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What did I do to my PDP-8 today.

antiquekid3 said:
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And some shots of KALEID. For what it's worth, the manuals specify that the horizontal pitch is larger than the vertical pitch, or in other words, the aspect ratio should be rectangular and fill the screen. However, I feel like the square aspect ratio looks better. I guess Vince can decide what he wants to use—right now, it's square, but a single pot on the horizontal deflection amp board in the VR14 can change that.

I suspect we'll look at the broken auto start function and why the START 20 switch is flaky next. Or, maybe see if we can get one working TU55 from three broken ones...
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Wow - blown away!!

Great job!

I wish one day I can see one of these machines in-person - on the bucket list!

-Chris
 
I'll try to get a video. Need to disable a few of the noisy air pushers first. Maybe Vince will be persuaded to put in all Noctua fans!
 
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Modified my LIFE.PA to support the 12. Still need a little work, but it definitely is showing signs of life! I'll need to do some better code cleanup before I push my changes.

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We had an issue with +10V that we didn't notice until we tried to run the LINCtape drives. Turns out whoever put the power supply together last inadvertently connected the fifth green wire to the anode side of the zener diode rather than the cathode side with the other four green wires. That would certainly do it! Fortunately, I don't see any signs of damage. In fact...

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We loaded a scratch tape with unknown contents on it and attempted to boot LAP-6/DIAL. The simple bootstrap seemed to successfully pull data off the tape, and starting it running showed us a FOCAL prompt! Mind you, the LINCtape processor and other bits of this side of the 12 had really not been tested since Vince got it. Incredible! Now we just have to learn how to use it since all of us can work our way around OS/8 quite well, but this is a different animal altogether.
 
antiquekid3 said:
We loaded a scratch tape with unknown contents on it and attempted to boot LAP-6/DIAL. The simple bootstrap seemed to successfully pull data off the tape, and starting it running showed us a FOCAL prompt! Mind you, the LINCtape processor and other bits of this side of the 12 had really not been tested since Vince got it. Incredible! Now we just have to learn how to use it since all of us can work our way around OS/8 quite well, but this is a different animal altogether.
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We have never been able to get the LINCtapes to work reliably on the RICM's PDP-12. It will pass all of the logic diagnostics, but will not reliably read a tape. Turn the speaker on when you run LINCtape controller diagnostics. It will make some noises like church bells.

We have an RK05 disk on the RICM PDP-12. LAPS/DIAL supported booting and running from the RK05, but I have never found a disk image containing LAPS/DIAL. I have been thinking of trying to patch together a disk image so we could try booting LAPS/DIAL from the RK05.
 
Today I played a bit with the PDP-12. I wanted to get some demos together, like those I have for the VC8E.

I found a "Pong" game called PING.SV on one of the LINCtapes.

I rebuilt SPCWR3 without EAE, and it is gorgeous on the VC12/VR14. Even the constellations look good! I actually recognize a couple of them.

Then, I gathered up the modules needed for the EAE option, ran them through the flip-chip tester, then installed the EAE option. I rebuilt SPCWR3 again to use it, and sure enough, the ships seem to move faster, and the EAE row on the light display has come alive!

I wish that I knew how to use my cell phone camera to take photos that don't look like crap. Maybe if I turn the intensity way down and take the pictures in the dark. But then I'd need a tripod or something, as otherwise my tremor would fuzz the picture.

For some reason I haven't figured out, TANK doesn't run. (Rather, it runs and runs, but no picture.)
 
Made a little more progress. Got TANK working (I think it just needed the EAE) and got KALIED to start properly by writing a little stub at 0200 to switch to LINC mode and branch to the LINC code.

It is weird that it's called KALEID on the -8, but KALIED on the -12.
 
While visiting Jack Rubin's Computerarium I got the opportunity to work on his PDP-8i restoration. Since this is not one machine but a collecion of parts it is a little more challenging than some. Vince, Malcolm and of course Jack are all here as well. The power supply was pulled and Jack cleaned that up and reformed the caps. We (me and Vince) tested cards. Of the cards tested we had a very small number of failures, in fact it was only one. We commented on the fact that this was a very high working percentage. This was perhaps 2/3 of the cards.

Next issue was damage to one of the cables connecting the front panel switch assembly to the backplane paddle. We stupidly forgot to take a before picture but as many of you know these are flat ribbon cables and the failure mode is the adhesive that attaches the two sides has dried out and they delaminate allowing the conductors to move around causing shorts. In this case the delamination was confined to the last couple of inches at the paddle that connects to the backplane. Here is a photo of the paddle card after removing the cable and cleaning up the pads.
IMG_20230906_151453555.jpgThe black stuff is the original foam double stick tape to hold the ribbon cable in place. This was still usable so we decided to keep it. Here is the photo just before soldering the cable back on.
IMG_20230906_160651404_HDR.jpgThe cable was trimmed with scissors to make a square end just past the delamination area. The difficult part of this whole thing was stripping the plastic off the cable without damaging the copper foils. I could probably do it in an hour now but it took about two hours the first time. The bottoms of the conductors are tinned so it is just a matter of touching the conductors with the iron and then pressing it into the pad below it.
IMG_20230906_173126943_HDR.jpgAnd the completed repair. We didn't have rivets long enough to reattach the strain relief so a cable tie was used. It is not as pretty as I would like but if it works I will be happy. Total time for this repair was about 4 hours. I don't recommend this as a long term repair as the original cable is going continue to degrade. Vince has a kit using modern ribbon cable with IDC connectors and headers which is going to be far easier and reliable long term. We didn't do it this way because we didn't have the kit.

Photos by Vince.

More news later!
 
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On Jack's 8/i. We finished running all the cards that we could test through the flipchip tester. Jack has a hand held blower which I used to blow out the backplane. I installed all the cards back in the machine. Vince and Malcolm double checked my work. Jack, Malcolm, and Vince put the power supply back in the cabinet. With a 30 ohm load on the 5 volt, to prevent the crowbar from tripping, we powered it up and measured all the mostly unloaded voltages as being close enough that it would be ok to hook it up.

Next is to reinstall the front panel hardware and connect up the power supply to the backplane and the fun will then begin.

Since VCFMW starts tomorrow I am not sure how much more we will get done.

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DougIngraham said:
While visiting Jack Rubin's Computerarium I got the opportunity to work on his PDP-8i restoration. Since this is not one machine but a collecion of parts it is a little more challenging than some. Vince, Malcolm and of course Jack are all here as well. The power supply was pulled and Jack cleaned that up and reformed the caps. We (me and Vince) tested cards. Of the cards tested we had a very small number of failures, in fact it was only one. We commented on the fact that this was a very high working percentage. This was perhaps 2/3 of the cards.

Next issue was damage to one of the cables connecting the front panel switch assembly to the backplane paddle. We stupidly forgot to take a before picture but as many of you know these are flat ribbon cables and the failure mode is the adhesive that attaches the two sides has dried out and they delaminate allowing the conductors to move around causing shorts. In this case the delamination was confined to the last couple of inches at the paddle that connects to the backplane. Here is a photo of the paddle card after removing the cable and cleaning up the pads.
View attachment 1263815The black stuff is the original foam double stick tape to hold the ribbon cable in place. This was still usable so we decided to keep it. Here is the photo just before soldering the cable back on.
View attachment 1263816The cable was trimmed with scissors to make a square end just past the delamination area. The difficult part of this whole thing was stripping the plastic off the cable without damaging the copper foils. I could probably do it in an hour now but it took about two hours the first time. The bottoms of the conductors are tinned so it is just a matter of touching the conductors with the iron and then pressing it into the pad below it.
View attachment 1263818And the completed repair. We didn't have rivets long enough to reattach the strain relief so a cable tie was used. It is not as pretty as I would like but if it works I will be happy. Total time for this repair was about 4 hours. I don't recommend this as a long term repair as the original cable is going continue to degrade. Vince has a kit using modern ribbon cable with IDC connectors and headers which is going to be far easier and reliable long term. We didn't do it this way because we didn't have the kit.

Photos by Vince.

More news later!
Click to expand...
I have several of Vince's boards and male and female connectors and ribbon cable if you need it.
 
Yes, that's really great!
Would be awsome you where here to help me restoring my PDP-12. At the moment I've about 10% of defective Flipchips....
 
From VCFMW:

Friday afternoon. Unloaded the decset8000 and inserted all the boards.. Plugged in and turned on and the fans spun up. But no joy was experienced. I did the basic debugging possible with no tools and found nothing. Borrowed a cute little RadioShack DVM and found no +5 or -15 volts. I had decided to just show it as a static piece and fix it after I drove it home (about 1000 miles). But then Kyle arrived and we had to fix it. I pretty much let Kyle drive the repair. We took the power supply out and he took it apart and looked at everything. Saturday morning started fresh and in not too much time had isolated the issue to the 5 volt fuse holder having high resistance to the fuse. How much? 11 megaohms. A little corrosion removal and everything is back to normal! Thanks Kyle!

Kyle put his audio board in the machine and we got to demo MUSIC.SV in all its glory. It is kind of surprising how many people will stop and talk to you when they hear this.

Later we installed Vince's "Space War" board and someone found an appropriate scope. We scavenged the free bins for video cables to carry the signal to the scope and Vince stripped and tinned the ends so we could insert them into the BNC connectors on the scope. This was not as successful as the audio although Kaleidoscope runs and sort of looks ok. The scope is not in very good shape and the board had just been populated but never tested, and the wiring is not really all that neat going to the scope so the issues could be in a number of places. But we can move a dot around on the scope screen. And some days that is good enough.
 
I got home 5 days ago and promptly realized I had caught Malcolm's cold. Must have been some extra virulent down under variant of a cold. I felt a lot better yester day and finally hauled the decset8000 in from the car. PDP-8/e's are too heavy. If I am going to take big iron to shows I need to find a solution to that.

I reinstalled the cards this morning. Kyle had commented that he thought I should do something about how difficult inserting the cards is. I cleaned all the edge connectors with a Chemtronics product called Gold Guard and this did the trick.

Just need to make sure it works after its 2000 mile road trip.
 
The decset8000 was acting weird again and again it turned out to be the fuse holder. Specifically it looks like the cap for the 5V 25 amp fuse is the issue. At VCFMW I thought it was just a corrosion issue but after closer inspection with magnifying gear it looks like the issue is the spring is no longer very springy. There is a spring in the fuse holder cap that pushes the fuse against the bottom of the fuse holder when the cap is bayoneted into place. I have the machine working now but I fully expect this to go out again. Maybe time to go hunting for a new fuse holder cap. It looks like it is original but the 5V one is grey instead of the black of all the others and it does look a little more heavy duty than the others.
 
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