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Repair ATX power supply

Discussion in 'Electronic Repair' started by Skeleton Man, Nov 24, 2007.

  1. Skeleton Man

    Skeleton Man Guest

    I did remove both of them from the circuit for testing..
    That's correct.
    Can you buy replacements ? (original or newer models)

    Would bad caps have caused them to fry ?

    Chris
     
  2. JANA

    JANA Guest

    These power supplies are replaced, and not repaired. The time and cost is
    not worth it.

    --

    JANA
    _____


    Hi All,

    I was wondering does anyone here have a good guide for how to go about
    repairing an ATX computer power supply ?

    I've never done anything like this before, so any help is appreciated..

    Chris
     
  3. JANA

    JANA Guest

    If you have a way to operate the supply without it connected, and you can
    have the schematics, and necessary test gear, go ahead and start
    troubleshooting. It can be as little as a simple component, to an array of
    parts!

    Take care when working on these switching supplies. The drive voltage and
    drive current can be lethal!!!

    --

    JANA
    _____


    I have replaced the power supply, and now I want to repair the old one.. I
    shouldn't have to throw out a $50 peice of equipment because a 25c part is
    broken.. (spending a day or two finding the problem doesn't worry me)

    The problem is that it still supplies +5V standby, but refuses to turn on (I
    have a load attached and I do have the correct wires for PS_ON and ground).

    No fuses are blown, and nothing appears or smells obviously burnt.. I was
    told to check for open/high resistors near the large filter caps on the high
    side, so I did and they both read the correct ~220Kohms.. there's two
    diodes on the high side and both those are ok also.. what else should I test
    ?

    Chris
     
  4. Could be.

    Throw it away. At this point, not only will it cost more to replace
    all the bad parts than buying a new spare supply, you're likely to
    never repair it as many other things can blow, and if you fail to find even
    a single one and replace it, they may all blow again instantly.

    --- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
    Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
    +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
    | Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

    Important: Anything sent to the email address in the message header above is
    ignored unless my full name AND either lasers or electronics is included in the
    subject line. Or, you can contact me via the Feedback Form in the FAQs.
     
  5. Eeyore

    Eeyore Guest

  6. Meat Plow

    Meat Plow Guest

    Not to be mean but if you you don't know something basic like what these
    reading mean it's not likely you're going to repair this device by
    yourself.
     
  7. Franc Zabkar

    Franc Zabkar Guest

    I find it strange that your chopper (?) transistors/MOSFETs are
    shorted C-to-E or D-to-S, yet the fuses are intact. Maybe you have an
    open NTC resistor ???

    - Franc Zabkar
     
  8. Skeleton Man

    Skeleton Man Guest

    Throw it away. At this point, not only will it cost more to replace
    It's more an exercise in troubleshooting and repair than anything.. If I
    wanted a spare I would buy one..

    Also, if I can repair a $30 power supply, the same basic skills should apply
    to a $200 power supply.. you wouldn't just throw it away and buy a new one
    then.. (doing component level repairs is an an extra skill I'd like to teach
    myself)


    Chris
     
  9. James Sweet

    James Sweet Guest

    Yes, you can buy replacements, what are the numbers on them? Make sure you
    check all the other semiconductors, this sort of repair is challenging, if
    another defective part remains, everything you replaced can blow again
    before you know what happened.
     
  10. James Sweet

    James Sweet Guest

    He said the fuse blew.
     
  11. Doesn't work like that in real life.

    The parts alone will cost more than the replacement of the power supply.
    Likely even for the $200 power supply.

    And whether or not you like it, your time IS worth something, and it's
    usually a LOT more than a measly $200 for a power supply.

    There may be some conditions that control this, such as this may be a
    special-purpose supply that can't be replaced, or off-the-shelf replacements
    are not available for some time, and you can fix it faster than the time the
    replacement comes in.

    And, from what you've described, it doesn't appear you're up to the task
    anyway, and 'fixing by correspondence' doesn't work in this case. Much like
    trying to get your mother to completely dismantle your car engine, repair and
    reassemble going off instruction on usenet.
     
  12. James Sweet

    James Sweet Guest


    Huh? I've repaired a lot of power supplies over the years, and never
    encountered one where anywhere near $200 in parts was required.

    The value of the power supply is nothing compared to the value of the
    education it could provide. When I started repairing things, I learned by
    working on equipment that was mostly pretty worthless, some of it I fixed,
    some of it I broke worse, the odds steadily improved with practice. You've
    gotta start somewhere.
     
  13. Dave

    Dave Guest

    Sorry, but SMPS's are A REAL BASTARD to diagnose and repair... that's why so
    many very competent professionals who repair electronic gear for a living
    have suggested that you throw it away. It's like saying "I'd like to learn
    math, and I'm going to start with this advanced calculus text." If you want
    to learn to fix something, choose a) something fixable and b) something
    worth fixing. The way in which switch-mode power supplies operate makes
    them by nature dangerous to work on as well, which is less than ideal for a
    novice as you really can hurt yourself.
    Good luck.

    Dave S.
     
  14. Another thing to consider is: Would you trust that repaired power supply
    to be a spare for your new turbo-charged PC if its power supply dies,
    given that you may have barely understood what you did to get it working?

    --- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
    Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
    +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
    | Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

    Important: Anything sent to the email address in the message header above is
    ignored unless my full name AND either lasers or electronics is included in the
    subject line. Or, you can contact me via the Feedback Form in the FAQs.
     
  15. Yes. You can probably replace them with about any high voltage
    transistors from another PC PSU, even an old AT one, provided they're
    they same type (NPN) and are rated for at last as much voltage,
    current, and power. But if the new ones come in different packaging
    you may have to add electrical insulation, such as a silicone rubber
    transistor insulator sheet between the transistor and heatsink or a
    flanged nylon washer for the mounting screw, emphasis on "flanged".
    Be absolutely certain that the transistors are insulated from the
    heatsink or they'll instantly blow out when the power is turned on.
    BTW the heatsink for those transistors is often connected directly to
    about 350V DC, so don't plug in the power unless the PSU cover is
    installed and screwed on.

    A spec sheet for the 2SC2625 can be seen here:

    www.ortodoxism.ro/datasheets/mospec/2SC2625.pdf

    This website:

    www.smps.us/computer-power-supply.html

    has information about computer PSUs, including schematics for a couple
    of them.

    I think that your PSU has three transformers: main, standby, and one
    to drive the high voltage transistors. The fourth thing that looks
    like a transformer (in the lower right of your picture) is actually an
    AC line filter (OK, it works as a transformer).
     
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