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Thread: I have a couple questiosn regarding the mainboard on my Osborne 1

  1. #1
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    Default I have a couple questiosn regarding the mainboard on my Osborne 1

    Here are some photos of my osborne 1 system board : http://s613.photobucket.com/user/Ver...brary/Osborne1

    First off , is the daughter card a high density card for the floppy drive? IF so that would make the drives 160KB rather than 80KB is that correct?

    Secondly, the board has a card-edge connector with a loopback cover over it labeled Ext Video. IF the cover is removed no video goes to CRT. Behind the cardedge connector are header pins. Here is my next question. I know some osborne 1 units have composite video out. If I want to implement a composite video out, what do I need to do?

    My case has a date of Feb 15 1983 and the model revision of the systemboard is 3A10063 Rev K

  2. #2
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    Not high density but double-density (FM vs. MFM).

  3. #3
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    Ok got it, so am I right on the 160Kb? or are these actually 360Kb?

  4. #4
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    Depends on the board (which I'm not familiar with), but the usual scheme was this:

    Bog-standard single-sided FM : 37 cylinders of 10 x 256 byte sectors = 94,720 bytes of user + directory space. Some early O1 implementations used only 35 cylinders, so 32 x 10 x 256 = 81,920 bytes of user space. (3 cylinders in either case were reserved for system boot).

    Single-sided MFM: 37 cylinders of 5 x 1024 bytes = 189,440 bytes.

    By replacing the drives using the "Osmosis" kit, using 96 tpi DS drives, you could essentially quadruple that to about 788,480 bytes.

  5. Default

    Hi

    There is a Daughterboard that goes onto the motherboard. It may be the 80 column board. It has a two pin connector on it. A cable plugs into and has a female RCA
    connector on the other end. It goes into a hole that is drilled by the Ext Batt connector. Then you plug in your monitor to it.

    A Second option, is a plug that goes into the Ext Video port. You remove the factory plug and put in the plug. It has a RCA plug on the side. You just plug in the monitor.
    The one I have is called Exmon by JJM Enterprises.

    Another option is to get a Osborne GM-12 monitor that plugs into the Ext Video port.

    There maybe other options out there.

  6. #6
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    it connects via Ribbon to the main board next to IC MB8877
    From his photo description. The MB8877 is a floppy controller.

  7. #7
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    Anyone have any insight about my composite out question on the Osborne 1?

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