Samsung LN46C800 No Backlight

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  • Ltank
    Badcaps Veteran
    • Jun 2013
    • 776
    • USA

    #1

    Samsung LN46C800 No Backlight

    The power supply turns on. I reviewed the threads to the other Samsung set that used the same BN44-00341B Power Supply. I did download the power supply schematic. This set has sound and Picture if you hold a flashlight to the screen. The correct votages are on CN802 from the mainboard and
    CN1802 to the backlight board. There is no H.V. off CN1801 to the back light board. I do have 380 vdc to caps CP802 and CP803. I checked the diodes and transistors in that area. The HV transfoemers checked good with a Blue Ring Tester.
    I did not check ICM801 or any of the SMD parts on the foil side. I did find any shorts to ground on the inverter board and ttried the P.S. without the inverter as a load and there was not any voltage on CN1801 to thge inverter.
    Is it ok to run these without a load? I even jumped the 5vc to the Ps-on.
    pins 17 to 18. any thoughts anyone? I guess I need to put P.S. Booard in holder and put jumpers on CNCN802 . I jumped 5vdc to Ps-on and to SW_inv to turn on the inverter power. it measured 5vdc when connected to main board. Does it need to go low to turn on the HV inverter?
  • budm
    Badcaps Legend
    • Feb 2010
    • 40746
    • USA

    #2
    Re: Samsung LN46C800 No Backlight

    This power supply-inverter combo board has built-in pull-up resistors, so when you disconnect the cables between the power supply board and the main board, the backlights should comec on right away the minute you apply 120VAC to the TV, no need to use resistor to force on the board.
    Did you check CI818 (0.47Uf 450VDC) cap? That is one commonly failed cap, check its value.
    What do you have on LD?
    Last edited by budm; 11-08-2013, 04:55 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

    • Ltank
      Badcaps Veteran
      • Jun 2013
      • 776
      • USA

      #3
      Re: Samsung LN46C800 No Backlight

      I did remove the cable from the main board to the power supply and the backlight did not turn on and there was 0vdc on the pins to the inverter board. I will check that capacitor Monday when back at the shop. Thanks

      Comment

      • Ltank
        Badcaps Veteran
        • Jun 2013
        • 776
        • USA

        #4
        Re: Samsung LN46C800 No Backlight

        I replaced the C1818 .47uf 450v and the backlight came on. Works fine!
        Thank you Budm

        Comment

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