VGA from Trident 9000 cut off


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  • #22117

    I have just received my OSSC and have hooked it up to my retro rig: 286 with TVGA 9000. The OSSC feeds into an HDMI grabber which in turn feeds OBS.

    The test pattern looks good and centered, see this screenshot:

    test pattern

    However when I switch to AV3/RGBHV I get 449p, 31.83kHz 70.91Hz and the image is cut off:

    BIOS display is cut off

    So I think the image needs to be tweaked to be centered. How do I do this?

    More images here:

    Screenshots of BIOS and DIAG on my 286 through OSSC


    You can tweak the image with the Advanced timing tweaker in Sampling opt:

    H.backporch & V.backporch affect horizontal/vertical position. & affect size/cropping.

    However you should update to firmware 0.81 which added a 640×400 preset that should already have the correct settings.

    BTW the black looks crushed in the test pattern. You should select Full Range at Video recording device settings and try other video formats like XRGB.


    Good to know! I will update the firmware. Currently at 0.78a as it was shipped.

    Yeah, I played a bit with the OBS settings, since my VGA output has the black a bit bright. But I will test how to get a decent dynamic range.


    Ok, I upgraded to 0.81 and the image is a bit better. However it is still shifted and cut off.

    I tried fiddling with the advanced timings, but I only managed to get it barely correct.

    Is there any guide to this? Am I missing something?


    Does it show correctly when connected to a monitor instead of the capture device?

    FirebrandX made a video where he shows shifting the image at 3:24

    Its basically just changing H.synclen or H.backporch.

    If that does not work with your capture device you can try to set 384p to Passthrough so the capture device receives 640×400 instead of 1280×800.


    Yes, image is fine on my LCD screen.

    I managed to center and size the image now. I will post the parameters later, for documentation.

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