The Restoration of the PDP-12 Minicomputer (PAGE 3)
The first 160mF/20V capacitor is now done, and the second is in progress.
So, all of the power supply capacitors should be done by tomorrow.
The current plan of attack is as follows:
- Check backplane for bent/damaged pins
- Check all cards to see that they are in the correct slots
- Clean all card connectors with alcohol
- Remove all "extraneous" connectors that (currently) don't go anywhere
- Route 30A/120V wiring from downstairs circuit breaker panel to upstairs one, install, and test.
- Smoke Test! :-)
The PDP-8/I ended up occupying a lot more of my time than I expected,
so the PDP-12 has been sitting for a while. I did manage to test some cards from the 12 because I needed them
in the PDP-8/I -- so, for example,
I know that the M452 baud-rate generator works (this is a Caglec 452 "clone" that
does higher baud rates; 2400 seems to work just fine), and the M706 /
M707 TTY cards work as well. The next
thing to do is to inventory all the cards, pull them out, and clean them.
Generally, people restoring PDP machines will tell you not to pull all the cards out, for the simple
reason that sometimes a card with a bad gate or flip-flop may be used in a position where the bad gate or flip-flop
isn't used, so that the card appears to be functioning. By swapping the cards around, you may end up putting a
card into a position that does use the bad gate/flip-flop, and a previously working machine may no longer
work. However, I'm going for 100% functionality, so all of the cards will be tested before they are re-inserted
into the machine -- this makes it easier later to swap cards around, knowing that every gate is operational on
I'm embarrassed to report that I have done nothing on this PDP-12 for a full year now. However, my contract
work will hopefully be done soon, so I'll be getting around to doing something over the winter time (I'm
thinking that testing all the cards and maybe the tape drives and display could be done during the winter, and
then power up the main unit over the spring/summer).
Instead of being embarrased some more, I'll simply state that my contract work has finally finished, but that
I received an 8/M that I started restoring a few days ago.
Soon, my pretty, soon! :-)
Having obtained a variable DC (0-120VDC) power supply, I decided to reform the big caps one more time,
this time right up to their working voltages.
I did that, and reinstalled the caps into the power supply.
At this point I discovered that I had missed a 9.3mF @ 15V cap; so I'm reforming that one (it won't take too long).
I slipped in a quick PDP-8/L restoration in the meanwhile.
I also cleared out the "extra" cables that were connected to the backplane on one end but nothing on the other
(stuff that went to other peripheral/memory expansion boxes, but that I don't want to bring up on the first
The initial powerup was done with a really kludgy power connector.
The PDP-12 wants a 30A connector, but I only have 15A power into the garage (so far; this is planned to change).
So, I took a regular 15A power cord, and the 30A connector, and hacked together a little power box.
Kids, don't try this at home! It was safe for me to do it because as configured (without applying power to the
top fans, the CRT, nor the two TU55s) it consumes only 580W.
Anyway, I disconnected everything from the power supply box except the fans and powered it up.
Which is always a good thing!
Several fans don't turn, so the standard boxer fans I'll just replace, but the big 12" fans at the top of the
cabinet I'll need to fix (I don't have spares).
Ok, only one boxer fan needed to be replaced, the other just needed some cleaning.