Bringing An ADM-3A Back To Life

August 16, 2023 by Chris Lott 22 Comments

[David] at Usagi Electric ended up with an old Lear Siegler ADM-3A terminal in a trade a couple of years ago. But the CRT face was plagued with so-called cataracts, and the condition of the insides was unknown. The video ( below the break ) shows the restoration process, which went quite smoothly. [David] was relieved that the CRT repair in particular was easy, a fact he attributes to the Texas weather —

The temperature was 110 F / 43 C when he set the CRT outside to bake in the sun for a few hours. Afterwards, removing the “integral implosion protection” plastic screen went better than expected. Everything cleaned up nicely and the screen reinstalled. Introduced in 1976, the main electronics board is chock full of TTL chips with nary a microprocessor in sight. Fortunately the board was substantially intact, and a single missing chip was found hidden underneath the board. [David] gets the terminal up and running in short order, and is confronted with an annoyance familiar to gray-haired programmers who grew up in this era. Most terminals had different sets of commands to control features such as cursor control and clearing parts or all of the screen. Programs often assumed a certain type of terminal. Some terminals could be configured to behave in different ways, and some programs offered the user a choice of terminals. Today your terminal emulator probably still has a few choices of which kind of terminal to emulate, VT-100 being the most common. And eventually some operating systems provided a terminal abstraction, like Unix’s termcap for example.

If you were around in the era where terminals like the ADM-3A were scattered everywhere, what was your favorite terminal and/or terminal feature? And today, do you have any favorite terminal emulator to recommend? Let us know in the comments below.

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Recreating A Numpad For The ADM-3A

January 8, 2023 by Matthew Carlson 1 Comment

[Evan] already had a working ADM-3A (a dumb terminal from 1976) but was starting to eye the accessories hungrily. He had only seen the numpad on Wikipedia and in the manual. So when he found some authentic stackpole numpads on a surplus sale, he grabbed them and converted them to be ADM-3A compatible.

Looking at the schematic for the ADM-3A, [Evan] figured out that the numpad was parallel to the keyboard matrix, not adjacent. This meant that pressing a five on the keyboard was electrically equivalent to pressing a five on the keyboard. So holding shift while punching on the numpad leads to some unexpected characters for those of us used to more modern keyboards. Since [Evan] only needed to make one or two of these, he soldered wires directly to switch contacts in the matrix that the ADM-3A expects. A 3d printed housing, some rubber feet, and a ribbon cable later, it was done. While it looks slightly different from the original, the vibe is right, and given that it is a stackpole switch, it has the same feel. With the spare numpads, he created a replacement PCB that runs QMK and connects to a more modern computer via USB-C. The files for the 3d printed housing are also up on GitHub, along with the PCBs and QMK configuration files.

If you’re interested in what more you can do with an ADM-3A, why not hook it up to a Raspberry Pi?

CRT Cataract Surgery

August 11, 2017 by Dan Maloney 27 Comments

Back in the good old days, people got their information by staring into particle accelerators that could implode at any moment, and we liked it that way, by gum! To protect against disaster, CRT monitors were equipped with a safety screen laminated to the front of the tube. Decades of use often resulted in degradation of the glue used to hold the safety glass on, leading to the dread disease of “CRT cataracts.”

Luckily for aficionados of vintage terminals, [John Sutley] has come up with a cure for CRT cataracts. The video below shows the straightforward but still somewhat fussy process from start to finish. You’ll want to follow [John]’s advice on discharging the high-voltage flyback section of any stored charge; we speak from painful experience on this. With the CRT removed from the case, removing the safety screen is as simple as melting the glue with a hot air gun and applying gentle leverage with a putty knife. We’d think a plastic tool would be less likely to scratch the glass, but [John] managed to get them apart without incident. Acetone and elbow grease cleaned off the old glue, and the restored CRT looks great when reassembled.

With its cataracts cured, [John] says his next step is to restore the wonky keyboard on his Lear Siegler ADM-3A terminal. Perhaps he should look over this VT220 keyboard repair for ideas.

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RasPi Powered ADM-3A Dumb Terminal

February 8, 2014 by Todd Harrison 20 Comments

[Andrew Curtin] tipped us off to another excellent resurrected vintage one piece ADM-3A dumb terminal. [Andrew] not only resurrected this sexy machine by breathing life into her once more after 37 years but he also got it connected online to retro.hackaday.com for those coveted retro Super Nerd bonus points.

As with other ADM-3A terminals we have seen on Hackaday, the terminal screen can be interfaced over an RS-232 serial connector to a laptop, however, [Andrew] didn’t have a laptop to sacrifice so he utilized the now popular laptop stand-in RasPi. It’s a clever form factor solution which makes it appear more like a standalone computer for the first time in its life.

To make the hack work he needed a serial adapter to link the ADM-3A terminal to the Ras-PI so he constructed one for himself. It’s another clever solution but he didn’t share much information on this build. Maybe he’ll comment below or elaborate on his site with more details on the construction and utilization of the adapter board from the Ras-PI so others could easily repeat this fun hack.