Lear Siegler ADM-3A

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Well I finally got a hold of a ADM-3A terminal. This is one of those toys I’d been looking for a little while, and one finally popped on on eBay for a reasonable price ($29.95 before shipping).


The reason the unit went for such a low price is due to the condition of the screen - it suffers from “CRT cataracts”, a somewhat common malady on older CRT equipment. My understanding is that the glue layer (polyvinyl acetate or PVA) that binds the lens to the CRT breaks down over time and causes patches and specks which make it difficult to use the screen effectively.

There are a couple methods to repair this condition. One option is to remove the lens with a heat gun, clean and reattach. The entire CRT can also be replaced; new tubes can be had for around $50.



The ADM-3A arrived in its original packaging, which was quite a surprise. All the original manuals, warranty cards, etc. were included and in great condition. The ADM-3A itself wasn’t so lucky however - the unit and the plastic bag that contained it was smeared with a nasty, brownish liquid.

Indeed, the entire terminal was awash in this strange oily residue. I have no idea what it is - it almost looks like something that might leak from a battery, but the ADM-3A doesn’t contain anything like that. I opened the machine and couldn’t find anything that looked like a source - it was all over the place. It took me about an hour to clean it up, blotting at the logic board with a microfiber cloth.

Of course at this point the CRT cataracts were the least of my worries, and I was a bit too flustered to bother to take pictures of the oily mess. It’s kind of interesting in a way - the unit shipped from Houston and the auction closed right after Hurricane Ike. Whether it’s related, I have no clue - but I was concerned that the unit may not have even survived at the time.

PICT1484.JPG After the cleaning, I decided to give the unit a try. Upon power up, it beeped and a cursor appeared in the home position. I toggled the local mode DIP switch and typed some text on the screen. Yay!

The keyboard works great and the CRT actually seems pretty decent underneath the lens cataracts, so it may be worthwhile to try removing/cleaning the lens first. I figure if I break it I can always fall back on the new CRT route.

The other thing to look out for is a lowercase ROM - the socket is sadly empty. There is a site with some guidance on producing a lowercase ROM utilizing an EPROM and an adapter board - I’ll try contacting the author and see what can be done to get one going.

All in all, I’m happy now that the unit is cleaned up and functioning. The fluid bit is really weird though - hopefully I don’t sprout a new limb or something.

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This page contains a single entry by nekonoko published on September 26, 2008 6:31 PM.

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