PDP-12 Restoration at the RICM

Michael Thompson michael.99.thompson at gmail.com
Mon May 25 19:07:04 CDT 2015

Today we pulled all of the M113 flip-chips and tested them because SN7474
and SN7400 ICs seem to be a problem in these early DEC systems. The ones in
slots J33 and K30 were bad. Replacing them fixed the problem with the JMP
instruction. We did some more testing with the toggle-in programs and found
that ISZ cleared the AC. Replacing the M119 in slot H28 fixed that. All of
the toggle-in tests pass, so the processor is substantially functional.

Core memory in field 1 with addresses X5XX didn't work. We replaced the
G221 in slot D10 to fix that.

We tried the ASR33 Teletype that came with the system. The mechanics were
sticky from not being used for 30 years, but we got most of it free and
working. We could send characters to the Teletype, but could not receive
anything. The M706 receiver failed in the board tester. The spare is also
broken, so we need to fix both.

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