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Apple ][ Plus ROM corruption or RAM issue?


Well-known member
I recently acquired a very strange Apple ][ Plus (let's just say the motherboard and power supply are the only original parts).

It seems to start up fine (so far I've only tested it with all the cards removed), but many actions will cause it to crash to the monitor or get stuck printing "?FORMULA TOO COMPLEX".

I'm suspecting there's something wrong in either the RAM or the ROM, but I haven't been able to play around with it much due to an injury. I have a feeling I'm going to have to lug out my IIgs to make a diagnostic disk using ADTPro, but that's assuming the disk card and drives work in this Apple ][.

Any suggestions on what to try first? I did a readout of E000L from the monitor and marked some bytes that are incorrect, but I can't make out a pattern that would imply a bit is stuck or something.