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Re: [Electronics_101] Re: PC power supply problem

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  • ravi sumith
    Yes, I replaced the fuse with a similar but again it blows up.Switching regulator is 2SK7565 MOSFETon which I have the datasheet.As you said I must check the
    Message 1 of 5 , Dec 4, 2003
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      Yes, I replaced the fuse with a similar but again it blows up.Switching regulator is 2SK7565 MOSFETon which I have the datasheet.As you said I must check the Caps. and also high value,high wattage resistors.Yes, I connected a dummy load (10ohms,25W resistor) to +5V rail and a dual filament auto head lamp to +12V rail.Also I powered the unit through series 100W lamp bulb. This is just to reduce the current to the unit.But still it did not work.The reason I want to repair this is to use as a bench power supply. 

      manifold <manifold_1@...> wrote:
      Ok, you know that replacing the fuse will not help; have you replaced
      the fuse to find out? Remember that a PC supply must be connected to a
      load to work correctly.

      It is generally cheaper in the US to look through dumpsters for an old
      computer case and then recover the supply rather than fix one that is
      broken. They are very cheaply built and are not designed to be easily
      repaired.

      If you still need to repair it, there are a few things you can try. It
      there any obvious damage like bubbled plastic on a capacitor or small
      chips of plastic missing from the center of a transistor case? Look
      carfully and replace obviously damaged parts.

      You may want to build a dummy load for testing. Make sure that the
      regulator is switching buy checking pins at the regulator or on the
      switching device; you will need a scope for this. Be careful, there
      can be up to 1000V at some points on the supply. Find out the part
      number of the switching regulator that the supply uses and get the
      datasheet.

      Most of the time it is fairly obvious what is wrong and it can be
      found by careful observation.

      --- In Electronics_101@yahoogroups.com, ravi sumith
      <mindover2003@y...> wrote:
      > Hi,

      > I have a compaq ATX -145W switch mode PC power supply which I have
      salvaged from an old PC. It is not powering up due to a problem and I
      want to fix it.The fuse has blown but I know replacing the fuse does
      not help. I checked the switching transistor (power MOSFET), the
      bridge rectifire,fast recovery diodes all of them are OK.

      > Can any one help me to figure out the problem please.

      > Ravi
      > Colombo
      > Sri Lanka  
      >
      >
      > ---------------------------------
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    • Dave Mucha
      ... ah.... the best approach would be to get another PC, and old one, and use a working power supply. for instance, if the 110 VAC was rectified and passed to
      Message 2 of 5 , Dec 4, 2003
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        --- In Electronics_101@yahoogroups.com, ravi sumith <mindover2003@y...>
        wrote:
        > Yes, I replaced the fuse with a similar but again it blows up.Switching regulator is 2SK2765 MOSFET on which I have the datasheet.As you said I must check the Caps. and also high value,high wattage resistors.
        >
        > Yes, I connected a dummy load (10ohms,25W resistor) to +5V rail and a dual filament auto head lamp to +12V rail.Also I powered the unit through a series 100W lamp bulb. This is just to reduce the current to the unit.But still it did not work.The reason I want to repair this is to use as a bench power supply.


        ah....

        the best approach would be to get another PC, and old one, and use a
        working power supply.

        for instance, if the 110 VAC was rectified and passed to a MOSFET to
        get 5 volts for logic circuits, and that MOSFET blew and the 5 V side
        got hit with 110 (220?) then everything on the entire 5 volt run is bad
        or will be soon.

        and that means they did not regulate, and everything that should have
        been regulated is bad, or will be soon.

        Short of just replacing everthing on the board, it would not be a good
        candidate.

        also, your current PC has way more power than you need. check the
        specs.

        put in a plug to connect the 12 and 5 V to the case, then bring that
        into a fused board with all your connections and LED's and meters and
        such. Most likely, you will never come close to using the power
        available, and if you use small fuses, you have a chance to alter teh
        current as you need to.

        Dave
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