Lear-Seigler ADM-3A+

[bladamson]

Hey folks. I picked up this LSI terminal today. It looks kinda like an ADM-5, but the top row is a little different and it says "ADM-3A+" on the back. I haven't been able to locate a manual for this particular model. Do any of y'all know anything about it? Thanks!

 

[Eudimorphodon]

Bitsavers has a repair manual which covers both the 3A and 3A+. It sure doesn't go into great detail what's different between the two. It kind of feels like it's just the different keyboard?

 

[bladamson]

Oh, derp. I was probably looking right at that one before and not realizing it was also for the 3A+, heh.

Thanks, and sorry for being such a dummy lol.

 

[Eudimorphodon]

Heh, no problem. A bad case of the derps can strike at any time without warning, no one is safe!

If you find out there's anything significant different between the two models besides the keyboard that would be interesting trivia, I guess. It's positively remarkable how the manual doesn't explain it at all, it just has a few figures that say they're for a 3A+ and... that's about it. Never seems to mention it in the actual text at all.

 

[tingo]

Interesting, Terminals wiki only have the ADM-3A, not the ADM-3A+. Perhaps you could add some info there.

 

[VERAULT]

Never seen an "a+" looks strange without the screw cover for the dip switches on the left side of the keyboard.

Great pickup Lee. Hope it didnt set you back too much. I traded my ADM 3/A to another member here I owed some money to.. The prices on those things have skyrocketed in just the past 4 years.

 

[Al Kossow]

Was this the version produced by Zentec after they bought LSi ? does it have a small microprocessor CRT board inside?
Pics and rom dumps would be useful.

 

[bladamson]

Was this the version produced by Zentec after they bought LSi ? does it have a small microprocessor CRT board inside?
Pics and rom dumps would be useful.

No, it's the big board with all the discrete logic except for the ROM and UART. Manufacture date stamped inside the case is 1981 though. Very late!

I promised myself I wasn't going to mess with this thing until I finished a couple of other projects, but I couldn't help bringing it up just to see. It appears to work! Although the CRT has some wear..... And I haven't tested the serial port yet.



The board appears to be a bit different than the board in the manual linked above. DIP switches are in different places and numbered differently, but everything is labeled according to function so no problem there.

 

[stepleton]

Was this the version produced by Zentec after they bought LSi ? does it have a small microprocessor CRT board inside?
Pics and rom dumps would be useful.

Jerry Walker had a repair series on YouTube for an ADM3 terminal with a small board inside. I can't recall whether the machine was his or someone else's, and I don't know if this is the Zentec article you mention, but he may still have access to the machine for photos and ROM dumps.

 

[VERAULT]

Jerry Walker had a repair series on YouTube for an ADM3 terminal with a small board inside. I can't recall whether the machine was his or someone else's, and I don't know if this is the Zentec article you mention, but he may still have access to the machine for photos and ROM dumps.

He did three or four ADM3 terminal repair series. I think the latest ones were his the first 1 or 2 were repairs. He did reverse engineer the main PCB which he sold for a while. Not sure if he still has them for sale.

 

[stepleton]

The video I linked is specifically for the terminal that has the small board.

 

[Bruce Tomlin]

ADM3 terminal with a small board inside

I was hoping that would be the answerback board plugged into the regular board, but it seems to be a not-so-dumb terminal board from a very late "Tenth Anniversary" ADM-3. There is almost no information about answerback in the service manual beyond "it goes here". I try to think about how it could have been done with a small PROM and discrete logic, and it makes my head hurt.

DIP switches are in different places and numbered differently

That second picture answers the question I had about where those config switches went. They almost could have put an access cover to allow changing them without opening the clam shell.

 

[granzeier]

Wow, it works, nice! Now I'm a bit jealous - I wish that I wasn't moving, but more, I wish that I hadn't been so lazy. I'm glad that this went to you.

 

[bladamson]

Wow, it works, nice! Now I'm a bit jealous - I wish that I wasn't moving, but more, I wish that I hadn't been so lazy. I'm glad that this went to you.

Well, I haven't actually tested the serial port yet, not even with a loopback plug. That stuff on the screen was just local echo with the switches set for half-duplex. It's entirely possible that there's something wrong with the UART and all that associated stuff.

But that can be fixed if it is broken. The high tension is definitely working, which is what I was really fretting about. It seems to be about impossible to get the right flyback transformers for any of this stuff nowadays, and I am not smart enough to rebuild them.

 

[Frankenrose]

Very jealous haha, let me know if you’re ever looking to sell. It’s one of the very few vintage computers I want. Currently my only one really.