Vizio M421VT LED no display

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  • ryan74
    Badcaps Veteran
    • Oct 2012
    • 471
    • usa

    #41
    Re: Vizio M421VT LED no display

    Originally posted by budm
    I am surprised that your meter can read the AC voltage on those test points since that transformer is driven at 50KHz to 80 KHz range, most cheap meter does not have the bandwidth to measure those high frequency on that switching power supply transformer.
    It's a Klein MM1000. $60 new

    Comment

    • ryan74
      Badcaps Veteran
      • Oct 2012
      • 471
      • usa

      #42
      Re: Vizio M421VT LED no display

      I just got part put in but while doing it I noticed I didnt verify spacing of leads when I ordered.
      Besides the spacing I had to install it upside down so pos. and neg. matched.
      See pic
      I hope it will be ok. I will update results after I test it.
      Attached Files

      Comment

      • ryan74
        Badcaps Veteran
        • Oct 2012
        • 471
        • usa

        #43
        Re: Vizio M421VT LED no display

        I still have issues.
        I left backlight disconnected (CN902,CN905) when I tested VLED voltage.
        After pressing power it was 40vdc. for a second then dropped off.

        I had the same results checking voltage with backlight connected.

        From BudM-I think once the bridge rectifier is replaced to get the voltage for the LEDs you will be OK unless the circuts that drive the transformer also failed due to shorted out bridge.

        What next?
        Last edited by ryan74; 04-29-2013, 01:26 PM.

        Comment

        • budm
          Badcaps Legend
          • Feb 2010
          • 40746
          • USA

          #44
          Re: Vizio M421VT LED no display

          So what voltage do you get at the +/- terminal of the bridge, it must be quite high since the filter caps are rated at 33uf 200V.
          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

          • ryan74
            Badcaps Veteran
            • Oct 2012
            • 471
            • usa

            #45
            Re: Vizio M421VT LED no display

            Grounded to chassis:
            All I get is the 40vdc on the + of bridge just like above post.(drops off)
            The - is 0-9.9mV.
            Last edited by ryan74; 04-29-2013, 02:23 PM.

            Comment

            • tom66
              EVs Rule
              • Apr 2011
              • 32560
              • UK

              #46
              Re: Vizio M421VT LED no display

              So, next step is to see if BLON comes on and stays high and also maybe DIM (I am not sure if this set modulates the voltage to vary brightness or uses PWM; it may use a combination of the two.)
              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

              • ryan74
                Badcaps Veteran
                • Oct 2012
                • 471
                • usa

                #47
                Re: Vizio M421VT LED no display

                I pulled and tested bridge just to be sure. Everything tested as below except:
                Pin 4 to 1 was .879V.

                Originally posted by tom66
                So, testing the bridge: Looking at device from top label side pin 1 is +, 2 and 3 are ~ and 4 is -.

                Meter probes in order (red) (black)
                Pin 2 to 1 you should see ~0.4V
                Pin 3 to 1 you should see ~0.4V
                Pin 1 to 2 you should see OL
                Pin 1 to 3 you should see OL
                Pin 4 to 1 you should see ~0.4V
                Pin 1 to 4 you should see OL
                Pin 2 to 3 you should see OL
                Pin 3 to 2 you should see OL

                Comment

                • tom66
                  EVs Rule
                  • Apr 2011
                  • 32560
                  • UK

                  #48
                  Re: Vizio M421VT LED no display

                  My error 4-1 is correct as there are two series diodes.
                  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

                  • ryan74
                    Badcaps Veteran
                    • Oct 2012
                    • 471
                    • usa

                    #49
                    Re: Vizio M421VT LED no display

                    I get the same reading as in post 1

                    Cn904
                    on-off = 4.91V
                    DIMM = 2.93V
                    12v = 12V
                    12v = 12V
                    G = 20mV
                    G = 20mV
                    G = 20mV
                    24v = 24.73V
                    24v = 24.73V
                    PS_on = 3.09V
                    5.2v = 5.09V
                    5.2v = 5.09V
                    ACD = 2.8mV

                    Comment

                    • budm
                      Badcaps Legend
                      • Feb 2010
                      • 40746
                      • USA

                      #50
                      Re: Vizio M421VT LED no display

                      The 40V reading at the output of the bridge seems too low since the filter caps are 200V rating.
                      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

                      • ryan74
                        Badcaps Veteran
                        • Oct 2012
                        • 471
                        • usa

                        #51
                        Re: Vizio M421VT LED no display

                        Originally posted by budm
                        The 40V reading at the output of the bridge seems too low since the filter caps are 200V rating.
                        I agree, I don't think it is getting up to correct voltage before shutting down.
                        I know transformers rarely go bad but could it be a bad transformer or most likely something else?

                        Comment

                        • tom66
                          EVs Rule
                          • Apr 2011
                          • 32560
                          • UK

                          #52
                          Re: Vizio M421VT LED no display

                          The capacitors on the output could be bad.
                          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

                          • budm
                            Badcaps Legend
                            • Feb 2010
                            • 40746
                            • USA

                            #53
                            Re: Vizio M421VT LED no display

                            or the drive circuit that drives the transformer is not driving it correctly, that is why I wonder if it gets damaged when the bridge shorted out.
                            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

                            • tom66
                              EVs Rule
                              • Apr 2011
                              • 32560
                              • UK

                              #54
                              Re: Vizio M421VT LED no display

                              I'd be surprised. Most drive circuits fail or work. Like shorted FETs. Won't work. A few exceptions, like bad coupling caps and current shunt resistors, of course.
                              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

                              • ryan74
                                Badcaps Veteran
                                • Oct 2012
                                • 471
                                • usa

                                #55
                                Re: Vizio M421VT LED no display

                                when I press power I get the 40v for a split second.
                                This may sound stupid but I don't know. The drive circuit for transformer- Is this the cold(north) side? or are you refering to the circuit before transformer?

                                I pulled all 4 caps in upper left of board(2-200v) and tested good.
                                200v 33uf=35uf
                                50v 47uf=48uf

                                Im stuck at this point but I think I found a board for $120 but Im not sure I want to give up yet.
                                Last edited by ryan74; 05-01-2013, 04:45 PM.

                                Comment

                                • budm
                                  Badcaps Legend
                                  • Feb 2010
                                  • 40746
                                  • USA

                                  #56
                                  Re: Vizio M421VT LED no display

                                  The hot side, there are two MOSFETs and little IC for driving them, you can look up the spec of that IC.
                                  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

                                  • ryan74
                                    Badcaps Veteran
                                    • Oct 2012
                                    • 471
                                    • usa

                                    #57
                                    Re: Vizio M421VT LED no display

                                    ok I guess I am starting from scratch again. I purchased a power supply board and still have the same problem.

                                    Comment

                                    • ryan74
                                      Badcaps Veteran
                                      • Oct 2012
                                      • 471
                                      • usa

                                      #58
                                      Re: Vizio M421VT LED no display

                                      I rechecked voltages:
                                      ------------
                                      on/off-4.91v
                                      dim - 2.93v
                                      12v - 11.91v
                                      12v - 11.91v
                                      G
                                      G
                                      G
                                      24v - 24.67v
                                      24v - 24.67v
                                      ps_on-3.09v
                                      5.2v - 5.11v
                                      5.2v - 5.11v
                                      acd -

                                      ------------
                                      Vled-194.7mV
                                      all #- 10.65v

                                      -------------
                                      Vsync- 25mV
                                      DIM- 58.5mV
                                      G
                                      DCLK- 49.1mV
                                      G

                                      I assume vsync and dim should be giving a reading and im not sure about ACD.
                                      Now im thinking it is the middle board(pc/tcon?) or possibly main board.
                                      http://www.shopjimmy.com/vizio-cbpft...2-pc-board.htm

                                      these are the original readings from old board:
                                      1)BL_on = 4.91V
                                      2)BL_DIM = 2.93V
                                      3)12V. = 12V
                                      4)12V. = 12V
                                      5)G = 20mV
                                      6)G = 20mV
                                      7)G = 20mV
                                      8)24V. = 24.73V
                                      9)24V. = 24.73V
                                      10)BS_on = 3.09V
                                      11)5V. = 5.09V
                                      12)5V. = 5.09V
                                      13)PWR_ok = 2.8mV

                                      CN902
                                      Vled = 235.6mV
                                      #4-1 = 10.69V
                                      #4-2 = 10.27V
                                      #4-3 = 10.67V
                                      #3-3 = 10.65V
                                      #3-2 = 10.66V
                                      #3-1 = 10.64V
                                      Vled = 236.2mV

                                      Cn905
                                      Vled = 237mV
                                      #2-1 = 10.25V
                                      #2-2 = 10.63V
                                      #2-3 = 10.64V
                                      #1-3 = 10.66V
                                      #1-2 = 10.27V
                                      #1-1 = 10.67V
                                      Vled = 237.0mV

                                      Any idea how to test pc board? Theres a connector from main board but nothing listed by it.
                                      Attached Files
                                      Last edited by ryan74; 05-13-2013, 01:21 PM.

                                      Comment

                                      • ryan74
                                        Badcaps Veteran
                                        • Oct 2012
                                        • 471
                                        • usa

                                        #59
                                        Re: Vizio M421VT LED no display

                                        I ordered the pc board to try. If it still doesn't work I don't know what I will do.

                                        Comment

                                        • ryan74
                                          Badcaps Veteran
                                          • Oct 2012
                                          • 471
                                          • usa

                                          #60
                                          Re: Vizio M421VT LED no display

                                          I have tried power supply board and pc board with no luck. Not sure if I should try main board or dig into panel lighting.

                                          Comment

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