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ADM-3A refurb

G

Greycon

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May 12, 2015
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Well, today I became the very proud owner of a working 1980 Lear Seigler ADM-3a. It's going to hopefully be the finishing touch to a homebrew CPU made from LS-TTL. I have a couple of questions, an this forum seems to be generally populated by adults who don't tear strips off people :)

1. The keyboard. A few keys stick down. I have been able to release them, and remove the keycaps. From my limited research to date, they are Hi-tek High Profile keyswitches. I will vacuum around all of them, and clean the keycaps. Can I spray electrical contact cleaner on the 2 little arms in the actual switches?

2. I haven't opened it up yet, that's tomorrow's job when it's bright. Should I re-cap it? As I mentioned it is working, but maybe it would be sensible?

3. Are there any other preventative measures that anyone might suggest , I'd like this wonderful thing to stay alive for a few more years :)
 

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Were it my piece of kit, I'd hold off replacing caps until one failed. "If it works, don't fix it"

I hated the ADM3A and Hazeltine 1400 terminals. There were better ones out there.
 
Chuck(G) said:
Were it my piece of kit, I'd hold off replacing caps until one failed. "If it works, don't fix it"

I hated the ADM3A and Hazeltine 1400 terminals. There were better ones out there.
Click to expand...

OK, good advice - thanks. I have sentimental attachment to the ADM-3a, I used one in the late 70s attached to an Apple II running UCSD Pascal.
 
I got brave and used a pointy-nosed pliers to remove one of the white plungers for a closer look. I can see the cracks in 2 corners. Then, ah, trying to put the damn thing back was nigh on impossible. the 2 metal contacts had sprung together, so I had to use a lock pick, through the plunger and spring to separate them, so the bar in the plunger could go in between them again. Not doing that again, so I am ruling out the idea of widening the waffle slightly with a dremel for each of the keys.

Does anyone know of any kind of currently available lubricant that would work between the plungers and the walls?
 
I recall a thread on these HiTek broken keys sometime in the last year which I can't locate at the moment but I believe I may be able to repair the cracked corners of the square tube plungers if anyone was willing to post me one or two to me (I'm in Australia) to try, I would post them back (whether repaired successfully or not).
 
I didn't like the angle of the screen and the non-detachability of the keyboard. I could live with both, but there were better choices.

The naked keyboards were available NOS on the surplus market for quite some time during the 1970s. I think I've still got a couple of keys from one that I had.

I didn't care for the feel, either.
 
I could understand that but how many terminals have lost thier accompanying keyboards since they are detacheable?

I have been on the lookout for a data terminal that prints to paper rather than a crt. Id like at least one of those in my collection.
 
There should still be quite a few TI Silent 700s around. That was probably the most popular portable one.

Some printer makers, such as Diablo and Qume had KSR models of their daisywheel printers.

And then there's the good old Teletype and the IBM 2741 golf-ball terminal.
 
I am familiar with the TI, not the DEC. I dont want anything too big so teletype is out. I just want something to make a project out of with one of my Raspberry Pi's.
There is someone up in the Boston area with a silent 700 who wants to sell it to me, he doesnt have a price in mind and I dont know if it works or not. What is a fair price on one of those?
 
Depends--is it operational? Recall that it does use thermal paper, so an intact printhead is very important. I think that you can still get thermal FAX paper.

Then there's the model. I'd expect an operational 780 to go for substantially more than, say, a 725.

As to value--you're asking the wrong person. :)
 
VERAULT said:
What is a fair price on one of those?
Click to expand...

They had been selling on ebay for less than $100, but the keyboard collectors discovered some models used Cherry and Microswitch keyboards (most didn't)
and now they're all over $100

You should be aware that it uses thermal paper, the print fades over time.
I don't know how difficult the paper is to find.
 
1944GPW said:
I recall a thread on these HiTek broken keys sometime in the last year which I can't locate at the moment but I believe I may be able to repair the cracked corners of the square tube plungers if anyone was willing to post me one or two to me (I'm in Australia) to try, I would post them back (whether repaired successfully or not).
Click to expand...

Hi,
This may be the one. This guys crafted little square collars that go on the top of the plungers and pull them into shape. I have ordered a set from Ponoko, so I might give them a go at some point. Right now the entore terminal is in bits, as I am cleaning it up, cleaning contacts, etc. Maybe when I re-assemble it the keys will behave.
 
And I forgot to add in my last comment, a thank you for offering to help. I would love to send the plungers to you, but the way the keys are assembled on the ADM-3a, you need a special tool to put them back - pretty much need to replace the contact reed switch when you remove the plunger. :-(
 
Chuck , if you ever happen to find those keys, I'd be delighted to buy them from you.
 
I honestly didn't know it uses thermal paper. I know I have a sealed roll of thermal fax paper in the box somewhere. It may fit. Cant say if it works or not and the seller "doesnt know" These are the only images I have of it.
image2.jpegimage1.jpegimage0.jpeg
 
If the seller's in your neighborhood and your Fax paper is the standard 8.5" wide, it should work for at least a test. Here's a guy who uses it on his unit If you need more thermal Fax paper, I've got several sealed rolls that you can have for the shipping expense. With VoIP, it's not likely that my fax machine will ever be used again.

TI sold a ton of these. Some have internal modems (300 baud with acoustic couplers) as well. I well remember taking one home with me to do some work. Given the age, it's pretty surprising how light the unit is. Here's one with said coupler

(Hmmm, I wonder if anyone's repurposed old Fax machines as cheap, quiet graphics printers?)
 
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Wait do theae TI units only use modems or do they have rs232 connectors as well. The modem aspect is useless to me. Chuck i will have to check my paper i may take you up on a couple rolls. Depending on the rs 232 connector question what should i pay for as is condition?
 
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