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Old AT power supply (model: API-3186S) troubleshooring/testing

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    Old AT power supply (model: API-3186S) troubleshooring/testing

    So... I tore it off a PowerMac 4400/200 that I'm trying to repair. Currently I'm at the stage of eliminating factors that would keep the thing from powering on (RAM is fine, HDD and peripherals are fine, no obvious damage on motherboard).

    Problem is, I know precisely nothing about AT-era PSUs and this particular one is an oddball at that. It's got the two auxiliary power connectors that according to schematics online have three +3.3V power lines (and ground obviously) along with a connector that goes to a "SOFT PWR" connector on the motherboard so apparently it's not like the other ones that power on as soon as they're plugged in.

    I took some pictures of the back of the board... I put them in an imgur album. I can attach them here if imgur albums are a problem.

    The current problem with the power supply, is that it makes a buzzing sound when I plug it in. I'm not an expert, but another AT PSU that I've had was silent (aside from the fan). I also don't know how to make this particular PSU power on on its own so I can test its outputs.

    If it turns out that the thing is completely blown, can I modify an ATX PSU to give out the same kind of outputs? I think the -5VDC and the multiple +3.3VDC are going to be a bit of an issue... although I guess I could use the +3.3VDC from the MOLEX connectors...?

    #2
    Re: Old AT power supply (model: API-3186S) troubleshooring/testing

    When you take pictures of a power supply board or anything that you are trying to repair you need to take pictures of both side of the boards

    Yes you need to post the pictures here because most people are not going to go to another website to view your pictures

    Do you know how to use a volt meter

    Do you understand the concept of troubleshooting
    Last edited by sam_sam_sam; 02-10-2020, 09:23 PM.
    9 PC LCD Monitor
    6 LCD Flat Screen TV
    30 Desk Top Switching Power Supply
    10 Battery Charger Switching Power Supply for Power Tool
    6 18v Lithium Battery Power Boards for Tool Battery Packs
    1 XBox 360 Switching Power Supply and M Board
    25 Servo Drives 220/460 3 Phase
    6 De-soldering Station Switching Power Supply 1 Power Supply
    1 Dell Mother Board
    15 Computer Power Supply
    1 HP Printer Supply & Control Board * lighting finished it *


    These two repairs where found with a ESR meter...> Temp at 50*F then at 90*F the ESR reading more than 10%

    1 Over Head Crane Current Sensing Board ( VFD Failure Five Years Later )
    2 Hem Saw Computer Stack Board

    All of these had CAPs POOF
    All of the mosfet that are taken out by bad caps

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      #3
      Re: Old AT power supply (model: API-3186S) troubleshooring/testing

      Originally posted by sam_sam_sam View Post
      When you take pictures of a power supply board or anything that you are trying to repair you need to take pictures of both side of the boards

      Yes you need to post the pictures here because most people are not going to go to another website to view your pictures

      Do you know how to use a volt meter

      Do you understand the concept of troubleshooting
      I took some more pictures of the main PSU board and a little daughterboard it has. I put them in another imgur album.

      I know how troubleshooting on ATX PSUs is supposed to work (connect a green wire to any of the black wires, check the various outputs...). But this isn't and ATX power supply. And as I've said on my post, the general consensus is that AT power supplies are supposed to turn on when you plug them in, but this doesn't - in fact there's a "SOFT PWR" plug in the motherboard itself.

      I can't attach pictures here, however. Whenever I try, I just get a message reading "Your submission could not be processed because the token has expired. Please push the back button and reload the previous window."

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        #4
        Re: Old AT power supply (model: API-3186S) troubleshooring/testing

        See the link below. It is a translation from a Japanese site, but easy enough to follow.

        https://translate.google.com/transla...n%2Findex.html

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