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Osborne 1 and Osborne Executive CRT Monitor issues

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    Osborne 1 and Osborne Executive CRT Monitor issues

    Greetings all and thank you for your help in advance. This is my first post here !!

    I just picked up 2 Osborne computers. 1 is the original Osborne 1 and the other is the Osborne Executive. Both coincidentally have the same exact issue. I can not for the life of me get the CRT's on either of them to work. There is no high voltage or neck glow on either. I confirmed that both units have working main boards as I can use an external monitor. I only have 1 shunt. It is the shunt for the Osborne 1 that has the composite out connector on it. This shunt when installed connects the main board the the CRT. Here is what I know so far:

    I get 12VDC at the CRT board.
    I get about 12Khz on my oscilloscope on the Horizontal circuit.
    1 can see adjustments being made on an oscilloscope when I move the brightness control.
    I have done a complete electrolytic cap replacement on the CRT board (OCC2) except for 2 caps as I didn't have them. I pulled and tested and they tested good.
    I checked the flyback on the OCC2 monitor. I removed it from circuit and used 18VDC and a VOM and got 12VDC across the primary. I would think if this was bad, it would be an open circuit ?

    Both CRTs have the same issue. I am not sure why they just don't power on when being supplied with 12VDC. I think I read somewhere that these TTL monitors require a horizontal sync to power on which is present.

    Is this a common issue with these ? Is there a component I can check right away that might be the culprit ? Find it strange that both have same issue.

    Thanks !!

    #2
    Hi,
    Have you found out the problem ?
    Maybe the shunt connector is not the correct one for using the internal monitor.

    Here is a link to the service manual which explains on page 43 the connections needed.

    https://amaus.net/static/S100/osborn...ual%201982.pdf

    Comment


      #3
      Originally posted by MaCJaX View Post
      I just picked up 2 Osborne computers. 1 is the original Osborne 1 and the other is the Osborne Executive. Both coincidentally have the same exact issue. I can not for the life of me get the CRT's on either of them to work. There is no high voltage or neck glow on either. I confirmed that both units have working main boards as I can use an external monitor. I only have 1 shunt. It is the shunt for the Osborne 1 that has the composite out connector on it. This shunt when installed connects the main board the the CRT.
      I had a similar issue when I recently acquired an Osborne Executive. It started, but wouldn't boot. So I took it apart and cleaned it (replacing the RIFAs while I was there).

      I wanted to check the floppy drives, so I didn't completely assemble it before trying to power it up. When I tried, the monitor didn't work.

      Short answer: The Drive C: add on that was in it, needed to be hooked to the IEEE488 and external video port. Once I rehooked that up, the monitor worked.
      There's probably a way to un-do that, but I haven't researched that yet.

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