SNES 1-Chip S-APU problem

Discussion in 'Repair, Restoration, Conservation and Preservation' started by playfortoday, Nov 7, 2017.

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  1. playfortoday

    playfortoday Member

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    Hi there!
    I've got a PAL SNES 1-chip that wasn't turning on. Replaced the fuse and the voltage regulator.
    Now it powers on, but won't boot games. The only one i tried which almost boots is super sf2 but only the first screen with copyright info appears, then it stucks.
    I've managed to boot the test cartridge and it says the APU failed. In fact i can't hear any sound, neither on another test cartridge.
    [​IMG]
    [​IMG]
    Any solution?
     
  2. josiahgould

    josiahgould Spirited Member

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  3. TriMesh

    TriMesh Site Supporter 2013-2017

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    There really isn't much to troubleshoot - on the 1CHIP, the whole audio section (DSP, SPU and the RAM) is integrated into a single chip.

    If you have another console handy, then you can try swapping the ceramic resonator that's just below the S-APU chip (it's marked X2, I think) - I've seen a few machines where those went bad.
     
  4. playfortoday

    playfortoday Member

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    Mhh... i swapper almost every capacitors. Almost same results. Almost because the error on the diagnostic was always "BB". Now it changes: "00", "55", "BB".
    I don't have that X2 part for spares, but if you say that can fix it i might buy one. In that case i'll need to know what component is that :D
     
  5. TriMesh

    TriMesh Site Supporter 2013-2017

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    It's a 24.576MHz 3-terminal ceramic resonator - but good luck finding one anywhere except on another SNES board...
     
  6. rama

    rama Gutsy Member

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    Unfortunately, these S-APU tend to blow. I have one such console here as well.
    I traced out all the connections and made it work again with a donor original APU module :)
    It's just a proof of concept though, way too many wires for my liking and even then, it needs additional logic for some delayed reset for the CPU. The S-APU was supposed to do that but yea..

    [​IMG]
     
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  7. TriMesh

    TriMesh Site Supporter 2013-2017

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    Honestly, it probably is the chip - I mentioned the clock resonator because it's much easier to change than the sound chip, and you really feel like an idiot if you find out that was the problem after you have already replaced the IC.
     
  8. rama

    rama Gutsy Member

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    Lol, I bet xD
    I did check on mine, thankfully. It's part of the activity check routine I like to try first.
    What I didn't know at the time (when the chip was still installed), was that the CPU requires an extra reset pulse that's supposed to come from the S-APU.
    I'll probably install it again and see if at least that functions.
    I'd hate to do all those wires for the APU module install, and then put an additional Arduino in there, just for some reset generator thing.
     
  9. TriMesh

    TriMesh Site Supporter 2013-2017

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    I have also seen cases where a dead chip will stop the oscillator from working, so that's a test that only works in one direction - if it's running, then the oscillator has to be good, but if it's stopped it's not necessarily bad.

    In this case, it wasn't running and I just assumed that the chip was the problem.
     

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