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Monitor screen dark but LED stays green.

My 7-year old CRT monitor has developed an intermittent fault. Sometimes the screen goes black but the power LED remains green (doesn't turn amber). A sharp rap often restores the display. When it decides to act up, the LED stays green even when it's turned on for several minutes while disconnected from the computer.

I did a lot of repair work on a wide range of electronic products up to the early nineties, but I'm quite rusty now. I've opened up the monitor but can't see anything obvious in the way of a dry solder or loose connector. The tube heater glows all the time. The signal cable goes first to the tube base PCB and connections to the main PCB are with two flat cables.

Which signal line does a computer monitor use to detect the presence of a signal? Where do you think I should start looking? Thanks in advance for any input.

Reply to
Pimpom
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I have several computers with CRT and LCD monitors but I like this one because it has analog controls for brightness and contrast.(other controls are digital) - much better than fiddly menus and preset levels when switching between different programs. It must be one of the last models with analog controls, which is why I've hung on to it all these years.

Reply to
Pimpom

It probably uses one of the sync lines. An intelligent approach would be to check resources such as

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and
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to see if you can find a schematic. Failing there, I would use a lighted magnifier and carefully examine the circuit boards for cracks, bad solder joints, etc. AFTER reseating all connectors.

Or you c ould get a rubber mallet to whack the monitor each time it fails.

PlainBill

Reply to
PlainBill47

Thanks.

I downloaded the service manual (Hungarian, it seems) from elektrotanya.com after I made my initial post, and another from electronica-pt.com just now after reading your post. They turned out to be identical. But my chassis is significantly different from them although the model number and the FCC ID match.

Already did that. No luck. I have a 16mm film projector lens which is more powerful and optically better than a magnifying glass. Seems I'll have to do this the hard way - step by step analysis. Electronics is both a profession and a hobby with me and, being my own boss, I can afford the time. Luckily, right now I don't have any major design project that can't wait for a few days.

There's always that, of course :-)

Reply to
Pimpom

I would check for solder breaks at the horizontal drive transformer, the horizonta drive transistor, the horizontal output transistor, the yoke socket and the H.O. transformer. Chuck

Reply to
Chuck

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