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RCA 42LA45RQ with no HV to the backlight

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    #1

    RCA 42LA45RQ with no HV to the backlight

    Greetings All,


    I have a back light issue. I have tried to detect high voltage with a high voltage probe which is giving me a zero reading. I have tried a second board that was supposed to be good and I get the same results. I have sound and the receiver is working. I am wondering if there is a separate trigger signal for the high voltage separate from the trigger for the receiver processor board. Anyone know? I assume that the larger chip on the back side of the board is some kind of modulator to get the HV transformers going. Is ther a way to check if it is woking?

    Thanks for any assistance,
    Russell

    Here is a slightly blurry picture of my board.

    [/QUOTE]
    Tags: None
    #2
    Re: RCA 42LA45RQ with no HV to the backlight

    You need to find out if you do have BL_ON signal or not + some voltage testing on the board.
    Can we get higher res picture so we can zoom in and able to see the components better? also good clear pictures of the bottom side of the board, and the whole back side of the TV so we can see what we are dealing with? Use attachment function to upload the pictures.
    https://www.badcaps.net/forum/showthread.php?t=1868
    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

      #3
      Re: RCA 42LA45RQ with no HV to the backlight

      Budm,

      thanks for the guidance and effort to help. I have several pictures of the board with close-ups of the labels on the board and TV frame. I hope this is good enough. I took it with a 6 M pixel Pro camera and I am sure the forum will shrink them. I hope the resolution stays readable.

      Well, it barfed on sending all so I will break them up into three posts. Almost forgot the back of the board!!

      Thanks for any advice,

      Russell
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        #4
        Re: RCA 42LA45RQ with no HV to the backlight

        Next 3 photos
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          #5
          Re: RCA 42LA45RQ with no HV to the backlight

          Last 3 Pix
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            #6
            Re: RCA 42LA45RQ with no HV to the backlight

            OK, I have more time today so I took some voltage measurements on the board. The picture gives some more detail but basically the 5 and 12 volts are where they should be. the RED square has a pin-out of the contacts above.
            The adjust is about 1.8 volts. I don't know what that should be but it sounds reasonable. The ON/OFF though is only 0.35 volts which to me means off. How do I trace that back to what is turning that on and off? That seems to be my problem. Also the chip is an LM324 pulse width modulator. I am assuming that is what is controlling the HV. I see others have a dedicated driver chip.
            Thanks for any help. You have to zoom in to see the text for the pin-outs.

            Russ
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