I've posted about it on Mastodon, but I recently finally got a Lear Siegler
ADM-3A dumb terminal from a seller on eBay! Owning one of these has been sort
of a lifelong dream of mine ever since, as a kid, I saw one featured on the
cover of an old kids' science book, Young Scientist's Space and Technology.
Something about it really captured me, and when I was a little older I was
able to learn more about the terminal online.
I actually bought a non-working ADM-5 terminal when I was in high school from
a seller on Craigslist, but as I was beyond inexperienced with electronics at
the time and had very little in the way of tools or skills I was never able to
fix it. I still have it, and still plan on fixing it at some point (in fact I
have a page on this very Gopher Hole about my ideas to retrofit a RPi and
modern keyboard inside of it), but it's definitely going to require a massive
overhaul. When I first got it all of the characters on the display were just
blocks and it didn't seem to respond to any input at all, so it's likely more
than a simple RAM issue. 2102 SRAM chips are also fairly expensive (at least
for a large quantity) and in my limited experience aren't very hardy, so it's
going to be a while before I touch it again. The video board needs recapping
and one of the voltage regulators is completely missing thanks to younger me.
Eventually I'll get around to it.
As far as the ADM 3A goes, they've gone up in price on eBay massively in the
past two years. Even non-working units can sell for upwards of $700, which is
insane. I lost an auction for a working one, and aggravted with this I set a
max bid of $800 on the next one that became available, tired of continuously
putting off the purchase, especially when they certainly weren't getting any
cheaper or easier to find. Thankfully I actually won the auction for around
$630. The pictures looked like they were taken using a potato, which was
fitting since it'd be shipping from Ireland, and the condition was listed as
non-working, so I wasn't completely sure what to expect. The seller asked for
a few details for the customs slip a few hours after I ordered it and then
shipped it the next day. To my shock there was a package from Dublin on my
back porch two days later, the terminal having arrived sooner than even some
of my very much so domestic Amazon purchases. I brought it into my house and
set the box on my kitchen floor, just hoping that it had made it here in good
condition.
And it had! It was dusty as all could get, both inside and outside, and the
end of the power cord was badly frayed, but it seemed like the picture tube
itself was in good shape and nothing seemed damaged. I got it all cleaned up
with paper towels, water, a magic eraser, and some rubbing alcohol, and I
managed to redo the European plug (so wonderfully designed and serviceable
that a jealous sigh penetrates my thoughts even writing about it). After that
I had to wait for a 240V transformer to arrive to do anything further with it,
so I set it up in my living room to let it wait. I actually did notice, in the
meantime, that the metal plate in the CRT assembly which holds the flyback
transformer had actually come loose from its mount, and I thanked my stars
that it hadn't resulted in damage to the neck of the tube.
Once my transformer arrived, I went to test turning on the machine, but
unfortunately it didn't power on. I grabbed my multimeter and double checked
that the internal fuse was still good (I'd already checked the fuse on the
plug itself when I'd repaired it before), and everything seemed to check out.
After some probing, all signs pointed to the power switch, which had seemed a
bit off in its action and in fact had had some strange green substance appear
on the sides of the button. I noted what color leads went where and pulled it
out to see if it was fixable. I popped it apart and sure enough the entire
inside of it was filled with green goo -- a mixture of old leaked plasticizer
and copper corrosion, at least according to my guesses and the internet. I
spent a good while trying to clean all the goo out of it, going between manual
cleaning with a brush and some funky sonic magic with an old ultrasonic
jewelery cleaner I had in the closet. I let it completely dry overnight, and
the next day still had a bit of goo to pick out with a toothpick before
reassembly. Once reassembled, the switch was nice and clicky and tactile, and
once back in the terminal it finally let power through.
The machine began buzzing to life, and then within a few seconds I watched one
of the power transistors flash blue right in front of me and start smoking. I
turned the machine off quickly, and a few minutes later turned it back on
without any further complication. No idea what that was all about, as the
transistor still seemed to work and tested OK with a very basic multimeter
diode test, but whatever. There were instead two pressing issues with the
terminal, which were that half of all the lines were simply blocks (a memory
issue) and also the brightness on the CRT was turned up too much, leaving a
whitish background instead of a black one and an artifact from the scanning
motion of the electron gun. The metal piece that had been dislodged before had
actually damaged the brightness pot on the video board, so that had to be
replaced, meaning I'd have to pull out the CRT. I ordered all the stuff I knew
I'd need (both to discharge the CRT and replace the pot and chips) and kept
waiting.
All the things for the video board arrived first, as I was able to order them
all from Amazon. I went a bit overboard and bought some insulated gloves for
electrical applications, but also did the reasonable thing and bought some
good alligator clips for attaching to the screwdriver I'd have to stick into
the anode cap to discharge everything. Thursday night I got everything
together, pulled out the tube and the boards, and managed to desolder and
resolder in the 100Kohm brightness pot while listening to an audiobook. It
took three or four hours, but after the reassembly, I was able to correctly
adjust the brightness of the display.
On Saturday my 2102 SRAM chips and 16 pin sockets got here, but since me and
Paul were going to see Suzume in theaters that day, I put the terminal on the
backburner. On Sunday I continued listening to my audiobook and spent a full
four hours desoldering the existing chips and soldering on sockets for the new
ones, promising myself that from then on I'd say to hell with it and use
chipquick to remove ICs as surely it had to be less painful than trying and
failing to suck up all the solder with a desoldering gun time and time again.
Either way, once fully reassembled I was still having issues, although the
character output was different than the blocks I'd seen before. I played
around with the chips for a bit before replacing them all again with more that
I had in the tube of them I'd bought, and thankfully that worked. I put all
the ones I had (including the ones I'd desoldered previously) back into the
plastic tube to test later with an Arduino whether they were good or bad.
Either way I'd now had a fully working ADM 3A terminal!! I am actually using
it now to write this very post, and my fingers are a bit tired from the pretty
heavy mechanical keys it has lol. It's really fulfilling to have a project
come together like this, and I'm really happy to finally have this terminal as
a part of my collection. The keyboard layout is a bit weird, so I don't know
how much I'll use it as a Linux terminal as opposed to my VT320, but I'm
definitely going to be using it with my Altair for an authentic experience.
It's great, and I love it!
Also at some point I may go into some more detail, but I also got a Cricut so
that I could make a somewhat faithful recreation of the Lear Siegler
coverplate which was missing from my terminal (and many others like it). I
used some high quality scans from the S100Computing Google Group and black
vinyl and aluminum sheet metal to bring it all together. I'd intended to paint
it blue like the particular version of the coverplate I was copying, but the
black and silver aesthetic really was much nicer to me than I would have
otherwise imagined.
Anyway, pictures are available on my Mastodon! Sorry for not posting more on
Gopher! There are phlogs which I tried to write but ended up quitting halfway
through, so it's been a while since I've actually put anything out there, but
hopefully this post will be useful or enjoyable to someone! I hope everyone is
doing well!
