Sanyo FVD48P4 - Decaying LED driver voltage, No Backlight Flashes Once

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  • habznation
    New Member
    • Mar 2017
    • 6
    • canada

    #1

    Sanyo FVD48P4 - Decaying LED driver voltage, No Backlight Flashes Once

    I have a Sanyo FVD48P4 with good audio and an LED backlight that just flashes once.


    *** LED driver voltage with and without load starts at ~60v and decays to 0.***

    I checked each indiviudal LED with 3.3v and found 5 open or shorted LED's.

    I got 3 replacement zener diodes from a TV repairshop, and replaced 3 bad LED's. I replaced the other two bad LED's with 5mm 35000mcd LED's I had from eBay as a trial, because i had no other zeners.



    The TV shop checked all capacitors and verified good capacitance.

    Same issue

    I have looked everywhere on the All-in-one motherboard for any type of LED inverter fuse of any type and cannot see one......I have looked hard online for a service manual for this board, with no luck.....

    Any help anyone could provide be greatly appreciated......

    Thank You!!
  • habznation
    New Member
    • Mar 2017
    • 6
    • canada

    #2
    Re: Sanyo FVD48P4 - Decaying LED driver voltage, No Backlight Flashes Once

    .

    Comment

    • Andrew F. Ali
      Badcaps Legend
      • Jan 2014
      • 2450
      • Trinidad & Tobago

      #3
      Re: Sanyo FVD48P4 - Decaying LED driver voltage, No Backlight Flashes Once

      So you found both bad LEDs and Zener diodes or did you replace bad LEDs with zener diodes??

      Comment

      • habznation
        New Member
        • Mar 2017
        • 6
        • canada

        #4
        Re: Sanyo FVD48P4 - Decaying LED driver voltage, No Backlight Flashes Once

        [QUOTE=Andrew F. Ali;732556]So you found both bad LEDs and Zener diodes or did you replace bad LEDs with zener diodes??[/QUOTE

        thank you for the reply!

        i replaced 3 bad LED's with zeners yes........the other 2 bad ones i tried replacing with actual LED's i had from something else

        Comment

        • budm
          Badcaps Legend
          • Feb 2010
          • 40746
          • USA

          #5
          Re: Sanyo FVD48P4 - Decaying LED driver voltage, No Backlight Flashes Once

          What is the current rating of the 5mm sub LEDs?
          Did you put the Zener diodes in the reverse bias position?
          3.3V 1W Zener?
          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

          • habznation
            New Member
            • Mar 2017
            • 6
            • canada

            #6
            Re: Sanyo FVD48P4 - Decaying LED driver voltage, No Backlight Flashes Once

            Originally posted by budm
            What is the current rating of the 5mm sub LEDs?
            Did you put the Zener diodes in the reverse bias position?
            3.3V 1W Zener?

            no i didnt put them reverse bias! thank you! i put the stripe to the negative where the LED would go! So reverse them?

            as for the substitute LED's , i checked on ebay where i got them and apparently theyre 20mA

            Comment

            • budm
              Badcaps Legend
              • Feb 2010
              • 40746
              • USA

              #7
              Re: Sanyo FVD48P4 - Decaying LED driver voltage, No Backlight Flashes Once

              Ar 20mA rating it will burnt so fast, the LEDs in the TV are rated at 1W with about 300~400mA rating.
              If you put ZENER in forward bias mode the Vf will be only 0.6~0.7V range.
              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

              • habznation
                New Member
                • Mar 2017
                • 6
                • canada

                #8
                Re: Sanyo FVD48P4 - Decaying LED driver voltage, No Backlight Flashes Once

                Originally posted by budm
                Ar 20mA rating it will burnt so fast, the LEDs in the TV are rated at 1W with about 300~400mA rating.
                If you put ZENER in forward bias mode the Vf will be only 0.6~0.7V range.
                thank you very much budm, i will reverse them

                further, i will get more zeners tomorrow and use them instead of these LED's

                BUT, should my voltage be decaying like that? shouldnt it be holding? I'm measuring with the LED's connected and again with them disconnected and its the same.....starts at around 60v and slowly drops to 0

                Comment

                • budm
                  Badcaps Legend
                  • Feb 2010
                  • 40746
                  • USA

                  #9
                  Re: Sanyo FVD48P4 - Decaying LED driver voltage, No Backlight Flashes Once

                  It sounds like it detected fault so it goes into shutdown mode.
                  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

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