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Sorting out old PC power supplies?

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    #41
    Re: Sorting out old PC power supplies?

    160v??
    where does that come from? he's got 340v dc after the rectifier.

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      #42
      Re: Sorting out old PC power supplies?

      Originally posted by stj View Post
      160v??
      where does that come from? he's got 340v dc after the rectifier.
      It should have been 340vdc, I overlooked that he was in the U.K. next time I will just call it Main B+
      EDIT
      The small smd transistor drives a larger mosfet that has it's Drain pin connected to the small standby transformer, I made a Red square around the standby mosfet and a yellow one around the drive transistor.
      On the small standby transformer, pin 1 should have 340vdc, and so should pin3 which is connected to the mosfet drain., this is the primary. There is likely a low ohm resistor connected to THIS mosfet's source pin to hot ground.
      Last edited by R_J; 11-22-2020, 07:45 PM.

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        #43
        Re: Sorting out old PC power supplies?

        Originally posted by R_J View Post
        The small smd transistor drives a larger mosfet that has it's Drain pin connected to the small standby transformer, I made a Red square around the standby mosfet and a yellow one around the drive transistor.
        On the small standby transformer, pin 1 should have 160vdc, and so should pin 3 which is connected to the mosfet drain., this is the primary. There is likely a low ohm resistor connected to THIS mosfet's source pin to hot ground.
        That's a great help RJ. Ok I took a reading on all you said and I dont get a voltage on Pin 1 of the standby transformer (my meter just goes straight to zero whatever that means) although I do get -310vdc on pin 4 and -310vdc at all 3 pins of the smd transistor.
        I am not sure if I am putting the negative meter probe at the correct place. I am taking the negative from the negative output of the Rectifier but all readings are -voltages which seams wrong. I always get confused where I should be taking the negative from especially on the AC side. I guess if I take it from negative output of Rectifier its got to be right (I hope). I also get a high pitched sound when turning the PSU on or off. Its what sounds like its in pain lol...

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          #44
          Re: Sorting out old PC power supplies?

          high pitch sound usually means something is shorted.
          check all ceramic capacitors

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            #45
            Re: Sorting out old PC power supplies?

            Did you remove the main capacitors at any time?

            If you are getting - voltage I think at least one of the caps are in backwards, see this picture from the internet.

            This schematic should help with the standby circuit
            Attached Files
            Last edited by R_J; 11-23-2020, 12:37 PM.

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              #46
              Re: Sorting out old PC power supplies?

              Thanks RJ for that Schematic and thank you everyone for your help.
              Thanks to you all I have finished repairing these PSU's and all the computers they go in are working again.
              Thanks!

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                #47
                Re: Sorting out old PC power supplies?

                Some more items that did not land into the landfill

                Go repairs
                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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