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Thread: Sanwel PSU schematics

  1. #1
    Join Date
    Aug 2016
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    Turin, Italy
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    156

    Default Sanwel PSU schematics

    Dear All,
    I know it's probably easier to win at the lotto but I try .
    I have asked to a friend if he can help me to repair an old AT PSU as for the attached picture:
    DSC_0003.JPG

    I have not found anything on the web... am I lucky and do somebody have the schematics?
    Thank you

  2. #2
    Join Date
    Apr 2015
    Location
    Austin, Texas
    Posts
    2,175

    Default

    If you're asking for schematics to a switching power supply, it's not something you should really be messing with. High voltage AC and high voltage, high frequency AC in the tens of kHz range is present inside the supply on at least one of the mosfet heatsinks. Touch anything inside the supply while it's powered up and death awaits. Even with power removed, the line capacitors can keep the unit powered for sometimes hours if there isn't bleeding circuitry present, or it's faulty.

    PSU manufacturers almost never release schematics for their power supplies, so it's pretty much certain you won't find one.

    I'd recommend studying generic switching power supply designs and also the various faults they can have before poking around inside the unit.

  3. #3

    Default

    What about:
    - Finding another of these PSUs?
    - Replacing the PSU with another one with the same case?
    - Replacing the board inside the PSU with one that does work?
    The chances for one of the above options should be much better than finding a schematic, IMHO.
    With kind regards / met vriendelijke groet, Ruud Baltissen

    www.baltissen.org

  4. #4
    Join Date
    Apr 2015
    Location
    Austin, Texas
    Posts
    2,175

    Default

    This is an AT style power supply, they're getting hard to find. There is at least one company that still makes AT power supplies, but with questionable quality and reliability.

    It is possible to retrofit an ATX power supply, but not without some DIY work and careful selection of the ATX PSU to get one with a strong 5V rail. Modern ATX power supplies tend to have most of their capacity on the 12V rail, where 20+ years ago, most of the capacity was on the 5V rail. There's also the issue of the -5v rail being removed from the ATX spec in 2004, which is usually required by old motherboards and the ISA bus. It is possible to make this rail by hanging an LM7905 (NOT 7805) off the -12v rail, but soldering is required.

  5. #5

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    Those old AT PSUs were almost always based on the TL494 pwm controller (or some clone), so not terribly difficult to troubleshoot.
    As other have already said, I wouldn't put my hands on it if I'd think I need a schematic.

    Frank IZ8DWF

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