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We replaced all of the defective bulbs in the indicator panel, and now they all light up.
The only thing left to do before debugging the controller is wire the 115VAC power for the TU55 motors, and make 3x indicator panel cables for the TC02.
Maybe next Saturday we can wire up the I/O cables, load the TC02 Basic Exerciser and see if the controller is alive.
6/23/19
We borrowed the Indicator Lamp Cables from the TC59 Magnetic Tape Controller for temporary use in the TC02 DECtape controller.
The TC02 powers up OK, but there is no response to any IOT instructions from the processor.
6/29/19
During the week we discussed the unresponsive TC02.
The first thing that we need to check today is the S107 Inverter module in slot D14.
We suspect that this is broken and preventing any of the W103 modules from decoding instructions.
Turned out that the S107 was fine.
There are margin switches on the left of the TC02 chassis that disconnect the normal power supplies and connect to an adjustable power supply in the processor cabinet.
We had not installed the margin power cable, and some of the margin switches were turned on, so there were parts of the TC02 that were not powered.
Turning all of the margin switches off got power to all of the TC02.
With all of the TC02 powered we see more reasonable behavior on the indicator lamps.
There are still problems with the IOT instruction decoding.
The maintenance instruction to load the Data Buffer works, but the Data Buffer is not cleared first.
The instruction to clear Status Register A doesn't work.
The instruction to XOR the AC with Status Register A loads the register and immediately clears it.
The instruction to read Status Register B doesn't work.
All of these instruction decoding issues may be timing related.
6/30/19
After a few hours of debugging we found an R202 Dual-Flip module in the slot where an R002 Diode Cluster module should have been.
This prevented all of the Status Register A related IOT instructions from working.
Now we can select a DECtape drive and tell it to go forward and backward.
There is still an issue with selecting DECtape drive 1 that we need to debug.
The Status Register B instructions still have issues.
If we read Status Register B the contents don't stay in the AC for long.
This could be a problem in the Processor or the TC02 DECtape controller.
There are two undocumented maintenance instructions that let you read/write the Data Buffer in the TC02.
Writing to the Data Buffer ORs the AC with the Data Buffer.
My guess is that the Data Buffer is not being cleared first.
On the TC59 Magnetic Tape controller you can execute an IOT instruction to force a data break.
You can read/write the Data Buffer to see of the data break worked correctly.
There is one unused decoded IOT instruction on the TC02, so maybe we can implement this same test capability.
We are making progress, but are not read to run diagnostics yet.
7/6/19
We can read now the Status Register A.
The Idle indicator is on when the controller is idle.
We can force a Select Error by selecting a drive that doesn't exist or executing Command 7, Select Error.
We can read now the Status Register B.
Loading a Move command into Status Register A causes the GO signal to the tape drive for 160ms and then it sends the STOP signal to the tape drive
The END error indicator is on, so it thinks that the tape went into the End Zone
The PWR CLR + ES signal goes high for 200ns and is clearing the MR1 flip-flop which clears GO
The END(1) signal on E27D goes high 160ms after the command which cause the PWR CLR + ES to go high
TP0 pulse 160 MS after command and MK END is high to it sets the END FF
TP0 should not go on until UP To Speed is active
0->WINDOW is high, and 150ms after the command goes low, then goes high after error
The Window Shift Register is active after the move command is sent, and eventually contains the code for END and stops the tape.
Where is the data for the Window Shift Register coming from? The G882s oscillate until they see real tape data
Why is TP1 active before the tape is up to speed?
Why is TP ENABLE active without the tape moving?
SWTM\ on D24J is not low enough, -1.8V, and is enabling TP ENABLE
Swapped S107 in slot C18, no change
Removed R113 in slot D24, no change
Is there another FlipChip connected to SWTM\?
The plan is to pull of the FlipChips that drive and sink the SWTM\ signal, make sure that the wiring is OK, and then put the FlipChips back one at a time
Hopefully we can find one that is loading the signal too much.
7/7/19
I looked at the SWTM and SWTM\ signals in the TC01 DECtape controller in the PDP-8/I
The signals are wired through an S107 Inverter FlipChip and go between -3.8V and -0.4V when active and not active
Time to investigate all of the connections to SWTM\ on the TC02
We found another slower R202 where the faster S202 belongs, and replaced it with the correct part
After removing and replacing all of the FlipChips tied to the SWTM\ signal it is now -2.3V when active
The END error is no longer present when we command the TU55 DECtape drive to move
We don't see the GO signal go active at the TU55 command cable and STOP is active
The X STA signal on the input pin H of the S107 in slot C18 is a nice -4V pulse, but the inverted output on pin F only went to -1V
We replaced the S107 in slot C18 of the TC02 with a spare
The XSA DY signal looks OK now
GO at the DECtape Control cable goes active for 150ms and then goes inactive
The END error indicator is on, so we are back to chasing the original issue from yesterday
Mattis kindly punched the DECtape diags and DECtape formatter for us
I formatted a DECtape in PDP-9 format on my PDP-8/e
It was a little confusing because the word size in the formatter questions is in 12-bit words and the tape specification for the PDP-9 has 18-bit words
I think that I had it right with 384 decimal words to make 600 octal 12-bit words or 400 octal 18-bit words per block
The DECtape block size is the same on the PDP-9 and the PDP-10, but the PDP-10 uses it as 200 octal 36-bit words
7/13/19
We had LOTS of visitors today, so we didn't get much done on the TC02 debugging
We still see the END error go on about 160ms after we command the TU55 DECtape to move
We checked all of the circuitry that clears the Window Register that holds the Mark Track data
All of the signals that start the R303 170ms Integrating One-Shot in slot C20 running are working OK
That One-Shot starts another 70us One-Shot in slot C19 running
That One-Shot sets the UP TO SPEED Flip-Flop in slot D27
The Flip-Flop gets inverted by the S107 in slot S22
The rising edge of the signal from the inverter clears the Window Register
Unfortunately by the time the Window Register is cleared the random data from the G882 modules is decoded to make the MK END signal
The MK END signal is gated by the TP0 pulses and sets the END Flip-Flop in slot E28
At this point the STOP Flip-Flop clears and the tape drive motion stops
We need to determine why the END error is going on
Are the TP0 pulses supposed to go to the END Flip-Flop this soon?
It looks like TP0 is enabled by TP ENABLE, which is enabled by UP TO SPEED (1)
When UP TO SPEED goes active it creates 0 -> WINDOW which will clear the WINDOW register
We should check again to see when the TP0 pulses go active
We should verify the One-Shot timing for U = M to make sure that it is set to 140 ms
7/21/19
The R303 module in slot C20 needed to be readjusted to have pin D go low for 140ms (see page 10 section B2 in the schematics)
Adjusting the module did not improve the TU55 DECtape drive behavior
140ms after the Move command the UP TO SPEED flip-flop goes active and 0->WINDOW goes inactive
About 8ms after UP TO SPEED the MK END error signal goes high (see page 8 section C7 of the schematics)
It looks like the problem is in the TU55 DECtape drive
With a tape in place, if I manually spin the drive reel, the controller is happy until I stop spinning
Now I suspect that the drive motor is not switching from the tension to the drive mode when commanded to move
The drive works correctly when in the LOCAL mode, but not in the REMOTE mode
The motor control circuits must be working OK when controlled by the switches, but not by the tape command bus interface
The control bus signals look OK on both sides of the W513 module in slot B07 in the TU55 DECtape drive
We chased the signals that control the MOTION and DIRECTION flip-flops
The DIRECTION flip-flop works OK from the bus, but not the MOTION
It looks like ALL HALT is always on
This signal stops the tape motion if the processor halts
We looked at the RUN (1) B2 signal in the TC02 that is ALL HALT in the TU55
It doesn't change when the processor is running or halted
We looked at RUN (1) B from the processor, and it changes when the processor is running or halted
The S107 inverter in slot F18 that makes the RUN (1) B2 from RUN (1) B is broken
We don't have a spare, so we will need to fix it
7/21/19
Transistor Q5 on the S107 in slot F18 in the TC02 controller was completely open
We replaced the Q5 transistor on the S107, but it didn't fix the inverter
Then we discovered that the leads on the replacement transistors were CBE on the EBC on original transistor
We removed and reversed the transistor, and now the inverter works OK.
In the process of testing and comparing several S107 inverters we found a bad Q2 and D3 clamp diode
Yay, the DECtape now moves when we send a MOVE command to the TC02 DECtape controller
