M7264 Troubleshooting

Mister PDP vintagecomputersmn at gmail.com
Sun May 19 22:05:36 CDT 2019

This is a continuation of my post from about a week and a half ago. The
weekend I had some free time, so I returned, armed with a oscilloscope and
logic analyzer, to try and figure out what is wrong with my H11A. At first,
I tried to use the logic analyzer to confirm that the four clock signals on
the MCP-1600 chipset were working properly. After a day of confusing and
mixed up signals (I don't really use this type of equipment very often), I
realized that my logic analyzer was picking up the signals incorrectly. I
switched over to the oscilloscope and was able to see that the very basics
of the CPU were working. After that, I decided to try and find out why the
Run/Halt light was not coming on when I hit the switch. Looking at the H11
schematics, the light relies on the SRUN signal coming off of the
backplane. The problem I am currently facing is I cannot find where the CPU
board generates the SRUN signal. If anyone who is more experienced that me
knows how the M7264 generates the SRUN signal, that would be wonderful.

Thank You, Gavin

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