RGB bypass problem. Please help.

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  • January 17, 2019 at 11:32 PM #24869
    Guineahog
    Participant

      Hi, I got a Voultar Sega RGB bypass revision 2 today and I’m having some problems.

      Mega Drive 1 VA6 PAL.

      I put a vid on YT so you can see what’s happening.
      My problem.

      The guide didn’t make much sense to me so I installed it like this:
      RGB bypass install
      You’ll have to excuse the shoddy soldering; I’ve been messing about with this too much today.
      The R, G, B, and sync are taken directly from the VDP and the pins are lifted.
      Voltage and ground are taken from c72.
      R, G, and B, are routed from the bypass board directly to the corresponding pins of the DIN.
      The sync is taken from the bypass board directly to the composite pin of the DIN (because my SCART cable uses that for sync).
      VDP pin 50 is lifted.

      DIN
      On the back of the board the traces for composite, sync, audio, R, G, and B, are cut near the DIN.
      The DIN voltage and ground are stock.

      On top of the video going black, the picture quality doesn’t seem to have improved at all.

      Anyone got any suggestions?

      January 18, 2019 at 12:14 AM #24871
      Guineahog
      Participant

        Update (I know, it hasn’t been long).
        I’ve discovered that if I manually change the source on the TV to SCART, then switch on the Mega Drive, the picture freaks out (this is not normal behaviour and didn’t happen before the mod).
        But, if I leave the TV on an HDMI source and switch the Mega Drive on, and let the TV change to SCART by itself, the picture behaves normally.
        I still have no idea what’s going on, or how to fix it.

        Hmm…
        Is the TV trying to change channel… voltage drop… or voltage fluctuation on the aspect ratio select line??

        January 18, 2019 at 10:37 AM #24875
        nzChris
        Participant

          I would try taking power and ground directly from the voltage regulator, its the 7805 closest to the front of the unit.

          January 18, 2019 at 10:40 AM #24876
          Guineahog
          Participant

            Power and ground for the bypass board or the DIN… or both?

            January 18, 2019 at 11:43 AM #24877
            nzChris
            Participant

              Power and ground as they go into the bypass board.
              It can be tricky to solder to these pins but I have heard Voultar recommend taking power and ground from here many times.

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