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Old 09-27-07, 02:19 PM   #1
jesmith
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Default Intermittent Black Dots on QFX4600

This is a weird one. We just started using Quadro FX 4600 cards, driving a 37" 1920x1080p display at 60Hz. (Previously we used 3500s, driving at 49Hz, and did not see this issue.)

When we put a system together like this, we often see a pattern of black dots, which I managed to capture using xwd. This pattern is always in the same place. We have seen it with multiple 4600 cards. Often, after a few days of "burn in" the pattern goes away, and then we don't see it on that unit any more. Until today, when we powered up a unit on which the condition had cleared, and it suddenly re-appeared. The next time we booted, it was gone.

Spooky.

One other tidbit: The pattern only appears when there is a static image on the screen. When our application is running at 60FPS, cranking triangles, the black dots disappear. They come back when the scene stabilizes. The dots are there persistently when looking at the X desktop, like the screen capture shows. They are also there when glxgears is running in a window.

We saw this with the 100.14.11 drivers, and it is still there after we just updated to 100.14.19.

We have tried turning triple buffering off and it had no effect.
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Old 09-27-07, 02:24 PM   #2
netllama
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Default Re: Intermittent Black Dots on QFX4600

This sounds like a hardware problem.

Does this problem persist if you use a native mode instead a custom modeline?
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Old 09-27-07, 02:53 PM   #3
jesmith
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Default Re: Intermittent Black Dots on QFX4600

It happens with multiple 4600's and multiple display systems, so if it's a hardware problem, PNY has a serious QA issue...

I can't test using a standard modeline with this monitor, because X won't drive a wide screen with ordinary mode lines. I can try connnecting a CRT, to see if it shows up, but then the resolution will be very different.

Right now I don't have any systems exhibiting the behavior, but the next time one does, I can try this.
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Old 09-27-07, 03:19 PM   #4
netllama
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Default Re: Intermittent Black Dots on QFX4600

I agree that if this problem is not unique to one set of hardware, that its unlikely to be a hardware problem.

That leads back to a suspicion that your custom modeline is at fault. Please clarify what you mean by "X won't drive a wide screen with ordinary mode lines".
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Old 09-27-07, 03:34 PM   #5
jesmith
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Default Re: Intermittent Black Dots on QFX4600

I mean that if you give a 16:9 screen to X without a custom modeline, it screws up the resolution.

So we run Windows on identical hardware, open the NVIDIA control panel, go to the "create a custom resolutions" section, copy all the front porch, back porch, etc. data into a spreadsheet, and generate a modeline for X.

I've attached the spreadsheet we used.
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Old 09-27-07, 03:39 PM   #6
netllama
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Default Re: Intermittent Black Dots on QFX4600

Unless you're trying to use a mode that isn't natively defined in the display device's EDID, there shouldn't be any problems. From what you're saying it sounds like you're trying to use a mode that isn't native to the DFP. In that case, corruption isn't an unexpected result.
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Old 09-27-07, 03:44 PM   #7
jesmith
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Default Re: Intermittent Black Dots on QFX4600

That is not consistent with my experience.

However, the next time this happens, I'll boot using no special modeline and see if it has any effect.
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Old 09-27-07, 03:47 PM   #8
netllama
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Default Re: Intermittent Black Dots on QFX4600

When using a DFP, the only mode(s) that are ever guaranteed to work perfectly are those defined in the EDID. I'm afraid that if that hasn't been your experience, then you've been lucky thus far.
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Old 11-29-07, 10:43 AM   #9
jesmith
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Default Re: Intermittent Black Dots on QFX4600

I've switched to using the built-in modeline, and also tried this with the new 169.04 drivers. No change, I still see the dots.
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