VIZIO V037L FHDTV20A powers up, backlight on, sound works, buttons work, no picture

Collapse
X
 
  • Time
  • Show
Clear All
new posts
  • budm
    Badcaps Legend
    • Feb 2010
    • 40746
    • USA

    #141
    Re: VIZIO V037L FHDTV20A powers up, backlight on, sound works, buttons work, no pict

    U37 is the MOSFET that we put the jumper wire between the Source (pin 1& 3) pin and the Drain pin (pin 5~8). The Gate pin (pin2 & 4) of U37 is connected to transistor Q26 pin C (C = Collector).
    The Q26 is getting the correct voltage to bias it on (0.6V on the E (Emitter) and B (Base) but the Collector voltage did not go down like it should and stuck at 12V, that means that Q26 is not functioning.
    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

    • triplefour
      Badcaps Legend
      • May 2014
      • 1747
      • USA

      #142
      Re: VIZIO V037L FHDTV20A powers up, backlight on, sound works, buttons work, no pict

      i am confused again...we put the jumper wire between pin 1-4 of the mosfet and the + side of the capacitor

      but you seem to be saying i put it between the source and the drain? on the same mosfet?

      also i tested the voltage on C (collector) and it was .3v not 12...
      Don't fear the repair...

      Comment

      • budm
        Badcaps Legend
        • Feb 2010
        • 40746
        • USA

        #143
        Re: VIZIO V037L FHDTV20A powers up, backlight on, sound works, buttons work, no pict

        "i am confused again...we put the jumper wire between pin 1-4 of the mosfet and the + side of the capacitor" No.
        If you look at that MOSFET U37, the bottom right has a little dot to indicate pin 1. Pin 1 and Pin 3 are the Source pins (which the 12v is fed into) which are connected to the + of the cap. pIN 5~8 (the left side) of U37 which are all tied together are the Drain pin (this Drain pin which where the 12v comes out, is then connected to pin 30 of J8), so what we did is to connect the S and D together to by pass U37. Pin 2 and 4 are the GATE pins which are tied together and connected to the Collector pin of Q26, Q26 get the ON/OFF signal to the BASE pin from processor, but the Q26 is not going on and off it is stuck in the off mode which causes the U37 to be stuck in the OFF mode.
        Now I may be wrong about the Q26 connection since now you are saying that the Collector pin is at 0.3V not 12V, then we need to find out if the Collector pin is actually connected to pin 1 and 3 of U37 MOSFET or not. That Collector pin should change state when TV is powered on and powered off.
        Last edited by budm; 05-15-2014, 03:08 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

        • triplefour
          Badcaps Legend
          • May 2014
          • 1747
          • USA

          #144
          Re: VIZIO V037L FHDTV20A powers up, backlight on, sound works, buttons work, no pict

          ok much clearer now i was thinking pin 1-4 were on the left side for some reason... but u say the source (1 and 3) get 12v but i only measured 11.95...is that close enough? pins 2 and 4 (the gate pins) are getting 12.05 each... what should q26 be doing to modify those voltages? what voltage does the gate want to see before it will push 12v out the drain?
          Don't fear the repair...

          Comment

          • triplefour
            Badcaps Legend
            • May 2014
            • 1747
            • USA

            #145
            Re: VIZIO V037L FHDTV20A powers up, backlight on, sound works, buttons work, no pict

            cause as i said, q26 puts .3v out its collector and i guess i just dont really see what is happening there...
            Don't fear the repair...

            Comment

            • triplefour
              Badcaps Legend
              • May 2014
              • 1747
              • USA

              #146
              Re: VIZIO V037L FHDTV20A powers up, backlight on, sound works, buttons work, no pict

              ok im gonna check some voltages on the collector and try some resistances to see where its going to?
              Don't fear the repair...

              Comment

              • budm
                Badcaps Legend
                • Feb 2010
                • 40746
                • USA

                #147
                Re: VIZIO V037L FHDTV20A powers up, backlight on, sound works, buttons work, no pict

                11.95Vdc is good enough for 12V, less than 1% off. The minimum turn on threshold Voltage between G and S is typical around 3~5V for the MOSFET to be on, right now the G and S voltage are about the same that is why it is not on. So far I cannot find the spec for the 4853 yet.
                So in 2 (or 4) of the U37 does not change state when TV is off and when the TV is on? Same for the Collector of Q26?

                http://electronics.stackexchange.com...et-as-a-switch
                Last edited by budm; 05-15-2014, 03:26 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

                • triplefour
                  Badcaps Legend
                  • May 2014
                  • 1747
                  • USA

                  #148
                  Re: VIZIO V037L FHDTV20A powers up, backlight on, sound works, buttons work, no pict

                  the collector does change states. when the tv is off, (standby) it is 0, when i push the power button it goes to .02v

                  with the tv off i measured high resistances between the collector and each of the 4 pins (source and gate) on 20k ohms scale i got 11.99, 8.97, 11.99, 8.97
                  funny thing about resistance with my meter if i reverse the probes i get a slightly different resistance.
                  in this case when i held the red probe steady on the collector and use the black probe to test resistances i got 7.10, 7.42, 7.10, 7.42

                  any idea how that would be happening? i thought resistance shouldnt matter which way the probes were?
                  Don't fear the repair...

                  Comment

                  • budm
                    Badcaps Legend
                    • Feb 2010
                    • 40746
                    • USA

                    #149
                    Re: VIZIO V037L FHDTV20A powers up, backlight on, sound works, buttons work, no pict

                    If the Collector of Q26 is connected to pin 2 (4) then it should show <1 Ohm, so the Q26 may not be the one that is used for controlling U37 MOSFET.
                    At this point, I would use the TV as it is for now. This is getting long to troubleshoot further more for me.
                    the resistance reading will be affected if there is semiconductor device connected to the circuit you are measuring the resistance.
                    Last edited by budm; 05-15-2014, 03:39 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

                    • triplefour
                      Badcaps Legend
                      • May 2014
                      • 1747
                      • USA

                      #150
                      Re: VIZIO V037L FHDTV20A powers up, backlight on, sound works, buttons work, no pict

                      yeah i think its fine without that mosfet in the way actually.... you were saying that there would always be 12v present there even in standby but there isnt. i think the capacitor doesnt get any power until you push the power switch, so theres no 12v going into the mosfet or coming out of it... ill just tidy up those solder connections and call it good. maybe ill try figure out whats feeding the mosfet some other day but if it doesnt affect the way the tv works... anyway thanks a lot for your help and i hope you will help me again with this other tv i got...it just doesnt turn on at all, making me think it must be the power supply...but i guess we'll see! Thanks again! one more TV saved from the dump... great job!
                      Don't fear the repair...

                      Comment

                      • budm
                        Badcaps Legend
                        • Feb 2010
                        • 40746
                        • USA

                        #151
                        Re: VIZIO V037L FHDTV20A powers up, backlight on, sound works, buttons work, no pict

                        The only time that the 12V will not be present is when TV is OFF, in standby mode (not off), the 12V will be present, normally that 12V feeding the T-CON will be off when TV goes into standby mode (not off mode, TV goes into standby when it does not detect video signal from PC or from any video source so it goes into standby mode (not the same as off mode), thati s why the MOSFET is used to swithc off the 12V feeding the T-CON, this is done to save power consumption when TV is in standby.
                        I also thing that U37 is 4953GM, not 4853GM.

                        Last edited by budm; 05-15-2014, 03:56 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

                        • triplefour
                          Badcaps Legend
                          • May 2014
                          • 1747
                          • USA

                          #152
                          Re: VIZIO V037L FHDTV20A powers up, backlight on, sound works, buttons work, no pict

                          ooh i just figured out tho that pin 2 and 4 have .3 ohms resistance to the left side of r351 and .4 ohms to the right side of r351 ....could that be a clue? should i see voltage coming from that...is it a resistor (hence the R) ?
                          Don't fear the repair...

                          Comment

                          • budm
                            Badcaps Legend
                            • Feb 2010
                            • 40746
                            • USA

                            #153
                            Re: VIZIO V037L FHDTV20A powers up, backlight on, sound works, buttons work, no pict

                            Yes, R = Resistor, C (or CE in this board) = capacitor for this board.
                            See my update on post 151.
                            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

                            • triplefour
                              Badcaps Legend
                              • May 2014
                              • 1747
                              • USA

                              #154
                              Re: VIZIO V037L FHDTV20A powers up, backlight on, sound works, buttons work, no pict

                              and no i have double and triple checked it, the j30 is not getting power, the u39 is not getting power, when the tv is in standby these things are defnitely at 0 volts. then go up to 12 when i push power
                              Don't fear the repair...

                              Comment

                              • triplefour
                                Badcaps Legend
                                • May 2014
                                • 1747
                                • USA

                                #155
                                Re: VIZIO V037L FHDTV20A powers up, backlight on, sound works, buttons work, no pict

                                oh wait i think youre saying that there is a difference between plugging the set in and not turning it on, and plugging it in and leaving it on until it goes into standby on its own with no input...i thought those 2 standby modes were the same...
                                Don't fear the repair...

                                Comment

                                • triplefour
                                  Badcaps Legend
                                  • May 2014
                                  • 1747
                                  • USA

                                  #156
                                  Re: VIZIO V037L FHDTV20A powers up, backlight on, sound works, buttons work, no pict

                                  but i guess theyre not...as one is waiting for video signal input, and the other is waiting for a push button input before it will turn on...hmm maybe i will have 12v always present in standby like u say...but thats not a big deal im a big fan of turning things off when im done using them
                                  Don't fear the repair...

                                  Comment

                                  • budm
                                    Badcaps Legend
                                    • Feb 2010
                                    • 40746
                                    • USA

                                    #157
                                    Re: VIZIO V037L FHDTV20A powers up, backlight on, sound works, buttons work, no pict

                                    No it is not the same. It all has to do with power saving. So you are fine, just turn off the TV when you are done.
                                    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

                                    • triplefour
                                      Badcaps Legend
                                      • May 2014
                                      • 1747
                                      • USA

                                      #158
                                      Re: VIZIO V037L FHDTV20A powers up, backlight on, sound works, buttons work, no pict

                                      yeah but if i wanted to sell the tv, i should repair the component or replace the board...
                                      so if i can ask just a couple more questions and then ill try to figure it out on my own from there.... u said the mosfet needs to see a different voltage on its source and gate... but the gate is being fed 12v from that r351 ... the source has to be 12v for it to be able to push 12v out the drain, so what im trying to figure out here is how to get the gate pins to read a significantly lower voltage, right?
                                      Don't fear the repair...

                                      Comment

                                      • triplefour
                                        Badcaps Legend
                                        • May 2014
                                        • 1747
                                        • USA

                                        #159
                                        Re: VIZIO V037L FHDTV20A powers up, backlight on, sound works, buttons work, no pict

                                        also i think because this mosfet is unable to do its job, even though im waiting forever, i dont think its ever going to go into standby on its own...or that is to say i dont think it can go into standby mode anymore?
                                        Don't fear the repair...

                                        Comment

                                        • budm
                                          Badcaps Legend
                                          • Feb 2010
                                          • 40746
                                          • USA

                                          #160
                                          Re: VIZIO V037L FHDTV20A powers up, backlight on, sound works, buttons work, no pict

                                          Put it into PC mode or disconnect the antenna/cable from the tuner when in TV mode, it should then go into STBY mode after a few minutes, some you can setup the time in the user menu for how long before it will go into standby if it does not detect signals.
                                          Last edited by budm; 05-15-2014, 04:58 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

                                          Related Topics

                                          Collapse

                                          Working...