Friday 17 October 2008
Tuesday 11 March 2008
1.High voltage shutdown due to X-ray protection circuits .
A TV that runs for a while or starts to come on but then shuts down mayhave a problem with the X-ray protection circuitry correctly or incorrectlydetermining that the high voltage (HV) is too great (risking excessiveX-ray emission) and shutting everything down. A side effect of activation of this circuitry is that resetting may requirepulling the plug or turning off the real (hard) power switch. Is there anything else unusual about the picture lately that would indicatean actual problem with the HV? If this is the case, then there may besome problem with the HV regulation. If not, the shutdown circuit may be overly sensitive or one of its components may be defective - a bad connection of leaky cap (or zener). One symptom of excessive HV (but not required) is an overly bright picture of reduced size. The HV shutdown circuit usually monitors a winding off of the flybackfor voltage exceeding some reference and then sets a flip flop shuttingthe horizontal drive off. On some Sony models, a HV resistive divider performs this function and these do fail - quite often. The red block called a 'HV capacitor' is a common cause of immediate or delayed shutdown on certain Sony monitors and TVs.
2.Low or no high voltage .
Most of these problems are due to faults in the horizontal deflectionsystem - shorted HOT, shorted windings or HV rectifiers in the flyback,defective tripler, or other bad parts on the primary side of the flyback. However, if you discover an inch layer of filth inside the TV, the HVcould simply be shorting out - clean it first. In most cases, these sorts of faults will put an excessive load on thehorizontal output circuits so there may be excessive heating of the HOT or other components. You may hear an audible arcing or sizzling sound from internal shorts in the flyback or tripler. Either of these may bet hot, crack, bulge, or exhibit visible damage if left on with the fault present. Most modern TVs do not regulate HV directly but rather set it viacontrol of the low voltage power supply to the HOT (B+), by snubbercapacitors across the HOT, and the turns ratio of the flyback. TheHV is directly related to the B+ so if this is low, the HV will be lowas well. Faulty snubber capacitors will generally do the opposite – increase the HV and the X-ray protection circuits may kick in. However, low HV is also a possibility. The only way the turns ratio of the flyback can change is from a short which will manifest its presence in other ways as well - excessive heating and load on the horizontal output circuits. While a shorted second anode connection to the CRT is theoreticallypossible, this is quite unlikely (except, as noted, due to dirt).
3.Excessive high voltage.
Any significant increase in HV should cause the X-ray protection circuits to kick in and either shut down the set or modify the deflection in such a way as to render it harmless. Symptoms include arcing/sparking of HV, smaller than normal picture, and under certain scenarios, possible excessive brightness. Causes of the HV being too high are: Excess B+ voltage to the HOT. The likely cause is to a low voltage regulator failure. Open snubber capacitors across the HOT. These are under a lot of stress and are located near hot components so failure is possible. Incorrect excessively long scan drive to HOT caused by failure of horizontal oscillator/sync circuits. However, other things like the HOT will probably blow up first. The picture will definitely be messed up. Failure of HV regulator (tube sets and a few solid state sets - actual HV regulators are relatively uncommon today.) This may result in an underscanned (smaller than normal) picture.
4.Arcing, sparking, or corona from CRT HV anode (red wire/suction cup) .
Symptoms could include a sizzling corona or more likely, an occasionalor rapid series of sharp snaps - possibly quite loud and quite visible – from the anode cap on the CRT to the grounded coating on the outside of the CRT or a chassis ground point (or any other conductor nearby). Corona is a high resistance leakage through the air without total breakdown. The snapping is caused by the sudden and nearly complete discharge of the CRT anode capacitance through a low resistance ionized path similar to lightening. There are two likely causes: Dirt, dust, grime, around and under the suction cup on the CRT are providing a discharge path. This may be more severe in humid weather.Safely discharge the HV and then remove and thoroughly clean the HV suction cup and the area under it and on the CRT for several inches around the HV connection. Make sure there are no loose wires or other possible places for the HV to discharge to in the vicinity. The high voltage has gone through the roof. Usually, the X-ray protection circuitry should kick in but it can fail. If cleaning does not help, this is a likely possibility. See the sections:High voltage shutdown due to X-ray protection circuitsAnd Excessive high voltage.
5.Arcing at CRT spark gaps
This is rarely due to a defective spark gap but rather is a safety mechanism like a fuse designed to protect the internal electrodes of the CRT if the focus or screen voltage should become excessive. The spark gap breaks down first and prevents internal arcing in the CRT. An arcing sparkgap is usually accompanied by total loss of picture or bad focus, brightness or focus fluctuations, or any of a number of similar symptoms. The usual cause is a breakdown inside the focus divider inside the flyback or tripler. Sometimes, it is in a component that can bedisassembled and cleaned but not generally. Replacement of the bad part will be needed.
6.Arcing from flyback or vicinity .
If the arc is coming from a specific point on the flyback - a crack orpinhole - this may be patched using high voltage sealer or even a fewlayers of plastic electrical tape. This may prove to be a permanentrepair although starting the search for a source for a new flybackwould not hurt just in case. The arc most likely did damage the insulation internally which may or may not be a problem in the future. In some cases, the pinhole or crack is an indication of a more seriousproblem - overheating due to shorted windings in the flyback or excessive secondary load. First, clean the areas around the arc thoroughly and then try severallayers of plastic electrical tape. If the TV works normally for say,an hour, then there is probably nothing else wrong and you can try fora proper sealing job or hope that tape holds out (put a few more layers on - each is good for about 8-10 KV theoretically). If the arc is from one of the sparkgaps around the CRT, this could alsobe a flyback problem indicating internal shorts in the focus/screen network. Once I had a TV where the main problem was a cracked flyback arcingbut this took out one of the fusable resistors for the power supply tothe VERTICAL output so the symptoms included a single horizontal line.Don't ask me to explain - replacing that resistor and the flyback (theflyback tested good, but this was for someone else) fixed the TV. In another case, a pinhole developed in the flyback casing probablydue to poor plastic molding at the time of manufacture. This resulted in a most spectacular case of sparking to a nearby bracket. A few layers of electrical tape was all that was needed to affect a permanent repair.
7.Ozone smell and/or smoke from TV .
Smoking is just as bad for TVs as for people and usually more quicklyterminal. White acrid smoke may indicate a failed electrolytic capacitor in thepower supply probably in conjunction with a shorted rectifier. Needless to say, pull the plug at once. A visual inspection should be able to easily confirm the bad capacitor as it will probably be bulging and have condensed residue nearby. Check the rectifier diodes or bridge rectifier with an ohmmeter. Resistance across any pair of leads should be more than a few ohms in at least one direction. Remove from the circuit to confirm. Both the faulty diode(s) and capacitor should be replaced (though the capacitor may work well enough to test with new diode(s). If a visual inspection fails to identify the smoking part, you can probably plug the set in for a few seconds until the source of the smoke is obvious but be prepared to pull the plug in a real hurry. If the smell/smoke is coming from the flyback, then it has probably gone belly up. You may be able to see a crack or bulge in the case. While the flyback will definitely need to be replaced, it is likely that nothing else is wrong. However, it might be prudent to use a Variac when performing initial testing with the replacement just in case there is a secondary short circuit or excess HV problem.
Should I be worried about X-ray exposure while servicing a TV or monitor?
The only source of X-rays in a modern TV or monitor is from the CRT.X-rays are generated when a high velocity electron bean strikes aheavy metal target. For anything you are likely to encounter, this canonly happen in a vacuum - thus inside the CRT. The higher the voltage, the greater the velocity and potential danger. The thick front CRT faceplate protects users adequately but there may be some emission from the thinner sides. At 25-30 KV (quite low as X-ray energies go) X-rays will be stopped by almost any metal so what you have to worry about is where there are no shields. However, realistically, there is very little and I would not worry aboutexposure unless you plan to be sitting for hours on the sides, behind, or under the TV or monitor - with a picture (there will be none if the screen is black).
8.Fly back shot by 4 year old .
Your 4 year son shot the Sony in the flyback transformer. Smoke and sparks everywhere. Great aim! Who says these FAQs cannot be funny? Needless to say, unplug the set immediately. Inspect around the target area for obviously blown or damaged components. Test fuses and fusable resistors. Repair burnt solder connections and circuit board traces. Once the set is entirely dried out, power it up - preferably through a series light bulb and/or Variac until you are sure nothing else will let loose. Look, listen, and smell for any unusual behavior. If it now works, then consider yourself lucky. If not, there may be damage to transistors, ICs, or other components. (The following from: edison@nelson.planet.org.nz (Richard Symonds)). We're seeing another 'hazard' these days, people cleaning theirtelevision screens with window cleaner - no problem in the days ofseparate chassis but with the entire p.c.b. jammed under the tube onmost t.v.s these days just a few drips and its all over. Some havejust corroded the switch banks (had one recently just got into theA/V switch - when you walked around the room the set changed to A/Vand back by itself!) but a few have got around the microprocessors and surface mount components and resulted in complete write-offs. Isuppose the damage is the opposite of electroplating as the microp'shave constant voltage to them. Never mind, they'll be a good sourceof parts for future use.
REFERENCE:
http://www.stedmundsbury.gov.uk/sebc/play/tvprobs.cfm.
http://www.epanorama.net/links/repair.html#tv.
Vertical lock lost:
This indicates a picture that is correct but rolling vertically. If the picture is rolling down the screen the frequency of the verticaloscillator is incorrect - too high - and this may be the problem. Generally,the free run frequency of the vertical oscillator should be a little belowthe video rate (of around 50 or 60 Hz depending on where you live). If it is rolling continuously without jumping, then there is a loss ofsync from the sync separator or faulty components in the vertical oscillatorcausing it to totally ignore the sync pulses. If it is rolling up rapidly and not quite able to remain locked, the freerun frequency may be too low or there could be a fault in the sync circuits resulting in an inadequate vertical pull-in range. On older sets, there was actually a vertical hold (and possibly even aSeparate vertical frequency) control. On anything made in the last decade, this is unlikely. There may be Vertical Frequency and Vertical Pull-in Range adjustments (and others) accessible via the service menu. However, if any of these ever change, it indicates a possible problem with the EEPROMlosing its memory as component drift is unlikely. As with everything else, bad connections are possible as well. You will need a schematic and possibly setup info to go beyond this.
Vertical squashed:
This is a vertical deflection problem - possibly a bad capacitor, badconnection, flyback/pump up diode, or other component. None of these should be very expensive (in a relative sort of way). If the symptoms change - particularly if they become less severe - as the set warms up, a dried up electrolytic capacitor is most likely. If they get worse, it could be a bad semiconductor. Freeze spray or a heat gun may be useful in identifying the defective component. It is often easiest to substitute a good capacitor for each electrolytic in the vertical output circuit. Look for bad connections (particularly to the deflection yoke), then consider replacing the vertical output IC or transistor(s). A defective deflection yoke is also possible or in rare cases, a bad yoke damping resistor (e.g., 500 ohms, may be mounted on the yoke assembly itself). The following are NOT possible: CRT, flyback, tuner (except for the famous RCA/GE/Proscan or Sony models where the controller is at fault - see the sections on these specific brands). 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.
Part of picture cut off:
The following applies if the part of the picture is missing but nototherwise squashed or distorted. For example, 85% is missing but theportion 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 holein 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 verticalOutput stage. The supply voltage is probably correct since that oftenDetermines the size. It almost sounds like the waveform rather thanbeing mostly on (active video) and off for the short blanking periodis somehow only on during the last part of the active video thus givingyou 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. Theproblem may be as far back as the sync separator. Then again who knows,maybe wait for the schematics.
Single Vertical Line:
CAUTION: To prevent damage to the CRT phosphors, immediately turn down the brightness so the line is just barely visible. If the user controls do not have enough range, you will have to locate and adjust the master brightness or screen/G2 pots. Since you have high voltage, the horizontal deflection circuits are almost certainly working (unless there is a separate high voltage power supply - almost unheard of in modern TVs and very uncommon in all but the most expensive monitors). Check for bad solder connections between the main board and the deflection yoke. Could also be a bad horizontal coil in the yoke, linearity coil, etc.There is not that much to go bad based on these symptoms assuming the high voltage and the horizontal deflection use the same fly back. It is almost certainly not an IC or transistor that is bad.
REFERENCE:
http://www.stedmundsbury.gov.uk/sebc/play/tvprobs.cfm.
http://www.epanorama.net/links/repair.html#tv.
Fuse blows or TV blows up when sync is disrupted:
This is a problem which is not going to be easy to identify. One possibility is a drive problem. The messed up sync resulting from swtiching channels,or changing input connections might be resulting in an excessively long scan time for just one scan line. However, this may be enough to cause a current spike in the horizontal output circuit or an excessive voltage spike on the collector of the horizontal output transistor. Normally, the HOT current ramps up during scan. During flyback, the current is turned off. This current is normally limited and the voltage spike on the collector of the HOT is also limited by the snubber capacitors to a safe value. If scan time is too long, current continues to increase. At some point, the flyback coresaturates and current goes way up. In addition, the voltage spike will be much higher - perhaps destructively so. Troubleshooting these sorts of problems is going to be tough. However, a likely area to investigate would be:
* Drive circuitry for the HOT including the coupling components.
* The chip that generates takes the sync input and generates the horizontal drive signal.
* A bad low voltage regulator might permit the B+ to rise to excessive levels during black scenes (i.e., video mute during channel changing). Internal fuse blew during lightning storm (or elephant hit power pole):
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 holdmomentarily 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 placeat any adjustment of the hold control. Look around the horizontal oscillatorcircuit: all of the oscillator parts will be right there, or check on the horizontal oscillator module. Another horizontal problem can occurif the set is an RCA made from around 1972-1980: these sets are designedto slip very far off sync if the high voltage is too high, to protectagainst radiation. Turning up the brightness will decrease the numberof 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.).
Vertical squashed:
This is a vertical deflection problem - possibly a bad capacitor, badconnection, flyback/pump up diode, or other component. None of these should be very expensive (in a relative sort of way). If the symptoms change - particularly if they become less severe - as the set warms up, a dried up electrolytic capacitor is most likely. If they get worse, it could be a bad semiconductor. Freeze spray or a heat gun may be useful in identifying the defective component. It is often easiest to substitute a good capacitor for each electrolytic in the vertical output circuit. Look for bad connections (particularly to the deflection yoke), then consider replacing the vertical output IC or transistor(s). A defective deflection yoke is also possible or in rare cases, a bad yoke damping resistor (e.g., 500 ohms, may be mounted on the yoke assembly itself). The following are NOT possible: CRT, flyback, tuner (except for the famous RCA/GE/Proscan or Sony models where the controller is at fault - see the sections on these specific brands). 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.
Vertical lock lost:
This indicates a picture that is correct but rolling vertically. If the picture is rolling down the screen the frequency of the verticaloscillator is incorrect - too high - and this may be the problem. Generally,the free run frequency of the vertical oscillator should be a little belowthe video rate (of around 50 or 60 Hz depending on where you live). If it is rolling continuously without jumping, then there is a loss ofsync from the sync separator or faulty components in the vertical oscillatorcausing it to totally ignore the sync pulses. If it is rolling up rapidly and not quite able to remain locked, the freerun frequency may be too low or there could be a fault in the sync circuits resulting in an inadequate vertical pull-in range. On older sets, there was actually a vertical hold (and possibly even aSeparate vertical frequency) control. On anything made in the last decade, this is unlikely. There may be Vertical Frequency and Vertical Pull-in Range adjustments (and others) accessible via the service menu. However, if any of these ever change, it indicates a possible problem with the EEPROMlosing its memory as component drift is unlikely. As with everything else, bad connections are possible as well. You will need a schematic and possibly setup info to go beyond this.
REFERENCE:
http://www.stedmundsbury.gov.uk/sebc/play/tvprobs.cfm
http://www.epanorama.net/links/repair.html#tv
Weak or distorted audio:
Assuming you are not attempting to play it at ear shattering levels,this may be due to an alignment problem in the IF/audio demodulator,a bad audio IC or other circuitry, bad connection, or a defective speaker. If your TV has an earphone or audio line out jack, try this to see if it is clear. If so, then your problem is in the final audio amp or speaker(s). If only one channel of a stereo TV is affected, it is almost certainly the audio amp or speaker for that channel. Interchange connection to the two speakers temporarily and see if the problem moves. If the problem is at all intermittent - try gently whacking the TV – then it is likely a bad connection - either a cold solder joint or a dirty or tired IC socket. The audio amplifiers in newer TVs are almost always ICs and replacements are usually readily available. If the IC is in a socket, remove the IC, clean the pins and socket contacts and reinstall it. Sometimes, the contacts on old socket lose their springiness and do not provide solid connections.Such a socket will need to be replaced. If the set uses discrete transistors, it s also possible for one of these to become noisy. If your TV is fairly old - 10 years or so - this may be an alignment problem requiring tweaking of a coil in the sound IF. See your service manual.It may be possible to have similar problems with newer TVs but this isrelatively rare.
Picture fine, no audio :
First check that any muting control is not activated. This might bea button on the remote or set itself. If you have a headphone jack, itmay have dirty contacts as plugging in a headphone usually mutesthe speaker. If the set is mono or only one channel of a stereo set is out, thencheck for bad connections to the loudspeaker. Test the loudspeaker bydisconnecting one of the wires (with the power off!) and measuring itsresistance with an ohmmeter (it should be less than 100 ohms - probablyless than 8 ohms). Or momentarily touch a 1.5 volt battery to the speakerterminals - you should get a click or pop from the speaker. Next, trace back from the speaker output terminals to the circuit boardand look for bad solder connections or a loose or dirty connector. If these tests do not reveal anything, you probably need a scope (oraudio signal tracer) and schematic. Or at least the part number off ofthe chip. Is the final amp a chip also or just a transistor? Have youtested the transistor? If there is little or no buzz from the speaker,that would indicate a problem fairly near the output. If the tuner/if werebad, I would expect some noise/humm pickup from the low level audio stages.Get the part number off of the chip. If it is in a socket, check the contacts for corrosion or looseness.
Weak or distorted audio:
Assuming you are not attempting to play it at ear shattering levels,this may be due to an alignment problem in the IF/audio demodulator,a bad audio IC or other circuitry, bad connection, or a defective speaker. If your TV has an earphone or audio line out jack, try this to see if itis clear. If so, then your problem is in the final audio amp or speaker(s). If only one channel of a stereo TV is affected, it is almost certainly theAudio amp or speaker for that channel. Interchange connection to the two Weak or distorted audio Assuming you are not attempting to play it at ear shattering levels,this may be due to an alignment problem in the IF/audio demodulator,a bad audio IC or other circuitry, bad connection, or a defective speaker. If your TV has an earphone or audio line out jack, try this to see if itis clear. If so, then your problem is in the final audio amp or speaker(s). If only one channel of a stereo TV is affected, it is almost certainly theaudio amp or speaker for that channel. Interchange connection to the two speakers temporarily and see if the problem moves. If the problem is at all intermittent - try gently whacking the TV - thenit is likely a bad connection - either a cold solder joint or a dirtyor tired IC socket. The audio amplifiers in newer TVs are almost always ICs and replacements are usually readily available. If the IC is in a socket, remove the IC, clean the pins and socket contacts and reinstall it. Sometimes, the contacts on old socket lose their springiness and do not provide solid connections.Such a socket will need to be replaced. If the set uses discrete transistors, it s also possible for one of theseto become noisy. If your TV is fairly old - 10 years or so - this may be an alignment problem requiring tweaking of a coil in the sound IF. See your service manual. It may be possible to have similar problems with newer TVs but this is relatively rare.
Buzzing TV :
Do you actually mean buzz - low frequency as in 60 Hz? Or, do youreally mean high pitched whine. If the latter, see the section:High pitched whine or squeal from inside TV. Is the buzz through the speaker or from the inside of the set? If it is the speaker, then it is a design issue with the audio circuitry.However, a buzzing that only occurs when the picture has sharply definedtext or graphics, may be an overload problem at the source - some TVssimply handle it better than others. If it is from inside the set, it is in the deflection or power supply. There is a slight possibility that the AC power in your house has someharmonic content - the waveform is not sinusoidal. This might be the case if you try to run on the same circuit as an active dimmer or something else with thyristor control. Proximity to heavy industry could also cause this. In neither case can you infer the severity of this annoyance from specs.It is strictly a design (e.g. cost) issue. The size of the TV is not a strong indicator of the severity of the problem but there will be some relationship as the power levels are higher for larger sets. Possibly running on a slightly different line voltage may change it butthat is not really an option. You could try a line conditioner (notjust surge suppressor) which includes filtering. I suspect it won't make must difference. If it is in the audio circuits - from the speakers or line out - thenconsider using a (HiFi) VCR for the tuner with an external stereo ampand the internal speaker disabled. If it is noise from the TV, then the best you can do is audition variousTVs very carefully to find one that you are satisfied with. BTW, when I got my new super duper RCA Colortrak in 1980, it had a similar annoying buzz - even had a repair guy out who behaved as though this was ton be expected. I did get used to it and am not even aware of it today – and still use that set.
High pitched whine or squeal from TV with no other symptoms :
First, make sure it is not coming from the loudspeaker itself. If it is,then we are looking at an unusual electronic interference problem rather than simply mechanical vibration. There are several parts inside the TV that can potentially make this noise - the horizontal flyback transformer and to a lesser extent, the deflection yoke would be my first candidates. In addition, transformers or chokes in the switching power supply if this is distinct from the horizontal deflection circuitry. I don't know about returning a set to a store that doesn't take refunds (I won't even ask about that!) but assuming that this sound level is normal for the particular model here are a couple of suggestions: You do not want to coat the TV as this may interfere with proper cooling, but the interior of the entertainment center cabinet could be lined with a non-flammable sounds absorbing material, perhaps acoustic ceiling tiles. Hopefully, not a lot of sound energy is coming from the front of the set. Move the TV out of a corner if that is where it is located - the cornerwill focus sound energy into the room. Anything soft like carpeting, drapes, etc. will do a good job ofabsorbing sound energy in this band. If you are desperate and want to check the inside of the set: It is possible to coat the flyback transformer, but this is used mostlywhen there a loose core or windings and you are getting not only the15,735 Hz horizontal (NTSC) but also various subharmonics of this. This improbably acceptable but may increase the temperature of the flyback. Using appropriate safety precautions, you can try prodding the varioussuspect parts (flyback, deflection yoke, other transformers) with aninsulated tool such as a dry wooden stick. Listen through a cardboardtube to try to localizing the source. If the sounds changes, youknow what part to go after. Sometimes a replacement flyback willcure the problem unless it is a design flaw. You do not want to replacethe yoke as convergence and other adjustments would need to be performed. Other transformers can be replaced. Note that the deflection frequency - just over 15 KHz for NTSC and PAL - ison the border of audible for adults but will likely be loud to younger people possibly to the point of being terribly annoying - or worse. If you are over 40 (men more so than women), you may not be able to hear the fundamental at all (at least you can look forward to silence in the future!). So, even sending the TV back for repair may be hopeless if the technician cannot hear what you are complaining about!
REFERENCE :
http://www.stedmundsbury.gov.uk/sebc/play/tvprobs.cfm
http://www.epanorama.net/links/repair.html#tv
Horizontal deflection shutting down:
Confirm that the horizontal deflection is shutting down (along with thehigh voltage since it is derived from horizontal deflection: listenfor the high pitched deflection whine, test for static on the screen,see if the CRT filaments are lit, turn up the brightness and/or screencontrol to see if you can get a raster) and then why:
1) Power is failing to the horizontal output transistor - this could be due to a low voltage power supply problem, bad connection, etc.
2) Base drive to the horizontal output transistor is failing - could be a fault in the horizontal oscillator or bad connection.
3) Problem with the fly back transformer or its secondary loads (fly back may provide other power voltages).
4). X-ray protection is activating - either due to excess HV or due to a fault in the X-ray protection circuitry. If the problem comes and goes erratically it sounds like a bad connection, especially if whacking has an effect. If it comes and goes periodically, then a component could be heating up and failing, then cooling, etc.
Horizontal lock lost:
A TV which loses horizontal lock when changing channels, momentarilylosing the signal, or switching inputs may have a horizontal oscillatorthat is way out of adjustment or has drifted in frequency due to agingcomponents. Note that the characteristics of this are distinctly different thanfor total loss of sync. In the latter case, the picture will drift sideway sand/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 oscillatorfrequency may just need to be tweaked (particularly with older sets).There may be an internal horizontal frequency adjustment - either a potor a coil - which may need a slight tweak. If a coil, use a plasticalignment 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.
Single Horizontal Line:
CAUTION: To prevent damage to the CRT phosphors, immediately turn down the brightness so the line is just barely visible. If the user controls do not have enough range, you will have to locate and adjust the master brightness or screen/G2 pots. A single horizontal line means that you have lost vertical deflection.High voltage is most likely fine since there is something on the screen. This could be due to:
1. Dirty service switch contacts. There is often a small switch on the located inside on the main board or perhaps accessible from the back. Thisis used during setup to set the color background levels. (On some sets, thisis located on the CRT neck board and may be a jumper plug or other means ofselecting service mode - not an actual switch).When moved to the 'service' position, it kills vertical deflection and vide to the CRT. If the switch somehow changed position or got dirty or corroded contacts, you will have this symptom. Flip the switch back and forth a couple of times. If there is some change, then replace, clean, resolder,or even bypass it as appropriate.
2. Bad connection to deflection yoke or other parts in vertical output circuit. Bad connections are common in TVs and monitors. Check around the pins of large components like transformers, power transistors and resistors, or connectors for hairline cracks in the solder. Reseat internal connectors. Check particularly around the connector to the deflection yoke on the CRT.
3. Bad vertical deflection IC or transistor. You will probably need the service manual for this and the following. However, if the vertical deflection is done with an IC, the ECG Semiconductor Master Substitution guide may have its pinout which may be enough to test it with a scope.
4. Other bad parts in vertical deflection circuit though there are not that many parts that would kill the deflection entirely.
5. Loss of power to vertical deflection circuits. Check for blown fusable resistors/fuses and bad connections.
6. Loss of vertical oscillator or vertical drive signals.The most likely possibilities are in the deflection output stage orbad connections to the yoke.
REFERENCE
http://www.stedmundsbury.gov.uk/sebc/play/tvprobs.cfm
http://www.epanorama.net/links/repair.html#tv
VIDEO IF PROBLEMS AND SOLUTIONS.
No color - black and white picture:
This means absolutely no color - equivalent to a black and white picture.Not even a hint of color. First, confirm that the source is actually in color - try another channel or input device. Next, check the settings of the color control - it may have accidentally been turned down. If your TV has some kind of automatic picture mode, try turning if off and adjusting the color control. Try adjusting fine tuning if you have such a control and the problem is with a broadcast or cable transmission. At this point with a confirmed color signal source, there is a problemwith the chroma circuitry. Note that to the average person, the obvious question becomes: is my color picture tube bad? The answer is a definitive NO. It is virtually impossible for a defective CRT to cause a total loss of color. A defective CRT can cause a lack of a primary color - R, G, or, B or a short between two colors which will mess up the color but is not likely to result in a black and white picture. Some possibilities in no particular order:
1. Weak signal or defect in tuner/IF causing loss of signal strength.
2. Coler killer set too high (internal control) if it has one.
3. Defective part around the chroma chip/circuit. Faulty color oscillator.
4. Bad connections in area of chroma chip/circuit.
5. Defective chroma chip (don't suspect this first just because it is probably very expensive). A service manual or Sams', DMM, & scope will help greatly in attempting to troubleshoot this unless it is an obvious bad connection. Try proddingthe main board around the chroma chip with an insulated tool to see ifyou can make the color come and go. I had one set where a $.02 resistor decided to open up causing just this problem - perfect BW picture, no color. Another had a coil with a broken wire.
Saturated color but almost no brightness:
This means you have lost the luminance input to the chroma decoder or final video chip. A failure of the brightness limiter may result in similarsymptoms. A few common causes are:
* Check the service switch (if any). Its contacts may be dirty and moving it back and forth a few times or using contact cleaner may be all that is needed.
* Check for open high value resistors around the chroma decoder IC.
* Check for open high value resistors in the brightness limiter circuit. With a scope and schematic (or even just a pinout for the chip), you should be able to trace the luminance signal to see where it is getting lost.
Brightness control has no effect:
The following assumes that the picture is fine but the brightness isfixed - probably at too high a level. However, there could be severalinterrelated problems if a common supply voltage were missing, for example. If it is a knob, then it should be varying the control grid (G1) voltagesrelative to the cathodes (K) of the CRT. This is not likely to be a very complex circuit. If you do not have a schematic, I would start by tracing from the control, check continuity and solder connections. Check the control itself for proper operation with an ohmmeter.
Tbe control grid voltage will end up on the little board on the neck of the CRT – check there as well for bad solder connections or open resistors. If brightness is a digital control, then you will need a schematic unless there is an obvious bad connection.
One color is too weak or too strong:
If the problem is slight and/or has gradually gotten worse, this may just require an adjustment of the color brightness/background/bias and/or color ain/drive controls inside the TV. See the section: "Color balance adjustment". Note that if it is possible to obtain a good black and white picture with the user color control set to its minimum, then this is not likely a problem with one of the primary color channels (red, green, or blue) but with the chroma decoding circuitry. Or, perhaps, you are just watching MTV! Even if it appears as though there is an excess, this may actually be areduction in one of the primary colors. For example, a magenta tinge is represents a reduction in the strength of the green signal.
* Too high an intensity for one of the color channels will result in a tint of one of the primaries: red, green or blue.
* Too low an intensity for one of the color channels will result in a tint of the complement of one of the primaries: yellow, cyan, or magenta.
* Problems mainly in the shadows or dark areas of the picture usually represent a fault with brightness/bias/background.
* Problems mainly in the highlights or bright areas of the picture usually represent a fault with the gain/drive. A color that that is now suddenly brighter or darker than normal resulting in incorrect color balance or a tint in the background could be due to a number of causes: * Bad connections or bad component in video amplifier or on CRT neck board for that color. * Fault in chroma decoder.
* Weak gun in CRT (reduced color). Psychodelic color:
The means colors that are not normal and that adjustment of the usercontrols is not able to correct it so that all colors of the pictureare properly displayed at the same time. For example, you are unableto get any yellows or blues in scenes that should have these colors.. Make sure the user color and tint controls have not been accidentallyturned while cleaning or purposedly misadjusted by small (or large) kids. Perform the user setup described in the section: "User pictureadjustment". Confirm that the source is not a weird color video - try anotherchannel or a tape. Verify that this is not a missing color problem - one of the primary R, G,or B, has disappeared. If so, refer to the section: "Intermittent or missing colors". Once these have been eliminated, you are left with thefollowing possibilities:
1. Defective part around the chroma chip/circuit. Misadjusted color oscillator.
2. Bad connections or short circuit in area of chroma chip/circuit.
3. Defective chroma chip (don't suspect this first just because it is probably very expensive).
4. Bad degauss circuit resulting in lack of degauss or abrupt termination of degauss current rather than smooth tail off. The CRT is not being properly demagnetized and color purity is totally messed up.
5. Bad CRT - the shadow mask has been damaged and it is impossible to properly adjust purity across the screen. A service manual or Sams', DMM, & scope will help greatly in attempting to troubleshoot this unless it is an obvious bad connection. For (1)-(3),try prodding the main board around the chroma chip with an insulated tool to see if you can restore normal color. For (4) try manually degaussing (see the section: "Degaussing (demagnetizing) a CRT". If this clears up the colors until at least when it is power cycled, then a degauss problem is likely. Something as simple as a bad resistor or inductor can be the cause - don't immediately suspect the most expensive and difficult to replace part.
Psychodelic color:
The means colors that are not normal and that adjustment of the usercontrols is not able to correct it so that all colors of the pictureare properly displayed at the same time. For example, you are unableto get any yellows or blues in scenes that should have these colors.. Make sure the user color and tint controls have not been accidentallyturned while cleaning or purposedly misadjusted by small (or large) kids. Perform the user setup described in the section: "User pictureadjustment". Confirm that the source is not a weird color video - try anotherchannel or a tape. Verify that this is not a missing color problem - one of the primary R, G,or B, has disappeared. If so, refer to the section: "Intermittent or missing colors". Once these have been eliminated, you are left with thefollowing possibilities:
1. Defective part around the chroma chip/circuit. Misadjusted color oscillator.
2. Bad connections or short circuit in area of chroma chip/circuit.
3. Defective chroma chip (don't suspect this first just because it is probably very expensive).
4. Bad degauss circuit resulting in lack of degauss or abrupt termination of degauss current rather than smooth tail off. The CRT is not being properly demagnetized and color purity is totally messed up.
5. Bad CRT - the shadow mask has been damaged and it is impossible to properly adjust purity across the screen. A service manual or Sams', DMM, & scope will help greatly in attempting to troubleshoot this unless it is an obvious bad connection. For (1)-(3),try prodding the main board around the chroma chip with an insulated tool to see if you can restore normal color. For (4) try manually degaussing (see the section: "Degaussing (demagnetizing) a CRT". If this clears up the colors until at least when it is power cycled, then a degauss problem is likely. Something as simple as a bad resistor or inductor can be the cause - don't immediately suspect the most expensive and difficult to replace part.
No picture/dark picture/erratic picture:
Remove the picture tube socket (carefully!) and clean the pins with fine sandpaper and use contact cleaner on the socket. This source of bad connections can result in a variety of erratic symptoms.
Intermittent or missing colors:
This is a catch-all for some of the most common TV and monitor problems.
* If gently whacking the set can make the color(s) come and go suddenly, then bad connections are probable. The most likely place for these are solderpads on the little circuit board on the neck of the CRT or even dirty CRT socket pins that are not making solid contact. Try prodding the CRT neck board with an insulated stick to see if you can affect the colors. Although not impossible, this is not likely to be a CRT problem.
* If the color fades in and out with a delay of about 10-15 seconds, it is probably intermittent power to the CRT filament for that color and probably means a bad CRT since the three filaments are wired in parallel inside the CRT. One of the internal connections has come loose. Look in the neck of the CRT to make sure all three filaments are glowing orange. If one is out or goes on and off, toss the set. Replacing the CRT is probably not worth it. However, if they all go on and off together (all colors would be fading in and out though perhaps not quite in unison), then bad connections for the CRT filaments on the CRT neck board are indicated. To narrow down the problem:
* Locate the output for the bad color on the video driver board on the neck of the CRT. This will probably read a significantly higher voltage than the corresponding pins for the good colors. A circuit problem is likely - probably on this board.
* Test components on this board for the good and bad color channels. A shorted transistor or open resistor can kill one channel. Swap parts between good and bad colors to confirm.
* Gently pull the CRT neck board off of the CRT and replace it. This will tend to clean the contacts.
* Connect an output of the video/chroma circuit/chip that is working (i.e., a color that appears on the screen) to *all* three color drivers on the CRT neck board. - If you now get a more-or-less black and white picture (there may be a moderate color tint as the relative intensities of R,G,B may not be balanced), the problem is likely with the chroma decoder or its support circuitry. Note: the picture will be the intensity of only one color channel so it will not be quite *normal* in any case. - If you still have missing or messed up colors, the problem is on the CRT neck board or with the CRT. Most of the causes of intermittent colors boil down to bad connectionsof one form or another. For totally dead colors - not intermittent – bad components are also a possibility.
* Printed circuit board on the CRT neck. This is a common location for cold solder joints. Check with a bright light and magnifying glass for hairline cracks around the pins of larger parts. Prod and tap with an insulated tool to see if the problem is effected. Resolder if necessary.
* Cold solder joints elsewhere in TV or monitor usually around the pins of large parts such as transformers, power transistors and resistors, and internal connectors.
* Internal connectors (including CRT socket) that need to be cleaned and reseated. Remove, clean with contact cleaner, burnish, and replace.
Dark picture:
A TV or monitor with a picture that is too dark may have a fault or the CRT may just be near the end of its useful life. First, confirm that your video source - computer, camera, etc. - is producing a proper signal. Is the brightness at all erratic? Does whacking the monitor have any effect?If so, then you may have bad connections on the CRT driver card or elsewhere. If the brightness tends to fade in and out over a 10 to 20 second period, a bad filament connection is likely. Check for the normal orange glow of the filaments in the neck of the CRT. There should be 3 orange glows. If they are excessively reddish, very dim, or fade in and out, you have located a problem. See the section: "Picture fades in and out". Common causes of brightness problems: 0. Dirty CRT faceplate or safety glass. Don't laugh. It sounds obvious, but have you tried cleaning the screen with suitable screen cleaner? It is amazing how dirty screens can get after a few years - especially around smokers! Wipe gently with a slightly dampened cloth - not soaking or you may end up with real problems when the water drips down inside and hits the electronics! On TVs with a separate protective faceplate, clean both the front and rear surfaces of this plate as well as the CRT itself.
1. Old CRT. The brightness of the CRT deteriorates with on-time. It does not matter much how bright your run your TV. An indication of a weak CRT would be that turning up the SCREEN (G2) or master brightness control only results in a not terribly bright gray raster before the retrace lines show up. There may be indications of poor focus and silvery highlights as well. A CRT brightener may help. See the section: "Brightening an old CRT".
2. Bad component in filament circuit or bad connection reducing filament voltage. This should be easy to check - there are only a few parts involved. If it is erratic, bad connections are likely.
3. Brightness control faulty - bad pot, bad connections, or problem with its power supply. Depending on specific problem, control may or may not have any effect. If digitally adjusted, there could be a problem with the logic or control chip. If the button or menu item has no effect at all, then a logic or control problem is likely.
4. Improperly set SCREEN (G2) voltage (usually on flyback) or faulty divider network. See the section: "Adjustment of the internal SCREEN and color controls".
5. Improperly set video bias (background) levels or fault in video drive circuitry. See the sections starting with: "Optimal procedure for setting brightness/background and screen adjustments".
6. Fault in video amplifiers. With all three color affected equally, this would most likely be a power supply problem. A video amplifier problem is likely if turning up the SCREEN (G2) or master brightenss control results in a very bright raster before the retrace lines appear. Check signals out of the video/chroma(IC.
7. Fault in beam or brightness limiter. Many TVs and monitors measure the beam current (possibly indirectly) and limit the maximum to a safe value. The purpose of this may be to protect the CRT phosphors, and/or to assure that the power supply does not go out of regulation, and/or to limit X-ray emission. If this circuit screws up, a dark picture may result. Checking the signals and voltages at the CRT socket should determine if this is the problem.
8. High voltage is low. However, this would likely result in other symptoms as well with focus, size, and geometry.
Brightness changes from left-to-right across screen:
Slight variations in brightness across the face of the CRT are not unusual.In fact, if you used a photometer to actually measure the brightness, you might be amazed at the actual variance even with the best TV - you just don't notice it. However, a major variation - usually a decay from left to right but could be the other way indicate a component failure. Of course, make sure the face of the screen is clean!
* A fault in the power supplies to the video amplifier and/or video output circuits. Most likely, an electrolytic capacitor has dried up and is not adequately filtering the power derived from the flyback which then has ripple at the horizontal scan rate and thus locked to the screen. The voltage decays from left-to-right between horizontal flyback pulses. The most likely location for these capacitors is in the vicinity of the flyback transformer on the mainboard or on the CRT neck board. Check the capacitors with capacitor tester or ESR meter and/or take a look at the power right at the video amplifier and video output drivers.
* Horizontal linearity is bad - this may actually be a horizontal geometry problem and not a brightness problem. See if objects on left side of the screen are stretched compared to those on the right (or vice-versa). If they are, the problem is in the horizontal deflection circuits - possibly a bad S correction capacitor or linearity coil.
* Inoperative degauss circuit, TV moved or rotated without degaussing, or magnetic field from some other device (like a permanent magnet) is affecting CRT - slight amounts of magnetization may reduce brightness (by moving the beams into the black space between phosphor dots) before affecting color purity (where the beams land on the wrong phosphor dots). Try deguassing manually. See the section: "Degaussing (demagnetizing) a CRT".
Picture fades in and out:
If the picture faded away on the order of 10-20 seconds (and if it comes back, also comes up to full brightness in same time frame – possibly with the persuasion of some careful whacking) AND with NO other significant changes such as size, focus, etc., then take a look in the back of the tube for the filament to be lit - the orange glow near the CRT socket. If there is none, then you probably have a bad solder connection on the circuit board on the neck of the CRT. Look for fine cracks around pins on that board.Try prodding it with an insulating stick to see if the picture comes back.Resolder if necessary. It is probably not a bad CRT as the filamentsare usually wired in parallel and all would not go bad at the same time. However, if only a single color fades in and out, then a bad connectioninside the CRT is a distinct possibility - look for only one of thefilament's glow to be coming and going. This is probably not worth fixing. If the picture faded away with other symptoms, then there is probablya fault in the video amplifier/output one of its power supplies -still probably a loose connection if you are able to get it back bywhacking.
Blank picture, good channel tuning and sound:
Since the tuner and sound are ok, horizontal deflection which usuallygenerates power for most of the set is also working. Does 'blank picture' means a totally black screen with the brightness and contrast controls having no effect whatsoever? Or, is there is no picture but there is a raster - light on the screen? The direction in which troubleshooting should proceed differ significantly depending the answer. Here are some questions:
1. As above, is there any light on the screen at any settings of the brightness and contrast controls, and/or when switching channels. Can you see any raster scanning lines?
2. Can you hear the high pitched (15735 Hz) of the horizontal deflection?
3. Looking in the back of the set, can you see the glow of the CRT filament?
4. Do you get that static on the front of the tube that would indicate that there is high voltage? Any cracking or other normal or abnormal sounds or smells? Possible causes of no raster:
* No or low high voltage (low voltage, deflection, or high voltage power supply failure).
* Fault with other voltages like G1 or screen (G2) to CRT.
* Filament to CRT not getting powered.
* Drive to CRT bad/shut off as a result of fault elsewhere. For example, failure of the vertical deflection may disable HV or blank the screem to protect the CRT from burn-in due to the very bright horizontal line that would result. With some sets, it is possible that the X-ray protection circuitry will blank the screen without affecting tuning or audio. Possible causes of no video (but a good raster): Problem in video IF, video amplifiers, video output, cutoff due to other fault. It could be as simple as a bad connection - try gently prodding the boards with an insulated stick while watching the screen. Check for loose connectors and reseat all internal connectors.
No color - black and white picture :
This means absolutely no color -equivalent to a black and white picture.Not even a hint of color. First, confirm that the source is actually in color - try another channelor input device. Next, check the settings of the color control - it may have accidentallybeen turned down. If your TV has some kind of automatic picture mode,try turning if off and adjusting the color control. Try adjusting finetuning if you have such a control and the problem is with a broadcastor cable transmission. At this point with a confirmed color signal source, there is a problemwith the chroma circuitry. Note that to the average person, the obvious question becomes: is my colorpicture tube bad? The answer is a definitive NO. It is virtually impossiblefor a defective CRT to cause a total loss of color. A defective CRT cancause a lack of a primary color - R, G, or, B which will mess up the colorbut is not likely to result in a black and white picture. Some possibilities in no particular order: Weak signal or defect in tuner/IF causing loss of signal strength. Coler killer set too high (internal control) if it has one. Defective part around the chroma chip/circuit. Faulty color oscillator. Bad connections in area of chroma chip/circuit. Defective chroma chip (don't suspect this first just because it is probably very expensive). A service manual or SAMs, DMM, & scope will help greatly in attempting to troubleshoot this unless it is an obvious bad connection. Try proddingthe main board around the chroma chip with an insulated tool to see ifyou can make the color come and go. I had one set where a $.02 resistor decided to open up causing just thisproblem - perfect BW picture, no color. Another had a coil with a broken wire.
TV and Monitor Manufacturing Quality and Cold Solder Joints
Any intermittent problems with monitors that cause random sudden changes inthe picture brightness, color, size, or position are often a result ofbad connections. Bad solder joints are very common in TVs and monitors due both to poor qualitymanufacturing as well as to deterioration of the solder bond after numerousthermal cycles and components running at high temperature. Without knowinganything about the circuitry, it is usually possible to cure these problemsby locating all bad solder connections and cleaning and reseating internalconnectors. The term 'cold solder joint' strictly refers to a solderconnection that was either not heated enough during manufacturing, wascooled too quickly, or where part pins were moved before the solder hada chance to solidify. A similar situation can develop over time withthermal cycling where parts are not properly fastened and are essentiallybeing held in by the solder alone. Both situations are most common withthe pins of large components like transformers, power transistors andpower resistors, and large connectors. The pins of the components havea large thermal mass and may not get hot enough during manufacturing. Also,they are relatively massive and may flex the connection due to vibrationor thermal expansion and contraction. To locate cold solder joints, use a strong light and magnifier and examinethe pins of large components for hairline cracks in the solder around thepin. Gently wiggle the component if possible (with the power off). Anydetectable movement at the joint indicates a problem. With the power on,gently prod the circuit board and suspect components with an insulatedtool to see if the problem can be effected. When in doubt, resolder any suspicious connections. Some monitors mayuse double sided circuit boards which do not have plated through holes.In these cases, solder both top and bottom to be sure that the connectionsare solid. Use a large enough soldering iron to assure that your solderconnection is solid. Put a bit of new solder with flux on every connectionyou touch up even if there was plenty of solder there before.
Intermittent or Missing Colors
If gently whacking the set can make the color(s) come and go, thenbad connections are a very likely possibility. The the effect is sudden - the color drops in and out instantly, it isnot a CRT problem. If the color fades in and out with a delay of about 10-15 seconds, it isprobably intermittent power to the CRT filament for that color and probablymeans a bad CRT since the three filaments are wired in parallel insidethe CRT and one of the internal connections has come loose. Look in the neck of the CRT to make sure all three filaments are glowing orange. If one is out or goes on and off toss the set. Replacing the CRT is probably not worth it. However, if they all go on and off together (all colors would be fading in and out though perhaps not quite in unison), then bad connections on the video driver board (on the neck of the CRT) are indicated. Locate the output for the bad color on the video driver board on the neck of the CRT. This will probably read a significantly higher voltage than the corresponding pins for the good colors. A circuit problem is likely - probably on this board. Test components on this board for the good and bad color channels. A shorted transistor or open resistor can kill one channel. Swap parts to confirm. This is a catch-all for some of the most common TV and monitor problems. Most of the causes of intermittent colors boil down to bad connectionsof one form or another. For totally dead colors - not intermittent - badcomponents are also a possibility. Printed circuit board on the CRT neck. This is a common location for cold solder joints. Check with a bright light and magnifying glass for hairline cracks around the pins of larger parts. Prod and tap with an insulated tool to see if the problem is effected. Resolder if necessary. Cold solder joints elsewhere in TV or monitor usually around the pins of large parts such as transformers, power transistors and resistors, and internal connectors. Internal connectors that need to be cleaned and reseated. Remove, clean with contact cleaner, burnish, and replace.
Red, green, or blue full on - fog over picture
This could be a heater-cathode (H-K) short in the CRT or a failureof a component in the chroma circuits or video output (driver board). Don't panic - heater-cathode shorts in CRTs can often be worked around. Some simple tests can confirm or rule out other possibilities. Compare the voltages for the video drive signals to the CRT on the littleboard on the neck of the CRT with the CRT both connected and unplugged.A schematic will help greatly in locating these signals. If there is a significant difference especially on the bad color, then theCRT is a likely candidate. Try tapping the neck of the CRT GENTLY (withit plugged in and while viewing a picture) to see if it is an intermittentproblem. Might want to have eye protection on while doing this! If there is no significant difference, you may have a bad driver or a problemin the chroma circuits. Look for bad connection/cold solder joints, probably on the littleboard on the neck of the CRT. Use an insulated stick to gently prodthe board and its components in an effort to induce/cure the problem.Look carefully for hairline cracks around the component leads. You can swap components between two colors and/or test with an ohmmeteron that driver board to determine what is bad. The nice thing aboutcolor monitors and TVs is that there three copies of each of thesecomponents. Swapping and/or comparisons between these is an excellentdiagnostic technique. Alternatively, interchange the outputs of the bad color with a good oneby jumpering on the video driver board (on the CRT neck). If the badcolor changes, then the problem is in the circuitry and not the CRT.
Rescuing a shorted CRT
If the short is filament-cathode (H-K), you don't want to use the followingapproach since you may blow out the filament in the process. If this is thecase, you may be able to float the filament and live with the short (see thesection on:Red, green, or blue full on - fog over picture. Shorts in the CRT that are between directly accessible electrodes canbe dealt with in a more direct way than for H-K shorts. At this pointyou have nothing to loose. A shorted CRT is not real useful. If the short is between two directly accessible electrodes like cathode-grid,then as a last resort, you might try zapping it with a charged capacitor.Start with a relatively small capacitor - say a few uF at a couple hundredvolts. Check to see if the short is blown after each zap - few may be needed.Increase the capacitance if you fell lucky but have had little success withthe small capacitor. If the fault is intermittent, you will, of course, need to catch the CRTwith the socket disconnected and the short still present. Try some gentletapping if necessary. If you do this with the charged capacitor acrossthe suspect electrode, you WILL know when the short occurs!
Brightening an old CRT
If performing adjustments of the internal background and/or screen controlsstill results in a dark picture even after a long warmup period, the CRTmay simply be near the end of its useful life. In the old days of TVswith short lived CRTs, the CRT brightener was a common item (sold in everycorner drugstore, it seemed!). You can try a similar approach. CAUTION: this may shorten the life ofthe CRT - possibly quite dramatically (like it will blow in a couple ofseconds or minutes). However, if the monitor or TV is otherwise destinedfor the scrap heap, it is worth a try. The approach is simple: you are going to increase the voltage to thefilaments of the electron guns making them run hotter. Hopefully, justhotter enough to increase the brightness without blowing them out. Voltage for the CRT filament is usually obtained from a couple of turnson the flyback transformer. It is usually easy to add an extra turn or twowhich will increase the voltage and thus the current making the filamentsrun hotter. This will also shorten the CRT life - perhaps rather drastically.However, if the monitor was headed for the dumpster anyhow, you have nothingto lose. There are also commercial CRT rejuvenators that supposedly zap thecathodes of the electron guns. A TV repair shop may be able toprovide this service, though it is, at best, a short term fix.
Bleeding highlights
On very bright areas of the picture, one or more colors may bleed tothe right resulting in a trail of those colors. The difference betweenthis problem and the section:Trailing lines in one or more colorsis that in this case, only highlights are affected. One cause of this is that the color gain, contrast, or intensity controls(whatever they are called on your set) are set too high. See the sectionon:Color balance.Check the settings of any brightness limiter controls as well.
Picture fades in and out
If the picture faded away on the order of 10-20 seconds (and if it comesback, also comes up to full brightness in same time frame - possiblywith the persuasion of some careful whacking) AND with NO othersignificant changes such as size, focus, etc., then take a look in the back ofthe tube for the filament to be lit - the orange glow near the CRT socket. Ifthere is none, then you probably have a bad solder connection on the circuitboard on the neck of the CRT. Look for fine cracks around pins on that board.Try prodding it with an insulating stick to see if the picture comes back.Resolder if necessary. It is probably not a bad CRT as the filamentsare usually wired in parallel and all would not go bad at the same time. However, if only a single color fades in and out, then a bad connectioninside the CRT is a distinct possibility - look for only one of thefilament's glow to be coming and going. This is probably not worth fixing. If the picture faded away with other symptoms, then there is probablya fault in the video amplifier/output one of its power supplies -still probably a loose connection if you are able to get it back bywhacking.
Occasional brightness flashes
These may last only a fraction of a scan line or much much longer. This could mean an intermittent fault in a variety of places includingthe video circuitry and SCREEN power supply: Brightness circuitry - SCREEN, master background or its power supply. Could be in or around flyback or focus/screen divider. Could perhaps be in the CRT, but probably less likely. Video amp before or at chroma demodulator - since after this point, you would most likely get colored flashes since only one of the RGB signals would likely be effected. If you get it from all sources, then tuner/IF is ruled out. Suppose you just have no signal to a direct video input. What do youget? If you still get flashes, it should be real easy to monitor eitherthe video outputs or SCREEN supply (with a HV divider on your scope) fornoise. Then trace back to power or noise source
Excessive brightness and/or washed out picture
Excessive brightness/washed out picture is often an indication of aproblem with the SCREEN supply to the CRT. May be a bad capacitoror resistor divider often in the flyback transformer assembly or on the board on the neck of the CRT. If the excessive brightness just developed over time, then a simpleadjustment of the SCREEN or background brightness controls may keepit (and you) happy for a long time. When good, a typical value would be in the 200-600 VDC at the CRT.The SCREEN (may be called master brightness or background) controlshould vary this. It could also be a problem with biasing of the video output transistors.There may individual controls for background brightness on the littleboard on the neck of the CRT. However, we are looking for a common problem since all colors arewrong in the same way. First, check for bad connections/cold solder joints by gently proddingwith an insulating stick. Check voltages and bias levels.
Bad focus (fuzzy picture)
Focus voltage on the CRT is usually in the range of 2-8 KV DC and shouldbe controllable over a fairly wide range by the focus pot. The focus pot is usually located on the flyback transformer or on anauxiliary PCB nearby. The focus wire usually comes from the flyback orif the general area or from a terminal on a voltage multiplier modulein some cases. It is usually a wire by itself going to the little boardon the neck of the CRT. If a spark gap (a little 2 terminal device with a 1/8 gap in the middle)is arcing with power on, then the resistive divider has shorted insidethe flyback, focus board, or HV multiplier - whatever you TV has - andthe this unit will need to be replaced. Ditto if the SCREEN control affectsfocus and/or vice-versa. Using a suitable voltmeter (range at least 10KVDC), you should be ableto measure it connected and disconnected. The ground return will be theoutside coating of the CRT which may or may not be the same as themetal chassis parts. If the voltage is very low (less than 2K) andthe pot has little effect: When measured right off of the source disconnected from the CRT circuit, thenthe problem is probably in the focus network in the flyback (or whereverit originates). Sometimes these can be disassembled and cleaned orrepaired but usually requires replacement of the entire flyback orvoltage multiplier. When measured with the CRT connected but reasonable with it disconnected, thencheck for a bad capacitor on the little circuit board. The CRT couldalso cause this but it is unlikely.
Focus drift with warmup or age
Focus is controlled by a voltage of 2-8 KV DC usually derived from the flybacktransformer and includes some resistors and capacitors. One of these couldbe changing value as it warms up. (assuming nothing else changes significantlyas the unit warms up. E.g., the brightness does not decrease.) Focus is usually a separate wire running from the flyback or its neighborhoodto the PCB on the neck of the CRT. Look for components in this general area.Use 'cold spray' to isolate the one that is drifting. If you have accessto a high voltage meter, you should be able to see the voltage change asthe TV or monitor warms up - and when you cool the faulty part. If it is inthe flyback, then sometimes the part with the adjustments clips off andcan be repaired or cleaned. Most often, you will need to replace the flybackas a unit. Focus voltage is derived from a subset of te high voltage winding on theflyback using a resistive voltage divider which includes the focus pot.These are extremely high value resistors - 200 M ohm is common - and soleakage of any kind can reduce or increase the focus voltage. All otherthings being ok - i.e., the picture is otherwise fine - I would suspect thistype of failure rather than the CRT. If you have a high voltage meter, you can measure the focus voltage to determine if it is being changed by the focus pot and if it is in theballpark (2-8 KV typical). Sometimes, the part of the flyback with thefocus pot can be snapped off and cleaned or parts replaced but usually youneed to replace the whole unit. There may a capacitor or two on the PCB onthe neck of the CRT that could have increased leakage as well thus reducingthe focus voltage.
Bad focus and adjustment changes brightness
This is the classic symptom of a short between the focus and screensupplies - probably in focus/screen divider which is part of the flybackor tripler. If you have a high voltage meter, measuring the focus voltagewill show that (1) it is low and (2) it is affected by the SCREEN controlSimilarly, the SCREEN voltage will be affected by the FOCUS control (whichis what is changing the brightness. There is a slight possibility that this may be in the CRT as well. Measurethe FOCUS and SCREEN voltage with a high voltage meter. If they are identicalpull the plug on the CRT. If they are now their normal values, then ashorted CRT is a distinct possibility - see the section:Rescuing a shorted CRT.
Bad focus and adjustment changes brightness
This is the classic symptom of a short between the focus and screensupplies - probably in focus/screen divider which is part of the flybackor tripler. If you have a high voltage meter, measuring the focus voltagewill show that (1) it is low and (2) it is affected by the SCREEN controlSimilarly, the SCREEN voltage will be affected by the FOCUS control (whichis what is changing the brightness. There is a slight possibility that this may be in the CRT as well. Measurethe FOCUS and SCREEN voltage with a high voltage meter. If they are identicalpull the plug on the CRT. If they are now their normal values, then ashorted CRT is a distinct possibility - see the section:Rescuing a shorted CRT.
Blank picture, good channel tuning and sound
Since the tuner and sound are ok, horizontal deflection which usuallygenerates power for most of the set is also working. Does 'blank picture' means a totally black screen with the brightness and contrast controls having no effect whatsoever? Or, is there is no picturebut there is a raster - light on the screen? The direction in whichtroubleshooting should proceed differ significantly depending the answer. Here are some questions: As above, is there any light on the screen at any settings of the brightness and contrast controls, and/or when switching channels. Can you see any raster scanning lines? Can you hear the high pitched (15735 Hz) of the horizontal deflection? Looking in the back of the set, can you see the glow of the CRT filament? Do you get that static on the front of the tube that would indicate that there is high voltage? Any cracking or other normal or abnormal sounds or smells? Possible causes of no raster: no/low HV, drive to CRT bad/shut off as a resultof fault elsewhere, blanking as a result of tuner/controller malfunction,filament to CRT not getting powered. Possible causes of no video: problem in video IF, video amplifiers, videooutput, cutoff due to other fault. It could be as simple as a bad connection - try gently prodding the boardswith an insulated stick while watching the screen. Check for loose connectorsand reseat all internal connectors.
Purple blob - or worse
Have you tried demagnetizing it? Try powering it off for a half hour, thenon. Repeat a couple of times. This should activate the internal degausser.See the section:Degaussing (demagnetizing) the CRT. Is there any chance that someone waved a magnet hear the tube? Remove itand/or move any items like monster speakers away from the set. Was your kid experimenting with nuclear explosives - an EMP would magnetizethe CRT. Nearby lightening strikes may have a similar effect. If demagnetizing does not help, then it is possible that something shiftedon the CRT - there are a variety of little magnets that are stuck on at thetime of manufacture to adjust purity. There are also service adjustmentsbut it is unlikely (though not impossible) that these would have shiftedsuddenly. This may be a task for a service shop but you can try yourhand at it if you get the SAMs Photofact or service manual - don't attemptpurity adjustments without one. If the set was dropped, then it is even possible that the internalshadowmask of the CRT has become distorted and you now have a hundredpound paper weight. It is even possible that this is a 'feature' complements of the manufacturer.If certain components like transformers and loudspeakers are of inferiordesign and/or are located too close to the CRT, they could have an effecton purity. Even if you did not notice the problem when the set was new,it might always have been marginal and now a discoloration is visible dueto slight changes or movement of components over time.
Color TV only displays one color
I assume that now you have no other colors at all - no picture and noraster. Let us say it is red - R. It is probably not the CRT. Do you have a scope? Check for the R, G,and B video signals at the CRT. You will probably find no signalsfor the defective colors. This is almost certainly a chroma circuit problem as any failure of theCRT or a video driver would cause it to lose a single color - the othertwo would be ok. Therefore, it is probably NOT the CRT or a driver onthe little board on the neck of the CRT. Try turning up the SCREEN control to see if you can get a G and B rasterjust to confirm that the CRT is ok. Locate the video drive from the mainboard for the good and a bad color.Interchange them and see if the problem moves. If so, then there isa video signal problem. If not, it is on the little CRT board. It could be a defective chroma IC or something else in the chroma decoder. Disappearing Red (or other color) Problem: I have been given an old colour TV. The reception is good, but veryoften, when the contrast and brightness of the TV image is low (e.g. whena night scene is shown), the red colour slowly disappears, leaving behindthe green and blue image and many red lines. The remaining red retrace are the giveaway that this is most likely nota CRT problem. (If there were no red lines, it could be the filament for the red gunof the CRT going on and off due to a bad connection inside the CRT -bad news.) How is a black and white picture? (Turn down the color control). If B/W picture is good, then the problem is somewhere back in the chromadecoder circuitry. Check the video input to the CRT video driver board and signals on that board.If B/W picture is also bad, then you can compare red and green signalsto determine where they are becoming different. The red lines in yourdescription sounds like the red video output circuit is drifting and messingup the background level, blanking, screen, or other setting. Could be acapacitor or other component.
REFERENCE
http://www.stedmundsbury.gov.uk/sebc/play/tvprobs.cfm.
http://www.epanorama.net/links/repair.html#tv