PDP-11/44 Restoration

This winter RICM has undertaken the restoration of a PDP 11/44.

The PDP 11/44 was the last PDP 11 designed with discrete logic for the processor.


    • Installed a DD11-DK 9-slot Unibus backplane that was removed from a spare BA-11 chassis.
    • Installed a M9300 Unibus terminator in slot 9 of the DD11-DK backplane.
    • Interconnected the two Unibus backplanes with a M9302 Unibus jumper.
    • Installed G727A jumpers in the Unibus slots where the NPR jumper was intact and installed G7273 boards in the Unibus slots where the NPR jumper was cut.
    • Both RA81 disks power up. The lower one has a flakey circuit breaker. They don't go ready so heads are probably locked.
    • The system powers up and the RUN LED and the LED on the M9076 MFM board both go on for a few seconds. Looks promising.


    • Installed two M8722 MS11-MB 256KW memory boards from MT's collection.
    • Installed the two boards for a UDA50 from MT's collection, the red SDI cables, and the SDI bulkhead from RICM spares.
    • The console cable was missing so we made one from a spare DL11 console cable and the connector housing from an Ethernet cable. We lucked out when we found that the plastic Ethernet connector housing and the one for the console cable were the same. We wired the console cable for DCE and used a male DB-25 connector so we don't need to use a null-modem cable to connect it to the terminal.
    • We tried two VT220 terminals and found that both work. We will use the green screen one for the console.
    • The console baud rate switches on the M9076 MFM board looked wrong so we took the easy path and set them all open for 19,200 baud.
    • We checked the settings of the M7090 Console Interface board. The jumpers look OK, but we found that one of the leads on the transistor Q1 was broken. Transistor Q1 is for the 20mA interface so we gave it a try as is.
    • On power up we saw nothing on the console, but the led on the MFM board indicated that data was being sent to the terminal. We installed an M7090 from MT's collection. On power up we saw some garbage on the screen and then ?22 CP H