[Suggestion] Documenting and translating the "2-Chip" SNES RGB fixes

Discussion in 'Modding and Hacking - Consoles and Electronics' started by lordnoc, Feb 21, 2017.

  1. rso

    rso Gone. See y'all elsewhere, maybe.

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    Are you able to break down for us what the basic idea is behind the mod? Because I'm useless at interpreting those circuit photos and can't even tell which of the diagrams posted apply to what he did and which are just "tried this, didn't work" addendums.
     
    Last edited: Feb 21, 2017
  2. syboxez

    syboxez Active Member

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    Basically, the mod is modifying the circuitry right after PPU2. It's a bit easier if you look at the SNES schematics as a reference: http://forums.nesdev.com/viewtopic.php?t=10470

    Look at where Q3, Q5, and Q7 are to the right of PPU2 (on the schematics) connected to PPU2's RGB outputs.
     
  3. rama

    rama Gutsy Member

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    It's an overdrive circuit. Sharp pixels are square waveforms but the PPU2 only outputs heavily filtered "sine-like" waveforms.
    This circuit takes the input and overdrives the rising flank to make it appear sharper.

    Edit: It tries to create a waveform like my profile pic by making the overshoot much bigger ;p
     
    rso and zzattack like this.
  4. Unseen

    Unseen Spirited Member

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    Does it always reach the intended level, even for large transitions like alternating black/white pixels?
     
  5. rama

    rama Gutsy Member

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    I forgot what the signals looked like, sorry. The circuit does clamp the overshoot though.
    I did some image captures back then, using an S-Video capture card. Here's the album:
    https://imgur.com/a/JxZo0

    Note that the quality drops when stuff is in motion. Pixels get kind of jittery, colors are a little misplaced. Composite Video becomes awful with more dot clock artifacts than actual colors.
    Also the mod adds jailbars. Probably because it routes the weak signals through quite a lot of components and nothing is balanced for impedance.
     
    Last edited: Feb 22, 2017

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