Repairing a Bad Case of Cataracts on an ADM-3A Terminal 

“It will give us an error hopefully.“, (c) usagi 2023.

I like how the Centurion has gone from a pile'o'bits to become the reference machine to test all the new projects with.

A couple of cautions about cataracts - different manufacturers used different glues, so not all removals will be this easy. Also, prying and stressing a CRT in the wrong place can lead to implosion, so be careful! Lastly, I'd suggest re-sealing the edge of the re-installed cover all around with tape or even silicone. The static of a CRT will pull dust and dirt into any opening, then you've got debris between the CRT and shield again.

10:05 14 RAM chips is 2 kilowords of 7-bit memory. ASCII only needs 7 bits to represent upper- and lower-case letters, numbers and control codes. 24 rows of 80 characters is 1920 in total.

Great job! You lucked out finding that missing chip. And the screen looks absolutely beautiful now! I don't even see any burn-in on it.

The Design Concept of these terminals were way ahead of their time, kind of like futuristic space age technology. Not only were they smart looking but they were also made to be very serviceable. Tremendous Job, well done!

Well, William Lear was no stranger to operating in wildly different markets! Besides making jet planes and data terminals, he also created the 8-track audio tape system that once was popular in the USA.

10:02 - RAM size - 24x80 = 1920 characters, 14 RAM chips is 2 banks of 1Kx7 bits per character=2048

Just as an FYI, back in the day (early eighties) we did a lot of development work and would need to change the baud rate, # of bits, etc., very often. So we just used a clear tape hinge up top of the DIP switch cover so we would not have to unscrew and re-screw the cover ALL. THE. TIME. Not elegant but functional. The previous owner may have had the same problem and just chucked the cover.

Wow! The inside looked amazing after cleaning, you weren't kidding when you said brand new.

Nice video about this great terminal. Back in the days when I was a student our university had rooms filled with these adm3a's which we called 'eitjes' in dutch (translates to 'little eggs'). The faculty board selected this model because they were the only ones that were 'student proof'. You could literally sit (or stand) on top of them, without breaking them. I spend years using them every day, hooked up to our pdp11 systems and IBM370 mainframe. Those where the days!

They became popular because they were also offered in kit form ($995) vs assembled ($1195). I built one for the Byte Shop in Raleigh NC (1974-5), and only missed one solder joint!

The chips in the ADM 3A you identify as ROM are the character generator ROMs. The chip closest to the edge is a 2513 CGR-001 which was also used in the Apple 1 and Apple ][ through the rev. 4 motherboard. This contains 64 uppercase ASCII characters. The CGR-002 next to it contains the lowercase letters and a set of special characters (including the characters to display sexadecimal values).

Ohhh, that's really cool. I love the shape of it. The way the CRT housing slopes down in the back, it's so atomic age it hurts. Love seeing your uploads!

For the cataract, my suggestion is first to use a body protection suit and an eye protection mask. The square CRTs in some cases don't react well if their bonding agent is removed. When reassemble the protection glass don't use the tape but silicone, so the dust don't go between the glass :)

I saw quite a few ADM-3's attached to Altairs and IMSAIs in the late 1970's and early 1980's. Not a single one of them had the cover over the dip switches!

Lear invented the cartridge player for cars, too. Which became 8-Track cartridges.. 👍

I left school at 16 but my learnings back then of 74series TTL and 4000 cmos still stands me in today with restoring old equipment.. :)

I’n my 2nd year at my uni (1988) I joined the IT staff and got this very ADM3A on my desk, hooked up to a Sun 3/50. It was … ok … but a bit lacking in controls for Emacs. I vaguely recall programs using it had to use a trick to write the very last char on the screen without scrolling: write it to the penultimate position, back up, write an insert char to move it into place. Despite its limitation and lack of speed, I did appreciate two things that made me use longer than you would expect: it was SILENT (fanless) and it took up little space on my desk, compared to a Sun 3. (I have a soft spot for this and would love to get my hands on one)

In the 80s, we had a PRIME minicomuter system that used these terminals at our college. Lovely keyboards and bright, clear green phosphor screens. About 2 years later I went for a job interview at the same college, and saw all these monitors outside just thrown in a dumpster/skip. If only I had been able to save at least one!

Back in the day to test these, we would use the rs232 serial loop back, as you did. Then type a [ U ] and an [ * ] (asterisk) would give you a data stream of 01010101 or 10101010, therefore one could check all data lines to make sure everything was working correctly, This method will find bad RAM memory bits also.

4:22 I don't know if anyone already mentioned it but the "integral implosion protection" refers to the metal band around the CRT, not the glass screen and the mouldy glue. By the way that sticky tape that you used, will probably get brittle over time and because you didn't close off the space hermetically, there will eventually be dust between the glass and the tube.

I'm surprised you didn't use the Shango066 method of de-cataracting. He also uses the heat of the day, but is a lot more careful with the extraction of the glue, resorting to wire knife in order to not put pressure on the CRT. After cleanup, he uses a silicone based adhesive to remarry the lens to the CRT, only with a single bead on the outside edge of the CRT.

The fact that the screen doesn't clear brings you right into the wonderful world of TERMCAP files. The Centrurion must have something like that, too.

Brings back a lot of memories. I used one in the early 80’s for assembly language programming for many years. Thanks for the trip back in time.

Oh, Dave you are seriously producing some amazing results here...both with this terminal AND with this video! A double bonus! So cool! Makes me proud to know you... 😉😉

Living in Houston and also suffering this unbearable heat, I'm glad at least one good thing has come from this misery

I cannot believe how *mint* this 3A turned out! Separating the front "shield" from the CRT was particularly satisfying to watch. I am interested to see how you tackle the missing key caps and DIP-switch covers. Truly this is a magnificent data terminal. Gorgeous.

Many people remember the ADM-3. There was an earlier model ADM-1. Digital Equipment is famous for their VT-100 and VT220 series terminals, but their line started with the VT05, VT50 and VT52 terminals. The VT52 was the first to have an 80 column screen with lower case display. I had a VT05 terminal back in the late 70's. Actually, I had a VT05 terminal case with a monitor and keyboard, but the electronics inside was missing. I had planned on building a small computer inside of the terminal case.

I think the implosion protection is the metal implosion band around the cap of the CRT, not the glue or shield (I worked in a CRT factory in my late teens). The implosion band helps to keep the screen from flexing and when the CRT does shatter, it helps to contain the energy imparted through the glass. When CRT's impose without the band, glass goes flying everywhere - at 3am on midnight shift, an implosion will wake you up in a hurry.

Brings back memories. I worked at Lear Ziegler in the late 1970s. I tested ADM-1, ADM-2, and ADM-3As.

Another fun fact about Lear-Siegler is a lot of the upgrade seats in GM products from the 80's and early 90's were produced by them. So the 12 way and such seats with the fancy lumbar.

8:16 That is a KSR33 (no tape reader/punch) and it is the model used as ICL operators' terminals from the 1900 series, including volume knob to listen to the processor being stuck in a loop 😁 Actually, we used to be able to tell when the highways department were running an illicit number intensive job from their MOP terminal, which interfered with payroll and creditor processing until they finally stumped up and paid for a floating point unit and an extra 32K of core! Happy days.

you really should have worn a face shield and long sleeved jacket when working on removing the protective glass. If the screen imploded you'd be showered in glass bits.

That was really cool and the bunny flop at the end was adorable. Thanks!

So good, made me so happy, brings back some amazing memories of being an engineer 40 years ago

I used one of those when I was in school in the 70's. It was great. It replaced a Teletype terminal that was slow and noisy. We still had to run a paper tape to load code. We used a HP2100 computer.

Makes me so happy to see this tech history get brought back to life!

11:28 this is so satisfying there should be entire channels of this

Small correction: The Lear Siegler corporation predates the Learjet corporation and was completely separate. Bill Lear had no connection with Lear Siegler past 1961 and started the Learjet corporation in 1962. Further, Lear Siegler only started making terminals in 1972. And Bill Lear had sold Learjet in 1967. As a serial entrepreneur Bill Lear was unique in the variety of areas of interest and invention. But he rarely stayed involved once a business idea was established.

I love it when the item you're working on gives back the missing parts. I've had two recently purchased wind-up phonographs cough up missing parts that would have been a pain to find. I don't even ask how it got there, I just thank the part for showing up again so it can get back to work! (I have radios older than that Bendix computer. Wait: I think one of my tube radios IS a Bendix!)

I used to sit around in the university library in my hometown, in the early 90s, playing DikuMUD on an engineering student's Apollo Domain 2500 that he somehow managed to get hooked up in the data center, via an ADDS Viewpoint 3A+. At the time, the library's "computer lab" was entirely populated with ADDS terminals hooked up to a concentrator via Gandalf connections.

A fantastic restoration of a beautifully designed device. They really put some thought into making it serviceable. "Asbestos a can", eh? Nicely cleaned. Winner winner, chicken dinner :) My goodness, 43 friggin' degrees? That's wireless energy transfer from a fusion reactor after all ;)

I remember using a Tektronix storage-screen terminal (I think it was a 4014) during my PhD. I used it because I nobody else wanted to. This was in 1991, so it really was a relic of a bygone age at the time.

Nice design. I couldn't afford an ADM-3A terminal. So I bought a Heathkit H9 terminal and assembled it. It had 7 circuit boards: power supply circuit board, keyboard circuit board, RAM and counter circuit board, input/output circuit board, character generator circuit board, timing and processing unit circuit board, and video circuit board.

Don't worry about the missing DIP switch cover. Most of the terminals at my school (in 1987) were missing it, most usually because people tinkered with the duplex settings. It was fun when people used ballpoint pens, or worse, pencils to set the switches!

You took me back to fall '76, when I first met my school's new Altair 8800a computers, one on an ASR33 and the other on an ADM3A. Cool!

Am I the only one feeling warm fuzzies while watching these machines get a new lease on life instead of rotting in a dump?

Spent the first couple of years as an EE using one of those to work on several computers including DEC 11/23s to program Fortan IV, assembly, and early CP/M computers to program assembly language on 8039 micros, and maybe other stuff - can't remember after 40 years 😂

When I worked for Dictaphone, we had a dictation management system that was built around the Intel SBC 80/20 and there were two ADM-3A terminals. They had a dark grey base and a light grey top, but I forget where the Disctaphone logo was placed. I loved those terminals. Wish I had one now.....

Finally a good use for all this Texas heat! Well done.

Nice work. Might be worth closing the air path into the cavity between crt and front glass : this will stop it filling up with new dust and grime (as it will probably tend to with the influence of the high voltage)

8:54 - Someone was allowed to really flex their industrial design degree on this one.

Woah, I didn’t know CRT’s with that damage could be fixed, great video!

siiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiCk! 110*f!!?? Don't bake to death out there, you're too precious to us.

Saw your gaff on 8 Bit Guy so I get why yr rabbit is that relaxed! Thank you for making the technical understandable!

Awesome to see those cataracts fixed! Great job!

Glad to see you finally got to work on this, and glad to hear that my "Texas sun" suggestion back at VCFSW worked for you! Funny about the UART chip hiding like that, but at least you have your lowercase ROM. I had to make an EPROM adapter board because mine was missing. Also my lid doesn't have those retaining ring thingies, the hinge rods are part of the lid and it just slides off sideways. All your chips are socketed, so I think yours is an earlier design. My case is brown, while you have what I think is the better blue color. And I'm glad mine wasn't anywhere near that dirty and had all the key caps! But I did have to swap a few keyboard plungers (the hollow square that goes up and down) from a junk keyboard because the corners were splitting. As for the glass, I didn't use as much sticky foam, you did a much better job. Seeing that raster is a wonderful thing, because you know that all the analog stuff is working! The good side of that shorter brightness pot is that it doesn't stick out where it can get bumped. EDIT: you might want to seal the edges of the CRT glass by wrapping clear packing tape around the edges. That keeps dust from getting in through the gaps of your foam. The screen frame has a surprising amount of overlap, so you can be sloppy by at least half an inch without it showing. You don't really need that 2-3 jumper to do local mode, there's a dip switch for that in there somewhere. (Also don't use a pencil to flip the switches, it actually says so in the manual!) The SRAM is 7 bits wide, with the second row being the difference between the 12 line version and the 24 line version, and the 7th bit for the lower case option. It's more obvious when most of the chips aren't socketed, and unlike yours, mine only has sockets for the big chips and 8/14 of the SRAM. And speaking of lowercase, you need to get yours showing some! The ADM-3A lowercase font is a bit unusual and distinctive, it sticks up by a scan line to give more room for descenders.

I remember back in school in the early 90s, if I was stuck using an ADM-3A, you had to wiggle that pot, hold your breath, and hope for the right phase of the moon, to get a solid image.

If there's some generous French person in this comment section who happens to still have a Minitel he has no use for, please consider offering it to David. I'm sure he'd enjoy the hell outta this landmark of _télématique_ technology...

Wow. I used an ASM-3A from 1977 to 1978. Nice little terminal.

Shango does a lot of cataract repairs, as he does a lot of older tube TV's. He usually uses a silicon around the edge to completely seal it as if there is any gap, like corners with double sided tape, it can allow dust to get in and I can imagine dust between the CRT and the shield would likely be really annoying. Looks like you have a bit more work to do on this terminal to just get it 100%, but I think finding the missing key may be a the hardest thing of this., but it really is fantastic to see it up and running. If I recall this could be even sharper than how you have it with a little tweek of the focus. Going on memory, I think these had a very sharply focused CRT.

I've watched a bunch of cataract removal videos from Shango066 here on the 'Tube. Never saw him de-cataract a terminal though; Just antique televisions. Great work. Love this channel!

@shango066 Has done many excellent videos on cataracts. Safety is super important. Flying glass is no joke.

The ram was probably organized as 2k x 7 bits. No need to use 8 bits to store ascii characters.

I was really excited seeing this terminal come to life. It's amazing how the terminal works without a CPU and only utilizes TTL logic. Video terminals played a big part in my early tech days. I worked for Visual Technology, as I mentioned before, building, testing, and eventually repairing various models as well as their PC-like equipment and later the Ontel Corp terminals and systems. The keyboard switches look familiar. I think they may also be used on some of the early Atari computers, not the later 800 X/L which was made with far less quality.

ADM-3A. I had one connected to the Altair 8800. Then moved it to a CPM-like OS called ISIS. I wish I could remember the manufacturer of that machine. Old memories triggered when that screen lit up! My experience with CRTs is more with black & white TV CRTs. When I replaced one and discarded the old I would take it to the dump and knock the neck off with a ten foot pole. I never had any glass shards, the neck popped off cleanly. But I would recommend treating the CRT as if it were a bomb, eye protection at minimum. A face shield would be good.

Brave soul with your face that close to the caps first power up!

this really loosened my glue

I remember that thing from the perspective of an extremely bored child. On more then three occasions waiting in the library checkout line in the 80's with my mother, I walked to the desk at the front of the line just to gawk at the side profile of that thing and laugh at how ugly it is. Many years later Apple came out with the first imac which looked similar enough to trigger the memory. Nowadays I understand most if not all of what's inside (and this video is very interesting cause I've never seen the inside). But it's still just about as silly looking. Iconic though now somehow!

My first experience with the ADM 3A was in 1985/1986 at SUNY at Buffalo. Along with VT220s and over VT100 compatible terminals was how we interfaced with the VAXes. It's also how we registered for classes. I never really took to them because I couldn't use the full screen editor mode of EDT.

"Fifty years of grime" - that would be a good title for a book

Great video. I've seen a few of your videos but this is the first one that caused me to subscribe. I'm old enough to have used many of the terminals mentioned. Including a Teletype ASR 33 with paper tape punch used in my first programming course in 1976 as a high school sophomore. I used to subscribe to the ACM Annals of the History of Computing journal because I think there is value is understanding the history of modern computers.

14:37 - Molex connectors are NOTORIOUS for flaky connections! IIRC, Southwest Technical Products' 6800 system (1975) in their infinite wisdom, used Molex connectors for data and address lines!

I started watching your videos when you did a cameo with the 8bit guy and at first I thought your videos were too long but now I am hooked! Plz feel up the good work!

Great job Dave. Really enjoy your videos and that terminal is a real looker!

Oh, yes, that brings back memories, "Mr computer engineer, my screen is blank." (I adjust the contrast.) "Oh, you've fixed it, aren't you brilliant!!"

You have such great skills on these old machines. Love watching your videos.

This unit looks great and your video was awesome. I used to work on these in the early 80s and the unit you have is in extremely good shape even compared to the ones I was working on 40 years ago great job

The aesthetic of the terminal is *chefs kiss*

Vim fan remembering Bram, and the huge influence of the ADM-3A

Very nice restoration. I'm amazed how good that Simple green worked on the power supply parts. You got super lucky with the finding of the missing chip. That text looks great on there and the keyboard works great after 47 years!

I love your show. Amazing job resurrecting those vintage computers - a pure pleasure to watch 🙂

Wow, really fun project, thank you.

The chassis color and everything about it is a product of it's time when business machines were art... and it's glorious. Even cars like computer hardware kinda all looks the same now. Dealing with a 5 volt rail in something that ran the regulator hot enough to turn the screw to charcoal and what I think is a dead op-amp in some radio station gear while watching this. Keep up the awesome content. Just like in my industry while some of the hardware is getting rare but the people that know everything about it are even more so. Us young... ish.. guys have to learn this stuff and archive it the things that ain't in the manuals before it's gone. Glad you and other youtubers I already see in the comments are a part of that.

Bonus Trivia - Bill Lear invented the 8 track stereo too.

I love this thing! Gorgeous! Iconic!

Great job! My only concern is that humid air could enter the space between the CRT and the protective glass and condense. It is amazing though, and it shaped up well!

I've had issues with caps in a 1958 tube/valve radio and also on an MD recorder - supplying caps with power for a while or switching on and off will usually caps that are still sleeping because of not being used in ages.

Beautiful!

this is the highlight of my day

Great work as usual! 👍

Great job restoring this beautiful computer!!

Great job on the cataract repair but you really should seal that thing ... Those open corners,,, something's gonna get in there and it's gonna be visible and drive you nuts.. Put a little silicone from double stick to double stick and seal that thing.... :)

Never seen such machinery live. But interresting A.F.!

Glad you got it going. These were awesome terminals when they came out. A huge step up from working on an ASR-33! I remember there was a big divider chain that generated all the frequencies from a single crystal; vertical and horizontal sync, dot clock, baud rates (getting 110 was complicated), all the way down to the cursor blink. These were also famous for having primitive keyboards with no debounce circuitry. Sometimes pressing a key once would generate a bunch of that character. The "debounce" (such as it was) was provided purely by a capacitor somewhere in the key scan circuitry. And the fix was just to replace it with a larger capacitor. I don't remember the details, but it should be pretty simple to figure out if you've got the schematics. I think LSI even provided a retrofit kit.

Dude works on useless terminals. That is dedication. I bet the picture looks better if there is a glue between the screen and protector. Try Super Clean. It’s like Hiroshima to grease. Nothing compares for cleaning oils.

Awesome fix for the cataract issue!!

Also don't be disappointed by the picture wobble. Ours did that--a 1970's era building had too many magnetic fields to count!

Wow!! That turned out *really* well! Can't believe the missing IC was just lying in the bottom of the case, and that it worked perfectly fine! Very nice!