DEC PDP-11/35 #2 Restoration


The processor chassis is a BA11-KA. This is an empty Unibus chassis with a power supply. This chassis doesn't have any provisions to mount a KY11-D blinky-light programmer's front panel. The other PDP-11/35 in the collection already has a front panel mounted. Instead of making brackets to mount the front panel on this system we will merge the two 11/35 systems that we have in the collection.

This 11/35 has all of the possible processor options. It will be easiest to debug the system by installing the least number of processor boards, getting that working, and then adding and debugging more processor options. There is a M9312 Bootstrap/Terminator board in this system. We can run the console emulator (ODT) option from a ROM on this board. That will allow us to use PDP11GUI to transfer diagnostics and eventually an operating system to the system. When we finally get this system running we will probably run UNIX V2.9 and a DEC operating system.

This machine has the board set for a VT40, the same boards that are used in a GT40 graphics terminal. That means we can run Lunar Lander if we get a light pen.

The complete system is similar to a DEC GT44 Graphic Display System. To make a complete GT44 we would need to add two RK05 disk drives. We will probably add two RL02 disk drives that each have 5x the capacity of an RK05 disk drive.


We mounted PDP-11/35 #1 chassis in the rack in place of the BA11-KA chassis. In the process of merging the two systems we found that the VT11 backplane has the larger power connectors used in newer PDP-11s. It would be quite a bit of work to cut the backplane power harnesses and put new connectors on. The power supply in the PDP-11/35 is also broken.

We have a mongrel PDP-11/40 chassis with a PDP-11/23 inside that we got from Fairfield University. That is another choice for a chassis for this machine. We could put the original PDP-11/40 CPU board set and backplane in that chassis. We have three 11/40 consoles so we should be able to get blinky-lights working.


We looked at  the 11/40 chassis in the warehouse. It had 9-slot and a 4-slot Unibus backplanes installed. These are of no use with the 11/23 Q-Bus processor and primary backplane so we removed the two Unibus backplanes. We should be able to install the 9-slot Unibus backplane in the PDP-11/35 chassis and use the power harness from the 4-slot Unibus backplane to power the VT-11 backplane.


We did some research on the MF11-L 9-slot Unibus backplane that we removed from the mongrel PDP-11/40 and had planned to use in the 11/35. Apparently this backplane is for core memory and is not a generic Unibus backplane. Maybe we can use the power harness from this backplane on the 9-slot that is in the BA11 chassis?

We powered on the 11/35 chassis. No lights and no response to switches. We measured the voltages on the backplane power connectors. -15V is on all connectors. +5V is on the left 4 connectors, but not on the two connectors for the processor backplane. Looks like we need to disassemble and repair the power supply. One of the DEC docs says that the larger 11/05 chassis uses the same power supply. I believe that there is one on the RICM warehouse. Maybe that H750 works better.


We tried to power on the BA11-KA chassis that contains the PDP-11/35. No luck, no signs of life at all.