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psu ac240as-01 dell Optiplex 7010 pc tower

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    Re: psu ac240as-01 dell Optiplex 7010 pc tower

    1KV will fail - like before
    that psu and a couple of similar ones have this problem - a 1KV cap cant handle the current.
    2KV caps a physically larger and can disipate the heat.

    btw, your 151/1kv is bad.
    151 - 15 and one 0 - so it should read 150pF


      Re: psu ac240as-01 dell Optiplex 7010 pc tower

      Thanks for your help stj, in this case I will order also a 2KV cap.


        Re: psu ac240as-01 dell Optiplex 7010 pc tower

        The caps arrived today, unfortunately I'm still waiting for the mosfet. I have more of this Dell 7010 optiplex SSF, so I opened up a working PSU and C6 and C10 also have a crack, but the PC was running normal?! I changed both caps to a new 2KV/680pf cap, to be on the save side. Maybe the mosfet died because of the broken caps. On a third one the caps seemed to be ok and it looks like they are labeled R 331K 1KV (very hard to see, I tried to take a foto, but it doesn't work), I changed them also (got more of this 2KV caps. The good PSUs are still working after I changed the caps ;-)

        I'm not an electronics engineer so it is a little bit strange for me that meassuring between the 2 holes of C6 on the board are showing a short (of course also between the two poles of C10). This is the same on the working PSUs and on the faulty one where I have taken away the shorted mosfet.

        As soon as the new mosfet is soldered in I'll tell you the result ;-)


          Re: psu ac240as-01 dell Optiplex 7010 pc tower

          you need to check all the resistors in the area, when the fet blows it can take other stuff with it.


            Re: psu ac240as-01 dell Optiplex 7010 pc tower

            I'm a litte bit confused now. Meassuring the restistors shows the following:
            R4 and R14 shorted (on faulty as on working PSU!)
            R46: 5 Ω
            R52: 100 Ω
            R4 should have 63 Ω, R14 not shure but I think ~21 Ω.

            Without R4, R14 and R46 connected, C6 (C10) is still shorted. I found another short with the near transformer (again also the working PSU shows the same short). Near diodes and caps seemed to be ok.

            Now I'm wondering how could the second PC work normaly with the same shorts in the working PSU?! The only difference I found until now was the shorted mosfet.
            Attached Files


              Re: psu ac240as-01 dell Optiplex 7010 pc tower

              your seeing something connected to the resistor
              if they dont look burned they are probably o.k.
              trace the gate pin of the mosfet and see what is driving it - thats the main thing to check.
              if it's a chip then dont be surprised to find a hole in it.


                Re: psu ac240as-01 dell Optiplex 7010 pc tower

                I also do some meassuring with the working PSU (which have the same shorts)
                Attached Files


                  Re: psu ac240as-01 dell Optiplex 7010 pc tower

                  Sorry stj, I didn't saw your quick answer. Which resistor do you mean? How could the resistors be ok, when showing a short instead the right Ω? The chips are looking good.
                  Attached Files


                    Re: psu ac240as-01 dell Optiplex 7010 pc tower

                    the resistors are connected to the rest of the circuit,
                    so when you meter them your seeing the circuit too.
                    to test a suspect resistor you have to lift one end first - unless it's surface-mount.
                    with surface-mount if they fail you can see a burn on them under the print.


                      Re: psu ac240as-01 dell Optiplex 7010 pc tower

                      Of course I've lifted them on one side before meassuring (is also shown on the fotos). They are also lifted while meassuring the shorts I mentioned.


                        Re: psu ac240as-01 dell Optiplex 7010 pc tower

                        r46 = 4.7ohms
                        so your within range

                        when you see a 3rd band is gold or silver it's a divider and your looking at very low resistances.

                        62.9ohms - blue-red-white-gold


                          Re: psu ac240as-01 dell Optiplex 7010 pc tower

                          Today the mosfet arrived, I soldered it in, after switching on, the new mosfet also is gone and shorted

                          But now I want to see how the cat jumps and ordered 2 more of this mosfets ;-)


                            Re: psu ac240as-01 dell Optiplex 7010 pc tower

                            so you didnt find the other bad bits.
                            trace the gate-pin back to it's source - 100% that chip or transistor is toast


                              Re: psu ac240as-01 dell Optiplex 7010 pc tower

                              No not until now. My plan is to solder in a new mosfet and then I'll compare the bad PSU with a running PSU and do some meassuring. Optical I didn't find a burned chip.


                                Re: psu ac240as-01 dell Optiplex 7010 pc tower

                                1st rule of switching psu design,
                                if you dont find all the bad parts before you power up, you blow everything again