Image Map Image Map
Page 1 of 2 12 LastLast
Results 1 to 10 of 15

Thread: Lear Siegler ADM-3A working

  1. #1
    Join Date
    Jan 2010
    Location
    San Antonio, TX
    Posts
    20

    Default Lear Siegler ADM-3A working

    About 20 years ago I found this at a thrift store. I couldn't get it working beyond somehow glitching a character onto the screen, which was just enough to confirm that at least it had raster. I was a bit disappointed that it was brown rather than what I think of as the "standard" blue. And I didn't know what to think of the cataracts, I thought it was some kind of mold. But it was a freaking ADM-3A, one of the coolest looking terminals ever. Even 20 years ago it was already vintage.

    So yesterday I got it out of the storage space and brought it home. I made sure to take my time looking at it, and at the technical documentation, at which point I noticed it had lower-case RAMs, but no 2513 character generator for lower-case. Then just now I took my time to look at the DIP switches to make sure it had sane settings. Sure enough, it was in full-duplex. For some reason I had never switched it to half-duplex for testing.

    And the keyboard is a mess. It looks fine, but keys are sticking. That is such a crappy mechanism, I never liked it back in the day with my old TRS-80 Model I, and I still don't like it. At least it has all the key caps. The escape key had fallen off, but somehow it fell inside the terminal and was rattling around. And the vertical position jitters like crazy, probably a scratchy pot on the video board.

    The blocks are of course the bus float from the empty 2513 socket. I'll have to make an adapter, but I got some assorted parts last month from Amazon that should make it possible.

    Now if I could just find my stupid EPROM eraser. I've been looking for that ever since a hurried move three years ago.

    P1050270...jpg P1050267...jpg

  2. #2
    Join Date
    Jan 2010
    Location
    San Antonio, TX
    Posts
    20

    Default

    So I found my eraser the next day. Then I made a lowercase board with a 2764 because I have so many more of those. And it didn't work, I just got blocks. I started debugging it yesterday and just found the problem. I had grounded PGM and the 2764 was in a verify mode or something.

    P1050280..jpg

    Now I still have to do something about the keyboard and the CRT.

    EDIT: I used this for the pin headers: https://www.amazon.com/gp/product/B07BS126FK

  3. #3

    Default

    Those sure are beautiful terminals. I hope you can get it working right!
    -- Lee
    If you get super-bored, try muh crappy YouTube channel: Old Computer Fun!
    Looking to Buy/Trade For (non-working is fine): Tandy 1000 EX/HX power supply, PS/2 Model 25-286 ISA expansion riser, Mac IIci hard drive sled and one bottom rubber foot, Multisync VGA CRTs, Decent NuBus video card, PC-era Tandy stuff, Aesthetic Old Serial Terminals (HP and Data General in particular)

  4. #4
    Join Date
    Jan 2010
    Location
    San Antonio, TX
    Posts
    20

    Default

    Hey, if there's a mod reading, can you move this to Genres -> Other? It didn't seem quite clear where to go when I originally posted this. Maybe there should be a category for Terminals/TTYs/Printers? There ought to be enough of them for a topic of its own.

    Bleeping Hi-Tek keyboards. My first computer was a TRS-80 Level II 16K, so my distaste for them goes way back. If I could get a set of ADM-3A key caps for Cherry, I would be so tempted to build one on perfboard with MX reds or blues.

    I think I've got the keyboard working now... I think. I had three hard sticking keys (left shift, E, Y) and tried various things to fix the split plungers. No good. So I dug around the garage and found my old Hi-Tek keyboard, a Radio Shack salvage-of-the-month part that I had once used on my Model I with an I/O chip. (I also found a TI-99/4 Alps keyboard still in the very worn RS peg packaging!) I practiced pulling and re-inserting a plunger a few times. Then I pulled the sticky key plungers and sanded down the sides. Two behaved, the E didn't. So I swapped a white plunger from the spare keyboard and it worked.

    Then I cleaned the keycaps by scrubbing with cotton swabs and IPA, picture below shows all but the L and bottom row between shifts cleaned, the difference is visible. Then I banged on each key a few times in succession and found unreliable keys. Those I sort-of cleaned by taking a cable tie, dipping the end in IPA, and lightly scrubbing it sideways between the contacts.

    I also squirted some Deoxit into the scratchy brightness pot. It even bubbled up a bit when I squirted it. Then I noticed that the picture didn't have vertical jitter anymore, maybe that was causing it? I'll have to watch for it.

    And then there's the cataracts. I've seen worse, maybe I could just call it the "Bubble Tea Special Edition", ha ha. I have some idea what to do, but it's going to take some courage to get there.

    P1050283..jpg

    So does anyone recognize the logo on that property number plate?

    One other thing. Looking at the schematic to see why the lower case data was in reverse order, I found that for some reason they used the inverted outputs from the character code latch for the LC chip. Maybe it helped avoid fan-out problems or something. It definitely settles any question that the lowercase chip was custom for Lear Siegler.

    But then I noticed how the chip selects worked. Either one chip or the other is selected at all times. It looks like with just one trace cut and a pull-up resistor to disable the main 2513, I can use the CS of the socket as another address line, and have the entire character set in a single ROM, though in reverse order. I didn't like the idea of pulling the non-socketed chip to add a socket, but I might go for cutting a trace that can be jumpered back, plus minor changes to my EPROM board. Then I could use a 28C64 to experiment with character sets.

    Quote Originally Posted by bladamson View Post
    Those sure are beautiful terminals. I hope you can get it working right!
    I've always loved the design, it's just so '70s futuristic. And yesterday I saw for the first time what a VT05 looked like, holy crap. Those '70s designs were so awesome.

  5. #5
    Join Date
    Dec 2011
    Location
    Dallas, TX
    Posts
    357

    Default

    Quote Originally Posted by Bruce Tomlin View Post
    If I could get a set of ADM-3A key caps for Cherry, I would be so tempted to build one on perfboard with MX reds or blues.
    Perfboard wouldn't give the right key spacing. The resulting keyboard wouldn't fit.

    The keycap set used my keyboard project (https://github.com/osiweb/unified_retro_keyboard) is inspired by the ADM-3A. It's not an exact copy, but it's very close. The following thread in this forum has some photos:

    http://www.vcfed.org/forum/showthrea...843#post624843

    Here are the differences:

    - The spacebar us 8u wide instead of 9u
    - RETURN is 1.5u instead of 2U
    - No "HERE IS" or "CLEAR" keys.
    - No Arrows over HJKL keys
    - No "HOME" over the ~^ key

    The design uses KiCad and is open source, and the layout is pretty close to the ADM-3A, so you could start with that and . You could start with the PCB in the project, and rewire to match the ADM3A matrix. You could add a 1u key next to the spacebar to fill the cutout, and substitute a 1.5u key (I have a TAB key, or you can order a blank) for the HERE IS key to compensate for the smaller RETURN.

  6. #6

    Default

    Quote Originally Posted by dfnr2 View Post
    Perfboard wouldn't give the right key spacing. The resulting keyboard wouldn't fit.
    Cut/punch a piece of sheet metal / plastic or 3d print something to mount the keys to with the right spacing. Then hand wire them.
    -- Lee
    If you get super-bored, try muh crappy YouTube channel: Old Computer Fun!
    Looking to Buy/Trade For (non-working is fine): Tandy 1000 EX/HX power supply, PS/2 Model 25-286 ISA expansion riser, Mac IIci hard drive sled and one bottom rubber foot, Multisync VGA CRTs, Decent NuBus video card, PC-era Tandy stuff, Aesthetic Old Serial Terminals (HP and Data General in particular)

  7. #7
    Join Date
    Jan 2010
    Location
    San Antonio, TX
    Posts
    20

    Default

    I was only half serious, but it's good to know that an 0.1" grid doesn't give proper keyboard spacing. Now that the keyboard is working, and the only thing wrong is CRT cataracts, I'm happy. And that Hi-Tek sound and feel is kind of nostalgic, even if it's fragile as hell.

    And I just got stuff out of my storage space today, I forgot I had an H-19 in there. I also brought home some of the VT-100 terminals that were there, and another VT-100 keyboard, yep, more Hi-Tek keyboards. This time I'm going to take some time powering it up, making sure the voltages are right, and no tantalum shorts and stuff. Only one sticky key, unstuck with a little sandpaper, and missing the F1/F2 key caps, which I replaced with a pair of "FUNC" key caps I had. Then maybe I'll build something to put inside it, either a simple Z-80 board or a RasPi running a CP/M emulator.

  8. #8

    Default

    Quote Originally Posted by Bruce Tomlin View Post
    I was only half serious, but it's good to know that an 0.1" grid doesn't give proper keyboard spacing. Now that the keyboard is working, and the only thing wrong is CRT cataracts, I'm happy. And that Hi-Tek sound and feel is kind of nostalgic, even if it's fragile as hell.

    And I just got stuff out of my storage space today, I forgot I had an H-19 in there. I also brought home some of the VT-100 terminals that were there, and another VT-100 keyboard, yep, more Hi-Tek keyboards. This time I'm going to take some time powering it up, making sure the voltages are right, and no tantalum shorts and stuff. Only one sticky key, unstuck with a little sandpaper, and missing the F1/F2 key caps, which I replaced with a pair of "FUNC" key caps I had. Then maybe I'll build something to put inside it, either a simple Z-80 board or a RasPi running a CP/M emulator.
    I love my Z-19. With the way it's built, I think it might be possible to swap the 8250 with a 16550, then wire the serial clock to something else on the clock divider, like x2 or x4 what the 8250 was running at. You'd lose the 50 and 150 baud modes, but the terminal might be able to run at 38.4 or 76.8 kbaud then, assuming the CPU could keep up. Also with the way the serial port is not soldered straight to the logic board, but is instead on a cable, I've thought about rigging something up so I can switch between the external serial port and a built-in raspberry pi (with the pi then taking over the external serial port). Prolly be safe to do that with some analog switch ICs or something, hrmmmm yeah.
    -- Lee
    If you get super-bored, try muh crappy YouTube channel: Old Computer Fun!
    Looking to Buy/Trade For (non-working is fine): Tandy 1000 EX/HX power supply, PS/2 Model 25-286 ISA expansion riser, Mac IIci hard drive sled and one bottom rubber foot, Multisync VGA CRTs, Decent NuBus video card, PC-era Tandy stuff, Aesthetic Old Serial Terminals (HP and Data General in particular)

  9. #9
    Join Date
    Jan 2010
    Location
    San Antonio, TX
    Posts
    20

    Default

    I redid the character generator images as asm files where the bits are represented with X and underline characters like "DB _X__X". I made it have exactly one copy (just use an external tool to put multiples together for a ROM image) to avoid unnecessary duplication. These should work with most assemblers with very little tweaking, and be much more convenient for making custom versions.
    Attached Files Attached Files

  10. #10
    Join Date
    Jan 2010
    Location
    San Antonio, TX
    Posts
    20

    Default

    Sark finally convinced me to fix those cataracts already. It's better to do it in the sun to get the glass warm before starting, tomorrow and Thursday are going to be the last two warm (90F-ish) days of the year here in Texas, and I have everything I need, even a roll of sticky foam. I just now discharged the anode (I think) since it's such a pain to reach. I'll do it again tomorrow to be sure.

Tags for this Thread

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •