Vizio VS420LF1A No picture/backlight

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  • Blackwolf
    Member
    • Mar 2012
    • 18
    • USA

    #1

    Vizio VS420LF1A No picture/backlight

    Ive got a Vizio VS420LF1A and having an issue with it:
    When power is connected, Vizio logo glows orange,
    i press power button... the logo turns to white and that's it. I see nothing on the screen, i don't see the back light come on, just a solid white Vizio Logo showing its powered on.
    I opened it up and looked for the obvious things like bulging/leaky caps
    and everything appears ok.

    I also took a flash light and tried to look closely at the panel when it was on to see if i could see anything on the screen (like if the back light wasn't working, but the display itself was) and i see nothing.


    Any suggestions on what to look into fixing/replacing would be much appreciated.
  • retiredcaps
    Badcaps Legend
    • Apr 2010
    • 9271

    #2
    Re: Vizio VS420LF1A No picture/backlight

    1) Please post clear focused top down view pictures of all your boards following my instructions in my sig file below exactly.

    2) Please state if you have a multimeter and are familiar with measuring voltage and resistance?
    --- 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

    • Blackwolf
      Member
      • Mar 2012
      • 18
      • USA

      #3
      Re: Vizio VS420LF1A No picture/backlight

      Attached are the pictures, I do have a multimeter and I am familiar with how to use it.

      Thanks for your help
      Attached Files

      Comment

      • tibimakai
        Badcaps Legend
        • Jan 2012
        • 3680
        • USA

        #4
        Re: Vizio VS420LF1A No picture/backlight

        how about inverter board pictures?

        Comment

        • Blackwolf
          Member
          • Mar 2012
          • 18
          • USA

          #5
          Re: Vizio VS420LF1A No picture/backlight

          These are the only 2 boards i see, i do see wires running from the PSU to either side of the panel, Im guessing these wires go to the inverters.
          I cant see any easy way to get to them, ill have to take the entire panel apart.
          I will try to do that if you think it could be an inverter issue.
          Ive repaired sets before that have bad inverters and usually im able to see something on the screen when using a flash light and looking very closely, in this case i cant so Im not sure if its an inverter issue or not but you guys would know much more about this then I so if you recommend i strip it down to get to the inverters i will.

          Comment

          • retiredcaps
            Badcaps Legend
            • Apr 2010
            • 9271

            #6
            Re: Vizio VS420LF1A No picture/backlight

            1) Vizio TVs, for whatever reason, seem to use or have bad voltage regulators.

            2) All the red circled components are regulators.

            3) List the part number for each.

            4) Measure the DC voltage of each pin (ignore the fat tab) for every regulator.

            5) Report each part number and readings.

            6) The blue circled component is the connector. Measure the DC voltage of each pin and report the legend (what is written on the pcb) and your findings. Pin 14 is your inverter on/off.
            Attached Files
            --- 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

            • Blackwolf
              Member
              • Mar 2012
              • 18
              • USA

              #7
              Re: Vizio VS420LF1A No picture/backlight

              Sorry for the delay in response, I was traveling and havent had a chance to test until today.

              The first thing i checked was the connector circled in blue.

              Legend is as follows

              Pin 1 - PSU on/off
              Pins 2 3 4 - +12v
              Pins 5 6 7 8 9 - GND
              Pins 10 11 12 - +5v
              Pin 13 Dim
              Pin 14 Inverter on/off

              I checked voltage on +5v and it checks out,
              however on the +12v line i am not getting +12v. Its reading 0.19v


              So im guessing this is the problem, no +12v coming from the power supply.

              (I haven't checked the voltage regulators yet, but i will, but im guessing ive found the issue.)

              Any suggestions on what to check on the PSU?

              Comment

              • ktulu909
                Member
                • Mar 2012
                • 40
                • USA

                #8
                Re: Vizio VS420LF1A No picture/backlight

                See my thread.The main board sends the signal to the PS to tell it to turn on the 12 and inverter lines.

                You have a different board than I do,but I would look very closely at the regulators as it turned out to be a single regulator on mine that was keeping it from turning on.

                Comment

                • budm
                  Badcaps Legend
                  • Feb 2010
                  • 40746
                  • USA

                  #9
                  Re: Vizio VS420LF1A No picture/backlight

                  You have power supply with PFC Voltage booster plus inverter. it is all in one board.
                  Check the DC voltage on that large 450Vdc with the TV OFF, you should read about 165~175Vdc, then turn on the TV, you should see the voltage goes up to about 380~400Vdc if the PFC is working, if it does, that means the PS_ON signal is OK. If not then it can be bad PFC or no PS_ON signal from the main board.
                  The two inverter transformers on the right of the pictures are driven by MOSTFET's which uses the 380~400Vdc voltage for the inverter circuits instead of the usual 24Vdc power supply.
                  Can we get the close up pictures of the connectors on the power supply/Inverter board so we can see the labels on them.
                  By the way, do not run the board without the high voltage wires from the lamp assemblies connected (the two white connectors on the top right of the picture of the power supply/inverter board)
                  Last edited by budm; 03-27-2012, 06:18 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

                  • Blackwolf
                    Member
                    • Mar 2012
                    • 18
                    • USA

                    #10
                    Re: Vizio VS420LF1A No picture/backlight

                    Ok i read the voltage on the 450vdc
                    it read 165v in standby, after powering the tv on, it went up to 387v.

                    Attached is the requested pics
                    Attached Files
                    Last edited by Blackwolf; 03-28-2012, 04:30 PM.

                    Comment

                    • budm
                      Badcaps Legend
                      • Feb 2010
                      • 40746
                      • USA

                      #11
                      Re: Vizio VS420LF1A No picture/backlight

                      OK, PFC and PS_ON are OK. We will now have to find out why the 12vdc PS not putting out. What do you get at Pin 14 the inverter ON/OFF line?
                      By the way, we nned real good pictures of the power supply board top and bottom sides, then picture 1/4 section each of the baord that we we can see the deatils of how the traces are connected. I need to trace out where the PS_ON goes to beside the PFC section.
                      Last edited by budm; 03-28-2012, 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

                      • Blackwolf
                        Member
                        • Mar 2012
                        • 18
                        • USA

                        #12
                        Re: Vizio VS420LF1A No picture/backlight

                        i get 2.09v when the tv is powered on

                        Comment

                        • budm
                          Badcaps Legend
                          • Feb 2010
                          • 40746
                          • USA

                          #13
                          Re: Vizio VS420LF1A No picture/backlight

                          That should be enough to turn on the transistor. I will wait for the pictures to trace out PS_ON line and the Inverter on line.
                          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

                          • budm
                            Badcaps Legend
                            • Feb 2010
                            • 40746
                            • USA

                            #14
                            Re: Vizio VS420LF1A No picture/backlight

                            Service manual
                            Attached Files
                            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

                            • Blackwolf
                              Member
                              • Mar 2012
                              • 18
                              • USA

                              #15
                              Re: Vizio VS420LF1A No picture/backlight

                              Did you need different pictures then the ones already posted? If so what exactly should i take pics of?

                              Comment

                              • budm
                                Badcaps Legend
                                • Feb 2010
                                • 40746
                                • USA

                                #16
                                Re: Vizio VS420LF1A No picture/backlight

                                I cannot see the whole board, I need to be able to see the components side, traces on the board VERY CLEARY so I can trace out the connections, without that it will be just impossible to troubleshoot down to component level from long distant. It is like trying to do surgery blindfolded.
                                Pictures of the whole board top and bottom, and 1/4 section of the board each.
                                At this point it looks like the problem is in the power supply/inverter baord, but we need to verify first.
                                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

                                • Blackwolf
                                  Member
                                  • Mar 2012
                                  • 18
                                  • USA

                                  #17
                                  Re: Vizio VS420LF1A No picture/backlight

                                  Here are the pics, please let me know if you need any retakes, i tried to do the best i could but my camera isn't so great.

                                  Also just wanted to say thanks for spending your time helping me out with this.
                                  Attached Files

                                  Comment

                                  • Blackwolf
                                    Member
                                    • Mar 2012
                                    • 18
                                    • USA

                                    #18
                                    Re: Vizio VS420LF1A No picture/backlight

                                    And heres the rest...
                                    Attached Files

                                    Comment

                                    • budm
                                      Badcaps Legend
                                      • Feb 2010
                                      • 40746
                                      • USA

                                      #19
                                      Re: Vizio VS420LF1A No picture/backlight

                                      OK, thanks for the pictures, I will download them and see if I can trace out the connections, it will be awhile.
                                      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

                                      • budm
                                        Badcaps Legend
                                        • Feb 2010
                                        • 40746
                                        • USA

                                        #20
                                        Re: Vizio VS420LF1A No picture/backlight

                                        Can you please get the number as printed on the IC circled in red?
                                        Attached Files
                                        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

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