Sci.Electronics FAQ: Repair: TV Repair Notes on TV Repair and Diagnosis INDEX V2.20 (3/26/96) Table of Contents Chapter 1) About the Author & Copyright Chapter 2) Introduction 2.1) Television at the crossroads 2.2) Television receiver fundamentals 2.3) TV repair 2.4) Repair or replace Chapter 3) TV Receivers 101 3.1) Subsystems of a television set 3.2) For more information on TV technology Chapter 4) CRT Basics 4.1) Color CRTs, Shadowmasks, Magnetic Fields, and Degauss 4.2) Why is the Shadowmask or Aperture Grill made of a magnetic material? 4.3) Tubes for all Nations 4.4) Degaussing (demagnetizing) a CRT 4.5) Why are indirectly heated cathodes used in CRT 4.6) Why do TVs overscan? 4.7) Scratches in CRT face Chapter 5) TV Placement and Preventive Maintenance 5.1) General TV placement considerations 5.2) Preventive maintenance Chapter 6) TV Troubleshooting 6.1) Safety 6.2) Safety Guidelines 6.3) Troubleshooting tips 6.4) Test equipment 6.5) Incredibly Handy widgets 6.6) Safe discharging of capacitors in TVs and video monitors 6.7) The series light bulb trick 6.8) Getting inside a TV 6.9) Dusting out the inside of a TV Chapter 7) TV Adjustments 7.1) User picture adjustment 7.2) Focus adjustment 7.3) Adjustment of the internal SCREEN and color controls 7.4) Color Balance 7.5) Horizontal position, size, and linearity adjustment 7.6) Vertical position, size, and linearity adjustment 7.7) Pincushion adjustments 7.8) Geometry adjustment 7.9) Why is the convergence on my set bad near the edges 7.10) CRT purity and convergence problem 7.11) CRT purity adjustment 7.12) CRT convergence adjustment 7.13) Tilted picture Chapter 8) Low Voltage Power Supply Problems 8.1) Low voltage power supply fundamentals 8.2) Power button on set is flakey 8.3) TV blows fuse 8.4) Internal fuse blew during lightening storm (or elephant hit power pole) 8.5) Fuse replaced but TV clicks with power-on but no other action 8.6) Power-on tick-tick-tick or click-click-click but no other action 8.7) No picture or raster and no sound 8.8) Reduced width picture and/or hum bars in picture and/or hum in sound 8.9) TV power cycling on and off 8.10) Dead TV with periodic tweet-tweet-tweet or flub-flub-flub 8.11) Shorted Components 8.12) Startup problems - nothing happens, click, or tick-tick-tick sound 8.13) TV turns off after warming up 8.14) TV doesn't power up immediately 8.15) Old TV requires warmup period 8.16) Relays in the Power Circuitry of TVs 8.17) Flameproof Resistors Chapter 9) Deflection Problems 9.1) Deflection fundamentals 9.2) Why are nearly all horizontal drivers circuits transformer coupled? 9.3) Picture squeezed in then died 9.4) Horizontal deflection shutting down 9.5) Horizontal lock lost 9.6) Vertical squashed 9.7) Part of picture cut off 9.8) Single Vertical Line 9.9) Single Horizontal Line 9.10) Loss of Horizontal Sync (also applies to vertical) after Warmup 9.11) Intermittent jumping or jittering of picture or other random behavior 9.12) Horizontal output transistors keep blowing 9.13) Vertical foldover 9.14) Squashed picture on late model GE, RCA, or ProScan TV 9.15) Pincushioning Problems 9.16) Testing of flyback (LOPT) transformers Chapter 10) High Voltage Power Supply Problems 10.1) HV power supply fundamentals 10.2) What is a tripler? 10.3) High voltage shutdown due to X-ray protection circuits 10.4) Low or no high voltage 10.5) Excessive high voltage 10.6) Arcing, sparking, or corona from CRT HV anode (red wire/suction cup) 10.7) Arcing at CRT sparkgaps 10.8) Arcing from flyback or vicinity 10.9) Ozone smell and/or smoke from TV 10.10) Should I be worried about X-ray exposure while servicing a TV or monitor? 10.11) Flyback shot by 4 year old Chapter 11) Raster, Color, and Video Problems 11.1) No color - black and white picture 11.2) Psychodelic color 11.3) TV and Monitor Manufacturing Quality and Cold Solder Joints 11.4) Intermittent or Missing Colors 11.5) Red, green, or blue full on - fog over picture 11.6) Providing isolation for a CRT H-K short 11.7) Rescuing a shorted CRT 11.8) Brightening an old CRT 11.9) Bleeding highlights 11.10) Trailing lines on one or more colors 11.11) Picture fades in and out 11.12) Occasional brightness flashes 11.13) Excessive brightness and/or washed out picture 11.14) Bad focus (fuzzy picture) 11.15) Focus drift with warmup or age 11.16) Bad focus and adjustment changes brightness 11.17) Blank picture, good channel tuning and sound 11.18) Purple blob - or worse 11.19) Color TV only displays one color 11.20) Disappearing Red (or other color) Chapter 12) Tuner and AGC Problems 12.1) No reception from antenna or cable 12.2) Picture is overloaded, washed out, or noisy 12.3) Interference when using VCR RF connection 12.4) Missing or noisy channel or block of channels 12.5) Loss of Channel after Warmup 12.6) Channel tuning drifts as set warms up 12.7) Noise in picture and sound due to bright scene Chapter 13) Audio Problems 13.1) Picture fine, no audio 13.2) Weak or distorted audio 13.3) Buzzing TV 13.4) High pitched whine or squeal from TV with no other symptoms Chapter 14) Miscellaneous Problems 14.1) General erratic behavior 14.2) Jittering or flickering due to problems with AC power 14.3) My TV has the shakes 14.4) TV was rained on 14.5) TV was dropped 14.6) Setup menus will not go away or hieroglyphics on screen 14.7) Setup Adjustments Lost 14.8) TV doesn't work after being in storage 14.9) Older TVs with multiple intermittent problems 14.10) TV has burning smell 14.11) Revival of dead or tired remote control units 14.12) Loudspeakers and TVs 14.13) Should I replace all the electrolytic capacitors if I find a bad one? 14.14) Phantom spot or blob on CRT after set is shut off 14.15) Disposing of dead TVs (CRTs and charged HV capacitors) Chapter 15) Items of Interest 15.1) An informal history of X-ray protection 15.2) Memory chips in TVs 15.3) Tony's notes on setting convergence on delta gun CRTs 15.4) Saga and general setup for large CRT TVs 15.5) About Instant On TVs 15.6) Can I add an S-Video input to my TV or VCR? 15.7) How do I add A/V inputs to a TV which does not have them built in? 15.8) Turning a TV (or monitor) into an oscilloscope? 15.9) Displaying a video signal as a picture on an oscilloscope 15.10) Use of surge suppressors and line filters 15.11) GFCI tripping with monitor (or other high tech equipment) 15.12) Multisystem TVs 15.13) Could a TV be modified for 3D (stereo) display? 15.14) Displaying TV on a computer monitor 15.15) Displaying computer video on a TV 15.16) What is Kell factor with respect to interlaced displays? 15.17) Homemade V-chip (or at least viewing limiter 15.18) Interesting TV Switch Mode Power Supply 15.19) IR detector circuit Chapter 16) International Color Television Standards 16.1) Some questions and answers about TV standards 16.2) Politically Correct TV Standards 16.3) Variations on a 'standard' - the PAL system 16.4) Color television standards worldwide 16.5) Cable channel allocation 16.6) Notes on cable and broadcast frequencies 16.7) Why is the NTSC color subcarrier such a weird frequency? 16.8) What is the maximal allowed deviation of the horizontal frequency? 16.9) Informal comparison of TV standards Chapter 17) Repair Information and Parts Sources 17.1) Advanced TV troubleshooting 17.2) Service manuals for really old TVs 17.3) Parts information 17.4) Information sources on the Internet 17.5) Suggested references 17.6) Interchangeability of components 17.7) Repair parts sources: Chapter 1) About the Author & Copyright Author: Samuel M. Goldwasser E-Mail: sam@stdavids.picker.com Copyright (c) 1994, 1995, 1996 All Rights Reserved 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) Television at the crossroads Television in substantially its present form has been with us for nearly 50 years. It is a tribute to the National Television Standards Committee (NTSC) that the color television standards agreed upon in the early 1950s have performed remarkably well making quite efficient use of valuable radio spectrum space and the psychovisual characteristics of the human eye-brain system. However, HDTV (High Definition TV) will supplant and ultimately replace the current standards. We will all come to expect its superior resolution, freedom from noise and ghosting, and CD sound. Yet, the perceived quality of TV broadcasts and cable will never likely be the major issue with most consumers. Content will continue to be the biggest problem. It is likely that in roughly 15 years, HDTV - digitally processed and transmitted as 1s and 0s - will completely replace the current system. Acceptance in the marketplace is by no means assured but with the merging of TV and computers - with the Internet as a driving force - it would seem that the days of the stand-alone analog TV set are numbered. 2.2) Television receiver fundamentals The basic color television receiver must perform the same functions today as 40 years ago. (Since B/W is a subset of the color standard, most references in this document will be for color except as noted). A studio video monitor includes all of the functions of a television receiver except the tuner and IF (which rarely fail except for bad connections or perhaps lightening strikes to the antenna or cable connection). Therefore most of the repair information in this document is applicable to both TVs and studio monitors. Modern computer monitors share many similarities with TVs but the multisync and high scan rate deflection circuitry and more sophisticated power supplies complicates their servicing. As of this writing, all but the smallest TVs are based on the Cathode Ray Tube (CRT) as the display device. Tiny pocket sets, camcorder viewfinders, and the like have started using LCD (Liquid Crystal Display) panels but these are still inferior to the CRT for real time video. There has always been talk of 'the picture on the wall' display. While we are closer than ever to this possibility, I believe that mass production of an affordable wall mural TV screen is still decades away. The reason is simple economics - it is really hard to beat the simplicity of the shadowmask 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 in the dumpster than make it to product do to manufacturing imperfections. Projection - large screen - TVs may, on the other hand, 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 HDTV. Since it is a reflective device, the light source can be as bright as needed. However, this is still not a commercial product but stay tuned. 2.3) TV repair Unlike VCRs or CD players where any disasters are likely to only affect your pocketbook, TVs can be dangerous. Read, understand, and follow the set of safety guidelines provided later in this section 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 TV set 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 television only displaying shows in black-and-white. The majority of consumers probably do not know even this simple fact. Such a problem is usually due to a bad capacitor or other 10 cent part. This document will provide you with the knowledge to deal with a large percentage of the problems you are likely to encounter with your TVs. 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. 2.4) Repair or replace If you need to send or take the TV to a service center, the repair could easily exceed half the cost of a new TV. 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). TV prices have been dropping almost as fast as PC prices. Therefore, paying such prices for repair just may not make sense. Except for picture tube problems, most TV faults can be corrected without expensive parts, however. Keeping a 5 year old TV alive may be well worthwhile as basic TV performance and important features have not changed in a long time. 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 game room or beach house. (I would suggest the kid's room but most TV watching just rots the brain anyhow so a broken TV may be more worthwhile educationally than one that works.) Chapter 3) TV Receivers 101 3.1) Subsystems of a television set A TV set includes the following functional blocks: 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. Sometimes, there is a separate switching power supply but this would be the exception. Rectifier/filter capacitor/regulator from AC line provides the B+ to the switching power supply or horizontal deflection system. Degauss operates off of the line whenever power is turned on (after having been off for a few minutes) to demagnetize the CRT. Horizontal deflection. These circuits provide the waveforms needed to sweep the electron beam in the CRT across and back some 15,734 times per second (for NTSC). The horizontal sync pulse from the sync separator locks the horizontal deflection to the video signal. Vertical deflection. These circuits provide the waveforms needed to sweep the electron beam in the CRT from top to bottom and back 60 times per second (for NTSC). The vertical sync pulse from the sync separator locks the vertical deflection to the video signal. 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, nearly every TV on the planet derives the HV (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. Tuner, IF, AGC, video and audio demodulators. Input is the antenna or cable signal and output are baseband video and audio signals. There is usually someplace inside the TV where line level video and audio are present but it may not be accessible from the outside of the cabinet unless you paid for the more expensive model with the A/V option. Very often, the tuner is a shielded metal box positioned on the bottom right (as viewed from the front) separate from the main circuit board. Sometimes it is on the main circuit board. The IF section may be in either place. On older or cheap TVs with a knob tuner, this is usually mounted to the front panel by itself. There are usually separate boxes for the VHF and UHF tuners. Chroma demodulator. Input is the baseband video signal. Outputs are the individual signals for the red, green, and blue video to the CRT. 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 chroma demodulator to the hundred volts or so needed to drive the cathodes of the CRT. Sync separator. Input is baseband video. Output is horizontal and vertical sync pulses to control the deflection circuits. Audio amplifier/output. The line level audio is amplified to drive a set of speakers. If this is a stereo TV, then these circuits must also perform the stereo demultiplexing. System control. Most modern TVs actually use a microcontroller - a fixed program microcomputer to perform all user interface and control functions from the front panel and remote control. These are becoming increasingly sophisticated. However, they do not fail often. Older TVs use a bunch of knobs and switches and these are prone to wear and dirt. Most problems occur in the horizontal deflection and power supply sections. These run at relatively high power levels and some components run hot. The high voltage section is prone to breakdown and arcing as a result of hairline cracks, humidity, dirt, etc. The tuner components are usually quite reliable unless the antenna experiences a lightening strike. However, it seems that even after 20+ years of solid state TVs, manufacturers still cannot reliably solder the tuner connectors and shields so that bad solder connections in these areas are common even in new sets. 3.2) For more information on TV technology The books listed in the section: Suggested references include additional information on the theory and implementation of the technology of television standards and TV receivers. For an on line introduction to TV and monitor technology, point your web browser to the Magnavox reference page at the following URL: http://www.magnavox.com/electreference/electreference.html There you will find links to a number of articles on the basic principles of operation of CD players, laserdisc and optical drives, TVs, VCRs, camcorders, loudspeakers, satellite receivers, and other consumer A/V equipment. Chapter 4) CRT Basics 4.1) Color CRTs, Shadowmasks, Magnetic Fields, and Degauss All color CRTs utilize a shadowmask 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 shadowmask 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 most 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 shadowmask 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 shadowmask. 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) Why is the Shadowmask or Aperture Grill made of a magnetic material? (From: Jeroen Stessen, (stessenj@am.umc.ce.philips.nl)) The question often arises: Well, if magnetization and the need for degauss is a problem, why not make the shadowmask or aperture grille from something that is non-magnetic? The shadowmask MUST be made of magnetic material! This may seem to be undesirable or counterintuitive but read on: Together with the internal shielding hood it forms sort of a closed space in which it is attempted to achieve a field-free space. The purpose of degaussing is NOT to demagnetize the metal, but to create a magnetization that compensates for the earth's magnetic field. The SUM of the two fields must be near zero! Degaussing coils create a strong alternating magnetic field that gradually decays to zero. The effect is that the present earth magnetic field is frozen into the magnetic shielding and the field inside the shielding will be (almost) zero. Non-zero field will cause colour purity errors. Now you will understand why a CRT must be degaussed again after it has been moved relative to the earth's magnetic field. This will also explain why expensive computer monitors on a swivel pedestal have a manual degaussing button, you must press it every time after you have rotated the monitor. The axial component of the magnetic field is harder to compensate by means of degaussing. Better compensation may be achieved by means of a rotation coil (around the neck or around the screen), this requires an adjustment that depends on local magnetic field. CRT's for moving vehicles (like military airplanes) may be equipped with 6 coils to achieve zero magnetic field in all directions. They use magnetic field sensors and active compensation, thus they don't need any degaussing function. This is too expensive for consumer equipment. 4.3) Tubes for all Nations (From: Jeroen Stessen, (stessenj@am.umc.ce.philips.nl)) CRT Manufacturers actually make different versions of their tubes for TV's for the northern and southern hemisphere, and sometimes a 3rd neutral type. These are so-to-say precorrected for the uncompensated field. (Note that the term 'tube' here includes much of the convergence hardware as well - not just what is inside the glass.) I remember when we exported projection televisions from Belgium to Australia, a couple of years ago. They all had to be opened on arrival to re-adjust the rotation settings on the convergence panel, due to the different magnetic field in Australia. Projection TV's don't have degaussing (there is nothing to degauss), and the customer can only adjust red and blue shift, not rotation. Our CRT application group has a magnetic cage. This is a wooden cube (approx. 2 meter long sides) with copper coils around each of the 6 surfaces. With this they can simulate the earth magnetic field for every place on earth (as indicated on a map on the wall). 4.4) 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 lightening strike nearby. A friend of mine had a lightening 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 shadowmask 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. 4.5) Why are indirectly heated cathodes used in CRT Here are three reasons: The cathode can be made of and/or coated with a material optimal for emitting electrons without regard to its performance as a heater. The separate cathode and filament can be electrically isolated so that the filament voltage and cathode drive signal, if any, do not interfere. The cathode can have an optimal shape for the application. This would be particularly significant for CRTs. The spot on the screen is a reduced focused image of the effective shape of the emitting portion of the cathode. 4.6) Why do TVs overscan? (The following includes material from: Jeroen Stessen (stessenj@am.nlvxe1.umc.ce.philips.nl)) Q: TVs are always set up to generate a picture which is 10-15 percent large than the visible face of the CRT. Why? In the early days of TV, this was probably done to make the design easier. Component tolerances and power line voltage fluctuations would be masked even if they caused changes in picture size. There certainly is almost no reason today to have any more than a couple of percent overscan. Most modern TVs have very well regulated power supplies and component values do not really drift much. Computer monitors, for example, are usually set up for no overscan at all so that the entire image is visible. We are constantly reminded of that, now that we are building TV's with VGA inputs (PD5029C1 in the USA, US$ 2000). This mixed application has overscan in TV mode and underscan in VGA mode. Geometry adjustment is quite critical if you see border-on-border. Unfortunately, TV's may be good but VCR's certainly are not. If you have too little overscan and then put the VCR in any feature mode (like picture search) then one (black) picture edge may become visible. Bad form. Viewers do not like this. While design considerations may have been the original reason for overscan, now it has become accepted as a defacto standard, and broadcasters are counting on the overscan being a certain percentage. One wonders whether it will ever change or whether this really matters. I suppose when we have true flat panel digitally addressed displays, we might have 0% overscan. At the Japan Electronics Show all the signs are pointed toward flat panel displays so maybe I will not have to hold your breath for much longer. Physically, as with an LCD display on a laptop computer, there will be 0% overscan (no need to build the extra pixels) but that doesn't mean that all 480 lines will be visible. 4.7) Scratches in CRT face Minor scratches can be removed with Jeweler's rouge or similar ultra fine abrasive. Jeweler's Rouge is the same stuff that is used in the final polishing of lenses and mirrors so it makes for a fine finish. However, any kind of scratch deep enough to be felt will not yield to this approach. WARNING: any kind of deep scratch on a CRT should be considered a serious safety hazard. This may be even more of a concern for modern CRTs that have 'integral implosion protection' - that steel band around the outside'. Older CRTs used either (1) a separate safety shield - that laminated glass plate in front of your grandmom's TV - or (2) a second contoured glass panel bonded to the actual tube face. In both of these cases, the second panel is strictly protective and serves no structural purpose. Therefore, any damage to it does not compromise the tube in any way. In the case of modern CRTs, the steel band in conjunction with the basic tube envelope is used to maintain the integrity of the overall CRT. Any damage significantly decreases the strength and increases the risk of CRT implosion. BTW, scratches in the CRT have absolutely no effect on X-ray emission. X-rays are blocked long before they come anywhere near the surface and glass has very little effect on their direction. Any scratch deep enough to have any detectable effect on X-ray emission (actually, it would need to be an inch deep gouge) would have caused the tube to implode. Chapter 5) TV Placement and Preventive Maintenance 5.1) General TV placement considerations Proper care of a TV does not require much. Following the recommendations below will assure long life and minimize repairs: Subdued lighting is preferred for best viewing conditions but I will not attempt to tell you how to arrange your room! Locate the TV away from extremes of hot and cold. Avoid damp or dusty locations if possible. (Right you say, keep dreaming!) Allow adequate ventilation - TVs use more power than any of your other A/V components. Heat buildup takes its toll on electronic components. Leave at least 3 inches on top and sides for air circulation if the entertainment center does not have a wide open back panel. Do not pile other components like VCRs on top of the TV if possible (see below). Do not put anything on top of the TV 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. If possible, locate the VCR away from the TV. Some VCRs are particularly sensitive to interference from the TV's circuitry and while this won't usually damage anything, it may make for less than optimal performance due to RF interference. The reverse is sometimes true as well. If possible, locate your computer monitor away from the TV. Interaction of the electromagnetic fields of the deflection systems may result in one or both displays jiggling, wiggling, or vibrating. Locate loudspeakers and other sources of magnetic fields at least a couple of feet from the TV. This will minimize the possibility of color purity or geometry problems. Make sure all input-output video and audio connections are tight and secure to minimize intermittent or noisy pictures and sound. Use proper high quality cable only long enough to make connections conveniently. Finally, store video cassettes well away from all electronic equipment including and especially loudspeakers. Heat and magnetic fields will rapidly turn your priceless video collection into so much trash. The operation of the TV depends on magnetic fields for beam deflection. Enough said. 5.2) Preventive maintenance Preventive maintenance for a TV is pretty simple - just keep the case clean and free of obstructions. Clean the screen with a soft cloth just dampened with water and at most, mild detergent. DO NOT use anything so wet that liquid may seep inside of the set around the edge of the picture tube - you could end up with a very expensive repair bill when the liquid shorts out the main circuit board lurking just below. If the set has a protective flat glass faceplate, there is usually an easy way (on newer sets with this type of protection) of removing it to get at the inner face of the CRT. Clean both the CRT and the protective glass with a soft damp cloth and dry thoroughly. 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 high voltage CRT 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. Chapter 6) TV 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 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 100-500 ohms/V approximate value (e.g., for a 200 V capacitor, use a 20K-100K ohm resistor). Monitor while discharging and/or 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-10M ohm 1W or greater wattage 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. Always wear eye protection. 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 TV, it may just be a bad connection or blown fuse. Remember that the problems with the most catastrophic impact on operation like a dead TV 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 interference or a TV that refuses to play 'StarTrek Voyager'. 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 TVs) and mostly non-productive (or possibly destructive). Whenever working on precision 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 the chassis first before any of the electronic components is a good practice. A basic set of precision hand tools will be all you need to disassemble a TV 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 and RF transformers. 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. 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 - both RF and baseband (RCA jacks). Unless you are troubleshooting tuner or video/audio input problems, either one will suffice. RF sources include a pair of rabbit ears or an outdoor antenna, a cable connection, or a VCR with a working RF modulator. This will be more convenient than an antenna connection and will permit 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 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). 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 TV gradually to make sure there are no problems but 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 all modern TVs use a line connected power supply, 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 TV 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 - about $15 for one suitable for all but the largest TVs. Also, see the section: Degaussing (demagnetizing) CRTs. 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. The circuit described below can used to provide a visual indication of polarity and charge. 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. 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: It will not destroy screwdrivers and capacitor terminals. It will not damage the capacitor (due to the current pulse). It will reduce your spouse's stress level in not having to hear those scary snaps and crackles. 6.7) The series light bulb trick When powering up a TV (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. 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) TVs. 150-200 W bulb for large color or projection TVs. Depending on the power rating of the equipment, these wattages may need to be increased. 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. 6.8) Getting inside a TV You will void the warranty - at least in principle. There are usually no warranty seals on a TV so unless you cause visible damage or mangle the screws, it is unlikely that this would be detected. You need to decide. A TV 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 TV is usually quite simple requiring the removal of anywhere from 4 to 16 Philips or 1/4 hex head screws - most around the rear edge of the cabinet or underneath, a couple perhaps in the middle. Disconnect the antenna and/or antenna or cable wiring first as it may stay with catch on the rear cover you are detaching. Reconnect whatever is needed for testing after the cover is removed. 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 TVs can still be positioned stably on any of three sides (left, right, bottom) even without the rear cover. However, some require the cover for mechanical strength or to not easily fall over. Be careful- larger TVs, in particular, are quite heavy and bulky. Get someone to help and take precautions if yours is one of the unstable variety. If need be, the set can usually safely be positioned on the CRT face if it is supported by foam or a folded blanket. 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. 6.9) Dusting out the inside of a TV 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! 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 TV unless it gets redeposited inside various controls or switches but will be bad for your lungs - and will spread it 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. Chapter 7) TV Adjustments 7.1) User picture adjustment For general viewing, subdued lighting but not total darkness is probably best. However, for most dramatic impact, a darkened environment may be preferred. Make the following adjustments under the expected viewing conditions. Tune to a strong channel or play a good quality tape. Turn the brightness, contrast, and color controls all the way down. Center the tint control (NTSC). 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. Initially adjust the color control for pastel shades rather than highly saturated color. Set the tint control for best flesh tones. Then, increase the color control to obtain the desired degree of color saturation. 7.2) Focus adjustment On a decent TV, you should be able to make out the individual scanning lines. If they are fuzzy, especially in bright areas, then focus may need to be adjusted. 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. Let the set warm up for at least half an hour. Display a good quality signal. Turn the user color control all the way down and the brightness and contrast controls all the way up. This will be the worst case. Adjust the focus control for best overall sharpness - you may not be able to get it perfect everywhere - center as well as corners. If best focus is at one end of the focus pot's range and still not good enough, there may be a problem in the focus divider, focus pot, or some related component. 7.3) Adjustment of the internal SCREEN and color controls The screen should be adjusted with a white pattern (snow from the tuner should do or turn the user COLOR control all the way down to get a black and white picture). Put the set in Service mode (horizontal line) if it has such a switch in the back or inside. If not, just use the raster in a darkened room. Adjust screen for a dim white line (raster). If the line is not white at its dimmest point, you will need to adjust the drive and cutoff controls for R, G, & B. Alternatively, you can use the following procedure: (From LEE) Turn R, G, and B screen (or background) controls down. Now turn color control fully counterclockwise -- off. Now turn up red screen until the screen just shows a red hue. Now turn red gun down until red tint just goes away. Now do the same with the green and blue screen controls. Now adjust the two DRIVE controls for the best black and white picture. That's all there is to it. I don't like to work with just a thin SETUP line. Cartoons seem to be the best thing to have on while doing the above procedure. You can also use just plain snow (no program) if you prefer. If you can obtain a good B&W pic. when you're done, the tube is good and the set if most likely functioning properly. Be patient and go slow while watching the large mirror that you are using during this procedure. 7.4) Color Balance Color balance needs adjustment if the highlights and/or shadows of a black and white picture (turn the color control all the way down) are not a perfectly neutral gray. To adjust the color balance: Turn the color control all the way down so that you get what should be a B/W picture. Set the user brightness and contrast controls about mid-range. The tint control should not matter (if it does at this point, you have other chroma problems or an 'autocolor' switch is on limiting the range of some controls). Adjust the sub-brightness controls (may be called color screen, background, or the like) so that the dark areas of the picture are just visible and neutral gray. Then, adjust the color gain controls until the brightest areas are neutral white but not so bright that there is 'color bleeding' in the highlights. This should get you close. If something is still shifting after warmup and get some cold-spray or even a little blower and try to locate the component that is drifting. Most likely a transistor or capacitor. 7.5) Horizontal position, size, and linearity adjustment Horizontal position may be set via a switch or jumper, a pot, or (mostly in B/W TVs) a set of rings on the CRT neck. Horizontal size should be set so that there is about 10-15 percent overscan left and right. 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 (fast play) modes. Many sets no longer have any horizontal size adjustments and depend on accurate regulation of the voltage to the horizontal output stage to control horizontal size. There may be a B+ adjustment to perform first. On those that do, the adjustment may either be done by setting the B+ voltage, by a pot, or a width coil in series with the horizontal deflection coils. Modern sets do not generally have any linearity control but you may find this on older models. You will need to go back and forth between size and linearity as these adjustments are usually not independent. Some of the newest sets control all these parameters via settings in non-volatile memory and use service menus accessed via the remote control for nearly all setup adjustments. 7.6) Vertical position, size, and linearity adjustment Vertical position may be set via a switch or jumper, a pot, or (mostly in B/W TVs) a set of rings on the CRT neck. Vertical size should be set so that there is about 10-15 percent overscan top and bottom. 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 (fast play) modes. Some sets no longer have any vertical size adjustments and depend on the accurate regulation of the voltage to the vertical output stage to control vertical size. On those that do, the adjustment is usually a pot in the vertical output circuitry. If your set has a linearity control, you will need to adjust this in conjunction with the size control as these are usually not independent. Some of the newest sets control all these parameters via settings in non-volatile memory and use service menus accessed via the remote control for nearly all setup. 7.7) Pincushion adjustments There may be 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 7.8) 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 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. 7.9) Why is the convergence on my set 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 TV. 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 effective writing rate of 20,000 mph across the face of a 27 CRT in a variable magnetic environment manufactured at a price you can afford without a second mortgage! 7.10) CRT purity and convergence problem Purity assures that each of the beams for the 3 primary colors - red, green, and blue - strikes only the proper phosphor dots 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. 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 best to face the set North-South (front-to-back) when doing any purity and convergence adjustments. Since you have no way of knowing what orientation will eventually be used, this is the best compromise as the earth's magnetic field will be aligned front-back. Of course, if you know the final orientation of the TV in your entertainment center - and you don't expect to be redecorating, use that instead. First, make sure no sources of strong magnetic fields are in the vicinity of the TV - loudspeakers, refrigerator magnets, MRI scanners, etc. A nearby lightening strike or EMP from a nuclear explosion can also affect purity. Cycle power a couple of times to degauss the CRT (1 minute on, 20 minutes off) - see the section: Degaussing (demagnetizing) the CRT. If the built in degaussing circuits have no effect, use an external manual degaussing coil. 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 set 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). 7.11) 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 TV, the following purity adjustment procedure may substitute green for red. This depends on the gun placement in the CRT. This description is based on the SAMs Photofact for the RCA CTC111C chassis which uses a slot-mask CRT. The procedures for dot-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 set 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. Move the yoke forward until you have the best overall red purity. Now, move the yoke forward until you have the best overall red purity. Tighten the clamp securely and reinstall the rubber wedges (if you set has these) to stabilize the yoke position. Reset the video adjustments you touched to get a red raster. 7.12) CRT convergence adjustment In the good old days when TVs were TVs (and not just a picture tube with a little circuit board attached) there were literally drawers 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. 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. If you do not have a test pattern generator, any static scene (from a camcorder or previously recorded tape, for example) with a lot of fine detail will suffice. Turn the color control all the way down so you have a B/W picture. 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. From the SAMs for the RCA CTC111C: adjust the center set of magnets 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 set may have a slightly different procedure. Dynamic convergence adjusts for coincidence at the edges and corners. On old tube, hybrid, and early solid state TVs, dynamic convergence was accomplished with electronic adjustments of which there may have been a dozen or more that were not independent. With modern sets, all 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. From the SAMs for the RCA CTC111C: Loosen the screws at the 6 o'clock and 10 o'clock positions to permit the yoke to be tilted vertically. Rock yoke up and down to converge the right and left sides of the screen. Tighten screw at 6 o'clock and loosen screw at 3 o'clock to permit the yoke to be tilted horizontally. Rock yoke from side to side to converge the top and bottom of the screen. Tighten screws at 3 o'clock and 10 o'clock. Many sets simply use the main clamp which locks the yoke to the neck of the CRT in conjunction with rubber wedges between the yoke and the funnel of the CRT to stabilize the yoke position position. Refer to your service manual. (Is this beginning to sound repetitious? For additional comments on convergence adjustments, see the sections: Tony's notes on setting convergence on delta gun CRTs and Saga and General setup for large CRT TVs. 7.13) Tilted picture You have just noticed that the picture on your fancy (or cheap) TV is not quite horizontal - not aligned with the front bezel. Note that often there is some keystoning 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, 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 TV picture is not perfect! BTW, I can sympathize with your unhappiness. Nothing is more annoying than a just noticeable imperfection such as this. There are several possible causes for a tilted picture: 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? 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. There is an internal tilt control that is misadjusted. Not common. 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. On some monitors, you can rotate the CRT slightly instead but probably not on your TV. If the TV 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 the set 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). External magnetic fields can sometimes cause a rotation without any other obvious effects - have you changed the TV's location? Chapter 8) Low Voltage Power Supply Problems 8.1) Low voltage power supply fundamentals TVs 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 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. There will always be: A power switch, relay, or triac to enable main power. 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. 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. 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. 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. 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. A startup circuit for booting the horizontal deflection if various voltages to run the TV 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. 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. Always use an isolation transformer when working on a TV 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. 8.2) Power button on set is flakey If the on/off (or other button) on the set itself behaves erratically but the remote control works fine, then it could be a dirty button or cable or other connections to the switch PCB, particularly if the buttons on the set itself are rarely used. There could possibly be a bad pullup resistor or something of that sort - but is it worth the effort to locate? Why not just continue to use the remote? There is no reason to suspect that it will develop similar symptoms. However, there is some risk that if the button is dirty, you may find the TV coming on at random times in the middle of the night (of course!). I think I have an older Sylvania that does that sort of thing - don't really know as I never use the power button on the set! If power is controlled by a hard switch - a pull or click knob, or mechanical push-push switch and this has become erratic due to worn contacts, replacements are available but often only directly from the original manufacturer to physically fit and (where applicable) have the volume or other controls built in. As an alternative, consider mounting a small toggle switch on the side of the cabinet to substitute for the broken switch. This will almost certainly be easier and cheaper - and quite possibly, more reliable. 8.3) TV 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 TV 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. Horizontal output transistor. Power supply regulator if there is one. Power supply chopper (switchmode) transistor if there is one. 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 or a shorted Posistor. Test the rectifiers individually or remove and retest the resistance. Some sets 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 set unplugged to measure the horizontal output transistor. Even better to remove it and measure it. C-E should be high in at least one direction. B-E may be high or around 50 ohms but should not be near 0. If any readings are under 5 ohms, the transistor is bad. The parts sources listed at the end of this document will have suitable replacements. If the HOT tests bad, try powering the set first with your light bulb and if it just flashes once when the capacitor is charging, then put a fuse in and try it. The fuse should not blow with the transistor removed. Of course, not much else will work either. If it tests good, power the set without the transistor and see what happens. If the fuse does not blow, then with the good transistor (assuming it is not failing under load), it would mean that there is some problem with the driving circuits possibly or with the feedback from the voltages derived from the horizontal not regulating properly. Look inside the TV and see if you can locate any other large power transistors in metal (TO3) cans or plastic (TOP3) cases. There may be a separate transistor that does the low voltage regulation or a separate regulator IC. Some TVs 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 lightening storms. However, the most likely parts to short are easily tested, usually in-circuit, with an ohmmeter and then easily removed to confirm. If you find the problem and repair it yourself, the cost is likely to be under $25. 8.4) Internal fuse blew during lightening storm (or elephant hit power pole) Power surges or nearby lightening 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 lightening 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 lightening strike - similar but on a smaller scale to the EMP of a nuclear detonation. Was the TV operating or on standby at the time? If it was switched off using an actual power switch (not a logic pushbutton or the remote control), 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 the TV was operating or on standby or has no actual power switch, then a number of parts could be fried. TVs 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 cover (unplug it first!) and start at the line cord. 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 - well certainly not less 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 25 or 30 ohms. If the reading is really low, there are other problems. If the resistance checks out, replace the fuse and try powering the TV. There will be 3 possibilities: It will work fine, problem solved. 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. 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: TV blows fuse. 8.5) Fuse replaced but TV 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. 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 (for shorts): Rectifier diodes Horizontal Output Transistor (HOT) Regulator pass or chopper transistor (if present) Main filter capacitor 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 everything here checks out, clip a voltmeter set on its 500 V scale or higher 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 set 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. Other possible problems: Bad hybrid voltage regulator bad startup circuit Bad relay contacts as mentioned above. 8.6) 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. 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 - momentary 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 until it warms up. A bad filter capacitor on the output of a series regulator may result in excessive voltage and subsequent 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 TV with periodic tweet-tweet-tweet or flub-flub-flub. 8.7) No picture or raster and no sound The screen is blank with no raster at all. There are indications that the channel numbers are changing in the display. 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). 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. 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+ - probably between 100 and 150 V. If there is no voltage, you have a low voltage power supply problem and/or you have not found all the bad/open parts. If there is voltage and no deflection (no high pitched whine and no HV), 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 Zeniths use a simple multivibrator for this - a couple of transistors. Others power the horizontal osc. IC from a special line-derived voltage. The multivibrator type are sometimes designed to fail if someone keeps turning the set on and off (like kids playing) since the power rating is inadequate. 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 risky - you can blow things up if not careful (including yourself). If you hear the high pitched whine of the deflection 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. 8.8) Reduced width picture and/or hum bars in picture and/or hum in sound 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: 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). Hum in the sound. This may or may not be noticeable with the volume turned down. 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. 8.9) TV 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 TV 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 TV 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 (most common). 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 TV 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. 8.10) Dead TV with periodic tweet-tweet-tweet or flub-flub-flub A TV 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 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). 8.11) 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. 8.12) 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 100-150 V, 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: Discrete multivibrator or other simple transistor circuit to provide base drive to the HOT. IC which is part of deflection chain powered off of a voltage divider or transformer. 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 8.13) TV 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? 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. 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 pull-knob (or other hard on/off switch), then this may be like pulling the plug and would reset any abnormal condition. 8.14) TV doesn't power up immediately The TV 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: 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. 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. 8.15) Old TV requires warmup period So, what else is new? In the old days, a TV 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! A TV (from around 1983) needs at least 5 min. to warm up (lighting up the screen and making sound if I give it a cold start. Once warmed up, you can it off and on again from the front panel and it will work immediately. Another thing this TV has a sub-power switch in the rear. 1983 sounds a bit late, but sets in the late '70 during the transition from tubes to all solid state chassis often had the 'sub-power' switch providing some power to the filaments of the CRT and other tubes - usually in the deflection and high voltage circuits since these would take a while to heat up and stabilize. The idea was to leave this switch on all the time (except when going on vacation - it was sometimes labeled 'vacation') so that you would have nearly instant warm up. Supposedly, this led to an increased risk of fire as well (see the section: About instant on TVs). If it is a totally solid state chassis, then there is some component - probably a capacitor in the power supply since it affects both picture and sound - that is drifting with temperature and needs to be located with cold spray or a heat gun. 8.16) Relays in the Power Circuitry of TVs What exactly is the purpose of such a relay ... i.e., why doesn't the power switch on the TV just apply power directly instead of through a relay? 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? The 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. Some big public libraries carry the SAMs photofact series for TVs and VCRs. If not, take 10 minutes and trace it. You should be able to get far enough to determine the relay connections. 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. 8.17) 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. 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 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. For NTSC and PAL, the vertical scan rates are 60 and 50 Hz (approximately) respectively. 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: Sync separator to obtain horizontal and vertical synchronization pulses. Horizontal oscillator which locks to horizontal sync pulses. 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 is a large discrete power transistor, most often an NPN bipolar type. Vertical oscillator which locks to vertical sync pulses. Yoke requires sawtooth waveform for linear vertical deflection. Vertical drive/output which feeds vertical deflection yoke. Newer TVs use ICs for vertical drive and output. 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. 9.2) Why are nearly all horizontal drivers circuits transformer coupled? One (probably secondary) reason is that this provides one of the isolation barriers between a line-connected HOT and flyback primary and the signal circuits of the TV. A more important rational is that a transformer is nice easy way of impedance matching the horizontal driver circuit (100s to 1000s of ohms) to the few ohm input impedance of the horizontal output transistor base which requires upwards of several amps for proper drive. A typical driver transformer may be in the 5-10:1 turns ratio representing 25-100:1 impedance ratio. A byproduct of all this is that it is almost impossible for a faulty driver stage to kill the HOT. 9.3) Picture squeezed in then died You were watching 'Knight Rider' reruns and all of a sudden, the picture squeezed in slowly from the right hand side. It squeezed in about 2 inches or so when the entire picture 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 set probably didn't like Knight Rider - at least that episode! Seriously, how old is the set? Is it a totally solid state chassis or are there tubes in the deflection circuits? Is there any indication of light on the screen? Any indication of the 15735 Hz horizontal running at all? (You would normally hear the high pitch sound). Newer TVs almost always derive voltages for the sound circuits from the horizontal deflection but older hybrids may run the sound off of its own power. 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. 9.4) 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, 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: Power is failing to the horizontal output transistor - this could be due to a low voltage power supply problem, bad connection, etc. Base drive to the horizontal output transistor is failing - could be a fault in the horizontal oscillator or bad connection. Problem with the flyback transformer or its secondary loads (flyback may provide other power voltages). 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. 9.5) Horizontal lock lost A TV which loses horizontal lock when changing channels, 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. 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. This could be a capacitor or other similar part. Or, the oscillator frequency may just need to be tweaked (particularly with older sets). 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. A schematic will be useful to locate the adjustment if any or to identify possible defective parts. Try a large public library for the SAMs Photofact for this set. 9.6) Vertical squashed This is a vertical deflection problem - possibly a bad capacitor, bad connection, or other component. None of these should be very expensive (in a relative sort of way). Start by substituting 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). The following are NOT possible: CRT, flyback, tuner. (I am just trying to think of really expensive parts that cannot possibly be at fault). Note that some movies or laser karaoke discs are recorded in 'letterbox' format which at first glance looks like a squashed vertical problem. However, the picture aspect ratio will be correct and turning up the brightness will reveal a perfectly normal raster above and below the picture. 9.7) 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? Since the size of the picture fragment is correct but 85% is missing, my first thought would be to 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, maybe wait for the schematics. 9.8) Single Vertical Line 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. 9.9) Single Horizontal Line 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: 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. 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. 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. Other bad parts in vertical deflection circuit though there are not that many parts that would kill the deflection entirely. Loss of power to vertical deflection circuits. Check for blown fusable resistors/fuses and bad connections. Loss of vertical oscillator or vertical drive signals. The most likely possibilities are in the deflection output stage or bad connections to the yoke. 9.10) 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. Rotate the hold control: 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. Another horizontal problem can occur if the set is an RCA made from around 1972-1980: these sets are designed to slip very far off sync if the high voltage is too high, to protect against radiation. Turning up the brightness will decrease the number of bars if this system is in question, as the high voltage is decreasing. In this case, check around the high-voltage regulation system on the deflection systems board. I've had 2 1970's RCA's with this problem. (C.P.H.). 9.11) 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. One other 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. 9.12) Horizontal output transistors keep blowing Unfortunately, these sorts of problems are often difficult to definitively diagnose and repair - with expensive component swapping. You have just replaced an obviously blown (shorted) horizontal output transistor and an hour later, same symptoms: Did the new transistor short? Would the next logical step be a new flyback (LOPT)? Not necessarily. If the set 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: Insufficient drive to horizontal output transistor (HOT). A weak drive would cause the HOT to either turn on or shut off too slowly greatly increasing heat dissipation. Check driver and HOT base circuit components. Excessive voltage on HOT collector - check LV regulator (and line voltage if this is a field repair), if any. Defective safety capacitors or damper diode around HOT. (Though this usually results in instant destruction with little heating). New transistor not mounted properly to heat sink - probably needs mica washer and heat sink compound. 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 - properly mounted to the heat sink, 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 set 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. 9.13) 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