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Thread: Kaypro II power supply - Need transformer info for replacement.

  1. #1
    Join Date
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    Default Kaypro II power supply - Need transformer info for replacement.

    Hi, I'm new to the forums and just getting back into classic computing after picking up a Kaypro II machine. The Boschert power supply doesn't work and there is a short across the input transformer (right after the fuse). All of the transformers look pretty bad and I want to replace them all but I can't find any reference to order/get new ones. Does anyone have a diagram outlining the rating of the transformers? It wouldn't hurt to have ratings for all the components if someone has a complete list. OR if someone knows of a place to get a working power supply that would be great. Thanks for your help.

  2. #2
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    It's more Likely a Shorted Diode in the Full Wave Bridge Rectifier, or the Power Transistor that is
    the Switcher for the Transformer. I've got a few documents that will be helpful. One thing you
    need for sure is a 60 Watt Incandescent Bulb in series with the Line going to the Power Supply.
    That way a short will just light the Bulb and won't blow the fuse.

    I sent a PM.

    Larry

  3. #3

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    You could also replace the whole power supply with a safer, more efficient modern one like the Meanwell MPT120B.
    mpt120b.jpg

  4. #4
    Join Date
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    I havent had a kaypro PSU ever really fail. They seem reliable. What I have run into several times is the connector of pins on the side get tugged hard when the connector is removed cracking the solder points. Causes intermittent issues worst case. Visual inspection and reflowing fixes that problem.

  5. #5

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    I'm having a similar problem, my transformers are all swolen and leaking, I also hear a clicking at about 20 hz coming from the main transformer.
    Larry do you mind sending me the same information? I have not been able to find a schematic of the power supply. it is a boschert!
    -Ty

  6. #6
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    Quote Originally Posted by tymerica View Post
    I'm having a similar problem, my transformers are all swolen and leaking, I also hear a clicking at about 20 hz coming from the main transformer.
    Larry do you mind sending me the same information? I have not been able to find a schematic of the power supply. it is a boschert!
    -Ty
    Transformers don't swell, and certainly don't leak, at least the kind used on power supplies. Are you sure you're not confusing transformers for capacitors?

    https://www.classic-computers.org.nz...-on-kaypro.htm

    To me, it looks like some really primitive SMPS design. Not a lot can go wrong, you really don't need a schematic to troubleshoot it. If it has leaking capacitors, replace all of them, including the RIFA caps near the mains connection.

  7. #7

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    Quote Originally Posted by GiGaBiTe View Post
    Transformers don't swell, and certainly don't leak, at least the kind used on power supplies. Are you sure you're not confusing transformers for capacitors?

    https://www.classic-computers.org.nz...-on-kaypro.htm

    To me, it looks like some really primitive SMPS design. Not a lot can go wrong, you really don't need a schematic to troubleshoot it. If it has leaking capacitors, replace all of them, including the RIFA caps near the mains connection.
    I am new to it, but the transformers look like the large central wrapped piece, the top right at L1??? but right past the rifa caps and the fuse and the bottom left right next to the larger one in the middle!
    They may not be blown or swell or leak but they definitely look.... upset. I have been trying to test continuity through the board and learn as i go! But i will re post here if i find a solution to my problem! Thank you!

  8. #8
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    In the first picture in the above link and near the fuse is a RIFA and other square-ish looking cap's. There's also a yellow coil and in the far far left rear there's a transformer. Otherwise a bunch of black round tall capacitors and blue MOV's. Near the center of the board there's a couple of transistors on copper color heat sinks. Which one of these items are you referring to that appear damaged?
    Crazy old guy with a basement full of Pentium 1 laptops and parts

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