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PC power supply

Discussion in 'Electronic Repair' started by onyxx, Sep 16, 2005.

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  1. onyxx

    onyxx Guest

    Hello all, I am working açon a 250W SMPS from a PC. The primary part
    of the circuit work fine ( or so it seems) but the out put from the
    secondary is pulsating. I caonnect a small device i made out of 2 small
    light bulbs (one 5V the other 12V,I use this to quickly check for right
    voltage output)and i find is pulsating, like on off on off. Can anyone
    tell me why can this be? I tought of capacitors but they all seem fine.
    I dont have any equipment to check caps, I used a DMM. Any ideas?

  2. How much of a load are you lamps? You may need a couple amps on at least
    the +5 VDC line for stability.

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  3. Does it do this when connected to the motherboard? It actually sounds
    like something is unhappy on the primary side...

  4. Elec_Tech

    Elec_Tech Guest

    Is the supply current limiting? It sounds like its trying to start up,
    and then shutting itself down.
    If it is, then yes, it does sound like a control side issue. Closely
    inspect the pcb and components, using a jewelers eyeglass (95% of
    faults can be found, by careful inspection. To check that a transistor
    hasnt died, by desoldering one of its legs and measuring it. Also
    check for dry joints.
    Good luck.
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