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Thread: Siegler terminal troubleshooting

  1. #1
    Join Date
    Sep 2016
    Location
    Shrewsbury, MA
    Posts
    680

    Default Siegler terminal troubleshooting

    Just picked up a Lear Siegler ADM-3A in near mint condition, looks gorgeous in two tone blue. But it doesn't turn on. All I see when I flip the switch it the CRT heater glowing, nothing else happens. How should I go about troubleshooting it? I'm thinking bad capacitors either in the CRT board or the power supply but I have nothing to back that up. Where should I start?

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  2. #2
    Join Date
    Mar 2013
    Location
    Chaffee, MO
    Posts
    1,069

  3. #3
    Join Date
    Sep 2016
    Location
    Shrewsbury, MA
    Posts
    680

    Default

    Thanks for the link, I'll check it out. Hopefully I can get it working so it's slightly more useful than a paperweight!

  4. #4

    Default

    I have one in those colors working perfectly with a period correct B/W CRT. Definitely start at the power supply. If possible, isolate the output of the regulator from the rest of board. I have actually done this, but desoldering dozens of DIP IC’s is extremely unpleasant and somewhat expensive.

    Once you have voltages OK, see what comes out of the board to the video with an oscilloscope.

    BTW you are lucky to have an original DIP switch cover plate. I had to make mine.

  5. #5

    Default

    Looking at the manual, there are three 5v regulators. If just one is bad it won’t work.

    Also check the bridge. I recently pulled out a bad bridge from a Tek oscilloscope. Never saw one just go “bad“ for no reason other than age.

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