PDP-9 Restoration Blog Starting 2020

2/1/20
We tried the ASR-33 Teletype from the Altair 8800 as the system console
We blew one of the 3A fuses because the wires for the paper tape reader control inside the TTY were reversed
This looked like a short to the PDP-9, and the fuse protected everything

After we fixed the paper tape reader control wiring the TTP keyboard and printer worked OK
The paper tape reader would not turn on
We checked the transistors and diodes on the W040 that drives the printer and controls the reader
Diodes D2 and D7 were shorted
We replace them with NOS D-662 1N645 parts
The paper tape reader in the TTY is enabled when ADSS first boots, but is disabled after the first character is entered
Looks like we have some debugging to do in TTY input circuitry

2/8/20
We tried to demonstrate ADSS booting to a visitor, but ADSS would not restart from the core image or load from DECtape
Time for some debugging

2/16/20
We ran MAINDEC-9A-D01A-D Instruction Test Part 1 and MAINDEC-9A-D02A-D Instruction Test Part 2
Both ran successfully so we know the processor is mostly working OK
We ran MAINDEC-9A-D1AA-D PDP-9 Basic Memory Checkerboard Test
It failed and showed that bit-11 in the upper 4k of core was on when it should have been off
Rerunning the test resulted in the same error at the same address
We swapped the G009 Sense Amplifiers in slots C24 & C25 and the fault moved to bit 10
We put the good G009 from slot C25 back in slot C24 and replaced the G009 in slot C25 with spare
The diagnostic ran a little longer and then showed the same failure on bit-7
We swapped the G009 sense amplifiers in slots D24 & D25
There was no change, so we swapped them back to the original locations

2/22/20
We ran the MAINDEC-9A-D0CA Memory Address Test to check the G219 modules
It ran OK, but 20 minutes to complete

We ran the MAINDEC-9A-D1FA Extended Memory Address Test to do a more thorough test of the G219 modules
This also ran OK

Click on the image for a larger view.
We ran the MAINDEC-9A-D1BA Extended Memory Checkerboard Test
This showed errors at address 013223 where the contents should be 000000 and were 000040, so it is picking up bit-12
This showed errors at address 017274 where the contents should be 000000 and were 000400, so it is picking up bit-9

The problem could be in one of the 36 G219 Memory Selector flipchips for the Digit drive
We should check the G219s in slots AB06 & EF06 for bit-9, and in slots AB03 & EF03 for bit-12
It could be in one of the 8 G219s in slots HJ23 through HJ30 that are used for Word Selection
Since the failing addresses all have MA6= 0 or 1 & MA7=1 that points to the G219s in slots HJ24 or HJ26
The failing addresses all have MA10=1 & MA11=0 that points to the G219 in slot HJ29

It could also be in the G009 Sense Amplifier flipchips for bit-9 and bit-12 in slots C23 & D22 or the W612 Pulse Amplifiers in slots C26 & D26

2/23/20
Of course now that we are prepared to to fix the memory the diag reported four new errors and is now working OK
We should take a look at the memory timing and voltages to make sure that they have not drifted out of specification

ADSS booted on the first try, so now we are back to trying to determine why versions prior to V5 get a .SYSLD 4 error when loading any application
We also need to make some V5A bootable DECtapes, and get all three TU55 DECtape drives working

To-Do:

The system was disassembled for shipment and needs to be reassembled. (Done)

Find the four BC09 I/O cables to connect the TC59 to the PDP-9. (Don't have them. Maybe we can get some BC10 cables from the LCM)
If we don't have the cables we might be able to use seven cables from a PDP-8 or borrow some from another PDP-9/10/15 collector.
 
There is some unconfirmed information that when this system was in its last days of service they had problems with the ROPE memory for the microcode.
There a rubber sheet that compresses the "E" cores together. We will need to replace it.
We have several spare ROPE memory boards. We have no idea if they are good, or what microcode is programmed.
 
We have two spare 8k core stacks if we find problems with the core in the system. (Didn't, works OK)
 
We were also told that when someone was trying to fix the system they pulled modules while the power was still on.
That may make it challenging to revive this system.
This system uses some of the same transistor only R series Flip-chips as the PDP-8/S so we have some spares for the modules.
It also uses quite a bit of the faster B series modules. We have just a few spare B modules.

Fix the drive select for Unit 1 not working problem in the TC02 or TU55

Find out why swapping the B141 flip-chips in slots B11 & B13 breaks the paper tape reader

Rewind the coil in the paper tape punch
Fix the second 709 power supply and connected it to the paper tape punch
Fix the second TU55 DECtape drive
Determine why the PIE light doesn't go off when the I/O RESET switch is pressed. (Fixed 12/7/19)
Collect enough flipchips so we can add the EAE feature for SpaceWar!
Collect the remaining flipchips so we can add the 34H graphics option, also for Spacewar!
 
The rough plan:
Reform the capacitors in the 709 power supply for the processor and test the power supply. (Done)
Reconnect the I/O cables for the paper tape reader/punch. (Done)
Find and connect the Teletype interface cable. This is actually on the PDP-11/23 that was connected to this system.
Power up the system and see what works. (Done)
There was some discussion that many of the light bulbs in the front panel were burned out.
    (All of the Register, Memory Buffer, and Interrupt lights work.) 
Reform the capacitors in the TU20 power supply and test the power supply. (Done)
Power up the TU20 and see what works. (Done)
The tape drive uses vacuum columns so it may be a significant challenge to get it working. 
Reform the capacitors in the TC59 power supply and test the power supply. (Done)
Connect the TC59 tape controller to the I/O section of the PDP-9 and to the TU20. (Done using borrowed PDP-8 I/O cables)
Debug the TC59 and the TU20. (In process)

Wire the DC power to the TC02 DECtape controller and connect the I/O cables between the processor and the TC02.
See if the TC02 responds to any IOT instructions.
Try the TC02 diagnostics.
Install a TU55 in the rack with the TC02 and TU59.
See if the DECtape works.

Once we get a DECtape working we can make an OS DECtape.
If the PDP-9 actually runs the OS, it will be the only one on the planet that can.
7
The instructions tested so far are:
CLA    Works OK
CLC    Works OK
CLL    Works OK
CLOF   Turns the CLK light off.
CLON   Turns the CLK light on.
CMA    Works OK
CML    Works OK
DAC    Works OK
DZM    Works OK Fixed on 3/23/13
HLT    Works OK Fixed on 3/23/13
IOF    Turns the PIE light off.
ION    Turns the PIE light on.
IZS    Works OK Fixed on 3/16/13
JMP    Works OK Fixed 3/10/13, Fixed again 5/18/19
LAC    Works OK
LAS    Works OK
NOP    Works OK
RAL    Works OK
RAR    Works OK
RTL    Works OK
RTR    Works OK
STL    Works OK

Maindec Diagnostics
MAINDEC-9A-D0BA-D ISZ Test, 5/18/19
MAINDEC-9A-D0CA Memory Address Test, 2/22/20
MAINDEC-9A-D0DB-D-JMP Self Test, 5/18/19
MAINDEC-9A-D0EA-D JMP Y - Interrupt Test, 5/18/19
MAINDEC-9A-D0FA-D JMS Y TEST, 5/18/19
MAINDEC-9A-D01A-D Instruction Test Part 1, 2/16/20
MAINDEC-9A-D02A-D Instruction Test Part 2, 2/16/20
MAINDEC-9A-D1AA-D PDP-9 Basic Memory Checkerboard Test, 5/18/19
MAINDEC-9A-D1BA-D PDP-9 Extended Memory Checkerboard Test, 5/26/19
MAINDEC-9A-D1FA-D PDP-9 Extended Memory Address Test, 2/22/20
MAINDEC-9A-D2BA-D PDP-9 TTY Test, 11/2/19
MAINDEC-9A-D3BB-D TC02 Basic Exerciser, 12/14/19
MAINDEC-9A-D3RB-D TC02 DECtape Random Exerciser, 12/14/19
MAINDEC-9A-D7AD-D PDP-9 Basic Exerciser (no punch or tape reader), 5/18/19

The boards replaced in the PDP-9 processor so far are: 

B131 Adder in slot A23 of the processor, replaced Q4, 2N3669, 3/17/19
B169 Inverter (Multiplexor) in slot B26 of the processor with a spare, 3/30/19
B310 Delay Line in slot EF29 of the processor with a spare, and again with a repaired module 
B213 JAM Flip-Flop in slot H33 of the processor with a spare, 2/2/13
B213 JAM Flip-Flop in slot C39 of the processor with a spare, 3/23/19
B213 JAM Flip-Flop in slot C18 of the processor with a spare
B213 JAM Flip-Flop in slot C35 of the processor with a spare, and again with a spare
B213 JAM Flip-Flop in slot D20 of the processor with a spare
B213 JAM Flip-Flop in slot D21 of the processor with a spare 4/13/19
B213 JAM Flip-Flop in slot D27 of the processor with a spare
B213 JAM Flip-Flop in slot D28 of the processor with a spare
B213 JAM Flip-Flop in slot H33 of the processor with a spare
B213 JAM Flip-Flop in slot E20 of the I/O controller with a spare
B310 Delay Line in slot EF29 of the processor with a spare 
B310 Delay Line in slot EF36 of the Core Memory with a spare, put the original repaired board back 8/10/19
B360 Adjustable Delay Line in slot D33 of the Core Memory with a spare
G009 Sense Amplifier in slot C25 of the Core Memory with a spare
G219 Memory Selector in slot AB09 of the Core Memory with a spare 
G219 Memory Selector in slot HJ24 of the Core Memory with a spare 
G920 Repaired, and repaired again. 05/18/19 Replaced a diode with a 1N4149 for Microword 74
R111 Diode Gate in slot H23 of the processor with a spare
R123 Diode Gate in slot D15 in the I/O controller
R401 Clock Flip-Flop module in slot KD09-E03 of the I/O controller with a spare
S205 Dual Flip-Flop module in slot KD09-D07 of the I/O controller with a lower drive R205 spare. We need to repair the S205 and put it back in the system
S603 Triple Pulse Amplifier in slot J23 with a spare. Diode D42 on the original conducted in both directions
S603 Triple Pulse Amplifier in slot J10 with a spare
W040 Solenoid Driver in slot B33 of the processor, 2/1/20 replaced D2 & D7 with 1N3606

The boards replaced in the TU20 Tape Drive so far are:
 
2N1304 transistor in the EOT circuit on the Photosense Amplifier in the tape transport
G287 Write Driver in slots A02-A06, replaced 2x 2N3500 transistors for tracks B, 8, 2, and Parity. Some of the diodes on theses modules have small cracks
R113 Diode Gate in slot B20 with a spare
R123 Diode Gate in slot B17 has poor drive to pin P. Working OK, but should be checked further. The R123 Diode Gate in slot B17 was actually an R203 flip-flop. It was replaced with the correct spare
R203 Triple Flip-Flop in slot B27 with a spare
R205 Dual Flip-Flop in slot B04 with a spare
R205 Dual Flip-Flop in slot B05 with a spare
R302 Dual Delay in slot B09 with a spare. Set trimpots to the same values as on the original
R302 Dual Delay in slot D29 with a spare. Set trimpots to the same values as on the original
R303 Integrating One-Shot in slot A21, replaced the open Trimpot
R401 Clock module in slot A15 with a spare
R602 Pulse Amplifier in slot B13 with a spare
R602 Pulse Amplifier in slot B16 with a spare
R603 Pulse Amplifier in slot A09 with a spare
W501 Schmitt Trigger in slot C10 with a spare
W501 Schmitt Trigger in slot D09 with a spare

The boards replaced in the TC59 Magnetic Tape Controller so far are:
 
R602 Pulse Amplifier in slot A21 with a repaired module
W640 Pulse Amplifier in slot F22, replaced R17, Q8, and Q9

The boards replaced in the TC02 DECtape Tape Controller so far are:
 
G882 Reader/Writer in C23 with a donation from Anders, 4/20/19
R201 Flip-Flop in slot C02 with a spare, 8/10/19
S107 Inverter in slot C18 with a spare, 7/7/19
S107 Inverter in slot F18 replaced Q5, 7/21/19
S123 Diode Gate in slot F14 replaced Q3, 9/20/19
S202 Dual flip-flop from slot A5 needs repair, 8/10/19
S205 Dual flip-flop from slot B8 replaced D21 on 12/14/19
S603 Pulse Amplifier in slot C17, replaced D20 8/10/19

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