Switching to CSYNC and Sync-on-Luma on the OSSC

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  • January 19, 2020 at 9:42 AM #34601
    jsteel
    Participant

    I was noticing a checkerboard pattern on solid colours from various consoles though the OSSC to my LCD TV. After switching to a different sync type (away from composite sync) the problem was resolved on all; NTSC NES (CSYNC), NTSC SNES (CSYNC), PAL SNES (Luma), PAL PS2 (Luma).

    My question is, that I want to make sure I’ve done the modification correctly for the OSSC, as I read that for example I shouldn’t be using TTL sync, and instead a 75ohm sync, but I’m confused if this is just for CSYNC, or Luma too?

    Firstly for the PAL SNES and PS2 which are using Luma, I’ve just got Luma going to pin 20 on the SCART, should there be any components on the line? One SNES diagram I found suggested Luma should have a 75ohm resister to ground (not in series); is that necessary and would that be true for the PS2 sync-on-luma too?

    Finally for the CSYNC consoles, my NES RGB has jumper 8 open so I believe that is outputting TTL, and an NTSC SNES outputs TTL, however I’ve read that both of these TTL levels are low and likely not dangerous for the OSSC, but in any case I’d like to be safe and add a 75ohm resister to the CSYNC line of the cable (one cable that I use for both of these). I just want to check that the right thing to do is add a 75ohm resister in series, and no capacitor and nothing to ground?

    I’d appreciate any guidance.

    Cheers

    January 19, 2020 at 6:50 PM #34611
    BuckoA51
    Keymaster

    Luma is basically half of the S-video signal so you won’t need to worry there, it’s 75 ohm consumer standard.

    For your NES, if you add the resistor and it was outputting 75ohm all along, the OSSC won’t be able to sync (most likely it will try and the LCD will keep flickering). In that case you can probably assume it was 75 ohm and remove your resistor… though really, testing on a scope would be the best way to tell.

    January 19, 2020 at 11:13 PM #34639
    jsteel
    Participant

    Thanks for your help, I’ll try a 75 ohm resistor on CSYNC and any trouble and I’ll remove it and be happy that it’s OK.

    Does Luma need a resistor to ground though on PS2? I cannot find a (Luma-based) pinout for the PS2 but this one suggests the SNES does, but I wonder if that’s just true for SNES, or PS2 also: http://www.jaskagaming.com/wp-content/uploads/2015/09/snes-scart-pal.png

    Cheers

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