ADM-3A and ADM-3 terminals

This page Last updated Feb 4 2024. This Web page is about Lear Siegler ADM-3A and ADM-3 terminals. I describe other terminals on a terminals Web page.

I have a few ADM-3A terminals in various states of repair; this Web page discusses repairs and issues of shipping. I also discuss other ADM brand terminals. Some of these terminals I'll retain for parts, so parts may be available from me. However, due to 1) the Covid pandemic, 2) the trouble, risk, and expense of shipping, and 3) eBay sales of ADM-3A terminals at low as-is as-delivered prices: I am not offering complete terminals at this date. I'll discuss some issues about shipping and selling terminals based on my experiences; those are not offers to sell today. To email me or to ask about what I have, see see my ordering Web page for my email addresses.

LSI ADM-3A terminals
ADM3 terminal:
ADM3A Tenth Anniversary terminal:
ADM-5 terminal
ADM-3a+ terminal
ADM-3a and other models: sales, repairs, issues

LSI ADM-3A terminals

[ADM 3A terminal]

LSI brand ADM-3A terminals, the little blue (later tan) Lear/Seigler terminals so popular in the early 1970's! I acquired a number of these as surplus in the 2000's. Most have lower case text, display 80 X 24 characters, and have basic cursor control and scrolling. Some have graphics upgrades but those I won't likely offer. A Web search will find many Web pages about the ADM-3A. I'll take specifics of repairs and parts issues (mostly) on ADM-3A's on the rest of this Web page under "work"

Here's photos of a typical ADM-3A in "ordinary" well-used but usable condition.

A working ADM-3A terminal, just garbage typed on screen.
An image of the screen. This CRT display reasonably bright, they "dim" with age.
Here's the "terminal logic" board inside. The keyboard is part of the board!
Here's the CRT, and underneath the video board, which was not produced by Lear.
The CRT has "screen burn", years of repeated text display is burned into the phosphor.

more visual conditions of CRT and case

A "better" CRT will have modestly bright and unfuzzy text; a "good CRT" will have dim but usable text, some "mottled" CRT problems. A "poor CRT" will have CRTs which are working but too dim and not usable, and/or with a lot of screen burn, and/or a lot of "mottled" problems.

Here's a slightly mottled CRT and text. Some of these CRT's are obscured by a "mottled" or "moldy" appearance. This is due to some changes in the material between the front safety-glass plate and the CRT glass. This can't be cleaned on the outside, some people painfully remove that plate. The material between the layers is a kind of gel, which over time turns translucent and starts to liquify. Later it leaks and drains goo onto the terminal circuit board. I have some CRT's which look like partially frosted glass; with runs of goo inside the terminal.

People either repair these frosted CRT faces, or of course replace the CRT. I discuss either on this Web page.

Here's some images of a "better CRT" ADM-3A terminal:
the front
the back
the side
the CRT's light "burn in", old text burned into the screen. Not the bright light!.
the back ID plate and connectors the "modem" connector is for terminal use.
the screen with text displayed
the quality of character display Note how lower and upper case look, "decenders" and capitals.

ADM3 terminal

A few people have or spotted the ADM-3 terminal, no "A". It appears to be a variation of the ADM-3A. It has a similar TTL-only terminal board, and a Ball branded video/monitor board. I'll report on it as I get more information. has the ADM3 maintenance manual since 2020. The site also has many of the ADM-3A manuals, look around. - Herb

ADM3A Tenth Anniversary terminal:

During Nov-Dec 2019, George Hunt contacted me, about his repairs of an ADM-3A 10th Anniversary terminal and also a ADM3A terminal that needed lower case. Follow the Web link to see his 10th terminal and notes on his repairs.

ADM-5 terminal

[ADM 5 terminal]

I have one ADM-5 terminal which is white/tan colored, and in working order. The keyboard is different and the case is similar but has a different logic board than the ADM-3A. The CRT on this is clear and the text is readable. It's less iconic than the ADM-3a, it is a later model. It may be available for sale at some point.

ADM-3a+ terminal

[ADM 3A terminal]

In 2022 I acquired an ADM-3A+ or 3A Plus terminal, in working order. It's about the same design as the 3A, but the keyboard includes a numeric keypad. The case is tan, not blue. Here's some photos.

View of the terminal
The logic board, similar to the ADM3A but keyboard has number pad
the CRT and video board. Note the Zenith 121VCBP4 CRT
nameplate on the back

ADM-3a and other models: sales, repairs, issues

Most of my ADM terminal work is on ADM3A terminals. But much of that is common to the other ADM model terminals, and to terminal repairs in general. So this information may be useful for other terminals. Some of it is a little out of date; I'll fix it as time permits.

ADM-3A keycap replacements: DEC VT-100

It's hard to find ADM-3A keycaps. Salvage from other ADM-3A's is scarce. I happened to notice, these keycaps and keyswitches, look a lot like Digital Equipment Corp. (DEC) VT-100 keyboard caps and switches. I tried some VT-100 keycaps, and they fit! Pretty much. Here's photos.

VT-100 "Y" on the ADM-3A keyboard. These VT-100 caps are blacker, cleaner.

black VT-100 keys on the right, dirty ADM-3A keys on the left.
Note the stems on the ADM-3A caps are longer and squared; on the VT-100 short and angle-cut.

various VT-100 number and symbol keycaps.The equivalent ADM-3A keys may vary.

There's a whole engineering world of keycaps, keyswitches and more. I'll just make the point that keycaps vary in profile (construction) depending on which row they are in. Look at your own keyboards to see differences in how they sit, at what angle, and so on. That's all I have time for right now. - Herb

CRT replacements

For weak or cosmetically damaged CRTs, replacements had been available from a CRT vendor; since the 2020's only expensive industrial vendors offer them. Most of us find used CRT's from ancient TV's or computer monitors. The glass on these terminals is about 3/16 inch back from the cover. The CRT's on the oldest ADM-3a's (and some other old computer monitors) have an extra heavy (1/16 inch + thick) added glass plate "glued" over the tube glass. The "glue" seems to be quite thick (1/16 inches +), and over the years develops opaque "spots" and the glue leaks out. CRT's can be mounted flush by adding a few washers, spacers, and / or elongating 2 holes in the original four aluminum clips which hold the tube in the cabinet. You'll need hardware from the old CRT to support the replacement CRT. DO NOT REMOVE THE METAL BAND AROUND THE CRT FACEPLATE That band is structural to prevent implosion!

CRT's for the ADM-3A are called 12-inch CRT's - that's the diagonal measure. The band around the front of the CRT has four mounting tabs with holes. From hole to hole, they measure 11 inches wide by 8 inches tall. The neck is 7/8 inch diameter. The typical ADM-3A CRT is Samsung 12ZBY4N, white phosphor. Other CRTs of the same size, with mounting clips at the four corners like the one on the ADM-3A; and of the same neck diameter (to fit your yoke) may be compatible.

CRT's from other vintage computers or even vintage B&W portable TV's may work or be made to work. I"ve not provided details, but I was able to use a TV CRT with the same pinout, by changing a resistor value on one of the grids, to change the DC voltage to match the proper voltage for that CRT model; the beam was too bright (too much current) otherwise.

In 2021 I bought a rebuilt CRT from a shop, model number VDC1201DPWFBE (white phosphor) was one model they provided. Look on the Web for "rebuilt CRT", or for Ball Brothers TV-12 (a Ball OEM monitor of the same CRT and video board as in many ADM3A's).

graphics expansion products

A few companies, produced digital boards that fit under or atop the "terminal logic". These accepted special serial character sets called "escape sequencies", to create bit graphics on the ADM-3A screen. These were pretty popular in the 1970's and into the 80's, many were made and many stayed in use for DECADES. I have a few of these terminals with graphics cards. I gotta get to those sometime! Help and encourage me, tell me about YOUR ADM-3A with a graphics card, and maybe I'll tell you about mine.

ADM-3a sales, parts and shippping

As of year 2020, I'm not likely selling ADM-3A terminals. The chance of damage in shipping is too high. The Covid pandemic has stressed people in postal services - they won't be careful and things will break. The cost of shipping itself is signifigant. And finally, in year 2020, people on "that auction Web site" are selling ADM-3A's cheaper than I would sell one for. Unfortunately, some of "those sellers" pack large items poorly; they arrive broken. I get a number of customers who want a part because "... the device I bought arrived damaged" and it was clearly shipping damage.

I'll consider selling ADM-3A parts, if I have them and if they can be packed safely. You can ask for parts; please include your location information (city/state/country/postal code), I will insist on it, so I can inform you of the costs of shipping.

Costs of shipping are due to size of box, weight, and distance. Shipping weight for an ADM-3A terminal is 45 lbs. I"ve found that shipping weight for just an empty "shell" with AC transformer removed is about 20 lbs. The shell with CRT no transformer would likely be about 30 lbs. The AC transformer - very hard to remove adds several pounds. With double-boxing for protection, and especially if one ships a shell without CRT due to the empty void, a likely box size is 24 X 21 X 20 inches. most countries postal service Web sites will provide a postage estimate if you provide size and weight and destination (and your location).

ADM-3A repairs

Sometimes these terminals are mostly working but "lose characters"; the characters displayed are not the characters sent to the terminal. That's very likely a RAM error. Here's a Web page about some RAM repairs I did in 2013. I'll describe various other kinds of repairs as I get to them. I'll also decribe other people's repairs.

other people's repairs

Nick Papadonis repaired and restored his ADM-3A terminal during the summer and fall of 2011. The common problem he dealt with, was the mottled or "mold" between layers of glass on the CRT face. Also he did some logic repairs. He did a lot of work and by October 2011 the terminal was mostly operational. He and I discussed his progress, and I edited his notes into a Web page. Here's a Web page about what he did to restore his ADM-3A terminal.

Comments about CRT repairs

The problem with CRT repair in the 21st century, is that many people are inexperienced with CRTs. They can't assess the risk from prior knowledge, or advice from peers; they have to discover these risks by online research. One risk, is when removing cloudy "safety glass" from the front of a CRT. My problem became: I'm providing information on physically dangerous procedures on my Web site. That's an unacceptable liability for me. And of course, I don't wish someone to come to harm. Therefore I've removed some of that content from this Web page. But I'll try to warn about the risks - however I'm not responsible for any loss injury or damage to you or your equipment, from any information on this Web page. Use any such information entirely at your own risk.

In the last several years (2010-2018) or so, some technicians have determined that they can deal with what's called "mold", "fungus", "cataracts" etc. - the optical and physical deteroriation that clouds the screen of terminal CRTs. They choose to remove the "safety glass" faceplate from the CRT, by various physical methods. They then clean the gooey cloudy adhesive material, off the CRT glass surface. I previously described on this Web page, various methods of faceplate removal. Some methods involve use of heat or electrical-heated tools, or sunlight in the summer. These put the operator at risk. Cleaning agents which dissolve the goo, are fairly aggressive chemicals. That's all pretty risky stuff, I avoid doing that stuff myself.

WHile the "safety glass" apparently provides some protection from a breaking CRT, the safety glass itself can break! Doing something like "add some plexiglass to the front" is difficult because of the curved surface and limited space. MOre reason to not mess with modifying old CRT's. Newer CRT's have thicker glass on the front and use the metal band to tension it. About that band...

Some people informed me, they cut the metal band around the front area of the CRT. I discovered that removing the metal band around some CRTs, increases the risk of flying glass upon CRT implosion. The band is there on purpose to provide tension on the glass. That tension redirects the breakage of the CRT. But in any event, DO NOT REMOVE THE BAND PERIOD An implosion (explosion due to vacuum) propels flying broken glass.

What happens if a CRT breaks up violently? This is a discussion thread from 2010 on just that. I found this in 2022.

Working with CRTs and in particular physically modifying a CRT, puts you at physical risk. I suggest you replace damaged CRTs and not modify them. again: I'm not responsible for any loss injury or damage to you or your equipment, from any information on this Web page. Use any such information entirely at your own risk. - Herb Johnson

possible origins of "mold" "fungus"

In group-email discussion with Al Kossow in Oct 2018, he referenced a year 2008 published scientific paper, on the origins of the breakdown of certain plastics, in the context of perservation of technical equipment. Here's the article as published, "Microorganisms Attack Synthetic Polymers in Items Representing Our Cultural Heritage", Francesca Cappitelli* and Claudia Sorlini. Citation is "Appl Environ Microbiol. 2008 Feb; 74(3): 564569". It's also available online at this link..

It may also be the case, that the breakdown of the plastic material between the CRT glass surface and the plastic or glass faceplate, is otherwise due to age and accumulated heat energy. With terminals and monitors of the 1970's into the 1980's, some have CRTs which produce a "goo" that changes to a brown liquid, drips onto the internal logic boards. Apparently the liquid is somewhat conductive, and that prevents operation of the terminal logic. Therefore, if the terminal is in storage, consider means to isolate or clean that "goo" and keep it from contaminating the terminal logic. Or remove the CRT, or the terminal logic.


Some ADM manuals are available from me as PDF's or from paper, ask for costs of a copy, or search online:
..ADM-2 operator's handbook, polling descript. 80 pgs (half sized)
..ADM-3A operator's handbook, 50 pgs (half sized)
..ADM-3A Maintenance Manual, schematics, 110 pgs (full size)
..ADM-3A/3A+ Dumb Terminal Video Display Unit maintenance manual, 200 pgs
..ADM-5 Dumb Terminal Video Display Maintenance Manual, 160 pgs

In 2022, I found online, a service manual for the Ball Brothers video board, as part of their OEM (sold to manufacturers) CRT monitor manual. I have a PDF copy which I'll share, but the title is "5-017-1003 Ball CRT Data Displays 5" 9" 12" Service manual of September 1977".

I have other terminal manuals on my "terminals" Web page.

Herb Johnson
New Jersey, USA
follow this link to email me @ my email address

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