Sony PVM-1442QM monitor no picture

[naujoks]

I have received a Sony PVM-1442QM which has a fault with the two composite connectors.
Yesterday it was running just fine, when after half an hour or so the picture would go dark. Both composite connectors are affected.
This morning I tried it again, but no picture. I left the monitor on for a while, turned on the video source (a VHS player), no picture. Then I switched the monitor off and on again after 15 seconds - bam the picture is there again. Watched for half an hour.
Turned everything off for a few hours, then on again, and no picture. Leaving the monitor on for a good while and then switching it on and off brought the picture back.
I was wiggling the connector around a bit, but it doesn't make a difference, I would exclude a cold solder joint as a cause.
I was having problems with the SVIDEO connection as well, but here wiggling the plug around and pushing it in really deep made a difference. I checked the board for cold solder joints, but there were none, so I suspect there is a problem with the socket.
In either case, the SVIDEO problem seems unrelated the the composite connectors.
Any ideas what I could try? Capacitors maybe? Which ones though, there's literally a hundred on those boards.

[MathWizard]

Do you have an oscilloscope ? Maybe some rail voltages are close to unacceptable levels, and something shuts down kind of at random ? When it loses picture, is it just the backlight going out ? Anyway to see if the video data is still being sent out ??

[naujoks]

I do have a scope.
It would be odd if there's a problem with the power rails that only the two composite channels are affected?
It's a CRT, so there's no backlight.
The PCB is crazy complicated, I don't have the schematics, don't know if they exist. I'd need those to trace the video signal.

[decoder_82]

You can find the schematics in the service manual: https://archive.org/details/sony_PVM-1440QM_1442QM_1444QM_Service_Manual
I believe signal tracing is the best option. If you have a signal generator you can inject color bars and try to follow it.

[belzrebuth]

Did you ever fix this issue?
Happened to me as well with a PVM-1444QM.
RGB input is fine it's only the component input (not composite!) that gives trouble.
Funny thing is that it goes away when I power cycle the unit, and it's not the connectors because RGB utilises the same connectors.
After a minute or so it gradually goes dark..