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Voltmeter should work, hopefully. If yours has a logic tester that'd be ideal, but otherwise, measure the pin Vdc relative to ground and +5V, and Vac relative to either. If V(A0)-V(gnd) is 0V or 4V and Vac is 0V, the CPU actually crashed instead of a software infinite loop. If V(A0)-V(gnd) is 2ish ...

Crashes like what you're seeing imply only the CPU is having a problem. It's hard to say much more without better testing equipment, but it's remotely conceivable that the CPU RAM is slightly damaged. You might check after a crash to see if CPU A0 is high, low, oscillating, or floating. That part i...

So I'm posting here as a bit of a last resort as I'm at a dead end with getting this console working correctly. The initial problem was the blinking power light issue, but that was solved by correcting the height of the cartridge when it's pressed down. The current issue is that the output from the ...