SMPS Troubles

Discussion in 'General Electronics Chat' started by recca02, Apr 7, 2008.

  1. recca02

    Thread Starter Senior Member

    Apr 2, 2007
    1,211
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    Hi everyone,


    I am having a lot of trouble with my SMPS.
    From past couple of weeks my PC is not starting right away after I turn my UPS on, I think it is a capacitor taking longer time to charge, what say? I think it might be the SMPS capacitor(but again I don't know much).

    Also My SMPS fan makes a lot of nice initially(audible even in other rooms)....Is there a electronic-reason for it? Or is Mechanical problem?

    I blew up a SMPS about 8 months ago. I think I wud attempt a repair myself.
    The SMPS blew when I unwittingly changed the Voltage selector switch postion to 110 V from 230 V. A lot of fume came up after a hissing sound and a lot of hot fluid, which I think was the capacitor dielectric. So at this time I am thinking, I have only one blown capacitor..I opened it and found only one capacitor seemed to have its packing blown, everything else seemed alright.
    Cud there be any other component that might be damaged?

    Any advice?

    Recca.
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    If your fan is making a lot of noise, that is generally a symptom of the bearings wearing out, and the fan needs to be replaced. When the fan is making noise, it's not able to achieve the rotational speed necessary to provide adequate cooling by moving air through the PSU.

    I usually open up my computer every 6 months and blow out all of the accumulated dust using compressed air, taking care to prevent the fans from spinning. Spinning the fans using compressed air can cause severe damage to it due to overspeed.

    You could open up your PSU, clean it using air, and inspect all of the electrolytic capacitors for bulging or "blown-out" tops. If they are bulging, they are failing and should be replaced.

    For the one that you blew up by having the selector switch in the wrong position, try replacing the cap and check the fuse, and the power resistors. The power resistors (sand colored or white, rectangularly shaped) are usually the 2nd things to go (after capacitors blowing) - but no promises here.
     
  3. recca02

    Thread Starter Senior Member

    Apr 2, 2007
    1,211
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    Thanks a lot Mr Wookie, I'll definitely do that.

    The capacitor that blew up had 220 V rating to it, I was wondering why did it blow at 110 V when everything else was OFF or disconnected with the supply reaching only the SMPS.( he he, I was so amazed & horrified with the hissing sound that I cud not switch off the supply) Anyways, I think I won't understand that.
     
  4. S_lannan

    Active Member

    Jun 20, 2007
    247
    2
    when you change voltage selector switch from 230 to 110 its bad.
    basically those two capacitors are used as voltage doublers....
    that means each capacitor sees about 340 volts dc across it!!!!

    i've fixed truckloads of pc smps's in the last few years because of the dodgy low esr caps going around, i fixed my power supply a week ago because it was having trouble starting up.
     
  5. S_lannan

    Active Member

    Jun 20, 2007
    247
    2
    about having computer psu's that wont start up.

    When i switched the mains off then on and tryed to start my pc i'd press the power button and nothing would happen. after several goes and a few minutes it would magically spring to life.

    My first thought was a resistor had gone high in the start up circuit or a leaky high voltage transistor in the start up circuit... something simple like that..

    However after inspecting the supply a +5v filter cap and a +12v filter cap had cracked at the top and leaked fluid. They were obviously bad so i replaced them. and voila...

    anyhow after seeing that this is what i think was happening.

    any how i am thankful for electronics with 'brains'.. no poor little transistors getting blown to pieces, burnt tracks and melting power leads.

    on startup the pwm controller was seeing too much current go through the supply or bad regulation due to the faulty parts and shutting it down.
     
  6. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Yep.

    Modern computer power supplies (like the ATX form factor and later) expect to see the supply voltages come up in a certain order, and within a certain period of time. If they don't, the POWER OK signal stays low, preventing the computer from trying to operate with incorrect voltage levels which would likely cause severe damage.
     
  7. abcl1234

    New Member

    Sep 3, 2009
    1
    0
    i just want to do hot test for SMPS please guide

    thanks in advance
     
  8. Perfectboy

    New Member

    Sep 9, 2009
    9
    0
    If the fan got a problem, your PC couldn't start up. That's also my PC problem.
    [​IMG]
     
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