LP2407 Power Supply

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  • TechSuperDave
    New Member
    • Jan 2014
    • 7
    • United States

    #1

    LP2407 Power Supply

    Hoping you guys can point me in the right direction here. I'm lost without schematics.

    I have a friend's LP2407 LCD in my shop. She complained that it would take up to an hour to eventually turn on. I suspected the power supply so we went through it. All caps tested within spec however we replaced them all anyways (Besides the 150uf-450V).

    Previous to the repair, we'd get the blue light on the button eventually however now we get nothing. Initially we could hear the txformer squeal with power applied, however now it's silent.

    I've verified all the solder connections, checked the output side for shorts and so far have found no other failed components.


    The large 150uf, 450V cap (I don't have the board in front of me to check the C#) measured about 164V
    C876 measures 0V
    Q811 & Q812 aren't shorted, but I'm suspecting the issue is in that daughter board.
    0V on the outputs


    Thanks for any pointers!


    Dave
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  • budm
    Badcaps Legend
    • Feb 2010
    • 40746
    • USA

    #2
    Re: LP2407 Power Supply

    Are those solder bridge (top right of the board in picture #3) at the connector where it is connected to the cable that goes to the loacgic board?
    The PFC Voltage booster is not running either, otherwise you will have about 370~400VDC on that main filter cap.
    Since you did have Blue LED on before changing the caps, I would inspect all the solder joints, capacitor's polarity are correct when they are installed into the board.
    Last edited by budm; 01-23-2014, 02:38 PM.
    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

    • TechSuperDave
      New Member
      • Jan 2014
      • 7
      • United States

      #3
      Re: LP2407 Power Supply

      Yah, those bridges were there when we opened it up. The ones over to the right of that connector aren't though, we checked them. Those look to be through-connections from the AD board to the inverter.


      All the caps are in right, and joints are good.


      The only other issue we had was the ribbon cable that runs from the AD board over to the front panel of the bezel. We had one lead there that had a broken connection. We repaired the ribbon cable though, and it tested good after.


      Is there a schematic floating around for this board at all?

      Thanks,
      Dave

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