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:
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.
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.
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.
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.