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PDP 11/40 M7234 TIMING CPU Card Fail


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  PDP 11/40 M7234 TIMING CPU Card Fail by Bill Degnan - 09/25/2019 09:37
PDP 11/40 TIMING module DEC 5380 SN20628N 2-input NOR removed
Closeup of a PDP 11/40 TIMING controller card, M7234 where a Dual NOR DEC 5380 SN20628N 2-input NOR chip has been removed. It caught fire. A replacement chip was pulled from donor M7234 and the card appears to be working correctly again. Click image for larger view.

Full disclosure - I accidentally plugged the M7234 into the wrong UNIBUS CPU backplane slot, ug. Too much juice to the chip fried it.

Using three sets of 11/40 CPU controller cards I had been swapping cards around in the effort to get an EIS CPU card (M7238) running. The EIS is necessary to boot UNIX but I have been unsuccessful in finding a working set of CPU boards that like the EIS installed.

If you're familiar with the 11/40 CPU card set you may have been through the complicated jumper combinations necessary so that they all work correctly together. I need to recheck everything to compile a working base CPU configuration. Once I get back to a base CPU set I can run more complex diagnostics.



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