Sound and picture but no backlight

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  • JCdes
    Senior Member
    • Feb 2013
    • 91
    • USA

    #21
    Re: Sound and picture but no backlight

    It has 5 led strips consisting of 14 leds each. I dont know the value of each led. The tester starts from 0v increasing the voltage to the strip and it lights up very dim at around 70v and stops increasing at 83v full brightness. Tried disconnecting the "adj" wire on the board and that did not work, just wanted to try and see if it made a diff.
    Last edited by JCdes; 12-18-2020, 05:37 PM.

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    • petehall347
      Badcaps Legend
      • Jan 2015
      • 4422
      • United Kingdom

      #22
      Re: Sound and picture but no backlight

      are all led circuits same voltage on your tester ? must have connector unplugged from power board .
      if they are plug it back in and see if magic happened . dont know what it is with my tester but 2 sets still running after doing just that .maybe i got lucky . been a couple of months at least now .
      thinking about it though voltages from the supply and tester were not a lot different .
      Last edited by petehall347; 12-18-2020, 08:05 PM.

      Comment

      • JCdes
        Senior Member
        • Feb 2013
        • 91
        • USA

        #23
        Re: Sound and picture but no backlight

        Yup all same voltage, same amount of leds on each strip. I did test unplugged from board.

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        • budm
          Badcaps Legend
          • Feb 2010
          • 40746
          • USA

          #24
          Re: Sound and picture but no backlight

          You have 5 LED strings and each string has its own Cathode return line through MOSFET Q201, 205, 206, 207, and 208.
          The red wires are the Anode wire for each string which are connected together and fed by one Boost converter.
          All connectors in place, set the TV to OFF, keep black probe on the chassis, red probe on any one of the LED+, then turn on the TV while watching the meter (meter set to 200VDC) to see how high it goes up to then wait 10 seconds to see how low it goes to, turn the TV OFF, the repeat the same test using the red probe on all 5 LED - pins at a time.
          Last edited by budm; 12-18-2020, 10:05 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

          • JCdes
            Senior Member
            • Feb 2013
            • 91
            • USA

            #25
            Re: Sound and picture but no backlight

            59.8 on stdby 62.4v turned on. It does spike to 72 for a second then back to 62, power off is back to 59.8. Same behavior on all connections.
            Last edited by JCdes; 12-19-2020, 06:24 AM. Reason: Typo

            Comment

            • JCdes
              Senior Member
              • Feb 2013
              • 91
              • USA

              #26
              Re: Sound and picture but no backlight

              While I was at it, I saw 0v at the leg closest to the backlight header, gnd in center and .5v at the other leg on all q201,207,205,208 and 206. Both stdby and on. R255 had 67 on one side and climbs very slow to 12 on the other, R239 had 0v on both sides. I made a messy picture of a few measurements. D1a and D1b had -0v on anode and 5 on cathode side when powered on. D204 has 0v at all times.
              Attached Files
              Last edited by JCdes; 12-19-2020, 07:53 AM.

              Comment

              • Diah
                Badcaps Legend
                • Feb 2013
                • 6343
                • Germany

                #27
                Re: Sound and picture but no backlight

                Originally posted by JCdes
                59.8 on stdby 62.4v turned on. It does spike to 72 for a second then back to 62, power off is back to 59.8. Same behavior on all connections.
                i think yours measurements points not as the points other suggested.. you need the measurements on the LED SOCKETS

                Comment

                • JCdes
                  Senior Member
                  • Feb 2013
                  • 91
                  • USA

                  #28
                  Re: Sound and picture but no backlight

                  Those were taken at the led sockets, plugged and unplugged same results.
                  Attached Files
                  Last edited by JCdes; 12-19-2020, 10:08 AM.

                  Comment

                  • Diah
                    Badcaps Legend
                    • Feb 2013
                    • 6343
                    • Germany

                    #29
                    Re: Sound and picture but no backlight

                    Originally posted by JCdes
                    Those were taken at the led sockets, plugged and unplugged same results.
                    if so are you sure you got 59.8V when set on STBY ????

                    Comment

                    • JCdes
                      Senior Member
                      • Feb 2013
                      • 91
                      • USA

                      #30
                      Re: Sound and picture but no backlight

                      Yes

                      Comment

                      • JCdes
                        Senior Member
                        • Feb 2013
                        • 91
                        • USA

                        #31
                        Re: Sound and picture but no backlight

                        Stdby 59.8 and 62.4 turned on. When I turn it on it spikes to 74 after 6 seconds or so then back down to 62. Turn off then back to 59, unplug and slowly goes down to 0...
                        Last edited by JCdes; 12-19-2020, 10:14 AM.

                        Comment

                        • Diah
                          Badcaps Legend
                          • Feb 2013
                          • 6343
                          • Germany

                          #32
                          Re: Sound and picture but no backlight

                          measure please the V on CON4 PL_ON pins when set on and STB

                          Comment

                          • dick_barton
                            Badcaps Legend
                            • Aug 2015
                            • 6642
                            • Wales

                            #33
                            Re: Sound and picture but no backlight

                            Can you measure the voltage on the pins of U200. It may give some insight into what the problem could be.
                            Willing to help but I'm no expert.

                            Comment

                            • JCdes
                              Senior Member
                              • Feb 2013
                              • 91
                              • USA

                              #34
                              Re: Sound and picture but no backlight

                              I did measure that but cant remember if it was 4.9 I should have taken notes... I'll measure again when I get home. But it does go to 0 when turned off with power button.

                              Comment

                              • JCdes
                                Senior Member
                                • Feb 2013
                                • 91
                                • USA

                                #35
                                Re: Sound and picture but no backlight

                                Originally posted by dick_barton
                                Can you measure the voltage on the pins of U200. It may give some insight into what the problem could be.
                                Will do... I guess I'll have to juggle a bit since it is under the board. Can I measure just plugged in to the wall or do I need all connections to make it more accurate?

                                Comment

                                • dick_barton
                                  Badcaps Legend
                                  • Aug 2015
                                  • 6642
                                  • Wales

                                  #36
                                  Re: Sound and picture but no backlight

                                  I'm not sure what you mean by all connections.
                                  Are you able to turn the board over and rest it safely on an insulated pad to make the measurements.
                                  Willing to help but I'm no expert.

                                  Comment

                                  • JCdes
                                    Senior Member
                                    • Feb 2013
                                    • 91
                                    • USA

                                    #37
                                    Re: Sound and picture but no backlight

                                    All connection I mean main board and led plugs... Yes I have insulation...

                                    Comment

                                    • JCdes
                                      Senior Member
                                      • Feb 2013
                                      • 91
                                      • USA

                                      #38
                                      Re: Sound and picture but no backlight

                                      On my way back... I'll post measurements in about an hour..

                                      Comment

                                      • JCdes
                                        Senior Member
                                        • Feb 2013
                                        • 91
                                        • USA

                                        #39
                                        Re: Sound and picture but no backlight

                                        11.2 on leg 1
                                        4.6 on leg 8
                                        1.7 on leg 7
                                        6 on leg 6
                                        2,3,4,5 0v
                                        All cables connected
                                        Last edited by JCdes; 12-19-2020, 12:21 PM.

                                        Comment

                                        • JCdes
                                          Senior Member
                                          • Feb 2013
                                          • 91
                                          • USA

                                          #40
                                          Re: Sound and picture but no backlight

                                          Originally posted by Diah
                                          measure please the V on CON4 PL_ON pins when set on and STB
                                          BL-On 4.8
                                          Adjust 4.9

                                          Comment

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