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What did I do to my PDP-8 today.
- Thread starter DougIngraham
- Start date
gnupublic
Experienced Member
Yes, I also would like to thank all the helpful people here. Great community. Without the great work from Vince and Roland and David and Kyle and and and.... We would not be so far. Many thanks to you all.
Hopefully one day I can give something back from what I got here.
And for the topic: I managed to bring a TU-56M back to work this weekend.
Hopefully one day I can give something back from what I got here.
And for the topic: I managed to bring a TU-56M back to work this weekend.
vrs42
Veteran Member
I suspect it would be easier to order one of these:
If the shipping is too high, maybe this instead:
HT-174 Hand Rivet Clincher for 1/8" Diameter Tubular Rivets. Designed to BE Used in Conjunction with A Hammer to Clinch/ROLL Tubular Rivets. (Pack of 1): Amazon.com: Industrial & Scientific
HT-174 Hand Rivet Clincher for 1/8" Diameter Tubular Rivets. Designed to BE Used in Conjunction with A Hammer to Clinch/ROLL Tubular Rivets. (Pack of 1): Amazon.com: Industrial & Scientific
www.amazon.com
I'm using the latter in my drill press with success. The special anvil isn't strictly needed,. You will need something flat, and a small post might be useful to help with the centering. I'm lifting the board slightly, centering it on the nubbin in the staker, then lowering the whole thing to the table and then applying the pressure with the press knob in my other hand.
Vince
thunter0512
Veteran Member
I have now order the part from Digikey. I needed some other parts anyway, so shipping is for "free".
erd
Experienced Member
I don't know that a drill press makes a good rivet setter. Try looking at an arbor press. A small one shouldn't be expensive.
If you look at a manual rivet setter you'll get an idea about what the dies need to look like. The big deal with these is the small finger that sticks up. In the past, we've had to replace dies because someone lost control of a hex-height board and the weight of it was enough to snap that finger off the lower die. New dies aren't cheap.
vrs42
Veteran Member
From the comparison of what you've got vs what I've got, it looks like your rivet is installed the other way up. I've got the pre-formed side down, against the table. The "set" has a short alignment pin, and a curve that matches the shape I'd like to flare the cylinder end into.
One issue that I ran into is that the rivets probably should be longer than the vintage rivets that I have. Both the handles that I bought off Mouser and the modern PCBs are thicker than the vintage handles and PCBs, so there's not as much "flare" to hold the rivet in place. I'm not sure it is critical, though, because most of the insrtion/removal force is in the "Y" direction, with some in the "X" direction, but almost none in the "Z" (pull the rivet from the board/handle) direction.
Another issue is that the new boards need tweaking as to the placement of the holes. Some holes are too far from the board edge, and some have the spacing between the rivets rounded to the sixteenth, and so they don't line up perfectly with the holes in the plastic handles.
Vince
thunter0512
Veteran Member
Thank you very much for posting the closeup photos.
I can easily make the bottom die in my lathe, but the photos don't really show enough detail of the upper die.
It could be that the top die simply has a hole slight larger than the pin.
It is not clear to me how the bottom die is forming the mushroom head shape of the rivet as there is no visible flaring.
thunter0512
Veteran Member
I too noticed that the PCB holes are not perfectly aligned with the handle holes, but there is enough tolerance for M3 rivets to fit.
thunter0512
Veteran Member
I have been worried about accidentally knocking against my precious Lab-8/e front panel switches.
Below is a photo of my solution for the perceived problem using a 6 mm acrylic sheet held in place by two acrylic rails stuck to the sides with double-sided sticky tape.
To get access to the switches I simply slide up the acrylic sheet in the rails to remove it. After use I slide it back in.
Below is a photo of my solution for the perceived problem using a 6 mm acrylic sheet held in place by two acrylic rails stuck to the sides with double-sided sticky tape.
To get access to the switches I simply slide up the acrylic sheet in the rails to remove it. After use I slide it back in.
vrs42
Veteran Member
Progress! Doug was here to visit, and with his help, we were able to repair the first 4K of my PDP-12. It was a slog to debug, and the problem turned out to be an intermittent connection on the memory+ supply to the inhibit driver responsible for the least significant 4 bits of field 0.
When Doug left this afternoon, we'd just gotten the serial port working. Since then, I've put some stuff away, toggled in RIM, loaded BIN, then loaded FOCAL. I didn't load the dialog program, so it's prompt isn't that dramatic, but you can see it here:
So, a number of things are working now!
Vince
When Doug left this afternoon, we'd just gotten the serial port working. Since then, I've put some stuff away, toggled in RIM, loaded BIN, then loaded FOCAL. I didn't load the dialog program, so it's prompt isn't that dramatic, but you can see it here:
So, a number of things are working now!
Vince
vrs42
Veteran Member
Thanks! I must be tired, or perhaps it just hasn't sunk in yet
. I suppose I'll have to run the diagnostics and see what *isn't* working. I know the LINCtape stuff is wonky, and I can't remember ever seeing the CRT turn on. The AUTO key didn't seem to be working right either. There's a mess of stuff in there still to check out.Vince
DougIngraham
Veteran Member
Don't forget the stuck bit in the MQ.
I think we spent about 12 hours figuring out this one problem. The problem was a wire wrap wire in the backplane with partial connectivity. It was good enough that his meter would beep when testing from post to post on the connectors and it would work when single stepping the machine but when the memory would become active the voltage would plummet on that one card only. The resistance of that piece of wire wrap showed 0.8 ohms. Shorting the leads on that meter shows 0.5 or 0.6. One of the strangest problems I've worked on.
Overall this is a remarkably clean machine. It is pretty cool that FOCAL would run. I was expecting more debugging was in the cards before that would work.
Thanks for letting me assist you with this!
I think we spent about 12 hours figuring out this one problem. The problem was a wire wrap wire in the backplane with partial connectivity. It was good enough that his meter would beep when testing from post to post on the connectors and it would work when single stepping the machine but when the memory would become active the voltage would plummet on that one card only. The resistance of that piece of wire wrap showed 0.8 ohms. Shorting the leads on that meter shows 0.5 or 0.6. One of the strangest problems I've worked on.
Overall this is a remarkably clean machine. It is pretty cool that FOCAL would run. I was expecting more debugging was in the cards before that would work.
Thanks for letting me assist you with this!
vrs42
Veteran Member
You are most welcome. Thank you for the increased focus you bring to the debug efforts. Without that, I'm sure I could and would have procrastinated debugging the problem for years.
Vince
m_thompson
Veteran Member
We found a broken wire-wrap on the RICM PDP-8/I. Fortunately it was a solid break so it was easy to find.
vrs42
Veteran Member
More progress! I (finally) got the second serial port installed and working correctly at 115200 baud. I had to build a baud rate generator (it's really just a card with a single 1.8432MHz can oscillator on it. (There is a backplane wiring change since the desired baud rate is over 100K, though. ) Then I had a mess of problems with bad cables and connectors. Finally, I had to bypass one of the opto-isolators on the W076 replacement, as the optos are too slow for 115.2K. (I replaced it with a standard transistor instead, as that one was only used as an RTL inverter.)
From there it wasn't hard to get SerialDisk up and running. The left photo shows the headless Pi 0W that I bolted to the front (so the wireless signal can get in and out of there). Then there's a DIR listing and a RES/E.
Vince
m_thompson
Veteran Member
Very nice. Time to make a PDP-12 diag pack image and run all of the diags.
BitWiz
Veteran Member
OS/8 V3T? I'm aware of V3S. Does the standard Serial disk build give OS8 V3T? What are the differences between V3S and V3T?
vrs42
Veteran Member
I believe I started from Michael's PDP-12 image. Basically, I took the vanilla version of BUILD, and installed and uninstalled drivers until it matched Michael's previous configuration, but with newer SerialDisk. The stuff that wasn't affected by BUILD should be the same as his.
I've read that V3T was a DECmate thing, and not everyting in it was a good idea, so it would surprise me if that's what Michael got from CJL.
There's also an effort to upgrade to patch levels beyond V3D for the PiDP, so maybe that could be where the V3T comes from?
It's on my "someday" list to actually understand the umpteen versions of things OS/8 related, including the bewildering number of revisions to BASIC, but I haven't got there yet.
Vince
thunter0512
Veteran Member
After playing for a little with the 4K BASIC discovered by daver2 and described in the thread "DEC PDP-8/E EDUSYSTEM-10 4KW BASIC interpreter" I started having strange glitches with my PDP-8/e. Software which worked previously halted randomly. After a few more minutes the system became completely unusable. Not even a simple count program would run anymore.
I was about to start swapping boards for my good spares when I thought I better first check the power rails on the H724A power supply. Surprisingly the -15V rail was about -0.8V and the power-good signal was about 0.1V. The 5V rail was good and the +15V rail was about +17V.
I removed the power-supply from the PDP-8/e chassis to get access to the two regulator boards A1 and A2. It would be nicer if these would be accessible without having the remove the heavy and awkward power supply from the 8/e chassis.
On the A1 board responsible for regulating the -15V rail I then soldered some wires to the LM723 regulator (TO-100 package) to be able to check the interesting pins 2, 3, 4, 5 and 6 (pin 5 is V-).
V_ref on pin 4 was only 2.7V instead of the expected 7V. Pins 2 (inverting input) and 3 (non-inverting input) were very different. This means V_out on pin 6 should drive the pass-through transistor hard, but it was only about 0.2V which is too low for the external pass-through transistor to even start to conduct.
I concluded the LM723 had died. It looked somewhat corroded anyway. After swapping in a new LM723 I plugged regulator board A1 back into the H724A I was convinced that I fixed it, but disappointingly the -15V was still only about -0.8V.
There is not much else in the circuit other than a few resistors and a few capacitors (careful - not all are shown in schematic in the maintenance manual - reference the engineering drawings to see the accurate circuit). With A1 on the bench I checked all the resistors and the pot R5 with my multimeter and they looked fine.
Finally I started checking the 6 ceramic capacitors (10 nF 100V) and the 1uF 35V electrolytic cap C2. As it turned out C3 was conducting at about 700 Ohm both in and out of circuit.
I replaced all 7 capacitors on the board A1. When I plugged the repaired board A1 back into the H724A and powered on, all the rail were back at their nominal value including the power-good signal.
I finished the job by adjusting the 5V and -15V rails with the H724A inside the 8/e chassis sitting on two wooden blocks to raise it sufficiently to expose the regulator boards A1 and A2. The +15V rails just follows the -15V rails so there is nothing to adjust.
So what I think happened is that C3 started glitching before failing completely.
Now with everything re-assembled my PDP-8/e is nice and stable again.
My conclusion is - be careful when you run 4K BASIC - it might kill your power supply.
Tom
I was about to start swapping boards for my good spares when I thought I better first check the power rails on the H724A power supply. Surprisingly the -15V rail was about -0.8V and the power-good signal was about 0.1V. The 5V rail was good and the +15V rail was about +17V.
I removed the power-supply from the PDP-8/e chassis to get access to the two regulator boards A1 and A2. It would be nicer if these would be accessible without having the remove the heavy and awkward power supply from the 8/e chassis.
On the A1 board responsible for regulating the -15V rail I then soldered some wires to the LM723 regulator (TO-100 package) to be able to check the interesting pins 2, 3, 4, 5 and 6 (pin 5 is V-).
V_ref on pin 4 was only 2.7V instead of the expected 7V. Pins 2 (inverting input) and 3 (non-inverting input) were very different. This means V_out on pin 6 should drive the pass-through transistor hard, but it was only about 0.2V which is too low for the external pass-through transistor to even start to conduct.
I concluded the LM723 had died. It looked somewhat corroded anyway. After swapping in a new LM723 I plugged regulator board A1 back into the H724A I was convinced that I fixed it, but disappointingly the -15V was still only about -0.8V.
There is not much else in the circuit other than a few resistors and a few capacitors (careful - not all are shown in schematic in the maintenance manual - reference the engineering drawings to see the accurate circuit). With A1 on the bench I checked all the resistors and the pot R5 with my multimeter and they looked fine.
Finally I started checking the 6 ceramic capacitors (10 nF 100V) and the 1uF 35V electrolytic cap C2. As it turned out C3 was conducting at about 700 Ohm both in and out of circuit.
I replaced all 7 capacitors on the board A1. When I plugged the repaired board A1 back into the H724A and powered on, all the rail were back at their nominal value including the power-good signal.
I finished the job by adjusting the 5V and -15V rails with the H724A inside the 8/e chassis sitting on two wooden blocks to raise it sufficiently to expose the regulator boards A1 and A2. The +15V rails just follows the -15V rails so there is nothing to adjust.
So what I think happened is that C3 started glitching before failing completely.
Now with everything re-assembled my PDP-8/e is nice and stable again.
My conclusion is - be careful when you run 4K BASIC - it might kill your power supply.
Tom