OSSC to display Sega System 24 medium resolution arcade PCB

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  • #25200
    xtrasmiley
    Participant

    Ok I have a working (I think, can’t be 100% sure without seeing it work!) Sega System24 arcade PCB which I am using a HAS supergun with to an OSSC. This is the same setup I’ve used for about 46 arcade PCBs and I haven’t had any issues yet, but all other boards were standard resolution or high like Naomi, but again no problems. This is my first attempt with a medium resolution game.

    With this set up I get a sync lock on the OSSC, but get nothing on my TV.

    The OSSC screen shows:

    423p
    24.39kHz
    57.66Hz

    Which doesn’t seem correct as I don’t think the S24 board is 423p.

    Anyway, my TV keeps displaying the “resolution is not supported” message and nothing.

    Any thoughts to what settings I should use?

    #25202
    nmalinoski
    Participant

    Those are total line counts of the incoming resolution, not simply visible lines (so 480p will show as 525p, 576p will show as 625p, etc.); 423 lines seems appropriate for 384p.

    My assumption is that your display doesn’t like the resolution, refresh rate, or both. Assuming a resolution of 496×384, line doubled, that comes to 992×768, which is not any sort of standard PC or TV resolution. If the OSSC is framing this as 1024×768, that might have better compatibility, but I imagine there are TVs out there that don’t accept this over HDMI.

    As for refresh rate, 57.66Hz is enough off-spec from 60Hz that I can see displays outright rejecting it.

    You might need something like a Framemeister or Extron DSC 301 HD to scale and framerate convert this to use on your display.

    #25203
    xtrasmiley
    Participant

    Crap, thank you for the explanation, are there any settings I can adjust to try on the OSSC?

    Any settings that might allow my TV to display it?

    What if I bought an EGA to VGA device, like this thing:

    https://www.amazon.com/gp/product/B06XFPCXDF?pf_rd_p=c2945051-950f-485c-b4df-15aac5223b10&pf_rd_r=647V3G4VK2TW4DJSP9RH

    #25278
    xtrasmiley
    Participant

    Bump, anyone with a way to test some other options or am I totally out of luck with the OSSC and S24?

    #25316
    Harrumph
    Participant

    The scan-rate and number of vertical lines is quite a ways from standard 1024×768 after doubling.
    You might have better luck going for WXGA (1280×800). Increase V.Active to 400, Increase H.Active to 640, adjust backporches as needed.

    #25321
    nmalinoski
    Participant

    Could the horizontal samplerate be increased slightly in order to bring that 992 up to 1024?

    #25324
    Harrumph
    Participant

    Oh I didn’t realise that was the default. Probably the samplerate doesn’t need to be changed, just increase h.active to 512 to achieve 1024×768.
    Edit: and if he wants to try 1280×800 like i wrote above, he needs to increase h.samplerate to 780-800.

    #25608
    xtrasmiley
    Participant

    Thanks for the tips guys, I’ll test it out and post the results!

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