRT is connected or not.  The current should be

	negligible.

	

	One possibility is that glue used to hold components down on some circuit

	boards has deteriorated and turned conductive.  Check for tan to brown

	stuff shorting traces on the CRT neck board.  If this is present on the

	focus or screen traces or wires, it may just be your problem.  Scrape off

	all of the old glue and then clean thoroughly.  Repair any damaged traces.

	

	What happens to the HV?  A HV breakdown possibly inside the CRT would result

	in all the voltages being dragged down.

	

	What happens to the picture?

	

	If you connect a charged HV capacitor (guessing a couple hundred volts,

	a couple microfarads) between G2 and G1 or focus, you **will** know if

	tapping the neck results in a momentary short!  I cannot predict whether

	this will be a temporary cure or permanent killer.

	

	Here is another thing to try: put a 100 M ohm or so resistor between SCREEN

	(or FOCUS) and the CRT socket.  This should not affect the behavior much

	until the failure occurs.  Then, check the voltage on both sides with a high

	impedance voltmeter (>1000 M).  If the CRT is arcing, it will be much lower

	on the CRT  side.

Chapter 11) Raster, Color, and Video Problems

11.1) Blank picture, power light on, digital controls (if any) active

	Does 'blank picture' means a totally black screen with the brightness and 

	contrast controls having no effect whatsoever?  Or, is there is no picture

	but there is a raster - light on the screen?  The direction in which

	troubleshooting should proceed differ significantly depending the answer.

	

	Verify that you computer has not simply entered power saving mode and

	blanked the screen or shut off the monitor video and power circuits

	entirely.

	

	Confirm that the video source is not defective or blank - try another one.

	

	Here are some questions:

	

	1. Is there any light on the screen at any settings of the brightness

	   and contrast controls, and/or when switching channels.  Can you see any

	   raster scanning lines?

	

	2. Can you obtain a raster of any kind by adjusting the screen (G2) control

	   (probably on the flyback) or master background or brightness?

	

	3. Looking in the back of the monitor, can you see the glow of the CRT

	   filament?

	

	4. Do you get that static on the front of the tube that would indicate that

	   there is high voltage?  Any cracking or other normal or abnormal sounds

	   or smells?

	

	If the answer to all of these is 'no', then you have a power supply and/or

	deflection problem.  Refer the the section: "No picture but indications of power".

	

	Possible causes of no raster:

	

	* No or low high voltage (low voltage, deflection, or high voltage power

	  supply failure).

	

	* Fault with other voltages like G1 or screen (G2) to CRT.

	

	* Filament to CRT not getting powered.

	

	* Drive to CRT bad/shut off as a result of fault elsewhere.  For example,

	  failure of the vertical deflection may disable HV or blank the screem to

	  protect the CRT from burn-in due to the very bright horizontal line that

	  would result.  With some monitors, it is possible that the X-ray protection

	  circuitry will blank the screen.

	

	Possible causes of no video: problem in video input, video amplifiers, video

	output, cutoff due to other fault.

	

	It could be as simple as a bad connection - try gently prodding the boards

	with an insulated stick while watching the screen.  Check for loose connectors

	and reseat all internal connectors.

11.2) Brightness control has no effect

	The following assumes that the picture is fine but the brightness is

	fixed - probably at too high a level.  However, there could be several

	interrelated problems if a common supply voltage were missing, for example.

	

	If it is a knob, then it should be varying the control grid (G1) voltages

	relative to the cathodes (K) of the CRT.  This is not likely to be a very

	complex circuit.  If you do not have a schematic, I would start by tracing

	from the control, check continuity and solder connections.  Check the

	control itself for proper operation with an ohmmeter.  A power supply going

	to one side of the control (negative probably) may be missing.  Tbe control

	grid voltage will end up on the little board on the neck of the CRT - check

	there as well for bad solder connections or open resistors.

	

	If brightness is a digital control, then you will need a schematic unless

	there is an obvious bad connection.

11.3) No color - black and white picture

	This means absolutely no color - equivalent to a black and white picture.

	Not even a hint of color.

	

	If you are using a composite video input, troubleshoot the chroma circuitry

	like you would a TV - see the document: "Notes on the Troubleshooting and Repair of Television Sets".

	

	This is an extremely unlikely failure mode for  a computer monitor

	unless you are using a composite video input.  It is most likely to

	a software driver or program problem.  Sometimes, the PC will think that

	the monitor you have connected is not capable of color and certain programs

	will then display in B/W no matter what.

	

	In some cases this is due to an initialization problem - possibly a race

	condition during the boot process - especially likely if you are using an

	older video card with a new fast processor.

	

	First, confirm that the source is actually in color - try the monitor on

	another computer or vice-versa.

	

	Check the settings of any mode switches - in rare cases there is a color/mono

	switch or button.

	

	Note that to the average person, the obvious question becomes: is my color

	picture tube bad?  The answer is a definitive NO.  It is virtually impossible

	for a defective CRT to cause a total loss of color.  A defective CRT can

	cause a lack of a primary color - R, G, or, B which will mess up the color

	but is not likely to result in a black and white picture.

11.4) One color is too weak or too strong

If the problem is slight and/or has gradually gotten worse, this may just

require an adjustment of the color brightness/background/bias and/or color

gain/drive controls inside the monitor. See the section: "Brightness and color balance adjustment".

Even if it appears as though there is an excess, this may actually be a

reduction in one of the primary colors. For example, a magenta tinge is

represents a reduction in the strength of the green signal.

* Too high an intensity for one of the color channels will result in a tint of

one of the primaries: red, green or blue.

* Too low an intensity for one of the color channels will result in a tint of

the complement of one of the primaries: yellow, cyan, or magenta.

* Problems mainly in the shadows or dark areas of the picture usually represent

a fault with brightness/bias/background.

* Problems mainly in the highlights or bright areas of the picture usually

represent a fault with the gain/drive.

A color that that is now suddenly brighter or darker than normal resulting in

incorrect color balance or a tint in the background could be due to a number

of causes:

* Bad cable or pin bent on cable connector.

* Bad connections or bad component in video amplifier or on CRT neck board for

that color.

* Weak gun in CRT (reduced color).

* Bad video card or incorrect software color map settings.

* For monitors with sync-on-green capability, the monitor may think you are

using sync-on-green when in fact you have separate sync. In particular,

this may result in a problem with excessive green:

(From: Bob Myers (
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)).

Some monitors provide a user-selectable setup option for "sync-on-green"

vs. separate syncs. Sometimes, this doesn't really change where the

sync itself is coming from. In those cases, it's automatically detected

but *does* change where the reference level for the video is expected

to be. You might try checking this setting, if you have it, and changing

it back and forth to check the effect. It's not likely to be the problem

in a separate-sync system like a PC, but weirder things have happened

and it's easy and cheap to check out.

11.5) Psychodelic color

	The means colors that are not normal and that adjustment of the user

	controls is not able to correct it so that all colors of the picture

	are properly displayed at the same time.  For example, you are unable

	to get any yellows or blues in picture that should have these colors.

	

	* If you are using a composite video input, troubleshoot the chroma circuitry

	  as you would a TV - see the document: "Notes on the Troubleshooting and Repair of Television Sets".

	

	* Confirm that the input is not a weird color video - try another software

	  program or video source.  We have a draftsperson who always sets up his

	  Windows color scheme in this manner - we keep wishing it is the monitor

	  as **that** could be fixed!

	

	* Verify that this is not a missing color problem - one of the primary R, G,

	  or B, has disappeared.  If so, refer to the section: "Intermittent, flickering, or missing colors".

	

	* If this is a monitor with BNC connectors and you are using them, make sure

	  you had the video termination switches set correctly (75 ohms if this is

	  the only monitor or the last monitor in a daisychain; HiZ if an intermediate

	  monitor in a daisychain.)  A very common cause of unbalanced or blooming

	  colors assuming the monitor itself is good is incorrect settings of the

	  termination.

	

	* A bad connection, bad component, or short circuit in the video circuitry

	  or CRT neck board could also result in strange colors.

11.6) Monitor manufacturing quality and cold solder joints

	Any intermittent problems with monitors that cause random sudden changes in

	the picture brightness, color, size, or position are often a result of

	bad connections.

	

	Bad solder joints are very common in monitors due both to poor quality

	manufacturing as well as to deterioration of the solder bond after numerous

	thermal cycles and components running at high temperature.  Without knowing

	anything about the circuitry, it is usually possible to cure these problems

	by locating all bad solder connections and cleaning and reseating internal

	connectors.  The term 'cold solder joint' strictly refers to a solder

	connection that was either not heated enough during manufacturing, was

	cooled too quickly, or where part pins were moved before the solder had

	a chance to solidify.  A similar situation can develop over time with

	thermal cycling where parts are not properly fastened and are essentially

	being held in by the solder alone.  Both situations are most common with

	the pins of large components like transformers, power transistors and

	power resistors, and large connectors.  The pins of the components have

	a large thermal mass and may not get hot enough during manufacturing.  Also,

	they are relatively massive and may flex the connection due to vibration

	or thermal expansion and contraction.

	

	These problems are particularly common with TVs and monitors - especially

	cheaper monitors.

	

	To locate cold solder joints, use a strong light and magnifier and examine

	the pins of large components for hairline cracks in the solder around the

	pin.  Gently wiggle the component if possible (with the power off).  Any

	detectable movement at the joint indicates a problem.  With the power on,

	gently prod the circuit board and suspect components with an insulated

	tool to see if the problem can be effected.

	

	When in doubt, resolder any suspicious connections.  Some monitors may

	use double sided circuit boards which do not have plated through holes.

	In these cases, solder both top and bottom to be sure that the connections

	are solid.  Use a large enough soldering iron to assure that your solder

	connection is solid.  Put a bit of new solder with flux on every connection

	you touch up even if there was plenty of solder there before.  However,

	remove any obvious excess.  Inspect for solder bridges, sliver, splashes,

	etc. before applying power.

11.7) Why can't monitor manufacturers learn to solder properly?

	I can think of several potential reasons - all solvable but at higher

	manufacturing cost.

	

	1. Mass of large component leads (like shields) does not get adequately

	   heated during manufacture leading to latent cold solder joints.  While

	   they may look ok, the solder never actually 'wetted' the heavy pins

	   and therefore did not form a good mechanical or electrical bond.

	

	2. Thermal cycles and differential thermal coefficients of circuit boards,

	   traces, and solder.  While it is not easy to do anything about the

	   material properties, using plated through-holes or a similar mechanical

	   via would greatly increase the surface area of the joint and prevent

	   the formation of cracks.

	

	3. Vibration.  This is also directly related to the single sided circuit

	   boards without plated through-holes to strengthen the joints.

	

	4. Lack of adquate mechanical support (single sided circuit boards without

	   plated through-holes (vias).

	

	I believe that the single most significantimprovement would come about

	by using plated trhough-holes but this would add to the cost and apparently

	the consumer is not willing to pay more for better quality and reliability!

	Some designs have used rivlets - mechanical vias instead of plated ones.

	While this is good in principle, the execution has often been flawed where

	cold solder joints resulted between the rivlets and the circuit board traces

	due to lack of adequate process control.

	

	Monitors, due to their generally higher cost compared to TV sets, should

	be better constructed but not always.

11.8) Intermittent, flickering, or missing colors

	This is a catch-all for some of the most common monitor problems.  Most of

	the causes boil down to bad connections of one form or another.  However,

	defective components like bias resistors on the CRT driver board or in the

	video circuitry could also be at fault.

	

	* Does whacking the monitor have any effect?  If so, then bad connections

	  are confirmed.  If the color(s) come and go suddenly, then it is most likely

	  *not* a CRT problem.  The bad connections could be at the VGA cable, video

	  driver board on the neck of the CRT, or elsewhere (see below).

	

	* If the color fades in and out with a delay of about 10-15 seconds, it is

	  probably intermittent power to the CRT filament for that color and probably

	  means a bad CRT since the three filaments are wired in parallel inside the

	  CRT.  One of the internal connections has come loose.

	

	  Look in the neck of the CRT to make sure all three filaments are glowing

	  orange.  If one is out or goes on and off, toss the monitor.  Replacing the

	  CRT is probably not worth it.  However, if they all go on and off together

	  (all colors would be fading in and out though perhaps not quite in unison),

	  then bad connections for the CRT filaments on the CRT neck board are

	  indicated.

	

	Possible causes of intermittent or missing colors:

	

	* VGA or other video input cable.  Sometimes these develop intermittent

	  problems at the connector to the VGA board.  These may be internal

	  to the cable in which case it will need to be replaced or if you are

	  handy and have infinite patience, you can replace just the VGA connector.

	

	  Alternatively, the male pins of the cable may not be making good contact

	  with the female VGA socket.  First try contact cleaner.  If this does not

	  work, gently squishing the male pins with a pair of needlenose pliers may

	  provide temporary or permanent relief if the pins are a tad too small.

	  However, if you go too far, you can damage or break the pins or cause the

	  female socket to become enlarged and loose fitting for any other monitor

	  you may use.

	

	  If this just happened after reconfiguring your system and reconnecting

	  the monitor or installing a new monitor, check your video connector - you

	  may have bent over or pushed in pins 1, 2, or 3 - the R, G, and B video

	  signals respectively.

	

	  If you find a bent pin, ***carefully*** straighten it with a pair of

	  needlenose pliers.  If it is pushed in, try to grab onto it and pull it

	  out - then put a drop of Epoxy or other adhesive at its base (don't get

	  any on the part of the pin that makes contact) to prevent it from being

	  pushed in again.

	

	  There may be cold solder joints on the VGA board itself at the VGA

	  connector.  These can be resoldered.

	

	* Printed circuit board on the CRT neck.  This is a common location for

	  cold solder joints.  Check with a bright light and magnifying glass

	  for hairline cracks around the pins of larger parts.  Prod and tap with

	  an insulated tool to see if the problem is effected.  Resolder if necessary.

	

	* Cold solder joints elsewhere in monitor usually around the pins of

	  large parts such as transformers, power transistors and resistors, and

	  internal connectors.  Inspect with a strong light and magnifier if

	  necessary.

	

	* Internal connectors that need to be cleaned and reseated.  Remove,

	  clean with contact cleaner, burnish, and replace.

	

	* Bad filament connections inside the CRT (gradual fade in and out or

	  one filament not lit).  Replace CRT or monitor.

	

	To narrow down the problem:

	

	* Locate the output for the bad color on the video driver board on the

	  neck of the CRT.   This will probably read a significantly higher

	  voltage than the corresponding pins for the good colors.  A circuit

	  problem is likely - probably on this board but it could be in other

	  parts of the video circuitry.

	

	* Test components on this board for the good and bad color channels.  A

	  shorted transistor or open resistor can kill one channel.  Swap parts

	  between good and bad colors to confirm.

	

	* Gently pull the CRT neck board off of the CRT and replace it.  This will

	  tend to clean the contacts.

	

	* Connect an output of the video circuit/chip that is working (i.e., a color

	  that appears on the screen) to *all* three color drivers on the CRT neck

	  board.

	

	   - If you now get a more-or-less black and white picture (there may be a

	     moderate color tint as the relative intensities of R,G,B may not be

	     balanced), the problem is likely with the circuitry on the mainboard.

	

	     Note: the picture will be the intensity of only one color channel so it

	     will not be quite *normal* in any case.

	

	   - If you still have missing or messed up colors, the problem is on the CRT

	     neck board or with the CRT.

11.9) Some commentary on monitor and TV whacking

Anytime that intermittent symptoms are experienced, I recommend gently

whacking the patient to determine if mechanical shock or vibration affects

the behavior. Here are a couple of responses to this suggestion.

(From Marc Gelfond (
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)):

I just love the bit about "whacking it". It brings to mind an

episode from the old Andy Griffith show, where a new fangled piece

of electronics gear, was broght into Emmets repair shop. After

many long hours of fruitless troubleshooting, out of frustration

Emmet gave the thing a whack, and sure enough it fixed the problem.

As we say in the Telephony business, it "CCWT" or Came Clear While Testing.

Another saying is that it "CCBFM" Came Clear By F------ Magic!!

(To which Gavin Adams (
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) comments):

In the video industry we had a saying concerning malfunctioning gear:

"If it's broke, hit it with a hammer"

"If that doesn't fix it, paint it and sell it"

My DEC 16" monitor is case in point. Evey once in a while it would

lose sync, and smacking it would bring it back (sometimes a few

smacks). Recently it gave up the ghost completely, and after the local

DEC office gave me a quote of $900 to fix it (Bermuda), I ordered a

new Viewsonic 17" for the same price.

I ripped the guts out of the DEC beast, painted it with a marble finish,

put plants in it, and sold it! :>

11.10) Ghosts, shadows, or streaks in picture adjacent to vertical edges

	Complaints about these kinds of problems are very common especially as

	the screen resolution and necessary video bandwidth keeps increasing.

	Most are due to cable and video termination deficiencies and not actual

	monitor defects.

	

	The video signals for red, green, and blue (or just a single signal for

	monochrome) are sent over cables which are generally 75 ohm transmission

	lines.  These are coaxial cables that may be combined inside a single

	sheath for VGA, SVGA, MACs, and many workstations but may be separate coaxes

	with BNC (or other) connectors for other video applications.

	

	Without going into transmission line theory, suffice it to say that

	to obtain good quality video, the following conditions must be met:

	

	1. A good quality of cable must be used.  This means one in which the

	   characteristic impedance is close to the optimum 75 ohms, one which has

	   low losses, and one which has good shielding.   For installations

	   using BNC connectors, a good quality of 100% shielded RG59U is often used.

	   The BNC connectors must be properly installed or they will contribute

	   to mismatch problems.

	

	2. Where multiple monitors are to be connected to a single video source,

	   all wiring is done in a daisy chain fashion.  The only taps permitted

	   are the minimum necessary to connect each monitor to the chain.  This

	   usually means a BNC-T connector or a pair of connectors on the monitor

	   for each video signal.  T connections with cable must be avoided.

	

	3. Only the last monitor in the chain should be terminated in 75 ohms.  All

	   of the others must be set to Hi-Z.  Monitors with BNC connectors will

	   usually have one switch or a switch for each color to select termination.

	

	Monitors for PCs, MACs, and workstations usually have built in

	termination and do not offer the choice of Hi-Z.  This means that without

	a video distribution amplifier, it is not possible to connect multiple

	monitors of this type to a single video source with any expectation of a

	good quality display.

	

	Failure to follow these rules will result in video ringing, ghosts, shadows,

	and other unsightly blemishes in the picture.  It is often not possible to

	control all aspects of the video setup.  The cable is often a part of the

	monitor and cannot easily be substituted for a better one.  The monitor

	may not have properly designed circuitry such that it degrades the video

	regardless of the cable and display board quality.  The display card itself

	may not have proper drivers or source termination.

	

	Ironically, the better the video card, the more likely that there will

	be visible problems due to termination.  This is due to the very high

	bandwidth and associated signal edge rates.

	

	Some examples of common termination problems:

	

	* Overly bright picture with trails following vertical edges, perhaps with

	  periodic ringing.  This is due to a missing termination.  Check if the

	  monitor is set for Hi-Z instead of 75 ohms.  If there is no switch, then

	  the termination may be faulty or the monitor may need an external resistor.

	  For BNC connectors, plug-on terminations are available.

	

	* Bright ghost images adjacent to vertical lines.  This may indicate that

	  the terminating resistor is greater than the impedance of the cable.

	  You may be using Ethernet Thinnet cable by accident which is RG58 with

	  an impedance of 50 ohms.

	

	* Dark picture and ghost images adjacent to vertical lines.  This may indicate

	  that the terminating resistor is too low - multiple monitors on a chain all

	  set for 75 ohms instead of just the last one.  Or, an improper type of cable

	  such as audio patch cord.

	

	* Fuzzy vertical edges.  This may indicate a poor quality cable or a run

	  which is just too long.  For high resolutions such as 1280x1024, the

	  maximum cable length may be as short as 25 feet or less for poor quality

	  cable.  Better cable or fiber-optic repeaters may be necessary.

	

	* Other similar problems - check cables for defective or improperly installed

	  connectors.  This is especially applicable to cables with BNC or UHF type

	  connectors which require a kind of artistic talent to assembly properly and

	  consistently.

	

	If only 1 or 2 colors (of the R, G, and B) are effected, then look for

	improper switch settings or bad connections (bad cable connectors are really

	common) on the problem color cables.

11.11) General streaks or lines to the right of bright or dark areas

	The problem is that on a white background the various objects leave a shadow

	to their right. Not a duplicate image but more like horizontal dark streaks

	on the white background. Also it seems that high intensity colors display

	very bright but low intensity colors are overly dark (almost black).  The

	contrast and brightness adjustments may make no difference.

	

	This could be a number of things but they are all in the video amplifier

	and probably not the CRT driver board though this is possible.  Dried

	up filter capacitors could result in video dependent ripple on the power

	supply lines.  Bad coupling capacitors could result in similar symptoms

	but probably for only one color, not all of them.

	

	Since all colors are effected, look for something common like a bad power

	supply.  With a scope, this would probably be rather easy even without

	schematics.  If the brightness and contrast controls do nothing, this

	would suggest some fault in their general area or the IC or transistors

	they control in the video amps - and that this is not a CRT problem.

	Locate the video amp IC if it uses one and locate a pinout - this should

	be enough to determine which signals are faulty.

	

	First, do check carefully for bad connections and other obvious failures.

	

	This could also be a symptom of a bad CRT but this would be unusual

	with a not-ancient monitor (and not if the brightness and contrast

	controls have no effect).

11.12) Washed out picture

	If you can obtain a full intensity raster by varying the brightness or screen

	control, then your problem is most likely in the video amplifiers or power

	for the video amplifiers.

	

	If, however, the screen control varies the brightness but will not get

	a bright raster, you probably have problems either with the HV power supply

	or the filament supply for the CRT - is there the normal bright orange

	glow at the base of the CRT?  If it is dim or very reddish, there may

	be a marginal connection or bad component in the filament circuitry.

11.13) Retrace lines in picture

	During the time the electron beam is returning from right to left at the end

	of a line and bottom to top (over the course of multiple lines), it is supposed

	to be result in no visible light on the screen.  However, a number of faults

	can result in visible retrace lines.

	

	The appearance will likely be a general reduction in contrast from the visible

	horizontal retrace on every scan line and two dozen or so diagonal lines lines

	(lower left to upper right) resulting from the vertical retrace.

	

	The retrace lines may be either white or gray (possibly with a slight color

	tint due to unequal settings of the color adjustments) or a primary color -

	red, green, or blue.  Anything in between is also possible but less likely.

11.14) White/gray retrace lines

	Where all colors are involved - the lines are essentially white or gray (or

	with a slight tint due to slight unequal settings of the color adjustments),

	look for something common like an incorrectly adjusted screen (G2) or master

	brightness/background/bias control or a problem in one of these circuits, a

	defective power supply or a problem in the blanking circuitry:

	

	* Screen (G2) or master brightness/background/bias control - mark setting and

	  then see if a slight adjustment removes the retrace lines.  See the chapter:

	  "Monitor Adjustments".  Of course, if this happened suddenly, the problem is

	  not due to a misadjusted control though a dirty pot is possible - turn it

	  back and forth - this might clean it and restore normal operation.

	

	* Power supply or connection to CRT neck board - insufficient voltage will

	  result in the CRT never totally blanking.  Check (usually scan derived)

	  power supply components (from flyback).

	

	* General power supply - check B+ for correct value and ripple.  A main power

	  supply fault might result in these symptoms (and usually many others).

	

	* Blanking circuit - this may be a part of the video/chroma chip or separate.

	  Check waveforms to determine if the blanking pulses are making it to the

	  video output.

11.15) Red, green, or blue retrace lines

	Where only one color is showing, suspect an incorrectly adjusted individual

	background/bias control or bad part on the CRT neck board for that color.

	

	* Individual brightness/background/bias control(s) - mark setting of pot for

	  the problem color and then see if a slight adjustment removes the retrace

	  lines.  See the chapter: "Monitor Adjustments".  Of course, if this happened

	  suddenly, the problem is not due to a misadjusted control though a dirty

	  pot is possible - turn it back and forth - this might clean it and restore

	  normal operation.

	

	* Component or connection on CRT neck board - insufficient voltage to or

	  incorrect biasing of the video driver for this color can result in the

	  CRT never totally blanking.  Compare voltages and signals, and swap

	  components between good and bad channels to confirm.

	

	* Blanking circuit - this may be a part of the video/chroma chip or separate.

	  Check and compare waveforms of good and bad colors to determine if the

	  blanking pulses are making it to the video output.

	

	There is a slight possibility that a bad CRT may result in visible retrace

	lines.  To eliminate this possibility:

	

	* Disconnect the filament - all evidence of a picture, raster, and retrace

	  lines should disappear once the filaments/cathodes have cooled (15 seconds

	  or so.  If there are still visible retrace lines, the CRT is suffering

	  from cold or field emission from someplace (may not even be the cathode).

	

	* Turn down the screen (G2) control on the flyback (usually).  If one color

	  remains no matter how you set the control, again there is some kind of

	  weird emission from the CRT.  However, if white/gray retrace lines remain,

	  the problem may be in the screen supply.

	

	See the section: "Bad CRT causing retrace lines".

11.16) Bad CRT causing retrace lines

	(From: Jeroen H. Stessen (
 This email address is being protected from spam bots, you need Javascript enabled to view it
 )).

	

	The TV which I bought last started developing retrace lines after a month or

	so of use.  I took it back to the lab for warranty (special deal) and had it

	examined by the real experts. They found that even with the filament supply

	disconnected and VG2 at 0V the screen would still light up. They could even

	see that the electrons weren't even coming from the cathode.  That was with

	only the picture tube in a test rig.  So in this case the obvious conclusion

	had to be that the  tube was bad, and it was replaced (32" 16:9 SF, very $$).

	It had something to do with processing problems during manufacturing of the

	electron guns. 

	

	So even if this was a rare case, it *can* happen that retrace lines are due

	to a bad picture tube.  It's more usual to suspect the VG2 (screen voltage)

	or a defect somewhere in the RGB video path.

11.17) Red, green, or blue full on - fog over picture

This could be a heater-cathode (H-K) short in the CRT or a failure

of a component in the chroma circuits or video output (driver board).

Don't panic - heater-cathode shorts in CRTs can often be worked around.

Note: before proceeding, it is a good idea to make sure that the screen is

degaussed - else you could be attempting to track down problems with the wrong

color!

Some simple tests can confirm or rule out other possibilities.

* Compare the voltages for the video drive signals to the CRT on the little

board on the neck of the CRT with the CRT both connected and unplugged.

A schematic will help greatly in locating these signals.

- If there is a significant difference especially on the bad color, then the

CRT is a likely candidate. Try tapping the neck of the CRT GENTLY (with

it plugged in and while viewing a picture) to see if it is an intermittent

problem.

- If there is no significant difference, you may have a bad driver or a

problem in the chroma circuits.

* Look for bad connection/cold solder joints, probably on the little

board on the neck of the CRT. Use an insulated stick to gently prod

the board and its components in an effort to induce/cure the problem.

Look carefully for hairline cracks around the component leads.

* You can swap components between two colors and/or test with an ohmmeter

on that driver board to determine what is bad. The nice thing about

color monitors and TVs is that there three copies of each of these

components. Swapping and/or comparisons between these is an excellent

diagnostic technique.

* Another simple test: Disconnect the cathode for the full-on color from its

drive. If it is still full-on, there is probably an H-K short in the CRT

since the only way to get each color on the screen is via the cathode

connection to the CRT neck board. If it is removed and there is still that

color, the current must be taking another path inside the CRT.

* Alternatively, interchange the outputs of the bad color with a good one

by jumpering on the video driver board (on the CRT neck). If the bad

color changes, then the problem is in the circuitry and not the CRT.

Here is the procedure in more detail (example for red full on):

(From: J. K. Emerine (
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)).

To identify if the fault is in the crt or a control problem try this (WITH

SET OFF):

On the CRT board, lift the output end of the green cathode final resistor.

Do the same with the offending red cathode's resistor. Use short insulated

jumpers to 'swap' drive signals - drive the red cathode with the green

drive and the green cathode with red drive. (Note that if this problem

only occurs after a warmup period, color at turn on will be - well - wierd,

but it is just a test.)

- If the symptom returns = 'goes red' the CRT is shorting. (See the section:

"Providing isolation for a CRT H-K short". --- sam)

- If instead the symptom becomes 'goes green' then the red drive leg has

the fault and the CRT is probably good. (In this case, there may be bad

connections or a bad component on the CRT drive board or further back

in the chroma circuitry. --- sam)

11.18) Totally white screen (probably with retrace lines)

There may or may not be any indication of a picture. This may be a problem in

the high voltage power supply (SCREEN, G2), loss of power or a fault in the

video output drivers, other video amp problems, or a bad (shorted) CRT.

Is focus still reasonably sharp? If not, try adjusting it (usually on the

flyback or a separate little panel). If changing focus affects brightness

significantly, there is a short between the two supplies - either in the

HV power supply or CRT. See the section: "Bad focus and adjustment changes brightness". In this case, changing SCREEN (G2, also on the flyback) may

also affect focus or may not do anything.

Try adjusting SCREEN. If it has no affect, a problem in its power supply

from the flyback is possible. If you have a high impedance voltmeter (not

just a DMM, the resistance of the voltage divider supplying SCREEN is hundreds

of M ohms), check it while changing the SCREEN control. If it does not change,

you have found a definite problem.

Assuming that adjusting FOCUS and SCREEN result in normal behavior and do

not strongly interact, the problem is likely in the video circuitry or output

drivers.

Check the power to the CRT video output drivers on the little board on the

neck of the CRT. If this failed, all three video outputs will be full on.

If you have a scope, look at the video outputs - they should be varying

between over 100 V and a low value. If they are missing or very low all

the time, there is a problem further back in the video chain.

See the other sections relating to brightness and high voltage problems

as well.

11.19) Shorts in a CRT

	Occasionally, small conductive flakes or whiskers present since the day of

	manufacture manage to make their way into a location where they short out

	adjacent elements in the CRT electron guns.  Symptoms may be intermittent or

	only show up when the TV or monitor is cold or warm or in-between.  Some

	possible locations are listed below:

	

	* Heater to cathode (H-K).  The cathode for the affected gun will be pulled

	  to the heater (filament) bias voltage - most often 0 V (signal ground).  In

	  this case, one color will be full on with retrace lines.  Where the heater

	  is biased at some other voltage, other symptoms are possible like reduced

	  brightness and/or contrast for that color.  This is probably the most

	  common location for a short to occur.

	

	* Cathode to control grid (K-G1).  Since the G1 electrodes for all the guns

	  are connected together, this will affect not only the color of the guilty

	  cathode but the others as well.  The result may be a very bright overloaded

	  *negative* picture with little, none, or messed up colors.

	

	* Control grid to screen (G1-G2).  Depending on circuitry can result in any

	  degree of washed out or dark picture.

	

	* Screen to focus (G2-F).  Screen (G2) and focus voltage will be the same and

	  the controls on the flyback will interact.  Result will be a fuzzy white

	  raster with retrace lines and little or very low contrast picture.  Symptoms

	  will be similar to those of a flyback with breakdown in the focus/screen

	  divider network.

	

	* Focus to high voltage (F-HV).  High voltage will be pulled down - probably

	  arcing at the focus spark gaps/other protective devices.  Line fuse and/or

	  HOT may blow.

	

	* Other locations between electron gun elements as feed wires.

	

	Replacing the CRT may be required but there are a variety of 'techniques' that

	can often be used to salvage a TV that would otherwise end up in the dump

	since replacing a CRT is rarely cost effective:

	

	1. Isolation - this will usually work for H-K shorts as long as only one gun

	   is involved.

	

	2. Blowing out the short with a capacitor - depending on what is causing the

	   short, this may be successful but will require some experimentation.

	

	3. Placing the CRT (TV or monitor) face down on a soft blanket and *gently*

	   tapping the neck to dislodge the contamination.  Depending on the location

	   of the short, one side or the other might be better as well.  Sometimes,

	   this can be done in-place while watching the picture.

	

	A combination of (2) and (3) may be required for intermittent shorts which

	don't appear until under power.  See the sections below for additional

	details.  However, for shorts involving the focus and high voltage elements,

	even a sharp edge can result in arcing even if there is no actual short.

	There is no remedy for these types of faults.

11.20) Providing isolation for a CRT H-K short

	This procedure will substitute a winding of your own for the one that is

	built in to the flyback to isolate the shorted filament from the ground

	or voltage reference.  Note that if you have a schematic and can determine

	where to disconnect the ground or voltage reference connection to the

	filament winding, try this instead.

	

	The flyback is the thing with the fat red wire coming out of it (and perhaps

	a couple of others going to the CRT board or it is near this component

	if your set has a separate tripler) and may have a couple of controls for

	focus and screen.  It should have some exposed parts with a ferrite core

	about 1/2-3/4" diameter.

	 

	The filament of the CRT is the internal heater for each gun - it is what

	glows orange when the set is on.  What has happened is that a part of the

	fine wire of the bad color's filament (assuming this is indeed your problem)

	has shorted to the cathode - the part that actually emits the electrons.

	Normally, the heater circuit is grounded or tied to a reference voltage

	so when it shorts to the cathode, the cathode voltage level is pulled to

	ground or this reference.

	

	You will need some well insulated wire, fairly thick (say #18-22).  Find a

	spot on the flyback where you can stick this around the core.  Wrap two

	turns around the core and solder to the CRT filament pins after cutting the

	connections to the original filament source (scribe the traces on the board

	to break them).  Make sure you do not accidentally disconnect anything else.

	

	This winding should cause the filaments to glow about the same brightness as

	before but now isolated from ground.  If they are too dim, put another turn

	on the flyback to boost the voltage as this will result in low emission,

	blooming, and possible damage to the cathodes after awhile.  (Don't go

	overboard as you may blow the filament totally if you put too many turns on

	the core - you then toss the monitor.)

	

	Route the wires so that there is no chance of them getting near the high

	voltage or any sharp metal edges etc.  Your picture quality may be a tad

	lower than it was before because of the added stray capacitance of the

	filament wiring being attached to the the (formerly bad) video signal, but

	hey, something is better than nothing.

11.21) Rescuing a shorted CRT

	If the short is filament-cathode (H-K), you don't want to use the following

	approach since you may blow out the filament in the process.  If this is the

	case, you may be able to float the filament and live with the short (see the

	section on: "Red, green, or blue full on - fog over picture".

	

	Shorts in the CRT that are between directly accessible electrodes can

	be dealt with in a more direct way than for H-K shorts.  At this point

	you have nothing to loose.  A shorted CRT is not terribly useful.

	

	If the short is between two directly accessible electrodes like cathode-grid,

	then as a last resort, you might try zapping it with a charged capacitor.

	

	Unplug the CRT socket!

	

	Start with a relatively small capacitor - say a few uF at a couple hundred

	volts.  Check to see if the short is blown after each zap - few may be needed.

	Increase the capacitance if you feel lucky but have had little success with

	the small capacitor.

	

	If the fault is intermittent, you will, of course, need to catch the CRT

	with the socket disconnected and the short still present.  Try some gentle

	tapping if necessary.  If you do this with the charged capacitor across

	the suspect electrode, you **will** know when the short occurs!

11.22) Dark picture

A monitor with a picture that is too dark may have a fault or the CRT may

just be near the end of its useful life.

First, confirm that your video source - computer, camera, etc. - is producing

a proper signal.

Is the brightness at all erratic? Does whacking the monitor have any effect?

If so, then you may have bad connections on the CRT driver card or elsewhere.

If the brightness tends to fade in and out over a 10 to 20 second period,

a bad filament connection is likely. Check for the normal orange glow of

the filaments in the neck of the CRT. There should be 3 orange glows. If

they are excessively reddish, very dim, or fade in and out, you have located

a problem. See the section: "Picture fades in and out".

Common causes of brightness problems:

0. Dirty CRT faceplate or safety glass. Don't laugh. It sounds obvious, but

have you tried cleaning the screen with suitable screen cleaner? It is

amazing how dirty screens can get after a few years - especially around

smokers!

(From: A. R. Duell (
This email address is being protected from spam bots, you need Javascript enabled to view it
)).

"I once spent a morning battling with a DEC VT105 terminal with a very

dim and washed out picture, and only after checking everything on the

video board did I wipe over the screen. That cured it. It's amazing

how dirty screens can get after a few years use."

Wipe gently with a slightly dampened cloth - not soaking or you may end

up with real problems when the water drips down inside and hits the

electronics!

1. Old CRT. The brightness of the CRT deteriorates with filament on-time.

It doesn't matter much what you are doing or if you use a screen saver.

An indication of a weak CRT would be that turning up the SCREEN (G2) or

master brightness control only results in a not terribly bright gray raster

before the retrace lines show up. There may be indications of poor focus

and silvery highlights as well. A CRT brightener may help. See the

sections: "Brightening a old CRT" and "Monitor life, energy conservation, and laziness".

2. Bad component in filament circuit or bad connection reducing filament

voltage. This should be easy to check - there are only a few parts

involved. If it is erratic, bad connections are likely.

3. Brightness control faulty - bad pot, bad connections, or problem with its

power supply. Depending on specific problem, control may or may not have

any effect. If digitally adjusted, there could be a problem with the

logic or control chip. If the button or menu item has no effect at all,

then a logic or control problem is likely.

4. Improperly set SCREEN (G2) voltage (usually on flyback) or faulty divider

network. See the section: "Brightness and color balance adjustment".

5. Improperly set video bias (background) levels or fault in video drive

circuitry. See the sections starting with: "Optimal procedure for setting brightness/background and screen adjustments".

6. Fault in video amplifiers. With all three color affected equally, this

would most likely be a power supply problem. A video amplifier problem

is likely if turning up the SCREEN (G2) or master brightness control

results in a very bright raster before the retrace lines appear. Cheack

signals out of the video/chroma(IC.

7. Fault in beam or brightness limiter. Many TVs and monitors measure the

beam current (possibly indirectly) and limit the maximum to a safe value.

The purpose of this may be to protect the CRT phosphors, and/or to assure

that the power supply does not go out of regulation, and/or to limit X-ray

emission. If this circuit screws up, a dark picture may result. Checking

the signals and voltages at the CRT socket should determine if this is the

problem.

8. High voltage is low. However, this would likely result in other symptoms

as well with focus, size, and geometry.

11.23) Brightening an old CRT

	If performing adjustments of the internal background and/or screen

	controls still results in a dark picture even after a long warmup period

	(and the controls are having an effect - they are not faulty), the CRT may

	simply be near the end of its useful life.  In the old days of TVs with

	short lived CRTs, the CRT brightener was a common item (sold in every

	corner drugstore, it seemed!).

	

	First confirm that the filaments are running at the correct voltage - there

	could be a marginal connection or bad resistor or capacitor in the filament

	power supply.  Since this is usually derived from the flyback, it may not

	be possible to measure the (pulsed high frequency) voltage with a DMM but

	a service manual will probably have a waveform or other test.  A visual

	examination is not a bad way to determine if the filaments are hot enough.

	They should be a fairly bright orange to yellow color.  A dim red or almost

	dark filament is probably not getting its quota of electrons.  It is not be

	the CRT since all three filaments are wired in parallel and for all three to

	be defective is very unlikely.

	

	If possible, confirm that the video output levels are correct.  For cathode

	driven CRTs, too high a bias voltage will result in a darker than normal

	picture.

	

	CRT brighteners are available from parts suppliers like MCM Electronics.

	Some of these are designed as isolation transformers as well to deal with

	heater-to-cathode shorts.

	

	You can try a making a brightener.  Caution: this may shorten the life of

	the CRT - possibly quite dramatically (like it will blow in a couple of

	seconds or minutes).  However, if the monitor or TV is otherwise destined

	for the scrap heap, it is worth a try.

	

	The approach is simple: you are going to increase the voltage to the

	filaments of the electron guns making them run hotter.  Hopefully, just

	hotter enough to increase the brightness without blowing them out.

	

	Voltage for the CRT filament is usually obtained from a couple of turns

	on the flyback transformer.  Adding an extra turn will increase the voltage

	and thus the current making the filaments run hotter.  This will also

	shorten the CRT life - perhaps rather drastically.  However, if the monitor

	was headed for the dumpster anyhow, you have nothing to lose.  You can just

	add a turn to an existing winding or make your own separate filament winding

	as outlined in the section: "Providing isolation for a CRT H-K short".

	

	In some monitors, there is a separate filament supply on the mainboard - this

	should be obvious once you trace the filament wires from the video driver

	board).  In this case, it still may be possible to increase this output or

	substitute another supply but a schematic will be required.

	

	There are also commercial CRT rejuvenators that supposedly zap the

	cathodes of the electron guns.  A TV or monitor service center may be

	able to provide this service, though it is, at best, a short term fix.

11.24) Color balance changes across screen from left to right

	The characteristics are that a solid white screen will tend to be blue tinted

	on one side and red tinted on the other.  This is usually a subtle effect and

	may be unavoidable with some designs.

	

	There are several possibilities:

	

	1. Purity - this means the beams are landing on the wrong phosphor dots.

	   This is what would be affected by moving from one location to another

	   or even rotating the TV on its base without degaussing.  If the problem

	   just appeared, degaussing may be needed.

	

	   What do you have near the TV or monitor?  Loudspeakers or other devices

	   which generate magnetic fields can easily cause all sorts of color purity

	   problems.  Relocate the offending device(s) or the TV or monitor and then

	   degauss it.

	

	   See the section: "Degaussing (demagnetizing) a CRT".

	

	   If the problem still persists, purity adjustment may be needed.  However,

	   this isn't likely to  have changed so look for other causes before tackling

	   these adjustments.

	

	2. Unequal electron gun to shadowmask/screen distance - the electron beams for

	   the red and blue video travel slightly different distances on the left and

	   right sides of the screen so their intensity (due to focus not being optimal

	   and other factors) in each case may differ slightly affecting color balance.

	

	3. Doming - This would only happen in very bright areas and causes the

	   shadow mask to expand and distort.  (Doming should not be a problem with

	   Trinitron CRTs which use tensioned wires in their aperture grill.)  This

	   would also not really affect left-right color balance in particular.

	

	I don't really know how much of a problem (2) is in practice or whether some

	manufacturers compensate for it.

11.25) Bleeding highlights

	On very bright areas of the picture, one or more colors may bleed to

	the right resulting in a trail of those colors.  The difference between

	this problem and the section: "Trailing lines in one or more colors" is

	that in this case, only highlights are affected.

	

	One cause of this is that the color gain, contrast, or intensity controls

	(whatever they are called on your monitor) are set too high.  See the section

	on: "Brightness and color balance adjustment".  Check the settings of any

	brightness limiter controls as well.

11.26) Trailing lines in one or more colors

	Assuming this is not a form of ghosting resulting from cabling and/or use

	of switchboxes, etc, then it could be any of the following:

	

	* Poor decoupling in the power supplies for the video drive circuits - probably

	  on the CRT neck board.  Check for bad (low uF or high ESR) filter capacitors

	  (electrolytic mostly) on this board or the power supplies feeding it.

	

	* Insufficient CRT filament voltage.  This could be a result of bad connections

	  or a bad component in the filament power supply (probably from the flyback).

	  Check to see if the filaments are glowing bright orange and check the voltage

	  if possible (though this can be tricky since it is often fed from a winding

	  on the flyback and is a pulse waveform, not DC or a sinusoid.  The service

	  manual will probably have info and waveforms.

	

	* Bad CRT (more likely if only one color is affected).  A weak electron gun can

	  result in this behavior.  Swap it with one that work properly.  If the same

	  color is still bad, that CRT gun is weak.  The CRT will need rejuvenation or

	  need to be replaced (more likely, the entire monitor will be tossed into the

	  dumpster).

11.27) Purity problems with bright pictures

	Setting the brightness excessively high may result in enough heating

	of the shadow mask to distort it.  IF severe enough, the positions of the

	holes will shift enough to result in visible purity problems.  This is

	less of a problem with tubes using an InVar shadow/slot mask.  It should

	also be less of a problem for Trinitron aperture grille CRTs.

	

	The only solution is to reduce the brightness.

11.28) Why does the intensity appear so non-uniform in bright areas?

Actually, the intensity variation is likely to be even worse than you might

think - possibly as much as 2:1 from the center to the corners. In most cases

you do not notice it. With large deflection angle tubes, fewer electrons make

it to phosphor dots near the edge of the screen. It is simple geometry.

(From: Bob Myers (
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)).

It is extremely difficult for any CRT display to maintain perfect brightness

and color uniformity across the entire image. Just the geometry of the

thing - the change distance from the gun to the screen as the beam is scanned,

the changing spot size and shape, etc. - makes this nearly impossible, and

there can also be variations in the phosphor screen, the thickness of the

faceplate, etc.. Typical brightness-uniformity specs are that the brightness

won't drop to less than 70% or so of the center value (usually the brightest

spot on the screen).

On color tubes, the lack of perfect brightness uniformity is aggravated

by the lack of perfect COLOR uniformity and purity. What appear to be

"dark spots" on a solid gray image may actually be beam mislanding (color

purity) problems, which may to some degree be remedied by degaussing

the monitor.

Again, *some* variation is normal; if you think you're seeing too much, you

can try degaussing the thing and seeing if that helps. If it doesn't,

then the question is whether or not the product meets its published specs,

and that 's something you'll have to discuss with the manufacturer or

distributor.

11.29) Brightness changes from left-to-right across screen

	Slight variations in brightness across the face of the CRT are not unusual.

	In fact, if you used a photometer to actually measure the brightness, you

	might be amazed at the actual variance even with the best TV - you just

	don't notice it.  However, a major variation - usually a decay from left to

	right but could be the other way indicate a component failure.  Of course,

	make sure the face of the screen is clean!

	

	* A fault in the power supplies to the video amplifier and/or video output

	  circuits.  Most likely, an electrolytic capacitor has dried up and is not

	  adequately filtering the power derived from the flyback which then has

	  ripple at the horizontal scan rate and thus locked to the screen.  The

	  voltage decays from left-to-right between horizontal flyback pulses.

	

	  The most likely location for these capacitors is in the vicinity of the

	  flyback transformer on the mainboard or on the CRT neck board.  Check the

	  capacitors with capacitor tester or ESR meter and/or take a look at the

	  power right at the video amplifier and video output drivers.

	

	* Horizontal linearity is bad - this may actually be a horizontal geometry

	  problem and not a brightness problem.

	

	  See if objects on left side of the screen are stretched compared to those on

	  the right (or vice-versa).  If they are, the problem is in the horizontal

	  deflection circuits - possibly a bad (or in the case of a multiscan monitor,

	  correctly selected) S correction capacitor or linearity coil.

	

	* Inoperative degauss circuit, monitor moved or rotated without degaussing, or

	  magnetic field from some other device (like a permanent magnet) is affecting

	  CRT - slight amounts of magnetization may reduce brightness (by moving the

	  beams into the black space between phosphor dots) before affecting color

	  purity (where the beams land on the wrong phosphor dots).

	

	  See if the degauss button, if present, does anything.  Try deguassing

	  manually.  See the section: "Degaussing (demagnetizing) a CRT".

11.30) Picture fades in and out

	If the picture faded away on the order of 10-20 seconds (and if it comes

	back, also comes up to full brightness in same time frame - possibly

	with the persuasion of some careful whacking) AND with NO other

	significant changes such as size, focus, etc., then take a look in the back of

	the tube for the filament to be lit - the orange glow near the CRT socket.  If

	there is none, then you probably have a bad solder connection on the circuit

	board on the neck of the CRT.  Look for fine cracks around pins on that board.

	Try prodding it with an insulating stick to see if the picture comes back.

	Resolder if necessary.  It is probably not a bad CRT as the filaments

	are usually wired in parallel and all would not go bad at the same time.

	

	However, if only a single color fades in and out, then a bad connection

	inside the CRT is a distinct possibility - look for only one of the

	filament's glow to be coming and going.  This is probably not worth fixing

	since it will require CRT replacement.

	

	If the picture faded away with other symptoms, then there is probably

	a fault in the video amplifier/output one of its power supplies -

	still probably a loose connection if you are able to get it back by

	whacking.

11.31) Occasional brightness flashes

	These may last only a fraction of a scan line or much much longer.

	

	Make sure it is not the video source - try another one.

	

	This could mean an intermittent fault in a variety of places including

	the video circuitry and SCREEN power supply:

	

	* Brightness circuitry - SCREEN, master background or its power supply.

	  Could be in or around flyback or focus/screen divider.  Could perhaps

	  be in the CRT, but probably less likely.

	

	* Video amp before or at chroma demodulator (if composite input) - since

	  after this point, you would most likely get colored flashes since only

	  one of the RGB signals would likely be effected.  However, a bad power

	  connection to the video circuitry could cause all the colors to be

	  affected.  

	

	If you still get flashes, it should be quite easy to monitor either

	the video outputs or SCREEN supply (with a HV divider on your scope) for

	noise.  Then trace back to power or noise source.

11.32) Occasional static, lines, spots, or other unsightly blemishes

	First, confirm that these are not video source - PC - related.  Try the

	monitor on another computer.  This may be a problem with the hardware or

	driver (software) for the video card, the O/S, or memory or bus speed.

	

	If it is not computer related, then it could be arcing, corona, bad

	connections, or some electronic component breaking down.  See the

	appropriate sections for these problems.

	

	Note that problems in absolutely fixed locations or with an extent related

	to pixel sizes in the video card are nearly always computer/video card

	related and not due to a faulty monitor.

11.33) Flickering monitor

	First, make sure your scan rate is set high enough (but not beyond the

	capabilities of the monitor).  A scan rate less than 60 Hz is likely to

	result in annoying flicker especially at high brightness levels.

	

	See if the flickering correlates with any processor or disk activity indicating

	a software driver or video card problem.

	

	Assuming neither of these applies and you are not doing your work by

	candlelight, a flickering image is probably due to an intermittent arc

	or short, probably in the high voltage section near or at the flyback

	transformer.  However, it is also possible that it is due to a simple

	bad connection elsewhere.

	

	So the first thing to do will be to remove the cover and without touching

	anything, carefully examine for any obvious signs of bad connections, arcing,

	or burned areas.  In particular look for:

	

	* hairline cracks around the pins of large components like power transistors,

	  power resistors, transformers, and connectors.

	

	* any discoloration, cracking, other unusual signs on the flyback.  The flyback

	  also provides, via a high resistance divider network, the several KV for

	  focus and several hundred V for the G2 (screen) CRT electrode.  These are

	  the voltages that may be intermittently changing and resulting in flicker.

	

	Now, with the monitor powered in a darkened room with a normal picture

	(use the highest resolution at which your monitor will work as this should

	put the most stress on it, maybe).

	

	* Look for any arcing or corona around the area of the flyback or the neck

	  of the CRT first, then just anywhere.

	

	* Use a well insulated stick (wood or plastic) to gently prod the circuits

	  board, components, wires, etc. to see if you can induce the problem.

	

	There will probably be a pair of adjustments on the flyback itself.  One of

	these is FOCUS and the other is SCREEN - essentially a master brightness.

	

	* Now, with one hand in your back pocket, try turning each of these a fraction

	  of a turn in each direction.  Don't worry, you cannot hurt anything by

	  doing this.  The FOCUS should only change the sharpness of the picture.

	  The SCREEN should only change the brightness.  In both cases, this should

	  be a smooth effect.  Sometimes, these controls will simply get dirty and

	  cause the problems you have seen.  In this case, just moving them back

	  and forth may clean them.  If one affects the other - if turning focus

	  alters brightness or vice-versa, there is a short between the focus and

	  screen voltages, probably inside the flyback but it could be elsewhere.

	

	It is likely that all of the above tests will come out negative as

	you may have an intermittent short internal to the flyback which can only

	be fixed by replacement.  However, eliminate the easy fixes first.

11.34) Excessive brightness and/or washed out picture

	There are a number of possibilities including incorrect screen (G2) or bias

	(G1) voltages, or a problem in the video or blanking circuitry.  Any of these

	could be the result of bad connections as well.  A short in the CRT can also

	result in these symptoms.

	

	* Excessive brightness/washed out picture is often an indication of a

	  problem with the screen (G2) supply to the CRT.  May be a bad capacitor

	  or resistor divider often in the flyback transformer assembly or on 

	  the board on the neck of the CRT.

	

	* If the excessive brightness just developed over time, then a simple

	  adjustment of the screen or background brightness controls may keep

	  it (and you) happy for a long time.

	

	  When good, a typical value would be in the 200 to 600 VDC at the CRT.  The

	  screen (it may also be called master brightness, bias, or background) control

	  should vary this voltage.  However, it may be difficult to measure as the

	  resistors in the voltage divider network may be quite large - hundreds of M

	  ohms.  If your unit has an external screen control (less likely these days)

	  and it has no effect, trace out the circuitry in the immediate vicinity and

	  check the resistors and potentiometer for opens, look for bad connections,

	  etc.  If it is built into the flyback transformer and is sealed, the entire

	  flyback will need to be replaced unless the actual problem turns out to be a

	  bad connection or bad component external to the flyback.

	

	* Where the brightness control has no effect, suspect a missing bias supply to

	  the G1 (control grid) electrodes of the CRT.  This is usually derived from

	  the flyback with a simple rectifier/filter capacitor power supply.  Parts

	  may have failed (though not likely the flyback itself).  Adjusting the user

	  brightness control should vary this voltage over a typical range of 0 to -50

	  V with respect to signal ground.

	

	* It could also be a problem with biasing of the video output transistors.

	  There may individual controls for background brightness on the little board

	  on the neck of the CRT.  However, we are looking for a common problem since

	  all colors are wrong in the same way.  This is likely to be a missing voltage

	  from a secondary supply from the flyback.

	

	* A short between electrodes inside the CRT can result in brightness problems.

	  It may be possible to check this with an ohmmeter with the power off and the

	  CRT socket removed.  Test between G1, G2, and F where all colors are

	  affected though a short between F and G2 will result in the focus control

	  changing brightness and vice-versa - a classic symptom.

	

	  However, in some cases, it only shows up when operating and one must deduce

	  the presense and location of the short from its affect on voltages and bias

	  levels.

	

	  See the section: "Rescuing a shorted CRT" and other related topics.

	

	First, check for bad connections/cold solder joints by gently prodding

	with an insulating stick.  Check voltages and bias levels.

11.35) Focus problems

	Slight deterioration in focus can be corrected by adjusting the focus

	control usually located on the flyback transformer.  Sometimes, this

	is accessible externally but usually not.  On monochrome monitors, the

	focus control, if any, may be located on the main board.

	

	Don't expect to have perfect focus everywhere on the screen.  Usually there

	will be some degradation in the corners.  A compromise can generally be

	struck between perfect focus in the center and acceptable focus in the

	corners.

	

	If the adjustments have no effect, then there is probably a fault in the

	focus power supply.

	

	For most color TVs and monitors, the correct focus voltage will be in the

	4-8 KDC range so you will need a meter that can go that high or some big

	resistors to extend its range or a HV probe.  You must use a high impedance

	meter as the current availability from the focus power supply is very low.

	

	The pots in the flyback are sometimes accessible by removing their cover,

	which may snap on.  However, a typical focus circuit will have a large

	value resistor potted inside the flyback (like 200 Megohms).

	

	Try to measure the focus in-circuit.  If the value you read is very low

	(assuming your meter has a high enough impedance not to load the circuit

	appreciably), then disconnect the wire (from the PCB on the neck of the

	CRT or wherever) and measure again and observe any change in picture.

	

	If still low, then almost certainly there is a problem with the pot or

	the flyback.  See if you can open it enough to measure and/or disconnect

	the pot.  If the problem is inside the potted part of the flyback, the

	only alternative is a new flyback or an external divider if you are so

	inclined.  However, once the focus network goes bad inside the flyback,

	there is an increased chance other parts will fail at some point in the future.

	

	If the voltages check out with the CRT disconnected, there is a chance of a

	bad CRT or of a shorted component on the PCB on the neck of the CRT.  Look

	for shorted capacitors or burnt or damaged traces.

11.36) Bad focus (fuzzy picture)

	Focus voltage on the CRT is usually in the range of 2-8 KV DC and should

	be controllable over a fairly wide range by the focus pot - usually located

	on the flyback or a little panel in its vicinity:

	

	* If adjusting the pot results in a position of acceptable focus, you may be

	  done.  It is not unusual for the focus setting to drift a over time.

	

	* If the setting is already as good as possible but not really good enough,

	  the CRT may be tired.  Alternatively, the filament voltage may be too low.

	  Check for bad connections in the filament circuit.

	

	* If the optimal setting is out of range of the focus pot, the problem is

	  likely leakage in the focus divider in the flyback or one of the components

	  on the CRT neck board.

	

	Also see the sections: "Focus adjustment" and "Focus drifts with warmup".

	

	The focus wire usually comes from the flyback or if the general area or from a

	terminal on a voltage multiplier module in some cases.  It is usually a wire

	by itself going to the little board on the neck of the CRT.

	

	If a sparkgap (a little 2 terminal device with a 1/8" gap in the middle)

	is arcing with power on, then the resistive divider has shorted inside

	the flyback, focus board, or HV multiplier - whatever you TV has - and

	the this unit will need to be replaced.  Ditto if the SCREEN control affects

	focus and/or vice-versa.

	

	Using a suitable high voltage meter (range at least 10 KVDC, 1000 M ohm or

	greater input impedance), you should be able to measure it connected and

	disconnected.  The ground return will be the outside coating of the CRT which

	may or may not be the same as the metal chassis parts.  If the voltage is very

	low (less than 2 KV) and the pot has little effect:

	

	* When measured right off of the source disconnected from the CRT neck board,

	  then the problem is probably in the focus network in the flyback (or wherever

	  it originates).  Sometimes these can be disassembled and cleaned or repaired

	  but usually requires replacement of the entire flyback or voltage multiplier.

	  Note: you may need to add a HV (10 KV) capacitor between the focus wire and

	  DAG ground to provide filtering so you get a DC level for your meter.

	

	* When measured with the focus wire attached to the CRT neck board with the

	  CRT connected but reasonable with the CRT unplugged, there is probably a

	  short between the focus and another electrode inside the CRT.  See the

	  section: "Rescuing a shorted CRT".

	

	* When measured with the focus wire attached to the CRT neck board with the

	  CRT unplugged, there is likely a component on the CRT neck board that is

	  leaky or breaking down.  Also, check for decayed (tan or brown) glue which

	  may turn leaky with age.

11.37) Focus drift with warmup

	This could be due to a problem with the focus voltage power supply, components

	on the CRT neck board, or a tired worn CRT.

	

	Focus is controlled by a voltage of 2-8 KV DC usually derived from the flyback

	transformer and includes some resistors and capacitors.  One of these could

	be changing value as it warms up. (assuming nothing else changes significantly

	as the unit warms up - e.g., the brightness does not decrease.)

	

	Focus voltage is derived from a subset of the high voltage winding on the

	flyback using a resistive voltage divider which includes the focus pot.

	These are extremely high value resistors - 200 M ohm is common - and so

	leakage of any kind can reduce or increase the focus voltage.  All other

	things being ok - i.e., the picture is otherwise fine - I would suspect this

	type of failure rather than the CRT.

	

	The connection to the CRT is usually a separate wire running from the flyback

	or its neighborhood to the CRT neck board.  Look for components in this

	general area.  Use cold spray or a heat gun to isolate the one that is

	drifting.  If you have access to a high voltage meter, you should be able

	to see the voltage change as the TV or monitor warms up - and when you cool

	the faulty part.  If it is in the flyback, then sometimes the part with the

	adjustments clips off and can be repaired or cleaned.  Most often, you will

	need to replace the flyback as a unit.

	

	* If the optimal adjustment point of the focus control doesn't change that

	  much but the best focus is simply not as good as it should be, the CRT is

	  probably the problem.  However, if the optimal point produces acceptable

	  focus but it changes (and possibly moves off of one end of the adjustment

	  knob range) as the unit warms up, the flyback or one of the components on

	  the CRT neck board are likely drifting.

	

	* If you have a high voltage meter, you can measure the focus voltage to 

	  determine if it is being changed by the focus pot and if it is in the

	  ball park (2-8 KV typical).  Sometimes, the part of the flyback with the

	  focus pot can be snapped off and cleaned or parts replaced but usually you

	  need to replace the whole unit.  There may a capacitor or two on the PCB on

	  the neck of the CRT that could have increased leakage as well thus reducing

	  the focus voltage.

	

	* To determine if the CRT is the problem, for sharp focus after the unit has

	  warmed up.  Power-off for an hour or so and carefully pull the CRT neck board

	  off of the CRT.  Then, power up the unit.  Let it run long enough such that

	  there would have been a detectable focus drift.  Now, power-down, plug the

	  CRT neck board back in, and power-up.  Watch the image as it appears on the

	  screen:

	

	  - If the focus starts out fuzzy and sharpens up as the image appears and

	    gradually becomes sharper as the CRT warms up the CRT is likely tired.

	

	    The only catch here is that plugging the CRT neck board into the CRT

	    results in an additional load on the flyback due to the picture beam

	    current which heats it more as well.  Thus, if the problem takes a few

	    minutes to appear, keep the brightness turned down except to check the

	    appearance of the picture from time to time. 

	

	    You can set the focus control for optimum when warmed up and just turn

	    the monitor on in advance of when you will be needing it or add a user

	    focus adjustment by drilling a hole in the plastic case for an *insulated*

	    screwdriver or flyback focus knob extender :-).  The CRT may continue

	    to function for quite a while so this is not impending doom.

	

	  - If the focus is relatively stable as the image appears and increases

	    in brightness *and* is about as sharp as it would be with the monitor

	    warmed up, the problem is most likely in the flyback.  However, also 

	    check for bad components or decayed (tan or brown) glue on the CRT neck

	    board.  A drifting flyback will need to be replaced as it will probably

	    get worse and fail completely.  Clean the surface of the circuit board and

	    CRT socket in the vicinity of the focus and screen terminals and traces.

	    Contamination or just dirt and grime can easily cause problems especially

	    on humid days since the resistance of these circuits is extremely high

	    (100s of M ohms).

	

	  - If the focus is relatively stable as the image appears and increases

	    in brightness *and* is similar to what it would be with the monitor cold,

	    you have a very strange situation where some load on the high voltage

	    power supply, perhaps, is causing a thermal problem.  This would be rare.

11.38) About the quality of monitor focus

Question: I have 2 identical monitors. One is razor sharp from edge to edge.

The other is blurred at the corners- not from convergence problems,

but just plain out of focus. In this monitor, the focus adjustment on

the flyback can improve the focus at the edges, but then the center of

the screen becomes worse..My question is : Is this a problem in the

electronics and presumably a fixable flaw or is it caused by variance

in the picture tube itself and not correctable ? Or is it some other issue?

(From: Bob Myers (
This email address is being protected from spam bots, you need Javascript enabled to view it
)).

The adjustment on the flyback sets the "static" focus voltage, which is

a DC voltage applied to the focus electrode in the CRT. However, a single

fixed focus voltage will not give you the best focus across the whole CRT

screen, for the simple reason that the distance from the gun to the screen

is different at the screen center than it is in the corners. (The beam

SHAPE is basically different in the corners, too, since the beam strikes

the screen at an angle there, but that's another story.) To compensate

for this, most monitors include at least some form of "dynamic" focus, which

varies the focus voltage as the image is scanned. The controls for the

dynamic focus adjustment will be located elsewhere in the monitor, and

will probably have at LEAST three adjustments which may to some degree

interact with one another. Your best bet, short of having a service

tech adjust it for you, would be to get the service manual for the unit

in question.

It is also possible that the dynamic focus circuitry has failed, leaving

only the static focus adjust.

As always, DO NOT attempt any servicing of a CRT display unless you are

familiar with the correct procedures for SAFELY working on high-voltage

equipment. The voltages in even the smallest CRT monitor can be lethal.

11.39) Bad focus and adjustment changes brightness

	This is the classic symptom of a short between the focus and screen

	supplies -