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How do I fixed a shorted MOSFET?

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    #1

    How do I fixed a shorted MOSFET?

    Dell slimline Inspiron 530s

    the original symptom was processor fan just tries to start for just a split second and then nothing except solid amber light on motherboard and power button

    the reason I think it is a shorted MOSFET is that helpful forum member c_hegge had me do a test, unplugging the 4 pin power connector near the processor, and sure enough, this allowed computer to boot, mr. hegge said this indicates a shorted MOSFET (of which I can locate about 12 or so of them on the motherboard)

    How do I fixed a shorted MOSFET? - just replace it like a cap? - how do I test it in circuit to know which MOSFET is bad? - and why would it have shorted in the first place? - due to a bad cap? - this must be a common problem of these MOSFETS, because both of our Dell slimline Inspiron 530s computers have the same exact motherboard (Foxconn G33M02 - Dell p/n RY007) and same exact problem!

    the computer has lots of those dang Chemicon KZG and Lelon caps too! (but none puffy or leaking)
    Last edited by theOracle; 01-08-2013, 10:03 PM.
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    #2
    Re: How do I fixed a shorted MOSFET?

    The 4 pin power supply connector is used to provide +12 VDC to the processor voltage regulator. Posibly you may have a bad or shorted cap around the mosfet. Mosfets often most likely burn open after shorting. A bad cap not always is puffy or leaking, I have replaced hundreds of good looking caps. I use a MUL3333 cap tester.

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      #3
      Re: How do I fixed a shorted MOSFET?

      I think these motherboards are gonna get tossed, a great reliable replacement is just $44 new, and there are literally 40 suspect caps on this board I would have to replace - not interested!
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      ~~~ the top tier of low-ESR electrolytic capacitors ~~~

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        #4
        Re: How do I fixed a shorted MOSFET?

        Originally posted by theOracle View Post
        I think these motherboards are gonna get tossed, a great reliable replacement is just $44 new, and there are literally 40 suspect caps on this board I would have to replace - not interested!
        Ok... just beware you could be replacing crap with crap. Depending on why a cap (or whatever failed, a replacement could have the same crap part and just be a ticking time bomb.

        But if time is of the essense, then I understand.
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        (Insert witty quote here)

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          #5
          Re: How do I fixed a shorted MOSFET?

          In my experience, MOSFETs remain shorted most of the time, they don't blow open afterwards. Especially a VRM 'fet which is rated for 50A in the "on" state, if not over. I'd say more likely a shorted MOSFET in the VRM than a shorted cap... Shorted capacitors are rare.
          Originally posted by PeteS in CA
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            #6
            Re: How do I fixed a shorted MOSFET?

            ^
            +1

            The only time a MOSFET will go open after shorting is if it's being used as a high voltage switching transistor, and it blows itself in half. On a low voltage VRM, it will ALWAYS remain shorted.
            I love putting bad caps and flat batteries in fire and watching them explode!!

            No wonder it doesn't work! You installed the jumper wires backwards

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              #7
              Re: How do I fixed a shorted MOSFET?

              Originally posted by theOracle View Post

              the computer has lots of those dang Chemicon KZG and Lelon caps too! (but none puffy or leaking)
              The Lelon caps are probably just the tiny ones by the PCI slots.

              And back in August, 2011, a Dell Inspron 530S was brought to me with the board failing to boot in dual channel mode!

              https://www.badcaps.net/forum/showthread.php?t=16209

              Foxconn had to use Lelon for the tiny ones.
              Last edited by RJARRRPCGP; 01-10-2013, 05:16 PM.
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