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Thread: I have killed my Commodore PC30-III PSU - any ideas ?

  1. #1
    Join Date
    Nov 2017
    Location
    UK, South East
    Posts
    184

    Default I have killed my Commodore PC30-III PSU - any ideas ?

    Folks,

    I popped a 'stuck' SCSI drive in the machine and it has taken the PSU out attempting to power it up.

    Does anyone have a schematic for the PSU - Liton PA-3111-1B ?

    A visual inspection doesn't reveal any obvious problems - incoming mains fuse is fine, there are no other fuses in the DC output stage.

    Commodore must have used a few different types of PSU as the one shown at the link below is different to mine.

    Its a fairly non standard shape and mainboard connector so options for a straight swap are limited I think.

    https://oldcrap.org/2018/10/17/commodore-pc30-iii/

  2. #2

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    I once had a problem with PSU of an old PC10. I replaced the inner board with one from a Taiwanese AT-type PSU which board just happened to fit inside the case of the PC10's PSU. Because the holes didn't match, with one exception I glued risers to the board and then I glued the risers to the case.
    Two of the holes served as ground towards the case. The exception was such a hole. So I soldered a wire from the other hole to the one that was grounded by a screw.

    I hope this helps.
    With kind regards / met vriendelijke groet, Ruud Baltissen

    www.baltissen.org

  3. #3
    Join Date
    Nov 2017
    Location
    UK, South East
    Posts
    184

    Default

    Yes, thats quite a good idea to reuse the PSU case if I can find a suitable board - its a relatively modest 110W supply.

    I'll see what I can find that fits.

  4. #4

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    Power supply in my PC40-01 broke and I could not find any information about it, so I ordered all semiconductors on the board and attempted replacing one by one. Eventually replacing the bridge rectifier and one of the transistors (or it could be not exactly transistor I donít remember now but one of those three-legged beings) made it work again. These parts if only available are pretty cheap, it was worth it.

  5. #5

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    First check the voltage for the input. The rectified value across the transistor switching transistor, when it is not oscillating is about 300+ volts.
    Most of these supplies expect there to be a pulse of the +12V line when power is first supplied. With a scope you can see this pulse on the 12V secondary. This pulse gets the control circuit running on the secondary side. Since you most likely damaged the 12V, if something like the diodes being open, it won't power up. If you can see the pulse on the windings but not on the 12V filter cap, you'll know it is the 12 diodes that are out. If there is no pulse it is a failure on the primary side.
    Use the "one hand in your back pocket" when working on these supplies and be insulated form any possible ground path. If you are not sure if you are insulated, put your meter on a high ohms position, with one lead on a ground, the other on your finger. Any reading other than infinite is NOT insulated.
    Dwight

  6. #6

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    I should mention, the 12v diodes could be shorted as well. The pulse is absorbed and doesn't start.
    Dwight

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