Tuesday, 11 March 2008

TV VERTICAL SECTION PROBLEMS AND SOLUTIONS.

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.

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