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Thread: Flickering/Missing Pixels on Display

  1. #1
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    Default Flickering/Missing Pixels on Display

    I was using one of my other video cards (an ATI All-in Wonder Turbo) for a while based on how reliable it was, but now I'm starting to question it.

    It's most obvious when playing Doom for DOS, or the Boom sourceport.

    The sprite representing the Doom Marine's hand shows missing pixels, several HUD sprites, and several textures in the level show flickering or noise within lines of particular pixels. (Not per-texture, where the texture is corrupted; but at the per-pixel level, where the rendered image has visual glitches.)

    What makes this odd is that this visual corruption is always in the same place in the image.

    It's not memory, is it? (Mach64 Diagnostics say the ICs are fine.)

    Or is it a bad connection, based on age/bad GPU? (Yes, I understand these weren't exactly GPUs at the time, but bear with me.)

  2. #2
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    Default

    If the system behaves normally with a different video card, then it's going to be a fault with that particular video card. It could either be bad video memory, a fault with the video chip, or a bad connection on the PCI bus.

    I'd recommend to try cleaning the PCI slot and the card with something like Deoxit Gold or CRC precision lubricant. I have frequent problems with old cards and even RAM misbehaving due to oxidation on the contacts, and Deoxit gold is my go-to solution to fix the problem.

  3. #3
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    I have another theory. Would cheap PSU components (especially capacitors) cause noise for the system? I've looked in my Antec PSU and found that they used CapXon capacitors, which according to badcaps.net, are not top-tier (3rd place from best-to-worst, I believe).

    I should also mention that I am having these video problems on the VGA feature connector. The regular monitor is just fine: https://imgur.com/a/uGSKt6c

    Also, I tried an ATI Rage Pro PCI video card, and it's even worse. I even tried another one, but the problem is still apparent, so I'm theorizing that the capacitors in the power supply are not filtering properly.
    Last edited by T-Squared; May 28th, 2020 at 10:35 AM.

  4. #4
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    You're mixing information here, so let's clarify:

    Video through the feature connector (how are you connecting this up?) is bad, but video through the monitor connected normally through the external VGA port is fine. This implies the problem is with the feature connector path (including whatever you're hooking it up to) and not really anything wrong with the card or its RAM.

    You tried a different card and said "it was worse" but didn't clarify if that was also the feature connector you were testing. If you tried two cards, and the feature connector output is dirty on both cards, then something is wrong with whatever you're using to get video off the feature connector. What are you connecting to the feature connector?
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  5. #5
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    The feature connector is linked to a Forte VFX1 video decoder card that sends video information to the VR helmet.

    I did run into some problems 4 years ago that destroyed some traces inside the VR helmet's control board, but I was able to fix those.
    I am not so sure it is the helmet OR the video decoder card, because I am able to get stable and clean feature connector video on another video card brand: the S3 Virge / DX line of cards.

    I am more certain that the problem lies either with the video cards, OR with the capacitors inside of the PSU, because my previous motherboard showed the same kinds of problems.

    To further clarify, here's a list of video cards that I got to work (with included problems):

    *Diamond Speedstar (Normal)
    *S3 Virge (Normal at 2MB of VRAM, but 4MB seems to shift the image data to some other part of VRAM, causing a blank image on the helmet that only reacts to palette changes.)
    *ATI Rage Pro PCI (Dirtied image, as I showed you)
    *ATI Rage Pro Turbo, as an All-in-Wonder TV Tuner Card (Cannot show because of GPU reworking, but basic mockup below shows more subtle, but similar, image corruption. Although I could swear the image was normal and clear before.)
    Attached Images Attached Images
    Last edited by T-Squared; May 28th, 2020 at 03:05 PM.

  6. #6
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    A matrix of test results might help make sense of this. Something like:

    Card Feature Connector VGA Connector
    ATI All-in Wonder Turbo no yes
    ATI Rage Pro PCI no
    S3 Virge (2MB RAM) yes
    S3 Virge (4MB RAM) no
    All-in-Wonder TV Tuner Card no

    ...etc.
    Offering a bounty for:
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