Vizio M420NV no backlight

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  • nomoresonys
    Badcaps Legend
    • Jan 2013
    • 12085
    • U.S.

    #21
    Re: Vizio M420NV no backlight

    There's some other things you can test on the mainboard, looks like you need to know why the mainboard isn't sending the bl_on signal.

    Comment

    • sricechex
      Member
      • Mar 2018
      • 17
      • United States

      #22
      Re: Vizio M420NV no backlight

      Thank you for finding that video. I haven't gotten to the unit this evening yet, I'll keep you posted.

      Comment

      • budm
        Badcaps Legend
        • Feb 2010
        • 40746
        • USA

        #23
        Re: Vizio M420NV no backlight

        If you can force the backlights on using the resistor, then you can disconnect just the BL-ON signal wire going back to the main board and put all the connectors back in place, and then keep the pull-up resistor for the BL-ON pin on the power supply board in place, power up the TV and everything should then work normally if the BL-ON signal is the only problem on the main board.
        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

        • sricechex
          Member
          • Mar 2018
          • 17
          • United States

          #24
          Re: Vizio M420NV no backlight

          Nothing happens when I disconnect the motherboard from the power supply and plug in.
          In regards to the resistor test in post #8, my board lists no "PS_ON," as far as I can see. Are any of these other pins indicators of a ps_on?
          Attached Files

          Comment

          • sricechex
            Member
            • Mar 2018
            • 17
            • United States

            #25
            Re: Vizio M420NV no backlight

            The backlights do come on with a 1k between BL_ON and 5VSB!

            Comment

            • nomoresonys
              Badcaps Legend
              • Jan 2013
              • 12085
              • U.S.

              #26
              Re: Vizio M420NV no backlight

              Ok, you could test some of the components on the mainboard if you want to dig deeper, where to start is the question.

              Comment

              • sricechex
                Member
                • Mar 2018
                • 17
                • United States

                #27
                Re: Vizio M420NV no backlight

                This tv is certainly not worth a $100 mainboard ($25 pawnshop special), but in that I got it just for the learning, I'm tempted to swap the eeprom, if I can have some confidence that a failed eeprom is the culprit.
                Any thoughts on further testing on the mainboard?
                I greatly appreciate your input, nomoresonys and budm. You guys are kind to lend your expertise

                Comment

                • nomoresonys
                  Badcaps Legend
                  • Jan 2013
                  • 12085
                  • U.S.

                  #28
                  Re: Vizio M420NV no backlight

                  I'll try to help but it will be slow, not too good with troubleshooting mainboards.

                  Comment

                  • nomoresonys
                    Badcaps Legend
                    • Jan 2013
                    • 12085
                    • U.S.

                    #29
                    Re: Vizio M420NV no backlight

                    If you trace the bl_on wire from powersupply back to mainboard so you know which pin it is, unlpug connector at mainboard and see what voltage you have there, I always unplug tv first then unplug connector from mainboard then plug tv back in, to try not getting any strange surges.

                    Comment

                    • nomoresonys
                      Badcaps Legend
                      • Jan 2013
                      • 12085
                      • U.S.

                      #30
                      Re: Vizio M420NV no backlight

                      https://www.techwalla.com/articles/h...-board-of-a-tv
                      Rough guide on mainboard testing.

                      Comment

                      • sricechex
                        Member
                        • Mar 2018
                        • 17
                        • United States

                        #31
                        Re: Vizio M420NV no backlight

                        Great, dude, thanks. I'll let you know if I learn anything useful for future projects!

                        Comment

                        • nomoresonys
                          Badcaps Legend
                          • Jan 2013
                          • 12085
                          • U.S.

                          #32
                          Re: Vizio M420NV no backlight

                          https://www.youtube.com/watch?v=Sghh8BK5zIw Testing video, looks like hes testing eprom voltages, voltage regulators etc.

                          Comment

                          • nomoresonys
                            Badcaps Legend
                            • Jan 2013
                            • 12085
                            • U.S.

                            #33
                            Re: Vizio M420NV no backlight

                            https://elektrotanya.com/?q=keres Put your model number in there, see if they have a service manual.

                            Comment

                            • nomoresonys
                              Badcaps Legend
                              • Jan 2013
                              • 12085
                              • U.S.

                              #34
                              Re: Vizio M420NV no backlight

                              Vizio 32 inch (VA320M) Eco 1080p black screen
                              There's a thread there by KuDaH with some info.

                              Comment

                              • nomoresonys
                                Badcaps Legend
                                • Jan 2013
                                • 12085
                                • U.S.

                                #35
                                Re: Vizio M420NV no backlight

                                There's quite a few threads on this model, put M420NV in the search up there on this page.

                                Comment

                                • budm
                                  Badcaps Legend
                                  • Feb 2010
                                  • 40746
                                  • USA

                                  #36
                                  Re: Vizio M420NV no backlight

                                  Did you try post #23?
                                  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

                                  • sricechex
                                    Member
                                    • Mar 2018
                                    • 17
                                    • United States

                                    #37
                                    Re: Vizio M420NV no backlight

                                    Budm, that's what I did this morning, and the backlights work great! Ran off my Raspberrypi just fine. Thanks for the input.
                                    I had only a minute before work, so haven't been able to play with the other posts yet. I want to see if I can gain some experience isolating the culprit component(s) with some more precision.
                                    If it promises to be too frustrating or expensive, I'll just jam that resistor back in.

                                    That will keep my sunk cost at $25.01...not too shabby.

                                    Comment

                                    • budm
                                      Badcaps Legend
                                      • Feb 2010
                                      • 40746
                                      • USA

                                      #38
                                      Re: Vizio M420NV no backlight

                                      So all the TV functions are OK then?
                                      We can use other signal as the BL-ON.
                                      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

                                      • sricechex
                                        Member
                                        • Mar 2018
                                        • 17
                                        • United States

                                        #39
                                        Re: Vizio M420NV no backlight

                                        I haven't made time yet to try all functions, just menu functions, and successful HDMI input. When I get back to it I'll try different input and audio.
                                        Are you thinking of any specific functions?
                                        Where would you suggest sourcing the other signal?

                                        Comment

                                        • budm
                                          Badcaps Legend
                                          • Feb 2010
                                          • 40746
                                          • USA

                                          #40
                                          Re: Vizio M420NV no backlight

                                          You can use T-CON ON signal for BL-ON.
                                          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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