TV-Engineer said:Hello again. Okay, good points. Don't know how I missed adding the make and model!
1) United Kingdom of grey clouds and cold.
2) Sharp DV-6635H
I take it the Sony was airtight but not sealed enough to stop EHT escaping?
This set crackles nicely around the edge of the tube when switched off, even around the speakers next to the tube, but nothing is visibly leaking there.
Nothing across the isolation barrier.
HT is 149V, only 1V out from circuit diagram stated amount of 150V. I use a 60W light bulb on the HT line as a dummy load. Not sure what is meant by ps though?
I cannot know if this set has seen a bit of lightning, unfortunately. I do know it has previously suffered from a listed fault and been repaired - dry joints on deflection coils connector causing two resistors to fail (cook) in the line stage. All rectified, though. I've checked to make sure.
TV-Engineer said:No one seems to have heard of such a fault, even my father who has been in the trade most of his life, and is now retired.
We've wondered about LOPT failure being the culprit, but my inquisitiveness means I'd like to find out exactly how it has failed if that's the case. The internal diode is one thing which was raised as a possibility.
The fact that the charge still builds up on the 0V points when a picture is present, but the noise and screen disturbance disappear, has everyone so far convinced that the AGC is simply making the fault more apparent when no signal is present. Question is, is the EHT higher than it should be for some reason, even though the HT is normal... And even so, would excessive EHT cause 0V points to be charged.
The isolating components between the primary and secondary did occur to me as being possible culprits, but they check out fine. There must be somewhere from which the high potential is coming, and a reason it is surviving on 0V areas of the secondary, and the points where the mains goes into the set. One idea is that the potential is being produced in the secondary only, and that is it trying to find passage to earth and by doing so, making it's way to the primary side and hence the mains board, or the charge on the secondary is inducing charge in the primary which is flicking from the mains plug in an attempt to get to earth.
TV-Engineer said:Regarding the test, do you mean the earth of the mains? i.e. I take a wire from a plug socket earth or radiator pipe and clip it to the chassis (tuner can, etc)?
There's a very simple test, the chassis of the TV is isolated from the mains, so connect an earth lead to it and see what difference that makes!
Stoopid question... have you checked for a cracked neck? The tube could retain vacuum and yet a defect in the glass could allow for some leakage
maybe the tube has gone down with or without the lopt
in that case your moving away from the real problems and looking
for remedies in areas of no substance
for the flashes do a resoldering on the lopt and hout stage
then test tube and lopt
mains leakeage could be coming from a leakeage of the ps power transformer too
do mains leakage test by connecting a 1.5k resistor from chassis to earth ground and measure the voltage then find leakage current vm/1.5k
the 8.5M static discharge resistors are they in series or in parallel
most tvs have a value of about 10M
TV-Engineer said:Has everyone lost the will to fault find?
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