32X Scrolling bars issue

Discussion in 'Repair, Restoration, Conservation and Preservation' started by phillip, Jun 12, 2018 at 8:07 PM.

  1. phillip

    phillip Member

    Joined:
    Dec 13, 2015
    Messages:
    15
    Likes Received:
    0
    Hi all. I'm having a problem with my 32X with 2 horizontal bars that scrolling vertically upwards during gameplay. Below is a youtube link to a video so you can see what it looks like. (view the video full screen, otherwise it looks wrong with wavy lines.)



    More details:
    >Using the 32X with a model 1 Genesis.
    >There is a moderate humming sound that accompanies the scrolling bars.
    >I just replaced all capacitors on the 32X but observed no improvement with the scrolling bars.
    >I tried using a different AC adapter with the 32X with no success.
    >The 32X is s-video modded. (http://retrotimegames.com/page12.html)
    >The 32X, s-video mod and all, works perfectly as a pass-through for Sega Genesis games. No bars, no humming sound.
    >I've tested the 32X with a different Sega Genesis, an unmodified model 2, and it has the same issue.
    >The issue *may* be related to me using an overclock halt-switch on the Sega Genesis when a 32X game was being played, as the issue first appeared around that time and worsened after that. The system was not overclocked when playing a 32X game, however.

    Thanks for any and all help!
     
    Last edited: Jun 13, 2018 at 5:36 PM
  2. takeshi385

    takeshi385 Mojarra Frita Bandit

    Joined:
    Mar 29, 2011
    Messages:
    1,820
    Likes Received:
    134
    It could be ralated to the luma line on svideo.
     
    Last edited: Jun 12, 2018 at 11:00 PM
  3. phillip

    phillip Member

    Joined:
    Dec 13, 2015
    Messages:
    15
    Likes Received:
    0
    I don't think it is. If it were, why would it only affect 32X games and not Genesis games?
     
  4. teckman02

    teckman02 Active Member

    Joined:
    Jul 4, 2017
    Messages:
    32
    Likes Received:
    5
    do you have the RF shields clipped in between the model 1 and the 32x
     
  5. phillip

    phillip Member

    Joined:
    Dec 13, 2015
    Messages:
    15
    Likes Received:
    0
    I don't have the RF shields that go between the 32X and Genesis, no. But I never had them and the 32X worked fine for months before the issue showed up. Also, I've read/seen videos that say the RF shields for the Genesis cart slot are unnecessary.
     
  6. CkRtech

    CkRtech Spirited Member

    Joined:
    Sep 10, 2014
    Messages:
    132
    Likes Received:
    34
    That looks like a typical 60Hz bar/ground loop. Check all your grounds inside and out.
     
  7. phillip

    phillip Member

    Joined:
    Dec 13, 2015
    Messages:
    15
    Likes Received:
    0
    My research initially led me in that direction as well. I'll look into it some more. Any tips on how to avoid a ground loop in general?
     
  8. CkRtech

    CkRtech Spirited Member

    Joined:
    Sep 10, 2014
    Messages:
    132
    Likes Received:
    34
    I once had a ground loop problem around 1998 (wow... it has been awhile). I had a TV, DVD Player, stereo receiver, and coaxial cable from external wall connecting through a set top convertor box - a device that also used power. I can't remember exactly how I solved it (sorry - it was 20 years ago). I want to say that issue was due to the coaxial cable/Tuner part of the circuit. And I may have added extra components to the circuit to reduce it or remove it.

    On the other hand, it is also possible I was using mains plugs on both sides of the room for the equipment due to how everything was wired, and that caused a problem.

    I would try to baseline it - Make sure you have everything (TV, Sega Genesis + 32X) plugged into the same outlet. Hook up video only for now using your modded output - don't connect audio, and try a 32x game. If it looks like external possibilities have been eliminated in terms of wiring, you probably want to look internally.

    Did you ground both luma and chroma lines as well as the shell for your jack inside the 32X?

    What happens if you put in a 32x game (Virtua Racing) and don't use the passthrough cable from the Genesis? Does the 32x output its part of the video signal with the same problem?

    It would seem these two items perhaps eliminate your overclock halt suspicion since it also happens with an unmodified Model 2?
     
  9. phillip

    phillip Member

    Joined:
    Dec 13, 2015
    Messages:
    15
    Likes Received:
    0
    Thanks for the detailed reply. I'll hit this troubleshooting on the ground loop possibility hard tomorrow. I did ground everything in the s-video mod but I grounded it to the RF shielding and I think it's worth trying to ground it somewhere else on the board.

    The reason I mentioned the halt-switch was because I was concerned that perhaps using the halt switch on the Genesis while the 32X was running a game may have damaged the 32X system. I have no idea if that is a reasonable possibility, however. Just a suspicion.
     
  10. phillip

    phillip Member

    Joined:
    Dec 13, 2015
    Messages:
    15
    Likes Received:
    0
    Had a bit of an "ah ha!" moment today whilst troubleshooting. I haven't fixed it just yet but I think I know how.

    I have to pop open my Genesis to check, but I think I have both the S-video mod and stereo audio mod on the Genesis grounded on the RF shielding of the Genesis. Perhaps because both the audio and video of the Genesis are both being output to the 32X, which then grounds the video again before outputting to the TV, it's creating a ground loop?

    I feel stupid for not mentioning the Genesis S-video and stereo audio mod in the original post. My apologies. Thanks for the guidance. I can't wait to tinker with things. Unfortunately, I'm out of time today as I have an obligation this evening. I'll report back as soon as I've had a chance to try some things out.

    Thanks!
     
  11. CkRtech

    CkRtech Spirited Member

    Joined:
    Sep 10, 2014
    Messages:
    132
    Likes Received:
    34
    I wouldn't ground them to the shield. I would find a close ground point on the board and use that. Good luck with your endeavor!
     

Share This Page