Intermittent picture problems on old computer
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Author:  93143 [ Sat Aug 12, 2017 3:26 pm ]
Post subject:  Intermittent picture problems on old computer

I'm running an old P4 from 2004 with a GeForce FX5200 fanless graphics card, hooked up to an LG Flatron F700P CRT monitor. I only use it infrequently, partly because it has trouble booting; there are two or three points during the early boot sequence at which it can hang unless it's properly warmed up (by cold-booting it and letting it hang for a while). This may be related to what looks like a blown cap on the MB. But that's not what I'm posting about.

What I'm worried about is that when it is running, I get intermittent flashes of glitched horizontal lines in the picture. They seem to happen in clumps (forming horizontal bars in the picture, which are mostly but not entirely non-solid) and show some consistency in location between flashes during an event (which generally takes a small fraction of a second, but clusters of events can span a couple of seconds before the display quiets down again). The glitching shows unusual brightness in some areas, which would seem to imply an analog problem. I've never seen it happen when the screen saver has the display blacked out. Sometimes it seems like it's triggered by using an input device (e.g. pressing a key on the keyboard), or taking the cover off the case, but usually those actions don't cause it, and sometimes it happens for no evident reason at all. And it seems to be more frequent since the last time I used the computer...

EDIT: The problem seems to go away as the computer (or the monitor?) warms up. I haven't seen it in a while now.

Any idea what's going on here?

Author:  Memblers [ Sat Aug 12, 2017 9:50 pm ]
Post subject:  Re: Intermittent picture problems on old computer

I remember something similar happening to me once, in my case it was simply because the VGA cable wasn't fully plugged in. Check both ends, look for corrosion on the pins too.

Though if the glitches are consistently happening on the same lines, it's probably not a mechanical issue. If you've got bad caps on the mobo, all bets are off.

Author:  TmEE [ Sat Aug 12, 2017 10:49 pm ]
Post subject:  Re: Intermittent picture problems on old computer

Is there any sound when these flashes happen ? Most particularly inside the monitor. If yes you'll want to open it up and give it a thorough clean (there will probably be lot of hard to remove dust inside). You'll want to stay away from the biggest capacitor on the board, that one can kill you, rest will only shock mildly if not discharged.

But it may very well be caused by bad caps on the board or in the PSU. You already experience hangs, so you really want to take care of those and chances are all other problems get fixed from it aswell. Inside PSU there's one or two large capacitors, those can kill like the one in the monitor. Rest are not gonna be able to do anything.

Author:  93143 [ Sun Aug 13, 2017 7:23 pm ]
Post subject:  Re: Intermittent picture problems on old computer

I didn't notice any noise.

It might be related to the fact that I foolishly pressure-dusted the computer outdoors in winter. I figured out this was a bad idea when I took it back in and it started to get wet. So I took the cover off, aimed a space heater at it, and hoped for the best.

The boot troubles started around then, I think, and have gotten steadily worse. Maybe I should take it to an electronics repair shop? I'm not sure a modern computer shop would be able to handle this relic...

Memblers wrote:
look for corrosion on the pins too.

I'll take a look. Under the circumstances, though, the problem could well be deeper inside the assembly.

TmEE wrote:
You already experience hangs

Well, technically it's just failure to boot. Once it manages to start loading Windows, everything works fine software-wise.

But yeah, it sounds entirely reasonable that these problems might be related...

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