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Advice needed on SX-64 repair.

trr94001

Member
Joined
Jan 9, 2014
Messages
33
Location
Connecticut
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.

Thanks.
 

VERAULT

Veteran Member
Joined
Jan 30, 2012
Messages
5,079
Location
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.
 
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