(Topic ID: 196740)

Stern mpu 200


By gregh

2 years ago



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  • Latest reply 2 years ago by gregh
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#3 2 years ago

Immediate crash after 7-flashes is, in my experience, possibly due to bad NMI (Non-Maskable Interrupt) from the 555 timer IC (little 8-pin DIP). The NMI is supposed to tell the MPU to scan the switch-matrix, and strobe the displays, lights, etc., but if it's coming too fast it will crash the 6800. Could be the 555 itself, or associated capacitors/resistors. Alas, short of shotgunning parts (replace and see if it helps), you'd need a scope to diagnose this failure.

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