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Powerman has lost its power

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    #1

    Powerman has lost its power

    Got this Powerman IP-P350AJ2-0 350 watt power supply as dead freebie. Opened it up and found a huge black spot around the switching transistor. Alcohol, a brush, and lots of scrubbing took off the blackness and revealed a bad transistor and capacitor. Plenty of pictures to show what the power supply looks like, so thought I would include only the pictures showing the carnage!

    The switching transistor is a hefty 12N90 good for 12 amps at 900 volts. Lost one of its legs and lots of burn damage at bottom of FET. A 1KV capacitor had lots of burn damage at its bottom. Damage also included the pwm chip, a UC3843, several resistors between the pwm chip and the FET, and one shorted diode between the pwm chip and the FET.

    Just another power supply that flamed out. Lots of black smoke soot, and the usual switcher, pwm chip, and a few other components "failing".

    After repairs voltages are:
    12.13v
    5.12v
    3.34v
    4.98v 5vsb

    The only bummer was that hefty 12N90 FET cost five bucks!
    Attached Files
    Old proverb say.........If you shoot at nothing, you will hit nothing (George Henry 10-14-11)
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    #2
    Re: Powerman has lost its power

    Originally posted by everell View Post

    The switching transistor is a hefty 12N90 good for 12 amps at 900 volts. Lost one of its legs and lots of burn damage at bottom of FET. A 1KV capacitor had lots of burn damage at its bottom.
    900+ V rating don't even make sense for a computer PSU, LOL.

    900+ V sounds more like a strobe or a CRT.
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    Comment

      #3
      Re: Powerman has lost its power

      ^ A single 900V or 800V FET is very commonplace as the main switcher in single switch forward topology. Sometimes there will be two of them in parallel as a "modified" version of single switch forward. I wonder what caused the W12NK90Z to fail, unless something driving it did (if that bad capacitor was).

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        #4
        Re: Powerman has lost its power

        In my "opinion" the capacitor was the first to go, then the FET and the resistor between source and ground. Once the resistor between source and ground opens, the high voltage has no where to go except thru the pwm chip. Like a domino effect! I wonder if it made a big bang when it failed.
        Old proverb say.........If you shoot at nothing, you will hit nothing (George Henry 10-14-11)

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          #5
          Re: Powerman has lost its power

          ^
          With the damage you saw to the cap and FET, I'm sure it would have been a nice fireworks display
          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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            #6
            Re: Powerman has lost its power

            I have seen a few of these come in to work from catching on fire due to shorts from conductive glue. Was yours covered in that brown glue?

            Comment

              #7
              Re: Powerman has lost its power

              No, but a large area was covered in black soot!
              Old proverb say.........If you shoot at nothing, you will hit nothing (George Henry 10-14-11)

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