The picture on my old panasonic tv fades. It becomes lighter and lighter and then has thin white lines across it. The picture comes back when the set is turned off and then on again but then the picture is...
A competent tech with one particular instrument, a capacitance meter with DF, could find the problem quite quickly.
This is normally caused by a decayed electrolytic capacitor in the high voltage circuit.
Once their capacitance value shrinks and loss increases, their function becomes marginal and falls to inadequate once they are warmed up by surrounding components.
One possibility for DIY troubleshooting requires a can of 'freeze spray' available from Radio Shack or other electronic parts sources.
NOTE: Removing the back housing from your set exposes dangerous high voltage points so keep one hand in your pocket while trying this!
Place a large clean towel over the innards otherwise it may not get warm enough to find the failing part.
Turn it on and wait for the fading to start.
Remove the towel.
With the guts exposed, look for a large (nearly always) black device.
This is the 'flyback' transformer.
There will be a largish transistor on an aluminum heatsink near it; avoid touching this, it's hot and operating at high voltage!
Look for cylindrical parts with black or blue (rarely red) 'heat shrink' plastic surrounding them; nearly all of these will be capacitors.
From a safe distance, spray each one of these for several seconds while watching the screen in a mirror.
After each is sprayed, wait 5-10 seconds for the temperature to change from the spray.
There will be a lag between spraying and effect so be patient.
If you find one that has some influence on the picture, wait for a minute or two and repeat the cooling to make sure you have the culprit.
Once sure, turn off the set, allow a couple of hours for the voltages to drop to a safe level, look for the values on the part you isolated:
there will be several numbers and letters. If convenient, you could take a picture of it to show a parts store to get a replacement or comment back here and I will tell you where you can buy/order it.
The numbers/letters, these are ONLY examples: 22uFd. 50VDC & maybe a tolerance with a plus + and a minus - sign, +20 -10, these are percentages.
There may also be a + sign near one side (pin) or it may have the word: BIPOLAR on it.
You will need a small soldering iron to replace the part(s) and a bit of quality solder, also from RS or a parts store.
If they have solder 'wick' this will let you absorb the old solder and remove the part without board damage.
I wouldn't have taken the time to give you such explicit instructions but your set once repaired, will again last longer than a new 'flat panel' bought today; their reliability has not been good and the warranties are short.
You can verify the number of problems by entering 'LCD' or 'Plasma' or 'Projection TV' in the FixYa search window.
Oct 18, 2009 |
Panasonic Standard (CRT) Televisions