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Help needed on unstable HP PS-4321-2HF power supply

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    Help needed on unstable HP PS-4321-2HF power supply

    Hi all,
    Got this HP 320W pc power supply model PS-4321-2HF no power initially. After opening case and do some simple diode test, I found out the 2 pieces n chanel mosfet marked K12A50D (12A 500v)on heat sink 1 shorted and replaced with new ones.
    Before power on, I removed the 6.3A 250v fuse and connect to a 60w bulb as current limiter. To force start, I use a wire to short the green and black pin on P2 connector. Upon power on ac, the bulb starts blinking and I heard some tiny clicking sound from the pcb but could not point out from exact location.

    I suspect there is still some fault on board but has no idea. Appreciate if someone experience can kindly assist and guide me where to check and diagnose to revive this power supply. I do not wish this item to add to the dumpster.
    Attached Files

    #2
    Re: Help needed on unstable HP power supply

    After keeping this unstable hp power supply for almost one year, i suspected IC501 (TNY287PG) is faulty and with no exact replacement i decided to try with TOP258PN. In addition, i also desoldered two electrolytic caps at c503 and another one near c504. The original type is 120uf 35v with esr over 0.10 ohm, so i replaced with 330uf 35v for testing.
    Upon power on, while with fuse removed and connected to a 60 watt bulb as current limiter, the bulb lightly dim and no more blinking and no clicking sound. The psu fan spins briefly less than a second and stops. I probed the yellow connector for 12 volt dc but there is none. When i probed the purple wire(12vsb), i noticed the fan trying to spin but still there is no dc voltage. Can anyone kindly assist to guide and point me on what else to check to resuscitate this dead power supply. Thanking in advance for any help.
    Attached Files

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      #3
      Re: Help needed on unstable HP PS-4321-2HF power supply

      Some psu have APFC circuit that need more input power to work corectly, in my repair even 160w bulb isnt enough, so I put toaster istead for test, and work ok.
      Second, some psu need a real load, otherwise just briefly start and shutdown.
      The sb voltage must be present before and after you do power on.

      You can see this behaveour on video
      https://www.youtube.com/watch?v=aMMzu436MBA
      https://www.youtube.com/watch?v=d7jXHcYf9wk
      Both repair is on this forum, so you can see conversation, maybe help.

      This all supose that you entirely repair psu and not have any short anywhere.
      Last edited by harp; 05-30-2023, 06:39 PM.

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