C64 Cartridge port not working

[JoeGUSA]

I received my Diagnostic / Dead Test cartridge this weekend. I put it in the dead C64, and nothing happened. I'm pretty confident now that replacing the PLA will resolve that issue in that unit.

Just to make sure the cartridge was working, I put it in another working C64. It wouldn't see the cartridge or show anything on screen, so it appears that the cartridge port on that unit is faulty. Since the only cartridge I have is the diag / dead test, I tested the cartridge by putting it in a third working C64, and it works fine. So it's not the cartridge.

I checked continuity on all of the pins on the cartridge port, and they all checked out twice. The system boots fine, shows the correct amount of memory, and it passes other tests performed via software only. I just can't test the cartridge port or boot from it. On another Commodore discussion board, a member instructed me to connect a wire to pin 9 with the other end grounded in order to check the EXROM line. He also said to expect to see that the memory is 30719 when booting if the EXROM line is good. I ran the test, and after this connection it booted showing 30719 of memory. It returned to the normal amount of memory after disconnecting the wire.

I'm at a loss as to what to do next. Does anyone have any ideas what to check next?

Thank you

Joe

[rbernardo]

Heh, my suggestion is to send the board to Ray Carlsen for him to repair.

Truly,

[JoeGUSA]

Actually, Ray has been helping me diagnose the cause of the problem via remote (email). I'm getting close (per Ray).

Joe