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DEC PDP 8/e MM8Ej RAM (8K) Repairs


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  DEC PDP 8/e MM8Ej RAM (8K) Repairs by Bill Degnan - 11/21/2022 12:38
PDP 8e with H-19 terminal on the ground, displaying a directory from RK05 diskpack. Click image for larger view.

This thread will document the current progress with the PDP 8/e located at Kennett Classic. It's the same system written about earlier here.

The current issue is that the system boots from RK05 diskpack 0, but the MEMORY command says only 8K RAM is available, even when more RAM is installed. 8K is not enough for any useful operations on this system.

The proper next step is to run the MAINDEC DEC8X diagnostics, which naturally bombs without more RAM in the system. Love the classic chicken and egg DEC troubleshooting problems.

So, we have to experiment.

First, I confirmed that power to the backplane was still OK. Good.

Each 8K core memory stack consists of three controller cards. I set out next to confirm that I have the correct EMA jumpers on each core stack G111 controller. I have enough core stacks for 32K. The jumper configs for a 32K set of MM8Ej RAM is: 0-8 IN IN IN; 9-16 IN OUT IN; 17-24 OUT IN IN; 25-32 OUT OUT IN.

Next, I determined that I have a good first 8K stack. The core stack wired for the 2nd 8K must be faulty someplace. This means I have to switch cards around and see if I can identify the faulty component(s).

More to come.



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