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VIZIO VP423 HDTV10A -- Backlight Comes on When Plugged In, No Other Function

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    #1

    VIZIO VP423 HDTV10A -- Backlight Comes on When Plugged In, No Other Function

    Alright, so I have a VIZIO VP423. When you plug in the power cable it makes a click (as TVs do when you turn them on), the backlight comes on and there is some faint static on the screen. Neither the power button nor any of the other buttons seem to do anything at all, and there is a faint buzzing coming from the Y-main board. The readings off of the main power board are as follows:

    To Input Board:

    N.C = 0.00v*
    VT = 0.00v*
    GND = 0.00v
    GND = 0.00v
    VAMP = 11.98V
    VAMP = 11.98V
    GND = 0.00v
    A12V = 11.98v
    GND = 0.00v*
    ◄D5V = 5.23v*

    NC = 0.00v*
    5VSB = 5.23v
    GND = 0.00v
    PS_ON = 0.50v
    AC_DET = 5.19v
    GND = 0.00v
    GND = 0.00v
    DV5 = 5.23v
    DV5 = 5.23v
    GND = 0.00v
    ◄D5V = 5.23v

    *Denotes that there is no wire coming from this contact

    To X-main Board: (right side board)
    ◄VS = 207.1v
    VS = 207.1v
    GND = 0.00v
    GND = 0.00v
    VG = 15.01v

    To Y-main Board: (left side board)
    VG = 15.01v
    GND = 0.00v
    VA = 54.3v
    GND = 0.00v
    VS = 207.1v
    VS► = 207.1v

    I've also tested a fuse each on the power and X/Y boards, and three fuses on the input board. I'll be back with readings off of the voltage regulators shortly.

    Higher Res Pictures:
    Power Board
    X-Main Board
    Y-Main Board
    Input Board
    Attached Files
    Tags: None
    #2
    Re: VIZIO VP423 HDTV10A -- Backlight Comes on When Plugged In, No Other Function

    Voltage Regulators:

    U15
    1084
    0807DL
    Pin 1 = 2.08v
    Pin 2 = 3.34v
    Pin 3 = 5.19v

    U20
    1084
    0807DL
    Pin 1 = 0.56v
    Pin 2 = 1.82v
    Pin 3 = 3.32v

    U19
    1084
    0807DL
    Pin 1 = 1.26v
    Pin 2 = 2.51v
    Pin 3 = 5.20v

    U16
    AZ7805T
    -E1
    820D64
    Pin 1 = 11.96v
    Pin 2 = 0.00v
    Pin 3 = 5.06v

    U22
    K363
    G1117
    Pin 1 = 1.91v
    Pin 2 = 3.06v
    Pin 3 = 4.07v

    U17
    K363
    G1117
    Pin 1 = 2.07v
    Pin 2 = 3.32v
    Pin 3 = 5.20v

    U21
    K363
    G1117
    Pin 1 = 0.00v
    Pin 2 = 1.25v
    Pin 3 = 2.51v

    Comment

      #3
      Re: VIZIO VP423 HDTV10A -- Backlight Comes on When Plugged In, No Other Function

      U22
      K363
      G1117
      Pin 1 = 1.91v
      Pin 2 = 3.06v
      Pin 3 = 4.07v
      This device is a little suspect -- the output should be closer to 3.16V which is an unusual output voltage (as is 3.06V.) Please re-test it.
      Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
      For service manual, schematic, boardview (board view), datasheet, cad - use our search.

      Comment

        #4
        Re: VIZIO VP423 HDTV10A -- Backlight Comes on When Plugged In, No Other Function

        Just double and triple checked, definitely 3.06v

        Comment

          #5
          Re: VIZIO VP423 HDTV10A -- Backlight Comes on When Plugged In, No Other Function

          Originally posted by PohTayToez View Post
          Just double and triple checked, definitely 3.06v
          See the how to measure a voltage regulator guide in the link below to see why it is likely bad.

          Also, the input to U22 at 4.07 could suggest one or more bad caps in that area.
          --- begin sig file ---

          If you are new to this forum, we can help a lot more if you please post clear focused pictures (max resolution 2000x2000 and 2MB) of your boards using the manage attachments button so they are hosted here. Information and picture clarity compositions should look like this post.

          We respectfully ask that you make some time and effort to read some of the guides available for basic troubleshooting. After you have read through them, then ask clarification questions or report your findings.

          Please do not post inline and offsite as they slow down the loading of pages.

          --- end sig file ---

          Comment

            #6
            Re: VIZIO VP423 HDTV10A -- Backlight Comes on When Plugged In, No Other Function

            This is a plasma set, right? What you are seeing is the panel priming, not a backlight. There are no backlights on a plasma panel.

            Comment

              #7
              Re: VIZIO VP423 HDTV10A -- Backlight Comes on When Plugged In, No Other Function

              Alright, so I know the regulator is bad because the voltage measured between pins one and two is 1.16v instead of the expected 1.25v. I'll be honest though, I only know that because of a comment on the voltage regulator thread. I've been going over datasheets for a couple hours now and I still don't understand WHY I should expect it to be at 1.25v. I tried measuring resistance between ADJ and ground, and between ADJ and Vo, in order to calculate the expected output but I get 0 resistance on both.

              So I guess I'll be ordering a voltage regulator and all new caps for that board, but I'd like to try and understand this a bit better.

              Comment

                #8
                Re: VIZIO VP423 HDTV10A -- Backlight Comes on When Plugged In, No Other Function

                The regulator's control loop attempts to maintain 1.25V across the output to adjust. A fault in the regulator means it won't be able to do so, causing a low or high out-adj measurement.
                Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
                For service manual, schematic, boardview (board view), datasheet, cad - use our search.

                Comment

                  #9
                  Re: VIZIO VP423 HDTV10A -- Backlight Comes on When Plugged In, No Other Function

                  Got a good deal on the input board and ended up switching out the whole thing. That did the trick, thanks for your help.

                  This is an awesome community, I hope I can learn enough to start contributing back.

                  Comment

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