Alright, this problem is called hum or more correctly 60Hz-120Hz Hum it is caused by a partially open or an open filter capacitor in the power supply of the TV. The filter capacitor's job
is to filter out the 60Hz - 120Hz ripple voltage that is present on the
power supply's output.
When this cap fails the hum bleeds into the
various stages and causes the lines that you are seeing on the video
screen. To troubleshoot this problem you will need a schematic diagram
(to locate the power supply test points and to get pictures of the
correct waveforms that should be present), a signal generator (to
generate a reference signal), and an Oscilloscope (to view the
waveforms at the test points). What you will be looking at are the
outputs of the power supply checking to see the level of the ripple
voltage present on the outputs.
If you do not have the tools needed or any knowledge of working on electronics, then I would suggest getting a qualified repairman to fix this problem and the cheapest way is to take it in and not have them come out.
Let me know if you have any further questions on this problem
thanks
its not the amplifier
have you taken a look at my advice at all?
no problem, good luck with the replacing
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It looks like the TV might have retrace lines that are cause by a defective video amplifier IC, couple of fuse resistors burnt.
You might be able to make an adjustment to the blue screen voltage by reducing it slightly to get rid of the lines.
The devices that you connect to the TV have a different output and the TV is very sensitive to the higher video outputs from the DVD or any other device that you connect using the AV inputs.
Let me know if you need more assistance.
Plasmas are a bit more difficult to repair due to complexity of their boards.
At this point there might be the need for some adjustments to the voltages powering up all the assemblies on your TV.
It requires the use of a good multimeter, a 200Mhz oscilloscope and the know how.
Have you tryied Switch on P-NR in Picture menu to reduce picture noise?
Try connecting the other video sources directly to the TV with shorter cables, just to eliminate some noise that could be picked up by the long cables.
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Thanks very much for that.
All the video inputs go via the video processing function on a Yamaha AV system first. The set is 5 metres from the AV amp so a long component cable is used to connect them just to the component sockets.
Is there a video amplifier board that can be replaced?
Yes. It didn't help.
Bestdarngood,
Sorry not to responded.
Many thanks for your advice. I am inclined to think you are right about this. I have obtained a service manual, and although I am familiar with using a signal generator and scope; it is many years since I undertook this kind of work. Happy to pull a computer apart and fit boards etc but I think this is over my comfort limit.
The set is obsolete in terms of the way the UK is now rapidly moving, and the cost of a repair is high in relation to aquiring a new one. I didn't pay anything like the retail price on the high street for it in the first place, so I think it is time to replace it.
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