Panasonic Th-42PX75U Question

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  • eagle00799
    Badcaps Veteran
    • May 2012
    • 322
    • USA
    #1

    Panasonic Th-42PX75U Question

    Hi guys, I need some advice with this tv. I got it completely dead, no lights, no clicks, no signs of life. After some research I found this is a common problem with this tv so I bought the kit for the power supply which consisted of 2 ceramic fuses, 1 mosfet transistor and 3 diodes. I installed the fuses and diodes without any problems but when I tried to bend the middle leg of the mosfet it broke off, so I soldered it back together and installed it. When I plugged the tv in the mosfet let out a loud pop and a bit of smoke. The fuses didn't blow, they are still good. So my question is
    1) could the soldering of the middle leg cause it to blow or do I have other problems?
    2) When I took the old mosfet off the heat sink there was small evidence of thermal paste so I applied some Arctic 5, Would there be any problems with this?
    Tags: None
    • sordids999
      Badcaps Legend
      • May 2013
      • 2158
      • uk
      #2
      Re: Panasonic Th-42PX75U Question

      Posting pictures of the back of your tv showing the boards with clear pictures may help you more with fixing your problem

        Comment

        • eagle00799
          Badcaps Veteran
          • May 2012
          • 322
          • USA
          #3
          Re: Panasonic Th-42PX75U Question

          Here are some pics of the boards and a close up of the mosfet that popped. I have a new mosfet but don't want to install it if it's going to do the same thing.
          Attached Files

            Comment

            • eagle00799
              Badcaps Veteran
              • May 2012
              • 322
              • USA
              #4
              Re: Panasonic Th-42PX75U Question

              I just took the mosfet that popped out of circuit and compared it to the new mosfet I just got and they read the same. So not sure why it popped, soldered leg couldn't handle the power??

                Comment

                • eagle00799
                  Badcaps Veteran
                  • May 2012
                  • 322
                  • USA
                  #5
                  Re: Panasonic Th-42PX75U Question

                  Can someone tell me what the pink pad is called that's between the fet and the heatsink? maybe isolation pad? There is a small hole in it and I believe the metal back of the fet is shorting out on the heatsink causing the pop. I thought the metal backing on the fet was ground but apparently not?

                    Comment

                    • tom66
                      EVs Rule
                      • Apr 2011
                      • 32560
                      • UK
                      #6
                      Re: Panasonic Th-42PX75U Question

                      "SIL" pad, it's thermally conductive but electrically isolating. It MUST be installed. The metal back of the FET is almost always the drain, which is typically the most positive voltage for an N-channel FET.
                      Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
                      For service manual, schematic, boardview (board view), datasheet, cad - use our search.

                        Comment

                        • eagle00799
                          Badcaps Veteran
                          • May 2012
                          • 322
                          • USA
                          #7
                          Re: Panasonic Th-42PX75U Question

                          Thanks for the reply Tom66, So if its using the pad is thermal compound needed or maybe just an adhesive? If I fold the top over just enough to cover the hole it should be fine?

                            Comment

                            • eagle00799
                              Badcaps Veteran
                              • May 2012
                              • 322
                              • USA
                              #8
                              Re: Panasonic Th-42PX75U Question

                              Update: Found a "SIL" pad on another bad board I had laying around for parts. Swapped the pads and put in two 6.3amp fuses I had laying around in place of the 8amp fuses and plugged it in and it now works perfectly. Thanks for the input guys, your help is indeed priceless.

                                Comment

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