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teenix · (This post was last modified: 07-27-2022 01:58 PM by teenix.)

I did some experiments with my 67 emulator and if I fail the RAM at addresses 48 to 63 and only read 0's from this memory range, then I can recreate your problem.

It seems like the RAM in this address range has failed. I'm not sure which ROM IC this RAM belongs to as I haven't had a chance to read the 67 ROMs and run RAM tests for real yet.

Sorry :-(

Tony

EDIT:

It may be something simple like a dry joint on the DATA pin for this particular IC. The DATA pin transfers RAM data in and out of the device, it is pin #5. As mentioned, I don't know which IC has the problem, but you might consider checking for corrosion on the ROM IC's. If you are handy with a soldering iron, I would try re-soldering pin #5 on all the ROM ICs.

ID's for these 8 pin IC's are probably: 1818-0231, 1818-0232, 1818-0550 and 1818-0551.

Try not to touch the component connections on the board, the IC's can be damaged by static from your body.