thunter0512
Veteran Member
I have been restoring and fixing my new PDP-8/e leaving core to the end once I verified that everything else is working using Roland's 32k memory board (using the acceptance tests I have).
The 8/e had two MM8-EJ 8k core memory board sets one of which was faulty.
I also had a third set from Jack which too had a fault.
Both faults were on the G111 Sense/Inhibit boards.
I fixed both boards and the 3 x 8k cores were fully functional when exercised via the front panel.
To verify that it is robust I first run the "PDP-8/e Memory Extension and Time Share Control Test" with the file name "maindec-8e-d1ha-pb" with all 6 fields selected for a few minutes and all was well.
I then run the "PDP-8/e Extended Memory & Checkerboard Test" from Vince's site with the file name "maindec-08-dhkma-d-pb" with all 6 fields selected for several hours without a single error.
Then I added the front panel plastic & bezel and the case lid and rerun "PDP-8/e Extended Memory & Checkerboard Test".
It failed within a few minutes and is failing ever since.
Here are the steps I tried to resolve the problem:
Finally I run the "PDP-8/e Extended Memory & Checkerboard Test" just on the first MM8-EJ core board set servicing fields 1 and 2 (but leaving the core boards for field 3/4 and 5/6 plugged in) and I get no errors.
Trying again with fields 1 - 6 it almost immediately fails in field 1 which just tested good.
I have not yet retried to just run with Roland's 32k board limiting to field 1 and 2.
I also tried on my LAB-8/e and the "PDP-8/e Extended Memory & Checkerboard Test" runs without any problems.
I am reluctant to one by one swap the LAB-8/e boards with the PDP-8/e boards - meaning trying to break the LAB-8/e with the PDP-8/e boards.
The LAB-8/e is too nice and precious to stuff around with.
I could understand that the case lid and the front-panel plastic changes the airflow causing some localised overheating and subsequent fault, but I think I have eliminated almost everything.
What am I missing here?
I would appreciate any help/advice.
Thanks
Tom
The 8/e had two MM8-EJ 8k core memory board sets one of which was faulty.
I also had a third set from Jack which too had a fault.
Both faults were on the G111 Sense/Inhibit boards.
I fixed both boards and the 3 x 8k cores were fully functional when exercised via the front panel.
To verify that it is robust I first run the "PDP-8/e Memory Extension and Time Share Control Test" with the file name "maindec-8e-d1ha-pb" with all 6 fields selected for a few minutes and all was well.
I then run the "PDP-8/e Extended Memory & Checkerboard Test" from Vince's site with the file name "maindec-08-dhkma-d-pb" with all 6 fields selected for several hours without a single error.
Then I added the front panel plastic & bezel and the case lid and rerun "PDP-8/e Extended Memory & Checkerboard Test".
It failed within a few minutes and is failing ever since.
Here are the steps I tried to resolve the problem:
- checked all power rails (5.12V, -15.08V, 15.12V) - all are fine
- Removed the front panel plastic & bezel and case lid and let the system cool to ambient temperature - still fails (all subsequent test were done without front panel plastic and case lid).
- checked all power rails with oscilloscope while the test was running - no significant "wiggle" or noise.
- replace all core with Roland's 32k memory - it still fails.
- one-by-one I replaced all CPU boards (M8330, M8300, M8310, M837) and bus terminator (M8320) with known good spares - it still fails.
- replaced the front-panel PCB - it still fails.
- replaced the M8655 UART board - it still fails.
- consolidated everything into the first Omnibus (removing the two M935s and moving the terminator (M8320) into the last slot of the first Omnibus) - it still fails.
Finally I run the "PDP-8/e Extended Memory & Checkerboard Test" just on the first MM8-EJ core board set servicing fields 1 and 2 (but leaving the core boards for field 3/4 and 5/6 plugged in) and I get no errors.
Trying again with fields 1 - 6 it almost immediately fails in field 1 which just tested good.
I have not yet retried to just run with Roland's 32k board limiting to field 1 and 2.
I also tried on my LAB-8/e and the "PDP-8/e Extended Memory & Checkerboard Test" runs without any problems.
I am reluctant to one by one swap the LAB-8/e boards with the PDP-8/e boards - meaning trying to break the LAB-8/e with the PDP-8/e boards.
The LAB-8/e is too nice and precious to stuff around with.
I could understand that the case lid and the front-panel plastic changes the airflow causing some localised overheating and subsequent fault, but I think I have eliminated almost everything.
What am I missing here?
I would appreciate any help/advice.
Thanks
Tom