Vizio LED Backlight Issue? Dark areas

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  • roundbox52
    Member
    • Aug 2017
    • 25
    • USA

    #1

    Vizio LED Backlight Issue? Dark areas

    I just replaced the main board on my 50" Vizio LED, M502i-b1 which fixed my original issues. I now have an issue with dark areas on the screen, see picture. The image fills the entire screen it is just darker in some areas than others, like the lower right, lower left, center top...

    I do recall when diagnosing the main board issue I created a spark on the main board at the power supply connector. This did cause the backlight to flash and partially remain on.

    Any help on diagnosing this issue?
    Attached Files
  • jjanssen7
    Badcaps Veteran
    • Nov 2012
    • 252
    • Canada

    #2
    Re: Vizio LED Backlight Issue? Dark areas

    Is your main board an exact replacement? I had a very similar issue when replacing a main board with a similar (though not exact) replacement on that model.

    Comment

    • roundbox52
      Member
      • Aug 2017
      • 25
      • USA

      #3
      Re: Vizio LED Backlight Issue? Dark areas

      Originally posted by jjanssen7
      Is your main board an exact replacement? I had a very similar issue when replacing a main board with a similar (though not exact) replacement on that model.
      Yes it is the exact # as the previous board. Did a different board solve you're issue?

      Comment

      • roundbox52
        Member
        • Aug 2017
        • 25
        • USA

        #4
        Re: Vizio LED Backlight Issue? Dark areas

        Before diagnosing the main board issue I don't recall having back lights, however once I created a short on the 1 & 3 pin of cn701 of the main board, the upper left back lights came on but no others. I'm wondering if I sent too much voltage to those leds somehow and they remained on or at least brighter than normal.

        I'm thinking instead of having dark spots I really have bright spots. Would any of this make logical sense?

        This picture is from tonight after turning the tv on. Typically, when everything is working as it should, I would have an almost black screen. You can see how some spots are bright.
        Attached Files

        Comment

        • attainteddragon
          Badcaps Veteran
          • Apr 2013
          • 764
          • australia

          #5
          Re: Vizio LED Backlight Issue? Dark areas

          on the connector that powers the backlights (i can't read the connection number, but it has the 4x red and black wires coming from it), can you check the voltage on all pins as it is powered on and what the voltage settles too and report your results thanks.
          WHY CAN'T PHILIPS USE PHILLIPS HEAD SCREWS?

          Comment

          • roundbox52
            Member
            • Aug 2017
            • 25
            • USA

            #6
            Re: Vizio LED Backlight Issue? Dark areas

            Originally posted by attainteddragon
            on the connector that powers the backlights (i can't read the connection number, but it has the 4x red and black wires coming from it), can you check the voltage on all pins as it is powered on and what the voltage settles too and report your results thanks.
            I measured the voltages at the cn804 on the driver board, not the psu.

            Pin# / On / Settled

            1 / 20.11 / 19.49
            2 / 19.99 / 19.48
            3 / 20.15 / 19.48
            4 / 19.99 / 19.48
            5 / .7mv / .4mv
            6 / .7mv / .4mv
            7 / .7mv / .4mv
            8 / .7mv / .4mv

            Comment

            • roundbox52
              Member
              • Aug 2017
              • 25
              • USA

              #7
              Re: Vizio LED Backlight Issue? Dark areas

              Anyone?

              Anyone know what is going on or what I should check next?

              Comment

              • attainteddragon
                Badcaps Veteran
                • Apr 2013
                • 764
                • australia

                #8
                Re: Vizio LED Backlight Issue? Dark areas

                my bad, i didn't see the separate driver board. can you do the same thing for connector cn801 and cn802.
                WHY CAN'T PHILIPS USE PHILLIPS HEAD SCREWS?

                Comment

                • roundbox52
                  Member
                  • Aug 2017
                  • 25
                  • USA

                  #9
                  Re: Vizio LED Backlight Issue? Dark areas

                  cn801
                  Pin# / On / Settled

                  1 / 19.69 / 30.07
                  2 / 19.75 / 30.08
                  3 / 19.71 / 30.09
                  4 / 19.75 / 30.09
                  5 not used
                  6 not used
                  7 / 11.15 / .607
                  8 / 11.44 / 11.49
                  9 / 10.95 / 11.26
                  10 / 11.49 / 11.49
                  11 / 11.65 / 11.35
                  12 / 11.65 / 11.62
                  13 / 10.80 / 11.36
                  14 / 11.37 / 11.41
                  15 / 11.44 / 11.46
                  16 / 11.36 / 11.41
                  17 / 11.36 / 11.38
                  18/ 11.52 / 11.54
                  19 / 11.42 / 11.43
                  20 / 11.46 / 11.48
                  21 / 11.45 / 11.48
                  22 / 11.43 / 11.44
                  23 not used
                  24 not used

                  cn802
                  Pin# / On / Settled

                  1 / 19.77 / 30.11
                  2 / 19.77 / 30.12
                  3 / 19.74 / 30.12
                  4 / 19.77 / 30.12
                  5 not used
                  6 not used
                  7 / 2.5 / .742
                  8 / 9.4 / 11.56
                  9 / 8.9 / 10.48
                  10 / 11.1 / 8.53
                  11 / 5.3 / 3.93
                  12 / 11.2 / 11.67
                  13 / 2.4 / .762
                  14 / 8.9 / 11.33
                  15 / 2.2 / .605
                  16 / 10.9 / 11.37
                  17 / 9.4 / 7.69
                  18 / 11.36 / 11.39
                  19 / 11.12 / 10.88
                  20 / 10.76 / 10.75
                  21 / 11.28 / 10.93
                  22 / 11.45 / 11.54
                  23 not used
                  24 not used

                  Something seems goofy with some voltages on cn802 when compared to cn801 and even #7 on cn801. Not really sure what the driver board does or if these numbers indicate an issue.

                  Comment

                  • budm
                    Badcaps Legend
                    • Feb 2010
                    • 40746
                    • USA

                    #10
                    Re: Vizio LED Backlight Issue? Dark areas

                    https://www.badcaps.net/forum/attach...8&d=1503842055
                    It looks like you have some open circuits in the LED strings. You have 16 LED strings. (http://www.shopjimmy.com/vizio-lbm50...-16-strips.htm)
                    What are the P/N of Q801, U801?
                    Last edited by budm; 09-06-2017, 05:41 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

                    • roundbox52
                      Member
                      • Aug 2017
                      • 25
                      • USA

                      #11
                      Re: Vizio LED Backlight Issue? Dark areas

                      Originally posted by budm
                      What are the P/N of Q801, U801?
                      Sorry for my ignorance but is P/N stand for Possitive/Negative?

                      I found Q801 (which has test points labeled 1-7) and U801, but would be unsure of how to test U801. Any chance you can elaborate on what I should be checking?

                      Comment

                      • mmischni
                        Member
                        • Sep 2017
                        • 29
                        • USA

                        #12
                        Re: Vizio LED Backlight Issue? Dark areas

                        P/N in this case is Part Number of those components. What numbers are printed on them?

                        Comment

                        • budm
                          Badcaps Legend
                          • Feb 2010
                          • 40746
                          • USA

                          #13
                          Re: Vizio LED Backlight Issue? Dark areas

                          Originally posted by mmischni
                          P/N in this case is Part Number of those components. What numbers are printed on them?
                          Yes.
                          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

                          • roundbox52
                            Member
                            • Aug 2017
                            • 25
                            • USA

                            #14
                            Re: Vizio LED Backlight Issue? Dark areas

                            Great. See attached photos for part numbers.

                            Are we thinking these two components are bad and giving poor voltage to some of the leds?
                            Attached Files

                            Comment

                            • budm
                              Badcaps Legend
                              • Feb 2010
                              • 40746
                              • USA

                              #15
                              Re: Vizio LED Backlight Issue? Dark areas

                              Right now we are looking to see how those LEDs are being driven.
                              Dual MOSFET AO4892.
                              16 channel LED driver/controller AS3820.
                              Probing the IC and the MOSFETs Voltages are to be done next to verify if we have bad LED for sure or LED driver problem. Taking panel apart is the last thing you will want to do.
                              So far it looks like you have 32 set of LEDs not 16 as first thought.
                              Attached Files
                              Last edited by budm; 09-07-2017, 09:10 AM.
                              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

                                #16
                                Re: Vizio LED Backlight Issue? Dark areas

                                BTW, what is the model number of the LCD panel?
                                TPT500J1-HVN08????
                                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

                                • roundbox52
                                  Member
                                  • Aug 2017
                                  • 25
                                  • USA

                                  #17
                                  Re: Vizio LED Backlight Issue? Dark areas

                                  I think the LCD panel is 705TXES235200X, see picture.

                                  Let me know what to probe and if it is anymore difficult than just getting dc voltage.
                                  Attached Files

                                  Comment

                                  • budm
                                    Badcaps Legend
                                    • Feb 2010
                                    • 40746
                                    • USA

                                    #18
                                    Re: Vizio LED Backlight Issue? Dark areas

                                    So far no luck finding info for the LCD panel. It does look like you have do have LED problem.
                                    You can take a chance on replacing the LED driver board for $15:
                                    http://www.shopjimmy.com/vizio-lntve...ed-driver.htm#
                                    I would get a LED tester similar to this:
                                    http://www.shopjimmy.com/sid-gj2c-le...ght-tester.htm
                                    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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