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iMac 24 PSU LITEON PA-3241-02A1 250W

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    iMac 24 PSU LITEON PA-3241-02A1 250W

    iMac 24 PSU LITEON PA-3241-02A1 250W

    Hi everyone, got an aluminum 24 imac with a faulty PSU. First LED on the motherboard is on so trickle voltage is OK. When pressing the power button, 3 lights flash and then only one, 2 seconds pass then again 3 flash then back to one. I've tested motherboard with working PSU and all is well so not a motherboard issue. I can hear a clicking sound coming from the PSU each time it tries to power on. Also, when the power cable is connected, I notice one of the fans on the imac twitches. Very ocassionaly the imac will power up a bit but will eventually die again. All capacitors look absolutely fine, no bulges, leakage etc. I've had a look at the back of the PSU and I think I found the culprit. One of the mosfets looks blown. The board is darkish in that area and the solder on the front of the mosfet looks bad and its slightly lifted. I've provided photos, problem mosfet is on upper right. Thoughts? Also, does anyone now the part number for the mosfet I can't really make it out as it's heated so much, the numbers arent really legible? Would like to try soldering a new one. So if anyone know I would greatly appreciate it... Thanks
    Attached Files

    #2
    Re: iMac 24 PSU LITEON PA-3241-02A1 250W

    Put a really strong light on it and figured it out....

    mosfet 060n03L
    Package: PG-TO252-3
    Cheap find on ebay...

    http://www.ebay.co.uk/itm/MOSFET-N-C...item3f265fcce0


    Schematics here:
    http://www.ic-on-line.cn/search.php?...03l&stype=part


    Thoughts of whether or not this will work? Appears to be the only rough looking area on the PSU

    Comment


      #3
      Re: iMac 24 PSU LITEON PA-3241-02A1 250W

      It's cheap enough so why not? Check the MOSFET with your multimeter, it's probably shorted
      "Tantalum for the brave, Solid Aluminium for the wise, Wet Electrolytic for the adventurous"
      -David VanHorn

      Comment


        #4
        Re: iMac 24 PSU LITEON PA-3241-02A1 250W

        Well, received the mosfet yesterday. Desoldered the presumed faulty mosfet and soldered the new one on and success! Working PSU for £1.70.

        For anyone that is interested, the faulty mosfet wasn't melted or anything but the numbers on it were very difficult to read and color was greyish black so must have gotten really cooked at some point. Hope this helps anyone with a similar issue in the future.

        Is there anything else I should look out for? Presumably, the mosfet may have gotten cooked due to another failing component on the PSU? Or it could have just failed through normal use..... I've power cycled the imac several times, had on for hours and everything is fine... Just want to make sure...

        Comment


          #5
          Re: iMac 24 PSU LITEON PA-3241-02A1 250W

          I don't know about this PSU specifically, someone else might. But failing capacitors can cause overheated switching transistors (assuming that's what this one is for in your PSU). Just because the capacitors look OK doesn't mean they can't be bad.

          The MOSFET control circuitry could also be faulty, or the snubber circuit (if it has one)

          Interestingly someone else seems to have had the same problem here: https://discussions.apple.com/thread/4303781

          So that could point to some specific issue with these PSUs, not just yours, either design problem or a certain part failing over time.
          "Tantalum for the brave, Solid Aluminium for the wise, Wet Electrolytic for the adventurous"
          -David VanHorn

          Comment


            #6
            Re: iMac 24 PSU LITEON PA-3241-02A1 250W

            could be the internal diode failed, and then the mosfet ran too hot.

            i'v noticed this on some invertors.
            when you have several fets,
            and you meter them to find the bad one, you often find that even the good ones have failing or dead internal diodes.

            i suspect in most msfet failures it's the protection diode that goes first.

            Comment


              #7
              Re: iMac 24 PSU LITEON PA-3241-02A1 250W

              Thanks for the replies guys. Nice find agent24, hadn't seen that thread before. Interesting that it is the exact same mosfet I replaced. Only difference is that one was really really cooked! Hopefully it was just a dodgy mosfet and it'll be OK. I'll report back if it fails again. Thanks again.
              Last edited by bosscharles; 06-20-2014, 10:28 AM.

              Comment


                #8
                Re: iMac 24 PSU LITEON PA-3241-02A1 250W

                I've got my hands on another one of these with the same symptoms. PSU physically looks absolutely fine, nothing burnt, capacitors in good shape. When plugged in, trickle charge is good, #1 LED on mobo turns on.... when power button is pressed, #1,2 & 3 light up, psu makes an odd noise, #2 & #3 go off... and it cycles like this for eternity! Last time mosfet sorted it so I've ordered one and will try out.... ANything else to look at? Thanks.

                Comment


                  #9
                  Re: iMac 24 PSU LITEON PA-3241-02A1 250W

                  You could check to see if that MOSFET is shorted or something. A power cycling issue can be other things too, shorted output rectifiers, bad PWM controller, bad startup circuit or run supply circuit\capacitor.
                  "Tantalum for the brave, Solid Aluminium for the wise, Wet Electrolytic for the adventurous"
                  -David VanHorn

                  Comment


                    #10
                    Re: iMac 24 PSU LITEON PA-3241-02A1 250W

                    Would I need to de-solder the mosfet to test? Or can I test while it's soldered o to the psu? Thanks.

                    Comment


                      #11
                      Re: iMac 24 PSU LITEON PA-3241-02A1 250W

                      You can test for shorts in-circuit, for anything else you have to desolder.
                      "Tantalum for the brave, Solid Aluminium for the wise, Wet Electrolytic for the adventurous"
                      -David VanHorn

                      Comment


                        #12
                        Re: iMac 24 PSU LITEON PA-3241-02A1 250W

                        Hi everyone. Right well I replaced the two mosfet's on the back of the board and the problem remains. The trickle charge led light works fine and turns on when plugged in. When power is pressed, LEDs 2 and 3 flash, fans spin a bit and then they go off and we are back at only led 1 on. Can anyone give me an idea of what to try out next? I actually have a supply exactly like this one that works. Anything I could compare using my multimeter to track down the problem component? I'm guessing there is some capacitor causing trouble...they all "look" fine though. I have used a working suply in this imac and everything fucntions properly so nothing wrong with GPU or logicboard. Any help would be appreciated.
                        Attached Files

                        Comment


                          #13
                          Re: iMac 24 PSU LITEON PA-3241-02A1 250W

                          Could be a shorted\leaky rectifier on an output somewhere. That would be the easiest thing to check first at least.
                          "Tantalum for the brave, Solid Aluminium for the wise, Wet Electrolytic for the adventurous"
                          -David VanHorn

                          Comment


                            #14
                            Re: iMac 24 PSU LITEON PA-3241-02A1 250W

                            Originally posted by Agent24 View Post
                            Could be a shorted\leaky rectifier on an output somewhere. That would be the easiest thing to check first at least.
                            What does it look like? Can yuo pinpoint it on the photos I'va attached? thanks,

                            Comment


                              #15
                              Re: iMac 24 PSU LITEON PA-3241-02A1 250W

                              Most likely the diodes mounted on heatsinks in TO-220 packages. There may be some big single diodes too. If you follow the traces from the output power connector, you will find them easily. There will be capacitors and inductors between the output and the rectifiers. The other side of the retifiers will be the secondary windings of the main transformer.

                              There will be at least one diode (usually a pair) on each voltage rail.

                              http://www.giangrandi.ch/electronics.../smpsfix.shtml

                              http://www.repairfaq.org/sam/smpsfaq.htm

                              Might help you too
                              Last edited by Agent24; 08-02-2014, 05:38 PM.
                              "Tantalum for the brave, Solid Aluminium for the wise, Wet Electrolytic for the adventurous"
                              -David VanHorn

                              Comment


                                #16
                                Re: iMac 24 PSU LITEON PA-3241-02A1 250W

                                those !
                                bend over the board and desolder the legs.
                                solder pump or wick.
                                check with meter on continuity test so it Won`t touch the pad and check the FET.
                                this is a solution so you wont have to take the heat sink out.
                                good luck!
                                Attached Files
                                Just cook it! It's already broken.

                                Comment


                                  #17
                                  Re: iMac 24 PSU LITEON PA-3241-02A1 250W

                                  Thanks dj_ricoh! So you've worked with this type of PSU in the past? I tried to power it on earlier today and lo and behold it powered on! it was fine for a while... let it go into sleep and when I tried to get out of sleep it beach balled. I then tried to power on again and it starts up, 2 diagnostic leds on then the third briefly comes on... then the apple chime sound starts and it cuts out mid apple chime....diagnostic leds then go back to only first on... then second goes on... chime, 3rd led on, chime cuts..... it then loops doing this over and over again.....rest of imac is fine... I-ve got it to work with another known working PSU....... Im no expert but It's almost like there is an under voltage protection of some sort? The chime cutting out seems to be exactly when you would expect the LED panel to turn on... perhaps it's not getting enough juice? Would this point more towards a capacitor problem? Thanks for your help!!!

                                  Comment


                                    #18
                                    Re: iMac 24 PSU LITEON PA-3241-02A1 250W

                                    Well today it won't even try to power on.... only led 1 on.... sometimes get 2 on.....ticking like noise coming from psu

                                    Comment


                                      #19
                                      Re: iMac 24 PSU LITEON PA-3241-02A1 250W

                                      Replace the 2 small start-up caps to the right of the large transformer in Post 16. One brown sleeve, the other black.

                                      T
                                      veritas odium parit

                                      Comment


                                        #20
                                        Re: iMac 24 PSU LITEON PA-3241-02A1 250W

                                        I'll give that a try Toasty. I've ordered some replacements... there is a 63v 47uf and a 50v 47uf..... I destroyed the 63v capacitor while removing it but managed to leave some nice holes on the pcb! The 50v I managed to remove intact. Checked it with my capacitor tester and it read 49uf so looks like that one is fine.... Hopefully the 63v was shot and replacing it will bring it back. All this being said, what do these start up capacitors do? Currently I do get some voltage... the #1 diagnostic led is on and the others flash when I try to power on.

                                        Comment

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