Minor monitor (TV) fault

big10p

big10p

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I have a de-cased TV in a cab that has an occasional, very quick flicker in the image, and also sometimes goes bright when it does this. I can cause this to happen by tapping on the side of the cab, so figured it was a bad connection somewhere. Probably a dry joint.

I've reflowed a load of stuff on the chassis, including SCART socket and all connectors, but it's made no difference.

Any other things to check that can be affected by banging on the cab sides? Presumably dodgy caps aren't affected by vibration, are they?

Thanks.
 
big10p

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tb2000 said:
That sounds like it's possibly a problem with the lopt, or at least the solder points or traces in the HV area.
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Oh no. I did re-flow the lopt, but if it's on it's way out, I very much doubt I could find a replacement. ☹️ The chassis is in good condition with no corrosion or damage that I noticed, but I'll double check the traces.
 
tb2000

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Found the service manual. Looked up the part number in there for the lopt and it apparently crosses to HR7944. I'm not that sure if it's the cause. Looking at the schematic (not the clearest of scans but not bad!) there's a 180v line that could be the problem (I think). If you lose the 180v line for a split second you'd get all three guns switched on full for a split second. Do you get flyback lines when it does it? Like a lot of later TV's there's a bunch of IC's in there as well, so could be a problem with one of those. Probably best to ask Gunblade for sure, or MKL.
 
big10p

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tb2000 said:
Found the service manual. Looked up the part number in there for the lopt and it apparently crosses to HR7944. I'm not that sure if it's the cause. Looking at the schematic (not the clearest of scans but not bad!) there's a 180v line that could be the problem (I think). If you lose the 180v line for a split second you'd get all three guns switched on full for a split second. Do you get flyback lines when it does it? Like a lot of later TV's there's a bunch of IC's in there as well, so could be a problem with one of those. Probably best to ask Gunblade for sure, or MKL.
Click to expand...
Thanks for the info! While tapping the side, I did get the screen to go bright for a couple of seconds, before it returned to normal. I could still see the screen image, but it was just very bright. I didn't notice any flyback lines, but I wasn't looking for them at the time, and now I can't replicate the fault.
 
big10p

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Ok, I gave the screen pot on the lopt a bit of a gentle wiggle to see if that had any effect. It didn't, but now the image seems stable, even when banging on the cab sides. Dodgy screen pot, then?
 
B

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big10p said:
It was still glitchy after I'd reflowed.

Normally, I'd try and locate the bad connection by tapping around on the chassis, but this is an un-earthed "hot chassis", so basically the whole damn thing is live. I'm a bit scared of it. Lol.
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At work fixing TV's they had Isolation Transformers to plug in TV's while repairing them, I had a massive one of them I had from somewhere and chucked it years back before my extension was built, wish i'd kept it
 
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