Pdp8 8k core repair

Repairlog PDP8/f

Our PDP8/f seems to have problems with its two corestacks. bank 0-3 are taken care of by a Keronics 812075A, a onr board/two slots memory card. Bank 4-5 is a DEC MM8-EJ 8k cardstack of three cards. As we have the docs for the 8k MM8-EJ stack, we started troubleshooting that one first

MM8-EJ

Adresses ending on xxx4 or xxx5 all return zero data, so something is wrong in the adress decoding part or in the stack itself. checking continuity on the X-Y lines of the stack is the first thing to check.

a test with our DSlogic analyzer reveiled a broken 7442 on position E59

wrong logic results

after desoldering the suspected chip

New and old chip

and replacing the chip with a spare did the job.

That was easy...