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Thread: Osborne Executive - vertical hold?

  1. #1
    Join Date
    Jul 2017
    Location
    California, USA
    Posts
    13

    Default Osborne Executive - vertical hold?

    I just recently bought an Osborne Executive computer. It's in good condition, but someone has definitely messed with it at some point. It was working ok, but the front cover was a little loose and if the computer was moved, it would turn off and restart. I took the cover off, hoping I could see what was causing the problem. I then noticed what looked to be a couple of jumper wires connected on the motherboard. One was just a clip lead loosely connected to a couple IC chips! It came off, and I have no idea what someone was thinking leaving that in there. The other jumper wire is soldered in place and I decided to leave it alone for now. The problem is that now the image on the monitor is slowly rolling, as if the vertical hold is off. Is there any way to adjust the vertical hold? I don't see an adjustment knob anywhere. I don't know if that jumper wire is related, but if someone meant to "fix" an earlier problem, just clipping in that wire was a realky lame, mickey mouse way to do it!

    When I connected an external tv with the composite video jack, the image was fine. So the problem doesn't seem to actually be with the computer, but the built-in monitor itself. What might cause the vertical hold to be off like that and does anyone have any suggestions on how I might be able to fix it? Thanks for any help!

    - Chris

  2. #2
    Join Date
    Jul 2005
    Location
    State College, PA
    Posts
    160

    Default

    The monitor in the Executive doesn't seem to have a vertical hold adjustment, at least according to the schematic I found. A monitor schematic can be found in the "sheets.zip" file, here:

    http://oldcomputers-ddns.org/public/...ual/sheets.zip

  3. #3
    Join Date
    Jul 2017
    Location
    California, USA
    Posts
    13

    Default

    Thank you for finding that! Those diagrams should be helpful. It seems like the jumper wire I disconnected must be somehow related to the vertical sync. But I still just don't understand why anyone would have "fixed" an earlier problem in such a sloppy way. I'll look at the computer again and compare it with the diagrams and see if I can figure out which pins the wire was connected to. (I know one chip it was connected to, but not the other). If I figure it out, this time I think I'll SOLDER a wire in.

  4. #4
    Join Date
    Jul 2017
    Location
    California, USA
    Posts
    13

    Default

    Ok, the jumper wire that was soldered in is connected between pin 6 on UF 7 and pin 6 on UF 11. I Remember that the other jumper wire that was clipped on was also connected on UF 7, but unfortunately I don't know where the other end was connected.

  5. #5
    Join Date
    Jul 2017
    Location
    California, USA
    Posts
    13

    Default

    Mystery solved!
    After looking in the diagrams, I got a clue from seeing a listing for "Spare Gates," which I assumed were unused pins on IC chips. Pins 5 and 6 on UF 11 were listed as spare gates. So I took a guess that what happened is that at some point a gate failed in UF 7 and someone decided to make a quick dirty fix by connecting it to a gate in UF 11 instead of replacing the chip.

    So I did a quick test and connected pin 5 and pin 6 of UF 7 to pin 5 and pin 6 of UF 11 respectively and that fixed it! The image on the internal monitor looked normal!

    What an annoying mess! But at least it wasn't something more serious!

    Probably the best thing to do would be to just replace that chip.

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