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.
