NESRGB / Twin Famicom problem

Discussion in 'Modding and Hacking - Consoles and Electronics' started by Romi, Feb 12, 2018.

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  1. Romi

    Romi Active Member

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    Hi all,
    I'm done with modding a TWIN Famicom and I have an issue I can't get to troubleshoot.

    I'm using the the original RF modulator port.
    The issue is I have small interferences particularly visible on the blacks (I can't see them on any color). Like tiny white dots all over the place.
    Where it gets strange is that I can remove those interferences by plugging either of the original composite port (image or sound) to any composite port on my tv.

    I've ruled out sync issue because the issue is exactly the same whatever sync I use.

    I even isolated the video composite port by removing r214, but still, interferences are here and disappear when plugging a jack.
    To be specific the jack needs to be plugged both ways. If it's plugged to the Famicom but not to the TV the interferences are back.

    I just don't understand how those ports I'm not even using could have that effect.
    Do you have any idea?
     
  2. Romi

    Romi Active Member

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    Small update, I've changed my wires to a slightly bigger caliber and it made things much better.
    The problem is still there though and plugging the RCA still fix it.

    Could the RCA somehow act as a capacitor?
     
    Last edited: Feb 12, 2018
  3. Romi

    Romi Active Member

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    Just to clarify my previous posts, here are some images :

    Twin Famicom W/ NESRGB using RF Out Port. No RCA plugged in :
    [​IMG]

    Twin Famicom W/ NESRGB using RF Out Port. Either RCA plugged in :
    [​IMG]
     
  4. Jord4n313

    Jord4n313 Member

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    I don’t know much about the NESRGB, but from my basic electronics knowledge, I would think it has to do with the composite cable acting as a ground between the monitor and the NES.

    If I were you I would ensure you have a nice solid ground connection and maybe use a higher gauge wire for ground.

    That’s the only thing that makes since in my head for why the composite connection would make a difference.

    Edit: I mean a good ground on the RGB port and the RGB cable (Scart, bnc, whatever)
     
  5. Oakleaf

    Oakleaf Spirited Member

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    as abowe, but also change the caps inte the PSU part of the twin. they are often bad, resulting in interference getting in the sync signal/composit. if that dosent do it. try adding a 220uf-330uf cap inline on the sync your using.
     
  6. Romi

    Romi Active Member

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    Thanks guys,

    A guy on the nesdev forum has also pointing me to an issue on the ground line. I have tried rewiring my ground pin to other point in the NESRGB board and directly on the Twin Fami (on one of the composite out port).

    The issue is in fact worse (more visible dot) when the ground is connected directly to the NESRGB.

    in both cases the problem completely disappears when either composite is wired to the TV.

    My contact on nesdev is now convinced something is wrong with either my Scart Cable, or with the connector itself. I have ordered a new, better quality cable.

    I will also change the cap, it's actually something I should have done to start with.

    Again thanks,

    Romi
     

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