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PDP-8/L Module Utilization Question

BitWiz

BitWiz

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Sep 7, 2021
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Glen Ellyn, Iil
I was comparing my new PDP-8/L modules to the Module Utilization Sheet and I found that my 8/L had M111 boards in slots D10 and D11. According to my Module Utilization Sheet from the PDP-8/L Maintenance Manual Volume II (DEC-8/L-HR2A-D) dated 1970 those two slots are reserved for Data Break interface and should be M216 (D10) and M113 (D11).

There are no other boards in the other data break positions (A34, B32, B33) or any other option positions.

Removing the boards changes the functionality (load address works except for bit 10 but exam would not advance the address) but it still does not work.

If it is relevant the serial number is 3199.

Is this some revision that is newer than my documentation or should these boards be removed?

Thank you,

Mike
 
BitWiz said:
If it is relevant the serial number is 3199.

Is this some revision that is newer than my documentation or should these boards be removed?
Click to expand...
They probably don't belong there. While not impossible that there was some revision, it is far more likely someone just plugged boards into those slots. If you haven't already done so it is probably a good idea to check every slot to make sure the correct card is present. Cards in wrong slot is not at all uncommon.
 
DougIngraham said:
They probably don't belong there. While not impossible that there was some revision, it is far more likely someone just plugged boards into those slots. If you haven't already done so it is probably a good idea to check every slot to make sure the correct card is present. Cards in wrong slot is not at all uncommon.
Click to expand...
I was doing exactly that when I discovered the two "extra" cards.

I am going to proceed with my repairs with them removed and see what happened.

No if only I could get my flip chip tester working.

Thank you.
 
TBH, it doesn't look like it. Please see the pics below.

The backplane label says M-27 Logic 3054.

Does that ring a bell for anyone?
 

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BitWiz said:
I was comparing my new PDP-8/L modules to the Module Utilization Sheet and I found that my 8/L had M111 boards in slots D10 and D11. According to my Module Utilization Sheet from the PDP-8/L Maintenance Manual Volume II (DEC-8/L-HR2A-D) dated 1970 those two slots are reserved for Data Break interface and should be M216 (D10) and M113 (D11).
Click to expand...
Mine has an M216 in D10 and an M113 in D11.
IMG_8016 with yellow dots.jpg
(The power supply was removed for restoration when this photo was taken)
Boards with blank yellow stick dots have been cleaned and tested on the flip chip tester.
Boards with an "o" on the yellow dot are replaced from the spares kit.
Not shown here, but boards with an "X" on the dot failed in the tester.
Boards with an "*" were tested on the tester and have been repaired and now work. (It's easy to convert an "X" into a "*" with two strokes of a pen :) )

BitWiz said:
There are no other boards in the other data break positions (A34, B32, B33) or any other option positions.
Click to expand...
I have an M111 in A34, and M906 in B32 and B33.

This machine was configured with a paper tape reader interface, notice the M715, M7050, and M710 in A/B 29, 30, 31. I had a problem where one of the boards in the reader/punch interface was always feeding a carry into the ALU so I now have the reader/punch boards removed.
Still have the cards in D10, D11, A34, B32, and B33 present, though.

BitWiz said:
Removing the boards changes the functionality (load address works except for bit 10 but exam would not advance the address) but it still does not work.

If it is relevant the serial number is 3199.
Click to expand...
My serial number is in the 2400's or 2600's, I think. Can check when I get home this weekend.

BitWiz said:
Is this some revision that is newer than my documentation or should these boards be removed?
Click to expand...
Not sure. Would need to look at the schematic to see whether there are logic paths through these boards that are necessary.

At this point it's probably best to pick simple issues (like load address bit 10 not working or address not advancing) and follow the clues. I learned a lot about the machine going through this process and it was pretty fun.
This interactive module chart was incredibly useful: https://www.pdp-9.net/docs/pdp-8-l/modules/index.html
 
Last edited:
gwiley said:
Mine has an M216 in D10 and an M113 in D11.
View attachment 1286335
(The power supply was removed for restoration when this photo was taken)
Boards with blank yellow stick dots have been cleaned and tested on the flip chip tester.
Boards with an "o" on the yellow dot are replaced from the spares kit.
Not shown here, but boards with an "X" on the dot failed in the tester.
Boards with an "*" were tested on the tester and have been repaired and now work. (It's easy to convert an "X" into a "*" with two strokes of a pen :) )


I have an M111 in A34, and M906 in B32 and B33.

This machine was configured with a paper tape reader interface, notice the M715, M7050, and M710 in A/B 29, 30, 31. I had a problem where one of the boards in the reader/punch interface was always feeding a carry into the ALU so I now have the reader/punch boards removed.
Still have the cards in D10, D11, A34, B32, and B33 present, though.


My serial number is in the 2400's or 2600's, I think. Can check when I get home this weekend.


Not sure. Would need to look at the schematic to see whether there are logic paths through these boards that are necessary.

At this point it's probably best to pick simple issues (like load address bit 10 not working or address not advancing) and follow the clues. I learned a lot about the machine going through this process and it was pretty fun.
This interactive module chart was incredibly useful: https://www.pdp-9.net/docs/pdp-8-l/modules/index.html
Click to expand...
George,

It looks like your 8/L has the Data Break Option installed. That would explain the boards in D10, D11, A34, B32 and B33.

I am working on converting your flip chip tester program from SD to SdFat. Apparently there are issues with the SD card drive and it is deprecated.

Thank you for your help.

Mike
 
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