Building the PiDP-1

It’s been just over a year since my last classic computer build (the PiDP-10) so it’s time to assemble Oscar Vermeulen’s latest project, the PiDP-1! I actually ordered the kit last Thanksgiving and it arrived about a week later (from Panama!) but then life got crazy: I ended up switching jobs which meant I was busy onboarding, getting benefits and such in order, and basically learning the ropes. On top of that, I lost the two weeks of winter break provided by my old employer and started with no PTO at the new place, which meant very little no free time over the holidays (just Christmas Day and New Year’s Day). I did manage to do a little prep work for the kit during that time, however, like purchasing another 4gb Raspberry Pi 5 with a 64gb microSD, imaging it with Debian 13 Trixie, and prepping the PiDP-1 software. Finally over the past two weeks I found some time to pull out my trusty soldering iron and get to assembling …

At this point, having built three kits, I shouldn’t surprised by the quality but Oscar and his colleagues at Obsolescence Guaranteed just continue to impress me and up the bar. The packaging, the quality of the parts, the clear assembly instructions and videos, it all makes for a fun build. One big change this time was the requirement to actually solder the case together which was a little challenging (more on that later) compared to the injection molded plastic (or wood) cases on the earlier kits. But like all the previous builds, you still need a little piece of cardboard between the Raspberry Pi and the PCB. 😉

The first part of the build (initial case assembly and adding all the components to the PCBs) took me about 7 hours over two days before I hit my first snag. While inserting the three ICs into their sockets, I ended up mangling the pins (and breaking one off!) of the 74HC138 chip. Oh no! Luckily the pin didn’t break off in the socket! I contacted Jose at CEDS and he said that while he could send me a replacement from Canada (or Panama again) it would take a while. Instead he recommended I buy a replacement on Amazon. Great! Except they came in a batch of 20 for $9. Oh well, spares! And they arrived in two days which allowed me to proceed.

The initial boot test worked (all 119 LEDs strobing) but when testing the switches I found one that wasn’t working. Here’s where my next problem started. Instead of reading the debugging and troubleshooting reference guide, I assumed the switch was bad and proceeded to try to remove it (had I read the docs they would have suggested additional test steps before going down the removal road). This exercise showed me my skills with a de-soldering braid are not all that great. After multiple attempts to de-solder and remove the switch (including some brute force) I was finally able to remove it but then had a problem with leftover solder slightly blocking the holes on on the PCB which wouldn’t allow the new switch to slot in. Aargh!

After watching a few YouTube videos on cleaning up and removing solder, I purchased a solder sucker (and a new multimeter) and two hours (!) later I had managed to clean out the holes in the PCB and get a new switch soldered in. Booted up the test program again and … same problem! The switch signal still wasn’t working. Ugh! In addition to that, when I launched the actual PiDP-1 software the LEDs started flickering/strobing like crazy which did not look right. Using my multimeter I tried checking the continuity of the switch pins and the resistance of the corresponding diode everything seemed fine. At this point I e-mailed Oscar and also posted on the PiDP-1 Google Group hoping someone could help me troubleshoot the issue.

I got a response from fellow kit-builder Bill who suggested I try his alternate repo for the control software, but I couldn’t get it to compile properly on under Trixie on the RasPi 5. After a few back-and-forth e-mails with him I finally got it working and oddly, somehow that fixed the flickering LEDs problem (but not the switch). Desperate, I pulled out my jeweler’s loupe (I forget why I bought this) and started checking all the solder joints around the problematic switch. All the joints looked okay but the area around the switch was a mess due to my multiple attempts at removing, and subsequently re-adding it. But up close, I noticed one of the joints for the diode above the switch looked … odd. Like I had snipped off the pin too close to the PCB. I fired up my soldering iron, added a little more solder to both of the diode pins and … it worked! The switch was functional! Hallelujah, time to move on!

At this point all that was left was to attach the front and lower switch panels to the case and solder everything together, which took me just over an hour. I managed to get everything square and lined up and soldered securely, even the little diode “hack” in the corner to keep the PCB pushed up against the front panel. I was pretty happy with the final result. The metal case is pretty solid and looks great.

Like last time, here’s the final soldering tally (not including the extra work repairing the switch/diode):

• PiDP-8: 370
• PiDP-11: 380
• Altair-Duino: 586
• PiDP-10: 696
• PiDP-1: 662

Slightly less than last year’s build, which makes sense since the PiDP-10 has 126 LEDs compared to 119 on the PiDP-1, and 74 switches (which each required 4 solder joints!) compared to 52 (with 2 solder joints each). The addition of the case assembly also added to the PiDP-1’s total (and after all my trepediation about the case assembly, it was really fun!) and I haven’t assembled the Spacewar controllers yet, so the final total will probably edge out the PiDP-10.

Now it’s time to go through the manual and start playing with my PiDP-1.

Here’s my latest timelapse assembly video (and more photos from the build can be found here):