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    Vizio VO42L, white logo, no backlight, no picture

    Hi all! I've got a Vizio VO42L. Plug it in, and logo flashes orange/white for a bit, then solid orange. Press power, and logo changes to white. There is no backlight.
    From reading some of the posts here I thought the inverter could have been the problem, but I've replaced it and still have the same issue. I noted that shining a flashlight on the screen shows nothing, so now I'm thinking main board?

    I took the following readings with the TV powered on. I also tried taking the readings with the CFL connectors unplugged - no change.

    Main board:
    Continuity across F1 & F2 = GOOD
    F1 = 5.12v
    F2 = 11.57v

    PSU Connector 1 (J21?):
    24V = 24v
    SGND = 0v
    A = 0v
    B = 0v
    C = 0v

    PSU Connector 2 (J22?):
    PSON= 3.27v
    12V = 11.57v
    SGND = 0v
    5VSB = 5.16v
    A = 0v
    B = 0v
    C = 0v

    Inverter:
    Continuity across F1 = GOOD
    Left leg @ Q7 & Q9 = cycles between 0v-1.2v
    Middle leg @ Q7 & Q9 = 24.96v
    Right leg @ Q7 & Q9 = cycles between 0v-1.2v
    Top leg @ Q8 & Q10 = 0v
    Middle leg @ Q8 & Q10 = cycles between 0v-1.2v
    Bottom leg @ Q8 & Q10 = 0v
    Voltages @ connectors to CFLs = 0v

    Do you think I got a second bad inverter? Or do I have a bad main board? What should I try next?

    Thanks in advance for your help!
    --Dave
    Attached Files
    Last edited by Daveleone; 02-20-2021, 05:03 PM.

    #2
    Re: Vizio VO42L, white logo, no backlight, no picture

    What voltages do you have on the Inverter Board connector
    1, 2, 3, 4 & 5 =
    6, 7, 8, 9 & 10 =
    11 =
    12 =
    13 =
    14 =

    Is the white fuse F1 showing continuity?
    Willing to help but I'm no expert.

    Comment


      #3
      Re: Vizio VO42L, white logo, no backlight, no picture

      Originally posted by dick_barton View Post
      What voltages do you have on the Inverter Board connector
      1, 2, 3, 4 & 5 =
      6, 7, 8, 9 & 10 =
      11 =
      12 =
      13 =
      14 =

      Is the white fuse F1 showing continuity?
      That connector is directly connected to PSU Connector 1 (J21?), so:
      1-5 = 24v
      6-14 = 0v
      I double checked the voltages just to be sure the cable was good.

      F1 does have continuity.

      Comment


        #4
        Re: Vizio VO42L, white logo, no backlight, no picture

        Can you provide a close up of what's given in the red box please.
        The Inverter On signal appears to be missing.
        Attached Files
        Willing to help but I'm no expert.

        Comment


          #5
          Re: Vizio VO42L, white logo, no backlight, no picture

          Originally posted by dick_barton View Post
          Can you provide a close up of what's given in the red box please.
          The Inverter On signal appears to be missing.
          Yes, I think you're right.
          12: VOnOff is 0V

          What should that voltage be? Should I jumper it to some other pin to see if the backlight will come on?

          Thanks!
          Attached Files

          Comment


            #6
            Re: Vizio VO42L, white logo, no backlight, no picture

            You need to check where the VonOff signal comes from. I would expect it to be around 3V when VonOff = On
            Have you checked the two fuses shown in photo 6 of 11 in your first post.
            Last edited by dick_barton; 02-22-2021, 01:02 PM.
            Willing to help but I'm no expert.

            Comment


              #7
              Re: Vizio VO42L, white logo, no backlight, no picture

              Originally posted by dick_barton View Post
              You need to check where the VonOff signal comes from.
              That wire is connected to "B" on the PSU Connector 1 (J21?) (photo 3 of 11 in my first post)

              Originally posted by dick_barton View Post
              Have you checked the two fuses shown in photo 6 of 11 in your first post.
              Main board:
              Continuity across F1 & F2 = GOOD
              F1 = 5.12v
              F2 = 11.57v

              Comment


                #8
                Re: Vizio VO42L, white logo, no backlight, no picture

                Originally posted by dick_barton View Post
                You need to check where the VonOff signal comes from. I would expect it to be around 3V when VonOff = On
                Have you checked the two fuses shown in photo 6 of 11 in your first post.
                I jumpered PSU Connector 2 (J22?) 5VSB to PSU Connector 2 "B" (which connects to Inverter Connector VOnOff). The backlight comes on with both inverters that I have. So, the main board appears to be the problem.
                Anything else I should check on the main board? Or should I just order a replacement?

                Comment


                  #9
                  Re: Vizio VO42L, white logo, no backlight, no picture

                  I would start checking LDO Voltage Regulator IC's on the main board.

                  There is Main board repair kit and EEPROM also.
                  https://www.shopjimmy.com/search.php...ery=Vizio+VO42
                  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


                    #10
                    Re: Vizio VO42L, white logo, no backlight, no picture

                    Just to close this out, I was able to get a replacement main board for $20 from ElectroParts, so I decided to order it and save my time (instead of working on the defective board). The replacement main board worked.

                    Comment


                      #11
                      Re: Vizio VO42L, white logo, no backlight, no picture

                      Thanks for the feedback Dave.

                      Comment

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