PDP-11/40 Restoration 2025

10/29/25

We did an initial assessment of the PDP-11/40 cabinet and CPU chassis.

This chassis is S/N 385 so it has the older AC and DC power distribution design, and the older Programmer's Console.
The first power distribution backplane has two burnt connector contacts for the +5V source. The mating power connector is missing the two +5V contacts, and the housing is burnt where the two contacts go. We don't have any spare power distribution backplanes.
The power feed harness where it connects to the first power distribution backplane was modified to feed the PDP-11/23 backplane. Two +5V wires need to be reconnected to the first power distribution backplane connector.
There are only two +5V power supplies installed. If we install Unibus boards in the back of the chassis we will need to install a third H744 +5V power supply.

11/1/25

We removed the new design 21" BA11-F expansion chassis from the short DEC cabinet and installed it in a full height cabinet. It was amusing to see a Compaq label on the cabinet. This was actually quite a bit of work to move the chassis because of the large and heavy parts.
We installed a DEC 861C AC power controller in the bottom front of the cabinet. This controller can be remotely controlled by the key switch in the PDP-11/40 console.
We used a new design bracket to install the programmer's console on the chassis. I guess this now makes the BA11-F a PDP-11/40 CPU chassis.
We need to repair the AC power wiring for the fans in the power supply.

11/5/25

Remove all of the Voltage Regulator Modules from the H742 Power Supply.
Connect AC power the H742A Power Supply and measure the +5VDC and +15VDC outputs.
- They were OK.
Added upper fan tray from one of the unused PDP-11/45 expansion chassis.
Verify that all of the fans in the CPU chassis and Power Supply are working.
- One upper fan and one lower fan are seized and need to be replaced.
Install the H744 +5VDC regulators in slots A, B, and C one at a time and verify that they work OK.
- They are OK and were adjusted to +5.0VDC
Install the -15V regulator in slot D and verify that it works OK.
- It was adjusted to -15.0VDC

11/7/25

Repair AC wiring to the fans in the H742 Power Supply.
Replace one upper fan and one lower fan in the CPU chassis.
Find, install, and test another H745 -15VDC regulator.
Find an 11/40 Console to 861C Power Control harness, P/N 7009053, and connect it between the Console and Power Controller.
Check the Line Clock, AC LO, and DC LO signals that come from the H742A power supply.
Install the 11/40 CPU backplane and boards.
Install the Unibus expansion backplanes and I/O boards.
Power on the system and readjust the +5VDC and -15VDC regulators.
Find and install a P/N 7009573 Jumper Harness from the first SU power distribution backplane to the second.
See if the CPU will show some signs of life.

Backplane Connector Voltage Measurements

0
2.27
0
0
0
0

Backplane Connector Voltage Measurements

+5
+15
0.02
+4
0
0
0
0
0
0
0
0
-15
0.02
0

The pinouts or the two connectors that feed signals and power to the backplanes.

To Do:

Replace the modified filler panel below the front console with a normal filler panel. (Done 29-Oct-25)
Replace the damaged KY11-D Programmer's Console with an undamaged one. The old and new chassis have different Programmer's Consoles and mounting brackets. The power enable wires connect to the left side on the old design and to the right on the new design. (Done 29-Oct-25)
Remove the non-DEC power supplies that are mounted to the rear swing frame. (Done 29-Oct-25)
Remove the PDP-11/23 boards and Q-Bus backplane from the CPU cabinet. (Done 29-Oct-25)
Remove the Tektronix RM504 oscilloscope and lab power supply from the CPU cabinet. The idea was to install this oscilloscope in the PDP-9 as a future graphics display, but we really should use an RM503. We have several RM503 oscilloscopes in the warehouse to choose from. (Done 29-Oct-25)
It might be a good idea to use one of the newer design CPU chassis. The newer chassis design, S/N 5000 and up, has an improved power distribution system. We have the three of newer chassis. One is in an empty cabinet, and two empty ones in the PDP-11/45 expansion cabinets. If the newer chassis is an expansion chassis, it might not have the signals for the line clock wired to the CPU backplane, or the wires that go from the Programmer's Console key switch to the AC Power Controller.
If we use the older design chassis: (1-Nov-25 we decided to use the newer design chassis)
- Repair or replace the first power distribution backplane.
- Repair the first power supply to power distribution backplane connector on the power harness.
Repair the AC power wiring for the fans in the power supply.
Connect the terminals on the PDP-11/40 console to the remote input connector on the 861C AC Power Controller in the bottom of the cabinet.
Test and possibly repair the AC and DC power subsystems.
Test and possibly repair the upper and lower fans in the CPU chassis and in the power supply.
Install the PDP-11/40 CPU backplane and CPU boards in the CPU chassis. Leave the KD11-E EIS Option, KD11-F FIS Option, KT11-D Memory Management Option, KJ11-A Stack Limit, and Kw11-L Line Time Clock boards out of the CPU backplane for the initial testing. Note: There are a bunch of jumpers that need to be changed if these options are left out.
Install the M9312 Bootstrap/Terminator in slot 9AB of the CPU backplane.
Test and possibly repair the KY11-D Programmer's Console.
Test and possibly repair the KD11-A CPU. Note: The 11/35 has another CPU board set, and Mike has another CPU board set at home.
Test and possibly repair the DL11 Asynchronous Line Interface Board.
Install the I/O expansion backplane in the CPU chassis. Move the M9312 to slot 16AB in the expansion backplane and install a M981 Unibus Jumper from slot 9AB to 10AB.
Perform simple tests on the MS11-LD 128kW MOS Memory board and possibly repair it.
Connect a laptop to the DL11, load PDP-11 GUI and verify that the CPU, Memory, and I/O board diagnostics run OK.
Verify that the minimal CPU board set, the MS11-LD 128kW MOS Memory, and any of the I/O boards that are in the expansion backplane pass diagnostics.
Install the KD11-E EIS CPU Option in the CPU backplane and verify that it passes diagnostics.
Install the KD11-F FIS CPU Option in the CPU backplane and verify that it passes diagnostics.
Install the KT11-D Memory Management Option in the CPU backplane and verify that it passes diagnostics.
Install the KJ11-A Stack Limit Option in the CPU backplane and verify that it passes diagnostics.
Install the TU60 in the top of the CPU cabinet. Install the TA11 controller in the I/O backplane and connect it to the TU60.
Test and possibly repair the TA11 and TU60. There is lots of restoration info here.
Install the RX02 diskette drive in the I/O cabinet and connect it to the RX211 board.
Create RX02 XXDP media using PDP-11 GUI and see if we can boot the XXDP Diagnostic Monitor from diskette. Note: The M9213 Bootstrap Terminator board has the DY (RX02) boot ROM.
Install the TU56-H DECtape drive in the I/O cabinet with the TC11 DECtape controller.
Connect the TC11 to the end of the Unibus in the 11/40 chassis. Move the Unibus terminator from the CPU chassis to the TC11 chassis.
Test and repair the TC11 and the TU56-H.
Install two RL02 drives in the DECtape cabinet.
Install scratch media in the RL02 drives and run the disk drive diagnostics.
Install XXDP or RT-11 media in one of the RL02 drives and see if the Diagnostic Monitor or Operating System will boot.
Install the VT11 backplane and boards in the CPU chassis. Move the M9312 to slot 17BC in the expansion backplane and install a M981 Unibus Jumper from slot 16AB to 17AB.
Install the VR14 in the CPU cabinet and leaving a 3U gap above the CPU chassis.
Connect the VR14 to the VT11 and see if the diagnostics will run.
Create BSD2.9 UNIX RL02 media and see if it will boot.
Remove either the KW11-P or DR11-C from the expansion backplane and install an RL11 disk controller.
Connect the two RL02 disk drives to the RL11 controller.
Replace the DL11 with a DZ11, connect it to the RS-232 distribution panel, and see if the diagnostics will run.
Remove either the KW11-P or DR11-C from the expansion backplane and install an RL11 disk controller.

This is the empty early design BA11-FF chassis for the PDP-11/40 system. The modifications have been removed. We have lots of repairs and assembly to do.

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