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Thread: PS/2 Model 70 power supply troubleshooting

  1. #1

    Default PS/2 Model 70 power supply troubleshooting

    Hi all.

    I have a PS/2 Model 70 that I'd like to restore. When turning the power on, nothing happens.

    I've observed the following:
    - opened PSU and both fuses are good
    - Measured PSU voltages as follows on the card edge connector output from the PSU:
    -12V showing around -3.58V
    +12V leads showing around 1.2V
    +5V leads showing around .62V
    - Doing a visual inspection, I don't see any burned components or anything.

    I've never really done circuit-level troubleshooting on a PSU before. I'd like to repair it if possible, but I do not know where to start looking. Any advice is appreciated. Thanks!

  2. #2

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    Quote Originally Posted by supertzar View Post
    PS/2 Model 70... When turning the power on, nothing happens.
    OK, step back from the window ledge...

    Did the green LED near the power switch come on? If the LED -DIDN'T- light up, something is preventing POWER GOOD.

  3. #3

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    Quote Originally Posted by ardent-blue View Post
    OK, step back from the window ledge...

    Did the green LED near the power switch come on? If the LED -DIDN'T- light up, something is preventing POWER GOOD.
    Negative, it doesn't light up.

  4. #4
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    Are you checking voltages while the PSU is separate from the system and if yes, are any of the rails showing a low continuity to ground?

    The fact the rails are TRYING to come up indicate either the crowbar kicked in or they are current limiting for some reason.
    [Need something to waste time on? Click here to visit my YouTube channel CelGenStudios]
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  5. #5

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    Quote Originally Posted by NeXT View Post
    Are you checking voltages while the PSU is separate from the system and if yes, are any of the rails showing a low continuity to ground?

    The fact the rails are TRYING to come up indicate either the crowbar kicked in or they are current limiting for some reason.
    I was testing it separate. This system is kind of screwy because the PSU's connection to the system board is a slot connector, and it can't be probed like a Molex connection could. With that said, I'll look a bit harder and see if there are any traces and I test while it's in.

  6. #6
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    Referring to the power supply my Model 70 386 (Astec AA15530, FRU 90x8626), You should be able to probe every pin you want on the power supply from the vias that run along the edge connector on the motherboard. You just need to remove the PSU fan to reach the front most points.
    [Need something to waste time on? Click here to visit my YouTube channel CelGenStudios]
    --------------------------------------------------------------------------------------------
    [No time for videos? Click here to visit my Twitter feed @CelGenStudios]

    = Excellent space heater

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