Completely dead VIZIO SV420XVT1A

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  • Cosmo66
    Senior Member
    • Nov 2012
    • 87
    • USA
    #1

    Completely dead VIZIO SV420XVT1A

    When plugged in there is no standby light, nothing at all. I found the 5A 250V fuse on the power supply ( bottom right side of picture) is blown.

    I disconnected all boards from the power supply, and powered up with a new fuse installed. The fuse blew immediatley. Obviously the power supply is bad.

    I will troubleshoot further and post my findings.

    Any input or assistance from someone that has worked on this model would be greatly appreciated...

    Thanks!
    Attached Files
    Tags: None
    • fleetwise
      Member
      • May 2011
      • 38
      • USA
      #2
      Re: Completely dead VIZIO SV420XVT1A

      failed bridge rectifier?

        Comment

        • jettboat
          Senior Member
          • Nov 2012
          • 63
          • USA
          #3
          Re: Completely dead VIZIO SV420XVT1A

          sounds like the bridge diode(s) is shorted I'd start there

            Comment

            • budm
              Badcaps Legend
              • Feb 2010
              • 40746
              • USA
              #4
              Re: Completely dead VIZIO SV420XVT1A

              Check the bridge, the PFC MOSFET and Diode, MOSFETs for the inverter transformer on the heatsinks, You can put the 75 Watts lamp in place of the fuse, if the lamp lights up real bright and stays that way after components are replaced, it means you still have shorted circuits on the board.
              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

                • Cosmo66
                  Senior Member
                  • Nov 2012
                  • 87
                  • USA
                  #5
                  Re: Completely dead VIZIO SV420XVT1A

                  I found a shorted mosfet, part number FQPF12N60C. Looks like it's a 600V 25A mosfet that has become obsolete. Neither Digikey nor Mouser have it in stock. I ordered one from china on ebay. I'll post a picture of it's location later for future site reference.

                  Thanks for the help

                    Comment

                    • JonathanAnon
                      Badcaps Veteran
                      • Jul 2012
                      • 457
                      • Ireland
                      #6
                      Re: Completely dead VIZIO SV420XVT1A

                      Be sure to check the other main components that Bud said... AND make sure and use the bulb tester when you get the new chip... Otherwise you risk blowing the new chip..

                        Comment

                        • budm
                          Badcaps Legend
                          • Feb 2010
                          • 40746
                          • USA
                          #7
                          Re: Completely dead VIZIO SV420XVT1A

                          The IC that drives the GATE of that MOSFET may be damaged also, I would replace that IC or you may take a chance of blowing the new one MOSFET due to bad IC. The components connected to the Gat should also be checked for damages.
                          I ouwld like to see good closed up pictures at the area (top and bottom side of the board) of this MOSFET to see if it is for the PFC or for the inveter circuits.
                          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

                            • Cosmo66
                              Senior Member
                              • Nov 2012
                              • 87
                              • USA
                              #8
                              Re: Completely dead VIZIO SV420XVT1A

                              Here is a picture of the mosfet. The one that is missing in the first picture is the one that was actually shorted. I changed the one next to it as well, since it was the same mosfet, and I assumed they are working together.

                              The TV came back to life. However, the picture quality is not great. I plan on recapping and replacing some other compnents on the power supply to see if it improves.
                              Attached Files

                                Comment

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