Everdrive N8 not working with square button Famicoms?

Discussion in 'Everdrive N8' started by harry1038, May 2, 2014.

  1. harry1038

    harry1038 Active Member

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    Hello, I've just received my Everdrive N8 (Famicom version, OS v9.1), but when I tried to run it with my square button Famicom (sbF), it kept getting stuck at startup, sometimes displaying blue, or orange, blue-grey or grey. I then tried to run it on a regular (but still early, with a plastic cart slot) Famicom and it worked! The games load properly and are fully playable, no issues at all. I then put the cart back in the sbF and it now kind of displays the Everdrive menu, but with weird graphics. I tried pressing down and start to try booting a game but it doesn't work, it's stuck in the glitchy menu, so it's probably not a video signal issue (I'm using 80's freak av mod for both Famcioms btw). I should also point out that official cartridges, including the FDS RAM Adapter, still work as usual on the sbF. Here are pictures of both Famicoms after booting the ED N8:

    sbF:

    [​IMG]

    regular Famicom:

    [​IMG]


    I tried reflowing the sbF's cartridge port but it didn't change anything.

    Do you have any idea where the problem might come from?
     
    Last edited: May 2, 2014
  2. Calpis

    Calpis Champion of the Forum

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    It's an electrical (signal) issue, perhaps the switching threshold is higher on the original chip revisions which the 3.3V ED can't reach or something.
     
  3. harry1038

    harry1038 Active Member

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    Then you're saying this particular Famicom's voltage may be different than the others? I have a multimeter, could you please tell me where to check the voltage that is delivered to the ED?
     
  4. Calpis

    Calpis Champion of the Forum

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    No, the input threshold voltage can't really be measured since you'd need to observe the output of the chip's input buffers to see at which voltage they change, and these outputs are internal to the chip. This is the voltage at which the inputs start to logically resolve to a 1 instead of a 0. I'm sure the ED will output <= 3.3V signals since it's powered by a 3.3V supply, but it very well may be that the early PPU chips need 4 V or higher to switch reliably. If that's the case, there isn't a perfect way to fix it. A quick fix may be to solder pull-up resistors on the offending signals (difficult to diagnose since nothing can be measured) and even if it seems to work, there may be other intermittent problems because the electrical characteristics of the line will change for the worse with the pull-up resistors. It might be easier to just swap the early CPU/PPU with later revisions, or just the entire PCB.
     

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