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

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  • PohTayToez
    Senior Member
    • Jun 2010
    • 80
    • USA
    #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
    • PohTayToez
      Senior Member
      • Jun 2010
      • 80
      • USA
      #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

        • tom66
          EVs Rule
          • Apr 2011
          • 32560
          • UK
          #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

            • PohTayToez
              Senior Member
              • Jun 2010
              • 80
              • USA
              #4
              Re: VIZIO VP423 HDTV10A -- Backlight Comes on When Plugged In, No Other Function

              Just double and triple checked, definitely 3.06v

                Comment

                • retiredcaps
                  Badcaps Legend
                  • Apr 2010
                  • 9271
                  #5
                  Re: VIZIO VP423 HDTV10A -- Backlight Comes on When Plugged In, No Other Function

                  Originally posted by PohTayToez
                  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

                    • johnboy1313
                      Badcaps Legend
                      • Nov 2012
                      • 1959
                      • USA
                      #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

                        • PohTayToez
                          Senior Member
                          • Jun 2010
                          • 80
                          • USA
                          #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

                            • tom66
                              EVs Rule
                              • Apr 2011
                              • 32560
                              • UK
                              #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

                                • PohTayToez
                                  Senior Member
                                  • Jun 2010
                                  • 80
                                  • USA
                                  #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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