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Apple A1407 Thunderbolt Display Power Supply PA-3251-3A

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    Apple A1407 Thunderbolt Display Power Supply PA-3251-3A

    Hi all, I’ve got a couple of these power supplies. Both of them power on the thunderbolt display without issue, but they won’t charge a macbook through the MagSafe cable. I’ve checked the output voltage on the MagSafe plug from the PSU and I have around 6.6-6.7V when this should be much higher. Probably around 14-18.5V. Everything on the board looks clean. No bloated or leaking capacitors. Could anyone tell me what capacities on the board are for the MagSafe charger specifically? Might change those and see what happens. In case you are wondering, the cable further to the right on the pic is the one which leads to the MagSafe cable. Any other pointers? Thanks



    Attached Files

    #2
    Re: Apple A1407 Thunderbolt Display Power Supply PA-3251-3A

    First of all do you have an ESR capacitor tester if not I would highly recommend that you replace all of the capacitors on this board

    The only ones that you might not have to replace are the main filtering capacitors on this board but this depends how old this device is and how much it has been used or not been used if it has been in storage

    The brand of capacitors ( greenish color ones )that are on this board are known for failure with no blotting or popping there tops
    Last edited by sam_sam_sam; 02-23-2021, 08:48 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

    Comment


      #3
      Re: Apple A1407 Thunderbolt Display Power Supply PA-3251-3A

      Thanks for the reply Sam. I do have a capacitor tester, ie- measure capacitance. I would need to desolder each one to measure them though wouldn't I? As they are I circuit on the board.... I did think the taicon caps were the primary suspects. Rubycon caps are probably fine.

      Comment


        #4
        Re: Apple A1407 Thunderbolt Display Power Supply PA-3251-3A

        Originally posted by bosscharles View Post
        Thanks for the reply Sam. I do have a capacitor tester, ie- measure capacitance. I would need to desolder each one to measure them though wouldn’t I? As they are I circuit on the board.... I did think the taicon caps were the primary suspects. Rubycon caps are probably fine.
        You really should think about getting your self an ESR capacitor tester just an ( ordinary capacitor ) tester can be used however if you get a reading different from what the capacitor UF value that is written on the capacitor and more or less than 5 % I would be surprised if it might be bad but you have better luck determining weather or not a capacitor good or bad or question able with an ESR capacitor tester

        Now what I will do sometimes is I get an reading of 0.00 resistance reading on a capacitor and the capacitor UF value is over 500uf then I would a ordinary capacitor tester to see what UF reading I am getting

        I have had this issue before but it does not happen very often but when it happens and I have a new capacitor with the same UF value capacitor I will compare the results from both meters and if think that it might be an issue I would just replace the capacitor
        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

        Comment


          #5
          Re: Apple A1407 Thunderbolt Display Power Supply PA-3251-3A

          Taicon output caps are of middling or lesser quality, and Lite On isn't the best at using them with really long-term reliability. at ~9 years old (there's what looks like an "1152" date code on a transformer) those Taicons may be ready for retirement.
          PeteS in CA

          Power Supplies should be boring: No loud noises, no bright flashes, and no bad smells.
          ****************************
          To kill personal responsibility, initiative or success, punish it by taxing it. To encourage irresponsibility, improvidence, dependence and failure, reward it by subsidizing it.
          ****************************

          Comment


            #6
            Re: Apple A1407 Thunderbolt Display Power Supply PA-3251-3A

            hey do you mind sharing images of this section of the board . The Power factor correction circuit of the thunderbolt display is shorted some of the components . I've changed the NPC1605G IC , but supporting over voltage protection and feedback circuits are still damaged .
            Ive highlighted the components I require in the attached images.

            thanks
            Attached Files

            Comment


              #7
              Re: Apple A1407 Thunderbolt Display Power Supply PA-3251-3A

              Originally posted by sam_sam_sam View Post
              First of all do you have an ESR capacitor tester if not I would highly recommend that you replace all of the capacitors on this board

              The only ones that you might not have to replace are the main filtering capacitors on this board but this depends how old this device is and how much it has been used or not been used if it has been in storage

              The brand of capacitors ( greenish color ones )that are on this board are known for failure with no blotting or popping there tops
              Hi Sam I have the same problem and I have changed all the electrolytic caps, except the 420v 68uf ones, I have checked the fuses but they are ok, but I don't have dc output, and what I can see is that the 420v are not charging more that 10v or so if I leave the board connected for 1 hour, everything seems to be good under the microscope, where else could I check? Tia

              Comment


                #8
                Re: Apple A1407 Thunderbolt Display Power Supply PA-3251-3A

                there really isnt much between the mains and those capacitors.
                check the bridge rectifier pins for mains going in and DC coming out

                Comment


                  #9
                  Re: Apple A1407 Thunderbolt Display Power Supply PA-3251-3A

                  Originally posted by stj View Post
                  there really isnt much between the mains and those capacitors.
                  check the bridge rectifier pins for mains going in and DC coming out
                  Thanks for the prompt reply, I didn't see it until now.
                  I'm a total newbie on Power supplies, can you show me where is the bridge rectifier in these pics? Tia
                  Attached Files

                  Comment


                    #10
                    Re: Apple A1407 Thunderbolt Display Power Supply PA-3251-3A

                    The fuses are not blown, so I think the bridge rectifier cannot be. So where else could I check?tia

                    Comment


                      #11
                      Re: Apple A1407 Thunderbolt Display Power Supply PA-3251-3A

                      Some of the caps are difficult to see the specs if you don't desolder them For those who want to know the capacitor's specs here they are:

                      470uf -35V
                      1000uf -16V
                      330uf -35V
                      4,7uf - 50V
                      22uf - 50V
                      2,2uf - 50V
                      220uf - 50V
                      47uf - 50V

                      Comment


                        #12
                        Re: Apple A1407 Thunderbolt Display Power Supply PA-3251-3A

                        After changing all the capacitors because I read it (facepalm)
                        I have discovered a Zener diode that is shorted, so Im going to change it tomorrow and let you know if it works.
                        Attached Files

                        Comment


                          #13
                          Re: Apple A1407 Thunderbolt Display Power Supply PA-3251-3A

                          The Diode is working fine so must be a short near that zone. Any advice?

                          Comment


                            #14
                            Re: Apple A1407 Thunderbolt Display Power Supply PA-3251-3A

                            Hi, just got accepted on the website.

                            I have two of these PA-3251-3A PS Boards and was wondering if anyone knew or had the Pin Outs for the 12-Pin connector (only 11 are pinned). And would that unpinned pin be No.1, 6, 7 or 12 ???

                            Comment


                              #15
                              Re: Apple A1407 Thunderbolt Display Power Supply PA-3251-3A

                              Originally posted by sbyseven View Post
                              The Diode is working fine so must be a short near that zone. Any advice?
                              Same problem here!
                              Zener shorted - but out its ok!

                              Without diagram, hard work!

                              Comment

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