Weird screen corruption issue

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Weird screen corruption issue

Postposted on Mon Nov 07, 2011 2:40 pm

Here's one I've never seen before.

My PC at work is a Dell Optiplex 780 with WinXP Pro, and includes a GeForce 9300GE driving dual 2700FPb monitors from analog. Desktop is spanned. When the system uptime grows into the range of a week or more, the monitors will start to develop these faint, whispy ghosting patterns that gradually grow in size. The pixels will still transition fully to white or black, but when displaying intermediate colors, the patterns emerge, almost as though there were smears or smudges on the monitor. Everything is fine after a power-down and reboot. I've seen this at least twice that I know of, so it wasn't just a random fluke.

Anyone got ideas? I don't have administrator rights on this machine so I can't be certain about the driver version, nor can I update them. Mostly, I'm curious about what causes this, and whether it signals an impending hardware failure. If so, I would like to have that info available to file a help ticket with IT, as I don't want the GPU to just quit on me one day.
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Re: Weird screen corruption issue

Postposted on Mon Nov 07, 2011 3:17 pm

Sounds like two possibilities:
The output driver IC of the video card is going kaput, or the cable between the card and the monitor has poor signal integrity (analog?) and needs cleaning or replacing.
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Re: Weird screen corruption issue

Postposted on Tue Nov 08, 2011 3:17 am

I don't think it's the cable. As noted, this only happens after a very long period of uptime. The display can be completely clean for a week or more, and when it finally occurs, it can affect both monitors. Here's an example I was able to catch with my phone camera a couple weeks or so ago, the second time it happened. The moire patterns were obviously caused by the camera, but the wavy dark lines in the lower half of the image are actually being displayed by the graphics card:

Image

Weird stuff. Almost looks like damage to the LCD but it's entirely in the signal. Notice how the upper line cuts off abruptly at the white of the login window -- drag that window away, and the dark line actually continues a short distance further, but again, it doesn't display anywhere that the image is full bright or full dark. Only on intermediate colors.
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Re: Weird screen corruption issue

Postposted on Fri Nov 11, 2011 11:59 am

So I'm guessing they'll name this one after me, because nobody else seems to have ever gotten it :D

Oh well. It doesn't come up very often, so I guess I'll be ignoring it unless it starts getting more frequent.
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Re: Weird screen corruption issue

Postposted on Fri Nov 11, 2011 12:17 pm

Try a different monitor of the same resolution.

This almost looks like analog signal interference and because of that I betting on a heat issue.

Either the monitor's driver circuitry is having issues or the ramdac on the video card. May also be gradual expansion of a solder joint somewhere in the connectors.

Are you using the regular old vga cable (15 pin din) or newer DVI or hdmi?
Definitely switch to DVI or hdmi if you are using the regular vga cable.
If you are already using a digital connection then switching cables probably wont help unless the cables do not have integrated chokes.
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Re: Weird screen corruption issue

Postposted on Fri Nov 11, 2011 1:59 pm

Just eliminate possibilities methodically and you'll get your answer. I've certainly never seen it before, but I've seen all kinds of weirdness that turned out to be environmental.

Once your GPU renders a digital image, it gets converted by the DAC on the card. Then it's sent to one of two DSUB VGA-ports, (either direct or via a DVI-to-VGA converter), and finally into the monitors where it hits another DAC.

So, you could have:
  • a faulty GPU DAC
  • a faulty converter (if you're using one)
  • faulty cables
  • faulty monitor

To eliminate each issue one at a time, find an identical workstation with a willing volunteer (I assume the company you work for buys x identical boxes and farms them out to people) who can assist. You don't need admin rights for any of this testing.
So:
  • start by swapping the converters, if you're using any - since these will be the quickest and easiest to change. If the black marks appear on his after a week, it's a dying converter.
  • Then swap the graphics cards. Whilst more work than changing cables, I would choose that as the most likely culprit.
  • Then swap the cables. It's unlikely to be cables - since the chance of two identically faulty cables on the same machine is pretty low.
  • Finally swap the monitors. As before, two monitors both exhibiting identical faults at the same time is unlikely.

Assuming that you eventually do all of this, You can pretty much rule out everything except the environment.
Look for sources of heat, kinks in your desk's cable routing, damaged power cables or extension leads, f'ckin' magnets (how do they work?), or other things that are different between your desk and your volunteer's.

If you can't find anything you might as well just live with it and assume your desk is haunted.
...otherwise it's PEBKAC - the error ID is 10T ;)
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