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C64 250407 No Sync even after replacing numerous parts?

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    C64 250407 No Sync even after replacing numerous parts?

    So, I was using this machine a few months ago and, while listening to some SID music, the screen suddenly went black. I tried rebooting it, but there was no sync. I've replaced the following chips with known good ones to no change:
    6510 CPU
    6567 VIC-II
    PLA (It has the 82S100 in it right now)
    556 Reset Timer
    7406 at U8
    7805 5 volt voltage regulator

    Nothing else I've seen can cause a no sync issue, other than the RF modulator and the 4 chips next to the VIC. Is there a way to test the RF modulator so I don't waste any time or risk the board replacing the 4 chips next to the VIC? Thanks!

    (I also have a newer board with the 8701 that has the same no sync issue, I replaced the 8701, but it didn't change. I plan on swapping U27 next since it's a MOS 7712, but if I should look elsewhere, I'd appreciate advice. Thanks again!)
    Looking for: Tandy TRS-80 Model 100/101/102, PowerBook Duo 230 or 180C, old Commodore stuff (disk drives, cartridges, etc.)

    Did you do any other tests before randomly swapping chips?

    You say "no sync". The C64 can output via RF, Composite and S-Video. Did you try them all to narrow-down the problem?


      I tried seeing if the 1541 initializes on boot, and it looks like it does. I did temperature checks and the 6510 was hot to the touch within a few seconds, which is why I assumed it had failed. I checked the voltage regulator before swapping the CPU and it was low (around 4 volts), so I think the CPU had an internal short that broke something else (or vice versa). I swapped it mostly because I don't trust the 30+ year old regulators. Most fail open, but I've seen enough that failed closed to not trust them.

      I've tried via composite and RF and neither worked. I don't have a cable (or TV) for s-video, but I'm guessing if composite doesn't work, s-video won't either. RF doesn't change on power up, and composite doesn't give the flash it usually does on power up.

      Looking for: Tandy TRS-80 Model 100/101/102, PowerBook Duo 230 or 180C, old Commodore stuff (disk drives, cartridges, etc.)


        Get a dead test cart and use it.
        Also look at Ray's Site for chips vs symptoms.

        Black screens are the hardest to diagnose without a deadtest cart.

        Article on blank screen 64s.

        Repair guides.

        Head over to lemon64 forums for tons of 64 help if needed.