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Famicom AV Grey Screen Fix?

Discussion in 'Repair, Restoration, Conservation and Preservation' started by Marmotta, Feb 17, 2017 at 11:35 AM.

  1. Marmotta

    Marmotta Intrepid Member

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    So, I got a super cheap Famicom AV, which was sold to me on the premise that it was completely dead, which it was, but I thought why not try and fix it. Despite the steps I've taken to revive it, I can only get a grey screen out of it when I turn the console on. Here are the steps I've taken so far:

    - socketed the CPU and PPU just so they're easier to work with
    - tested the CPU and PPU on another console and confirmed they work fine
    - the pad for pin1 of the CPU had been stripped. The pin is AD1 and appears to connect to the resistor right next to it on the board
    - the pad for ground on C41 had also been stripped. I just connected it to the edge of the board.
    - Q1 was missing. I replaced it with one from another working console.
    - C20, C40 and C41 appeared damaged. I replaced them, but the capacitors I used in C40 and C41 are physically larger than the previous ones. The board indicates they're supposed to be 0.01 which I assumed was uF, but I might be wrong.
    - Replaced the LM7805 and main capacitor
    - Cleaned the cartridge slot, although it wasn't really dirty at all

    Any ideas that I could try to get the board running?

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  2. citrus3000psi

    citrus3000psi Housekeeping, you want towel?

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    Here are some spots I would investigate. The Bottom arrow, that trace looks cut 100% from the picture.

    The other areas, I'd clean up and make sure nothing is bridged. I've accidentally bridged a near by trace with a pin. So go through each pin and make sure there is no continuity next to traces that are close. Sometimes the flux makes these areas hard to see.



    Mk5MNuy.jpg
     
  3. Marmotta

    Marmotta Intrepid Member

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    I cleaned up the areas mentioned, but couldn't find any bridges or shorts. I did notice that the pad for pin 4 of the CPU was in a bad state as well. It appears to just go to pin 13 of the cartridge slot, so I wired it up hoping that would fix the problem, but unfortunately not :-( The search goes on...

    [​IMG]
     
  4. Marmotta

    Marmotta Intrepid Member

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    I've checked whatever continuity I can within reason and also checked that the PPU and CPU are receiving the correct voltages, which they are. Next thing I'm going to try is to fit a Hi-Def NES to see if the issue is somewhere in the video output circuitry, which I suspect it might be.
     

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