Building the PiDP-10

Overall Impressions

I had been on the waiting list for a kit for a while but I delayed until June 2024 before ordering. The kit arrived quickly and I spent a couple of days building it, taking my time.

The kit is very high quality. The PC boards are well-designed and the white bezel is amazing, as is the light panel. Kudos to Oscar for a brilliant piece of industrial design. Based on his blog, it has taken years and great expense to bring this to fruition. He has mentioned that to break even, he needs to sell at least 1,000 kits. Hopefully, that will happen soon and he deserves to derive some benefit beyond the project being just a labor of love.

I created this separate page to document my build of the PiDP-10 kit. If others in the Google group are either contemplating getting a kit or having issues building one, this page might be of some use. Oscar's instructions on this page are very clear and well-written. But, some newcomers to electronic assembly might run into a few issues. As I mention on this page of my website for DIY beginners, if you have never soldered electronics before, I recommend getting a practice kit like this one.

Technique varies greatly with the type of soldering iron, temperature, and solder, but my approach with my 50-year-old Weller soldering station ("pencil" version) is to touch the solder and the iron to the joint and as soon as the solder flows (less than a second), I remove the solder and keep the iron on the joint for a quick 1-2 count. Most rookies tend to use too much solder, not enough heat, or too much heat. Stop as soon as the solder flows and fills the PCB pad.

One of the most important things is to keep the iron tip clean. I used to use a damp sponge but now prefer this iron cleaner from Hakko.

LEDs

Based on some comments in the Google group about a small number of defective LEDs - discovered only after soldering onto the lamp board - I decided to test them all before assembly. Since there are 126 LEDs (!) in the kit, I put some in series and powered them from my bench power supply through a 1 K current limiting resistor. Since the LEDs begin to light up with about 1.8 Volts across them, 16 in series require about 28 Volts. I had no defective LEDs, but it was worth checking them out. You could test them one at a time with a 9 Volt battery and a resistor, but it would take you a long time. You can also get a cheap diode/transistor tester, like some builders have done.

16 LEDs tested at one time

LED ambiguity

The positive (anode) lead of LEDs is supposed to be longer than the negative (cathode) lead. I had a couple in the kit where the leads were the same length. You can double-check for the cathode because the base of the LED will have a small flat adjacent to it. Fortunately, the CEDS team includes spare LEDs in case you are not sure.

Diodes

The switch board with the diodes inserted

There are 74 diodes on the switch PC board. I used the "calibrated finger" technique to bend the leads by hand (as opposed to using a lead bending jig) and they fit into the through-holes perfectly. I then used strips of 1" blue painter's tape to hold them tight to the board before flipping it over for soldering. The diode orientation for each device is clearly marked on the board.

Note my PCB holder which I recommend for tasks like this.

A note of caution - some of the adjacent diode pads are very close together and I managed to form a couple of bridges during the soldering process. I briefly touched the joints with my soldering iron after clipping the leads to remove the bridges.

Watch out for solder bridges here

Resistors

The resistors by the Pi GPIO connector do not lend themselves to the calibrated finger-bending technique. This is because the pad spacing is almost the same as the resistor body length. You should bend the leads as close as you can to the body, but even then, you may need to pull the resistors flush to the board with needle nose pliers. That is of course, unless you are OCD-free and don't mind the resistors sticking up a little.

Checking for daylight under LEDs

LED Soldering

Follow Oscar's write-up on the LED soldering - just do one lead at a time and then check for flush mounting to the pcb. Even with the guide firmly pressed down and blue tape over all the tops of the LEDs, I still had a few where I could see daylight under the bases looking across the board horizontally. As Oscar mentions, reheating the lead on an LED while pressing down on it will force the device flush to the board. Also - visually inspect the leads to ensure the longer (anode +) leads are all oriented the same way. Then solder all the second leads and clip.

Testing

Here is a video showing Oscar's initial test program running. This is with the Pi temporarily attached to the GPIO header and booted up with the PiDP-10 software installed. You invoke the test program from a terminal window and it randomly blinks all the lights. You can quickly tell if you have a bad LED or a short/open circuit on the boards. Then you can test the switch PCB by manually shorting each switch with a jumper and watching the test program output a code. This will verify the scanning circuitry and the diode array before installing the switches. Very nicely done, Oscar!

IMG_1357.mov

Switches

I used wide painter's tape to hold the switches in position before soldering per Oscar's instructions. This made alignment easier. I did groups of about 12-15 at a time and used the previously soldered ones to help hold the tape taut. I also soldered all the mounting tabs after final "bend" adjustments to ensure good mechanical rigidity. With my iron, I only needed about 2-3 seconds of heating to get good solder flow on the actual switch contacts, so I was confident that I was not melting the plastic. I have used similar switches on other projects and found they cannot take too much heat; the plastic body melts and the terminals become loose.

Assembly

Adding a tiny dollop of clear silicone grease to the sefl-tapping screws made them much easier to drive in and reduced the chance of breaking a plastic boss.

I had to find the optimal Phillips head driver for these screws - a PH-2 driver seemed to work best.

EDIT - one of the Google group members pointed out that these are actually called Posidriv screws - not very widely used here in the US - but you can find the proper driver on Amazon, like these. The drivers have designations like "PZ-2".

On the switch board, there was one screw that looked like it could cut through the solder mask and potentially short a couple of traces together, so to be safe, I added a small nylon washer under the screw head.

On the lamp panel there is a similar issue with the screw just to the left of the ribbon connector. Same thing here - a small nylon washer does the trick.

I had already installed the PiDP-10 software on a Raspberry Pi 5, so I just had to re-install the Pi into the GPIO header and connect the power supply. I already knew it worked during the initial test phase.

I had installed my Pi 5 with the official Raspberry Pi 5 Active Cooler attached, which I highly recommend. With several jobs running in ITS, the Pi's temperature tends to climb rapidly, so I think it is essential. Oscar mentions that the Pi cover that comes with the kit may have some interference with the cooler's mounting tabs. In my case it definitely did - the cover forced the mounting tabs to press in, causing the heatsink to lose contact with the Pi's chip surfaces. The solution, as Oscar suggests, is to drill two holes for the mounting tabs in the cover, as I show here. You definitely want to check this if using the cooler.

Holes drilled to prevent cooler tabs from being pressed in

Done

Final assembly was a breeze and ITS booted right up.

I did not install the big fans that Oscar likes - I did not see the need to simulate a loud computer room since I spent way too many years in them, haha.

Also, I did not install the RS232 options since I don't have serial terminals.

I want to learn more about the switches and their functions - but for now, playing with ITS software and the simulated terminals will keep me busy. I also intend to play with TOPS-10 at some point.

Many, many, thanks to Oscar and the team for making this a hugely enjoyable project!

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