Re: Is my Tek 468 beyond repair?


Roger Evans
 

John,

I was initially surprised that Reset out was low but that is correct since 8080 peripheral devices have an active high reset pin!

A couple of tests for next time you are looking at the scope:
Check that RST7.5 is 50kHz not 500kHz. 500kHz would indicate that U440 is dead and would probably saturate the processor with interrupts.
Check that pin 14 of U472 is also high so that we are not looking at a failed U472
Measure S0 and S1 (pins 29 and 33), that might show that the CPU had executed a HALT instruction and had at least done something after Reset.

The GPIB interrupt stuck high does need tracking down.

Regards,

Roger

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