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PowerMac G4 MDD ACBel Power Supply issues (API1PC36 400W)

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    PowerMac G4 MDD ACBel Power Supply issues (API1PC36 400W)

    Hello!

    First want to thank folks on this forum (Toasty, etc) for the very useful info I've found here that has allowed me to repair a PowerMac G4 MDD Samsung power supply and get this ACBel one working better!

    I got a PowerMac G4 MDD for free as it was dead (not booting at all). I was able to confirm it was it's ACBel power supply as another (above mentioned Samsung) power supply works ok with the system.

    With this ACBel power supply installed, the system would not boot at all, no power light blink, nothing. I've gone ahead and replaced the "12 shotgun approach caps" as noted in post 11 from this thread
    https://www.badcaps.net/forum/showthread.php?t=14077

    That includes C16, C29, C21, C10, C13, C43, C8, C7, C41, C35, C59, and C60. 4 of these measured bad on ESR tester, others were replaced for good measure.

    After replacing those, things improved. Now when I connect only power to the PS, I get +5V and about +25V standby from pin 1 and 14. There is however a fast clicking/ticking noise from the PS - not clear from where it originates, see attached sound clip.

    If I jumper the PS connector pin 11 to another ground pin, so that it'll trigger itself on, it does nothing - still hear the noise and the pins 1 and 14 voltages stay the same. Likewise, connecting it to the PowerMac (in case it needs to be under load?) still produces the noise and the system does not power on.

    Anyone have suggestions as to things I can try next?

    I know there's a least a few more caps on the "fan control" board as noted in the attached board layout picture, the caps in blue. I saw different comments in various places about the caps on this board, whether they're simply for fan control or if they also have some affect on other areas. So not clear if they simply just need replacing as well.

    Thanks!
    Attached Files

    #2
    Re: PowerMac G4 MDD ACBel Power Supply issues (API1PC36 400W)

    Obligatory photo of the power supply in question.
    Attached Files

    Comment


      #3
      Re: PowerMac G4 MDD ACBel Power Supply issues (API1PC36 400W)

      After some additional investigation, sounds like at least the C30, C32, and C45 caps also need to be replaced. Pulled them today, all three were bad. So will try with new ones next...

      Comment


        #4
        Re: PowerMac G4 MDD ACBel Power Supply issues (API1PC36 400W)

        The WT7515 on that PCB labeled "fan control" in your picture is the PSU supervisor.
        The PSU will not work if this chip gets unstable voltage supply.
        And my personal experience with small caps in PSU's is that they often go dry.
        Even when they are not in very demanding places.
        So if you already found a few that are bad I would just replace them all.
        Especially considering the age of this PSU.
        "The one who says it cannot be done should never interrupt the one who is doing it."

        Comment


          #5
          Re: PowerMac G4 MDD ACBel Power Supply issues (API1PC36 400W)

          Finally got them, and indeed replacing C30, C32, and C45 caps has now fixed the PS. It powers up fine, no longer making the noise either. Yay!!

          Comment


            #6
            Re: PowerMac G4 MDD ACBel Power Supply issues (API1PC36 400W)

            I have just fixed 2 of these power supplies, its essentially needed to replace the secondary caps, practically all of them with new ones, best to use brand name caps such as Elna, nichicon, etc. also pay attention to the diameter as the bigger buffer caps are all tall narrow types. i've also noticed the smaller caps, 10uF 47uF and 0.47uF had gone bad, best to also replace those capacitors. I have replaced the smaller caps with ceramic equivalents, this works well, and i think its a good replacement as they will likely last longer. both supplies are now running well!

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