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Advice needed on SX-64 repair.


Jan 9, 2014
I recently picked up an SX-64 that wasn’t working. I‘m not as good at diagnosing electronics or as familiar with Commodore systems as I’d like but I did some reading and got stuck in.

The computer starts to a white screen with no text or border. My first thought was the PLA so I ordered a modern replacement which is currently in the board. That did not change anything but a dead test cartridge showed what I _think_ is two flashes. I looked it up and that should mean the 4164 in UB4 is bad. I replaced the chip to no effect. Thinking I wasn’t interpreting the dead test output correctly, I also replaced the three RAM chips associated with one flash (Maybe what I thought was two flashes was one and a reset). Still no joy.

Attached is a picture of the main board as it now stands. UA4, UB4, UA7, and UB7 are socketed and replaced. I’ve double checked my solder work and I don’t think there are any cold joints, etc. The PLA is a modern replacement. I’ve checked the blue caps by the RAM with a multimeter and they do what I expected (Start at 0 ohm and go up) so I think they’re ok. I understand that the VIC could also cause a white screen but I’m hopeful about it because dead test gave a result.

Can anyone suggest something to try next? Any advice would be appreciated.



Veteran Member
Jan 30, 2012
Connecticut, USA
alot of the problems with most sx systems and mine when i got it was the connexting boards were not connected well. cleaned the xonnectora and made sure they were tight then i started aeeing life in the machine.