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Thread: Wang 2200 MVP-A 2236 terminal faded to black and stays black

  1. #1

    Default Wang 2200 MVP-A 2236 terminal faded to black and stays black

    Taking a long shot here, but maybe you guys can give me some hints or tips

    Picked up a complete Wang 2200 MPV-A system with terminal and disk unit.

    Cleaned everything, checked the insides, nothing rotten or blown. powered the things up, no smoke yet!

    The Terminal unit displayed a Small green line about 2-3 cm wide in the center of the screen, but after half a minute it started to fade away, i turned the brightness and contrast knobs but nothing helped.

    I rebooted the system hoping to see the post message from the terminal itself, but the display remains black.

    It does beep though! so it is still alive...

    I'm not handy with CRT displays, and this is 70's tech from way before I was born... where should I start to look? The capacitors are BIG in this machine, and nothing shows bulged or leaked. no humming or buzzing from the tube as far as i can tell...

    I'm willing to learn not the first time i've repaired computers, but i've always avoided repairing CRT's due to the HV, now i'm forced to since it is incorporated inside the machine...

  2. #2
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    Are you aware of http://www.wang2200.org/? There may be service documentation or schematics there to help.

  3. #3

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    Yes! and i've been plowing through the maintenance documents for az while now, but nothing shows up in the diagnostic charts that points me in the right direction (yet).
    I still have hundreds of pages to look through and i'm sure the solution is in there i just don't know in what direction to look for, capacitors? flywheel? CRT adjustment? So i'm looking for a hint to get going there aren't alot around anymore so i'm cautious not to break anything in the diagnostic process

  4. #4
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    Leaking or dried out capacitors are always prime suspects. Examine them for obvious signs of leakage. If you can identify the voltages in the power supply, you should check them first. Obviously you will need a DMM or other volt meter that can handle the voltage ranges. If you can get a hold of a high voltage probe with the proper maximum voltage you can even check the anode and other CRT voltages. Best to do those with the probe securely connected with the terminal turned off and your hands off it before powering on. The other thing to check is the socket connected to the base of the CRT, perhaps there is some oxidation there that gently removing it and reseating it might correct.

  5. #5

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    I'm no good with the CRT repair but there are at least 3 different emulators for the WANG Terminal, so you can hook up an old PC running DOS or Windows directly to the MVP.
    On www.wang2200.org there is at least one of them (windows version) that you can download and one of the manuals will also tell you how to solder the connecting cable correctly.
    I did get the dos version of the emulator working nicely on a raspberry with qemu.
    Of course not as much fun as the original terminal but at least you could figure out if the rest of your system is in working condition.
    If you want the wang terminal emulator (dos version) send me a pm, happy to share.

  6. #6
    Join Date
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    If you get a horizontal line on a CRT, IMMEDIATELY turn it off, it could leave a burn on the phosphor that will be visible after the problem (vert osc?) has been fixed.

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