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What would cause this fuse to be blown on this inverter?

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    #1

    What would cause this fuse to be blown on this inverter?

    I've got a Panasonic TC-20LA2 I got a while back... The symptom is that there's absolutely no display, not even a non-backlit display when I check with a flashlight. Changing the video inputs does not help.

    I opened it up, but can't find anything obvious. I want to check the voltages going from the logic board to the inverter, but I can't find any reference in the service manual as to what to compare them to.



    If you look at the red arrow, it points to a fuse labeled "100AC 5A". There are three of them on the inverter. That particular one is reading (infinite?) very high resistance. The other ones test fine.

    Attached is the service manual and a higher res photo.

    Anyone have any tips where I can order one online for a few bucks rather than having to pay digikey 8 bucks to ship it?
    Attached Files
    "We have offered them (the Arabs) a sensible way for so many years. But no, they wanted to fight. Fine! We gave them technology, the latest, the kind even Vietnam didn't have. They had double superiority in tanks and aircraft, triple in artillery, and in air defense and anti-tank weapons they had absolute supremacy. And what? Once again they were beaten. Once again they scrammed [sic]. Once again they screamed for us to come save them. Sadat woke me up in the middle of the night twice over the phone, 'Save me!' He demanded to send Soviet troops, and immediately! No! We are not going to fight for them."

    -Leonid Brezhnev (On the Yom Kippur War)
    Tags: None
    #2
    Re: What would cause this fuse to be blown on this inverter?

    Check those 8 pin ic's close to the fuse, one of them may be shorted. compare the reading from one of the other ic's on the board

    Comment

      #3
      Re: What would cause this fuse to be blown on this inverter?

      Those are Dual MOSFETs, I believe they are SP8M8.
      Check for shorted Source to Drain.
      Attached Files
      Never stop learning
      Basic LCD TV and Monitor troubleshooting guides.
      http://www.badcaps.net/forum/showthr...956#post305956

      Voltage Regulator (LDO) testing:
      http://www.badcaps.net/forum/showthr...999#post300999

      Inverter testing using old CFL:
      http://www.badcaps.net/forum/showthr...er+testing+cfl

      Tear down pictures : Hit the ">" Show Albums and stories" on the left side
      http://s807.photobucket.com/user/budm/library/

      TV Factory reset codes listing:
      http://www.badcaps.net/forum/showthread.php?t=24809

      Comment

        #4
        Re: What would cause this fuse to be blown on this inverter?

        Check those 8 pin ic's close to the fuse, one of them may be shorted. compare the reading from one of the other ic's on the board
        Those are Dual MOSFETs, I believe they are SP8M8.
        Check for shorted Source to Drain.
        Geniuses!



        Pins 3 and 4 on the circled MOSFET are shorted.

        All other MOSFETS test fine. Do you think the FET is the original cause or something that was taken out by something else, for example a dying CCFL tube?
        Attached Files
        "We have offered them (the Arabs) a sensible way for so many years. But no, they wanted to fight. Fine! We gave them technology, the latest, the kind even Vietnam didn't have. They had double superiority in tanks and aircraft, triple in artillery, and in air defense and anti-tank weapons they had absolute supremacy. And what? Once again they were beaten. Once again they scrammed [sic]. Once again they screamed for us to come save them. Sadat woke me up in the middle of the night twice over the phone, 'Save me!' He demanded to send Soviet troops, and immediately! No! We are not going to fight for them."

        -Leonid Brezhnev (On the Yom Kippur War)

        Comment

          #5
          Re: What would cause this fuse to be blown on this inverter?

          Most likely just the fet... it happens.
          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

            #6
            Re: What would cause this fuse to be blown on this inverter?

            I fixed a couple of this models due to blown MOSFETs, as you can see, they do not have much copper plane to act as the heatsink.
            Never stop learning
            Basic LCD TV and Monitor troubleshooting guides.
            http://www.badcaps.net/forum/showthr...956#post305956

            Voltage Regulator (LDO) testing:
            http://www.badcaps.net/forum/showthr...999#post300999

            Inverter testing using old CFL:
            http://www.badcaps.net/forum/showthr...er+testing+cfl

            Tear down pictures : Hit the ">" Show Albums and stories" on the left side
            http://s807.photobucket.com/user/budm/library/

            TV Factory reset codes listing:
            http://www.badcaps.net/forum/showthread.php?t=24809

            Comment

              #7
              Re: What would cause this fuse to be blown on this inverter?

              What did you use to replace SP8M8? I can't find them anywhere?

              I can find equivalent's but with different "Vgs(th) (Max) @ Id". I assume that I can use parts with higher maximum voltages and amperage as long as the resistance is the same or lower. But can I use something with a slightly different gate voltage, considering that the SP8M8 is between 1 and 2.5 volts?

              Also, did any of those tiny diode packs or resistors need changing as well?
              "We have offered them (the Arabs) a sensible way for so many years. But no, they wanted to fight. Fine! We gave them technology, the latest, the kind even Vietnam didn't have. They had double superiority in tanks and aircraft, triple in artillery, and in air defense and anti-tank weapons they had absolute supremacy. And what? Once again they were beaten. Once again they scrammed [sic]. Once again they screamed for us to come save them. Sadat woke me up in the middle of the night twice over the phone, 'Save me!' He demanded to send Soviet troops, and immediately! No! We are not going to fight for them."

              -Leonid Brezhnev (On the Yom Kippur War)

              Comment

                #8
                Re: What would cause this fuse to be blown on this inverter?

                You don't usually need to be worried about VgsTH as it's so variable (there, alone, it has a 250% tolerance -- most basic semiconductor properties are not well controlled.) Instead, compare RdsON vs Vgs; if the current device has x.x ohm at x.xV Vgs, you need to meet or go lower than that.
                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

                  #9
                  Re: What would cause this fuse to be blown on this inverter?

                  http://www.aliexpress.com/store/prod...598207795.html
                  Never stop learning
                  Basic LCD TV and Monitor troubleshooting guides.
                  http://www.badcaps.net/forum/showthr...956#post305956

                  Voltage Regulator (LDO) testing:
                  http://www.badcaps.net/forum/showthr...999#post300999

                  Inverter testing using old CFL:
                  http://www.badcaps.net/forum/showthr...er+testing+cfl

                  Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                  http://s807.photobucket.com/user/budm/library/

                  TV Factory reset codes listing:
                  http://www.badcaps.net/forum/showthread.php?t=24809

                  Comment

                    #10
                    Re: What would cause this fuse to be blown on this inverter?

                    Thanks.

                    I ended up using the Fairchild SI4542DY and a Littlefuse 451 series fuse.

                    Great little set. Had to go through a few universal remotes before I could find one that had the "enter" key working for the menu.
                    "We have offered them (the Arabs) a sensible way for so many years. But no, they wanted to fight. Fine! We gave them technology, the latest, the kind even Vietnam didn't have. They had double superiority in tanks and aircraft, triple in artillery, and in air defense and anti-tank weapons they had absolute supremacy. And what? Once again they were beaten. Once again they scrammed [sic]. Once again they screamed for us to come save them. Sadat woke me up in the middle of the night twice over the phone, 'Save me!' He demanded to send Soviet troops, and immediately! No! We are not going to fight for them."

                    -Leonid Brezhnev (On the Yom Kippur War)

                    Comment

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