smps not working

Discussion in 'General Electronics Chat' started by paachu802, Apr 1, 2014.

  1. paachu802

    Thread Starter New Member

    Feb 5, 2014
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    these are problems
    1.my computer turnsoff suddenly and restarted it then it works for 2 minutes then turnoff automatically

    2.i checked backside of cpu cabinet it seems smps fan doen't work

    3.so i unscrewed smps and cleaned dust put some oil in rotating part of fan....then i turned on smps shorting green and black wires...but it rotated for 2 rouds and stopped...

    4.then i checked caps and removed all top bulged capacitors(leaky)...
    2 rectifier filters(big caps 220V)
    3 1000uF ,16v caps

    5.but now it just works for 3 seconds and turns off automatically....plz help me what other components to check
     
  2. paachu802

    Thread Starter New Member

    Feb 5, 2014
    27
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  3. alfacliff

    Well-Known Member

    Dec 13, 2013
    2,449
    428
    check or replace the small electrolytic caps near the pwm (usually 8 pin) chip. they supply power to the pwm chip, and if the fan quit, are probably bad too. replace the fan.
     
  4. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,739
    759
    You need to check the caps in the primary side..
    As above post small electro's at the primary could be a problem.
     
  5. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    for the sake of £12 ($20) for a new one, it aint worth taking the back off it...
     
  6. ian field

    Distinguished Member

    Oct 27, 2012
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    Pretty much my opinion too.

    The OP was lucky - last PSU that failed on me overvolted, the graphics card sacrificed itself to save the MOBO.

    The times I've heard people say their PC PSU didn't start, so they kept trying the switch till it did - then it went POP!!!

    But I'd go a bit better than £12 for a PSU - at that price you're just asking for it!
     
  7. nigelwright7557

    Senior Member

    May 10, 2008
    487
    71
    I had one that did the same, it was simply the fan grill clogged with dust.
    Cleaned it and it has been fine since.
    The power supply was getting to hot and turning itself off.
     
  8. ian field

    Distinguished Member

    Oct 27, 2012
    4,413
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    I'd have at the very least; taken the cover off and inspected it for electrolytics with bulged tops.

    Usually the heatsinks inside have slotted fins that get clogged with dust - there's no point cleaning the fan if you don't clean those too.
     
  9. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
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    That's an ancient PSU! I've done a heap of those.

    Start by replacing the two small blue electros to the right of the yellow transformer, in the 3rd photo.

    You may need to replace the secondary electos, although in this unit they are away from the heatsink so they may be ok. They do not look to be bulged.
     
  10. paachu802

    Thread Starter New Member

    Feb 5, 2014
    27
    2
    ok...[​IMG][​IMG][​IMG][​IMG][​IMG]
    these blue 2 eloctro caps replace????

    ...there is one more blue cap without polarity
     
    Last edited: Apr 4, 2014
  11. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    The non-polarised blue blobs are HV polyester caps, they rarely fail and will not be the problem.

    The first thing would be to replace the two blue electros. :)
     
  12. paachu802

    Thread Starter New Member

    Feb 5, 2014
    27
    2
    replaced both....now it doesn't work for a second....earlier 3 seconds before caps removal....
     
  13. paachu802

    Thread Starter New Member

    Feb 5, 2014
    27
    2

    no use...fan is fine...problem is in circuit...something has to be removed because smps works for 3 seconds and turnoffs automatically...(the main problem is something had been overheated and blown since fan stuck)
     
  14. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Check all the solder joints with a good magnifier and bright light, to see if any have dry joints or circle fractures.

    The most obvious places are the pins of power components on heatsinks, they get more thermal expansion. And anywhere the PCB looks to have been hot (discoloured etc).
    :)

    PS. You do know it will not run properly without a load?
     
  15. paachu802

    Thread Starter New Member

    Feb 5, 2014
    27
    2

    yes you were right i checked all solder joints ...it is seen that coil has been dislodged....but how ?? i didn't touch there...how coil gets heated up...is coil ok????
     
  16. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Close up photos would help. :)
     
  17. paachu802

    Thread Starter New Member

    Feb 5, 2014
    27
    2
  18. paachu802

    Thread Starter New Member

    Feb 5, 2014
    27
    2
  19. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Ur photo's are so good tht we cannot figure out if it is burned or not
     
  20. paachu802

    Thread Starter New Member

    Feb 5, 2014
    27
    2
    suppose it is burned how to replace it???mh??
     
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