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iMac 20" (white) PSU Runs, Then Shuts Down? P/N 614-0363

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    iMac 20" (white) PSU Runs, Then Shuts Down? P/N 614-0363

    I have an iMac (white) 20" // 4,1 generation.

    Lately it only runs for a couple minutes before powering off. Just like the power has been cut. After which it won't turn back on again unless left alone for a good few hours.

    I removed the power supply and took it into work. We do basic electronic repair here. But I'm no electronics engineer, more a dabbler ... good with an iron, but not so hot on fault finding ...

    With a little help, I've determined that it is the PSU that is faulty. Under load here (on our test rig) it runs for a couple minutes and then turns off, just like it does when in the iMac.

    The part numbers for this PSU are as follows:

    Apple PN: 614-0363
    Celetronix PN: APP-22-LFM33

    I've replaced 4 out of the 5 output caps (didn't have the correct type on hand here for the fifth) though none are bulging / showing signs of wear.

    Can anyone give any pointers or hunches on what might cause this PSU to run and stop in this manner?

    Anything I could check in particular?

    Many thanks in advance,

    Jay

    #2
    Re: iMac 20" (white) PSU Runs, Then Shuts Down? P/N 614-0363

    As an aside: I did search through the many iMac PSU threads here before posting but I was unable to find any actionable advice related to the symptoms this PSU has.

    Comment


      #3
      Re: iMac 20" (white) PSU Runs, Then Shuts Down? P/N 614-0363

      Though there was no resolution to this thread, I will jump in - I have this same model iMac. Original Intel 20" (iMac4,1). (I will also note that I have no repair solution.)

      Same model PSU. I thought I could somewhat predict when the computer would shut off... under load of some sort, but I could load the crap out of the processor (100%) and then try to do some graphics at the same time (high res videos, etc) and it would be rock solid... then I close that and sit on a web page and POW it shuts off without warning.
      Same symptom - as if someone pulled the plug and then I have to wait a good solid hour with it unplugged to get it to turn on again. If I only wait 45 minutes, it will not "reset" enough (whatever it is doing in that time) and since I just plugged it back in, it means I have to wait ANOTHER... FULL hour for it to come back. So if I try it and it is still dead, my wait time resets.

      I have, however, been poking around inside and it seems that I can cut this wait time down significantly if I open the whole machine up, and unplug the PSU from the inverter and the inverter from the mainboard.
      For those who don't know this machine, the little rectangular power supply plugs into the "inverter" (DC-DC board, technically? but the backlight plugs in so I always say "inverter") and then the inverter into mainboard (so [PSU] > [Inverter] > [MB] )

      There are at least two different brands/designs of this power supply. They are allegedly compatible with the 17 and 20" G5 (pre-Intel) iMacs, and the original Intel 17 and 20", and even the late 2006 (switch to Core 2 Duo processor) 17 and 20". I wonder if this is true?

      I ordered a PSU. It is used. I will pop in later this week to relay whether it has fixed my machine. I would at least like to confirm that the PSU is, in fact, at fault.
      In fact, I ordered the OTHER available PSU. It has four large (output?) caps instead of the line of 5 small ones on this one. Bigger is better, right? It also appears to be a little less "cluttered" than my current one. Apple PN 614 0378, made by AcBel (?) (model API4ST03?)

      There's another great thread on these PSUs here, ( https://www.badcaps.net/forum/showthread.php?t=15205 ) and on the second page is info found by Toasty that clarifies that brown wire.
      Originally posted by Toasty View Post
      The mysterious brown lead** is a shutdown lead that outputs to the system in the event of a PSU malfunction (Over Voltage). The signal is provided via the 5 pin SIP, M51957B IC on the top side of the board next to the output wires.

      ** The brown lead was thought to provide the turn on signal via the onboard battery to these units. I have now confirmed, this is not the case.

      Toast
      So, the brown wire is for... yep... shutting the whole darn thing down if necessary. Thus the fault must be somehow connected (literally or figuratively) to this functionality.

      If I was really adventurous, I would consider severing that lead or giving an artificial signal in its place. But... I think I'll wait for the replacement PSU to arrive (fingers crossed it doesn't magically have the same problem...) and see how that works.
      Last edited by alecjahn; 05-13-2014, 05:08 PM.

      Comment


        #4
        Re: iMac 20" (white) PSU Runs, Then Shuts Down? P/N 614-0363

        i'v not worked on mac's,
        but this type of problem is usually cause by a bad semiconductor.

        obviously you cant test them - so you just replace them until you get lucky.
        but i'd start by replacing whatever is the main switching device.
        it could be an i.c. or one or two fets.
        if that wont fix it then i'd look at any other part that obviously runs hot.

        and re-solder any coils or transformers.

        Comment


          #5
          Re: iMac 20" (white) PSU Runs, Then Shuts Down? P/N 614-0363

          Originally posted by alecjahn View Post

          There's another great thread on these PSUs here, ( https://www.badcaps.net/forum/showthread.php?t=15205 ) and on the second page is info found by Toasty that clarifies that brown wire.

          So, the brown wire is for... yep... shutting the whole darn thing down if necessary. Thus the fault must be somehow connected (literally or figuratively) to this functionality.
          Hi, apologies for resurrecting such an old thread, but I do have the same issue with intermittent but predictable shut downs with a Celetronix psu P/N 614-0363 in an iMac 4,1. Id like to repair if i can.

          Would the issue be with the M51957B IC itself or result of another failing component on the psu, is likely to be a capacitor, as in the delay capacitor mentioned in this spec?

          Ill start by replacing all the capacitors

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