Faulty PSU Revival

Discussion in 'General Electronics Chat' started by b_gravedigger, Dec 19, 2011.

  1. b_gravedigger

    Thread Starter New Member

    May 12, 2009
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    Hello everybody,

    A faulty PSU recently came to my possesion and i need some advice on how to revive it, if possible.

    It was part of a desktop whose motherboard, vga and hard disk were rendered useless, possibly due to a spike in the supply voltage.

    To the point:

    When i connect the power supply to a working motherboard and try to turn it on, it seems completely dead. Same thing happens when i connect it to the xilence power supply tester.

    Upon opening the case i noticed 2 burnt resistors, 2 damaged ones and 1 burnt transistor (that one actualy fell off it's place when i touched it).
    Here, you can see the clearest photos i could take.

    The first step of the revival process would be to replace the faulty components (or at least the ones that seem to be faulty). But is there a safe way to replace a resistor, whose value i don't know (for the ones that are completely burnt)?
    Also, the code K619 C945 P is written on the transistor, but i can't find it's datasheet, so i can't find a suitable replacement for it.

    If there is another way of dealing with this piece of equipment, i would be happy to know.

    Thanks!
     
  2. Georacer

    Moderator

    Nov 25, 2009
    5,142
    1,266
    Do me a favor lads and solve this guy's issue. If we come up with empty hands I 'll hear no end of it about how I run my home forum, as opposed to his "awesome" moderating back here in Greece.
     
    Last edited: Dec 19, 2011
    jaygatsby likes this.
  3. paulktreg

    Distinguished Member

    Jun 2, 2008
    611
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    If you are repairing this power supply because you really need it or just for the experience then fair enough but god it's old!

    I can see a white wire there that's -5V that was made obsolete ages ago and it obviously hasn't got any power factor correction. Unless you're still running the older ISA cards you could probably pick up a replacement of equal (low) quality for about £10~£15! ;)
     
  4. b_gravedigger

    Thread Starter New Member

    May 12, 2009
    6
    0
    Oh yes, it's old :)

    [​IMG]

    I do need it, as i have an old 478 socket mobo with a pentium 4 waiting to become my new old-desktop, but i also cannot live with the idea that all those goodies attached on the pcb are useless because of a couple of burnt resistors.
     
  5. paulktreg

    Distinguished Member

    Jun 2, 2008
    611
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    If you are dead set on fixing it (I think you'll struggle to get the value of those resistors though) then I'd also replace all the electrolytic capacitors.

    Do yourself a favour and spend a couple of quid on a new one! :D
     
  6. jaygatsby

    New Member

    Nov 23, 2011
    185
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    Good exercise but consider this: if you are going to use the supply with a decent, high speed computer, forget it and get a really nice $100 supply from newegg. Good, fast computers can have issues with crappy supplies.
     
  7. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    If you're dead set on fixing the supply, the first thing you'll need to do is to get all of the crud off of it. Start with compressed air (or canned air if you don't have an air compressor). Then start getting the rest of it off, using isopropyl alcohol (90% or better) and a small coarse-bristled brush.
     
  8. spinnaker

    AAC Fanatic!

    Oct 29, 2009
    4,867
    994

    Old??? Unless it has tubes in it, it is no were near "old". :)
     
  9. Georacer

    Moderator

    Nov 25, 2009
    5,142
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    And then, what will the next step be? Will there be possible to find any schematics for it, or using some range of standard resistors?

    Tracing the board will be unproductive, won't it?
     
  10. whatsthatsmell

    Active Member

    Oct 9, 2009
    102
    4
    And those are only the things you can see. ;)
    I've circled what appears to be a bad cap.

    I agree with the other posters in that it would be easier (and, in the long run, cheaper) to just get a new one.

    But, that's just my humble opinion.
     
  11. ifixit

    Distinguished Member

    Nov 20, 2008
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  12. SgtWookie

    Expert

    Jul 17, 2007
    22,182
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    Here is a link to a slew of computer power supply schematics:
    http://danyk.wz.cz/s_atx_en.html

    After you get the supply pretty well cleaned up, find the regulator IC. It'll most likely have somewhere between 8 and 18 pins. Get the part number from the IC, and see if it is close to any of those listed on the above page.

    You may have one or two TL431's or equivalent used as voltage references; the regulator IC will be close by. You will also find an optocoupler/optoisolator or two; these are used to send feedback from the secondary side back to the controller on the primary side.

    Establishing what the controller is, and what relationship the fried components have to the controller, will help a great deal in establishing a reasonable range for the components.
     
  13. b_gravedigger

    Thread Starter New Member

    May 12, 2009
    6
    0
    Now there's some usefull advice. I will look into it and keep you updated.

    Thanks a lot everyone.
     
  14. sheldons

    Active Member

    Oct 26, 2011
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  15. tom66

    Senior Member

    May 9, 2009
    2,613
    213
    It looks a bit like Bestec. These power supplies have been known to cause the 5VSB to hit 17V due to a bad capacitor, and kill motherboards. They usually kill their controller chip eventually as well.
     
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