This ADM-3A was purchased from Glitch at a workshop held at the Vintage Computer Federation in NJ. Glitch got this and many other ADM terminals mostly 3As and 5s from an estate out of a barn… To say the least they were grungy, but the price was right and so I purchased one with the intent to repair, some people purchased ones for parts, some were in not as bad of shape and needed minor cleaning/repair. This one was all there but had horrid cataracts as seen below. This inevitably leaked all down the board which caused damage we will see later.
This is probably some of the worst CRT cataracts I have ever seen, the protection glass nearly wanted to fall off on its own, it only required minor heating with a heat gun to get it to pop loose. My friend Sark helped me remove the glass since I had never done a cataracts repair before this so he showed me how to safely remove the protection glass without imploding the tube :)
After the CRT was cleaned up we re-mounted the implosion protection glass with some proper thickness double sided foam to hold it at the edges then ran around the edge with clear silicone to keep anything from getting between the two layers of glass. This is how the terminal looked after a rough cleaning with some wipes and the cataracts gone. Looking much better already! But there was plenty more work to do…
After the CRT was visable and we gave the board a rough washdown we could start debugging the terminal itself. We powered it up and it showed some rough signs of life! I believe we were able to receive on the terminal but got no character being displayed and could not transmit. The video of the cursor was at-least stable and quite bright. So it was quite promising that we were getting some receive and clean video!
First point of inspection was the chips that took the brute of the goop that dripped from CRT. Removing all those and inspecting traces for any visable damage. Below we can see what it looked like under some of those chips… Quite nasty, this goop was over a lot of the board around those chips and going down into the keyboard which was not a good sign for the keyboard.
Once these chips were removed the sites were cleaned up and inspected for damaged traces, suprisingly most of the traces seemed to fair pretty well. Just needed a lot of scrubbing and some manual scraping to get all the gunk cleaned out.
The board after cleaning:
This is where the project sat for awhile until I got one of the chips I didn’t have readily available in the mail (a 74159). Once I had this chip I populated the sockets and installed new chips. Further testing showed all the same as before. Poking around I found the receive chip was working and sending data down into the logic the transmit chip was getting no signal. At this point I printed out schematics and pulled out the logic probe.
I ended up finding a broken trace from the keyboard decode logic up towards the transmit logic, repaired this missing trace then found that I could now transmit! But we were still getting no characters being displayed… The cursor was just moving forward with each character received. First guess was video ram but that seemed alright, poked at the character roms and found none of the addressing was working! So I traced it back to a chip which wasn’t receiving a chip select signal! I traced this back through some logic to find another broken trace, go figure! I repaired this as-well with some more 30awg wire and what do you know, it worked! I could now transmit and receive and everything was working! Other than half the keyboard… Which of-course was right down the center of the keyboard where the worst of the goop seeped down to.
So the next step was to remove the keyboard. Here is what it looked like under where the keyboard sat, and in frame as-well is our replaced chips.
You can clearly see where the goop ran down… Not looking good. And here we can see what the bottom of the keyboard looks like… Not good at all. This was to be expected really though.
With the keyboard removed I decided to go scrub the back roughly to get a better idea of what I was working with… I believe I also removed the key-caps at this point and knocked off most of the general crud that had collected over the years under the keycaps. I had to be careful not to damage any of contacts inside the key-switches themselves.
After the scrub down it was quite apparent that the damage to the keyboard was quite bad, a lot of broken off pins, more than the keys which actually tested bad, just desoldering and cleaning knocked off a bunch of pins as-well… At this point I knew if I wanted to repair this nicely I had to remove every pin and inspect every one and get replacements. Here is what the pins looked like under the scope, you can clearly see what the corrosion did to some of the pins.
A lot had faired pretty well but many were damaged beyond repair. Luckily I had some random keyboards I bought as scrap from a guy a few years previously that were pulled out of some other terminals and they were in good shape and had the same pins, so I worked on removing them from there. While I did this I threw the now empty keyboard housing and keycaps into the dishwasher and ran them threw a few times to get them clean. Even after that there was a lot of corrosion and broken pins left stuck in the pin’s holes. This took poking at with tweezers to push most everything out, some stayed behind though enevitably, though so long as its neutralized it shouldn’t hopefully hurt anything going forward.
I took the new and old contacts and the old springs which were corroded and ran everything through the ultrasonic cleaner to get all the rest of the corrosion and gunk off them. The springs were corroded which concerned me initially but it turns out its just a copper coating over the spring that corroded away, the steel spring itself was fine!
After gathering all the cleaned parts I started to try and install these pins by hand with tweezers and with some small flat head screwdrivers to push down on the side pins… This was futile in my opinion, I just ended up damaging the contacts and mangling them. The manual shows a tool to insert these pins, so I got to work designing my own in Fusion 360 and after a few revisions and attempts I got a 3D printable pin insertion tool that worked great! Here is what that turned out like:
This worked great and with little effort I got all new pins in the keyboard! Then I installed all the springs and key-stems and had the keyboard ready to be soldered back into the keyboard! Note, there is a longer spring with some extra strength to it, I can’t remember which key it came out of when I was re-assembling, but me and Sark’s best guess was under the space bar for return strength for the larger heavier key, I may be wrong though! Please feel free to let me know if I’m wrong!
Once the keyboard was all soldred back up and I installed all the keycaps again and got everything back in the terminal for one final test, and drum-roll please!
It lives! And pretty much every key works too! Except the “/?” key which I bet is a broken trace… I will beep that out and repair it with some wire later. But hey, for being barn ridden, having a leaky cataract crt and a corroded keyboard. I’d say it faired pretty well only needing 3 traces repaired and some keyboard overhaul. I may have even gotten away with the old chips I replaced but I snipped them out to make removal of pins easier so to not damage the board too much. But hey, a few TTL chips is peanuts in comparison to the value of this historic terminal of whom we can thank for many influences on unix!
Thanks for reading, this is the first of many posts here on my blog about things I am up to. These may vary from long repair blogs to random posts about aquisitions or poking at machines.
UPDATE 2/12/2020: After poking at the terminal again while Glitch was over at my house I found the “/?” key to be unsoldered… Opps! After soldering the switch in the terminal works great now!