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TCL 65S517 No Backlight, Picture and Sound OK

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    TCL 65S517 No Backlight, Picture and Sound OK

    Hi All, I have a TCL 65S517 Roku TV it was brought to me with the following problems. It will turn on, stand by light comes on, tv powers on (sounds and picture are present) but has NO BACKLIGHT.

    I am a novice at this but I am learning a little more each time and I have combed through other threads and solutions and tried to narrow it down. Suspecting a T-Conn board or an LED Strip short, here is what I have done.

    I Power cycled and reset the tv. no change. I opened it up and checked AC power (good) Checked voltage to the main board pins while on.
    Top to bottom on that gray ribbon top right of main board I am getting

    3.26V
    0V
    0V
    0V
    12V
    12V
    12V

    I reseated all the cables and tightened ground screws. I checked some of the pins on the Tconn ribbon cable and I am getting 12v on a few of them but I dont have any reference of what should read what. I checked the onboard fuse right below the ribbon cable on the Tconn and I am getting 12v on both sides of it. I unseated left side ribbon on Tconn and powered on to see if it would make a change in the screen. It did not, nor did the right side.

    I checked the red and white and black and brown cable pins coming from the bottom left PS board (guessing by where they are running these are the LED supply lines) I have 0v on all of those while powered on.

    So that is where I am at I tried to rule out as much as possible before I posted here. Any help is greatly appreciated. Pics will follow.

    #2
    Re: TCL 65S517 No Backlight, Picture and Sound OK

    Pics
    Attached Files

    Comment


      #3
      Re: TCL 65S517 No Backlight, Picture and Sound OK

      There are 14 pins on that red connector,
      Your report on the pins does not help since you do not provide the pin number and also you should look at the bottom side of that power supply board to see if they print the pin names on the bottom side of the 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


        #4
        Re: TCL 65S517 No Backlight, Picture and Sound OK

        Sorry, I flipped the Main Board when I was first testing to look for pin outs, I hadn't noticed this cord had a double pin set. my mistake. here are voltages and a picture of the bottom of the PS for reference.

        P-Dim=3.26v BL_ON=3.26v
        GND= -34mv P_ON = 2.34v
        NC=0 A_DIM=12mv
        GND=-35mv GND= -35mv
        12V = 12v 12V = 12v
        12V= 12v 12V= 0v
        12V= 12v 3D_En= 0v

        Comment


          #5
          Re: TCL 65S517 No Backlight, Picture and Sound OK

          Pics
          Attached Files

          Comment


            #6
            Re: TCL 65S517 No Backlight, Picture and Sound OK

            Lets see good clear straight shots pictures of the whole bottom side of the power supply board so we can see if the LED connector has pin labels or not.
            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


              #7
              Re: TCL 65S517 No Backlight, Picture and Sound OK

              Here are the front side and back side photos
              Attached Files

              Comment


                #8
                Re: TCL 65S517 No Backlight, Picture and Sound OK

                I am not getting any voltage over a few mv on any of the LED backlight plug pins. Same with the LED Backlight plug unplugged. Should I try to test for continuity across the LED strip -/+?

                Comment


                  #9
                  Re: TCL 65S517 No Backlight, Picture and Sound OK

                  Originally posted by rebelkustoms View Post
                  I am not getting any voltage over a few mv on any of the LED backlight plug pins. Same with the LED Backlight plug unplugged. Should I try to test for continuity across the LED strip -/+?
                  while the set OFF remove the LED socket from PSU. and measure with Ohm the 2 SMT resistors R581 R580

                  Comment


                    #10
                    Re: TCL 65S517 No Backlight, Picture and Sound OK

                    Are you getting about 380 ~ 400 VDC measured between the two legs of the main filter caps CE1, CE2?
                    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


                      #11
                      Re: TCL 65S517 No Backlight, Picture and Sound OK

                      Originally posted by Diah View Post
                      while the set OFF remove the LED socket from PSU. and measure with Ohm the 2 SMT resistors R581 R580
                      So I am thinking you mean R681 and R680 (the ones right next to the LED Pinouts) they are both reading 0.1 ohm or 0.2 ohm.

                      Comment


                        #12
                        Re: TCL 65S517 No Backlight, Picture and Sound OK

                        Originally posted by budm View Post
                        Are you getting about 380 ~ 400 VDC measured between the two legs of the main filter caps CE1, CE2?
                        HI Budm, I am getting 396 VDC on both of those caps.

                        Comment


                          #13
                          Re: TCL 65S517 No Backlight, Picture and Sound OK

                          Originally posted by rebelkustoms View Post
                          Sorry, I flipped the Main Board when I was first testing to look for pin outs, I hadn't noticed this cord had a double pin set. my mistake. here are voltages and a picture of the bottom of the PS for reference.

                          P-Dim=3.26v BL_ON=3.26v
                          GND= -34mv P_ON = 2.34v
                          NC=0 A_DIM=12mv
                          GND=-35mv GND= -35mv
                          12V = 12v 12V = 12v
                          12V= 12v 12V= 0v
                          12V= 12v 3D_En= 0v
                          you might want to try trace back the one pin that is not showing 12v as that seems rather strange.

                          Comment


                            #14
                            Re: TCL 65S517 No Backlight, Picture and Sound OK

                            Originally posted by budwich View Post
                            you might want to try trace back the one pin that is not showing 12v as that seems rather strange.

                            Here are corrected voltages, I checked again twice, i must have gotten a pin off towards the bottom. That pin did have 12v, also all those 12v are on the same trace.

                            P-Dim=3.26v BL_ON=3.26v
                            GND= 0v P_ON = 2.34v
                            NC=0 A_DIM=0v
                            GND= -35mv GND= -35mv
                            12V = 12v 12V = 12v
                            12V= 12v 12V= 12v
                            12V= 12v 3D_En= 0v

                            Comment


                              #15
                              Re: TCL 65S517 No Backlight, Picture and Sound OK

                              What is the P/N of the LED driver IC U601?
                              Also check that rectangular grey cap C620, it looks like one of the leg did not poke through to the bottoms side of the board.
                              Last edited by budm; 10-08-2020, 09:50 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


                                #16
                                Re: TCL 65S517 No Backlight, Picture and Sound OK

                                I would first test voltage on the power supply board LED connector pins. disconnect the connection I circled, if you are getting voltage while they are not connected to the board then its going to be bad LED's and would require that you open the display assembly to test. if you don't get any voltage when powering on then the fault is in the Power Supply board.

                                My Company works repairing TCL tv's under warranty so i have gotten lots of experience with these type of issues. my best guess would be that your LED strips are the problem.

                                Best of luck and be careful if you end up opening the screen assembly. the screen is very thin and fragile. especially near the bottom flex cables.
                                Attached Files

                                Comment


                                  #17
                                  Re: TCL 65S517 No Backlight, Picture and Sound OK

                                  Originally posted by rebelkustoms View Post
                                  So I am thinking you mean R681 and R680 (the ones right next to the LED Pinouts) they are both reading 0.1 ohm or 0.2 ohm.
                                  yes you are correct R680/R681..
                                  Ov reading at BL socket are 100% open circuit / crack at power boards connection or at printing lines so start with re solder TS3, and also the driver circuit of it at Hot area.
                                  just be sure if you working on Hot area the GND should be taken from same area not from GOLD Area or TV chassis.

                                  Comment


                                    #18
                                    Re: TCL 65S517 No Backlight, Picture and Sound OK

                                    Originally posted by budm View Post
                                    What is the P/N of the LED driver IC U601?
                                    Also check that rectangular grey cap C620, it looks like one of the leg did not poke through to the bottoms side of the board.
                                    Here is what is on the IC from what I can read

                                    OZ9976AGN
                                    CK765K. 1N
                                    1839 A1

                                    Also that was just a bad picture angle on the Capacitor 620, Both legs are through the board and the joints look good.
                                    Attached Files

                                    Comment


                                      #19
                                      Re: TCL 65S517 No Backlight, Picture and Sound OK

                                      Originally posted by Diah View Post
                                      yes you are correct R680/R681..
                                      Ov reading at BL socket are 100% open circuit / crack at power boards connection or at printing lines so start with re solder TS3, and also the driver circuit of it at Hot area.
                                      just be sure if you working on Hot area the GND should be taken from same area not from GOLD Area or TV chassis.

                                      I am about to resolder TS3, I included a pic there is a resistor on the hot side R649 that has some weird coloring around it. Not sure if it is flux or a light corrosion but it looks odd. Thoughts?
                                      Also when you say resolder the driver circuit what are are we talking about on the hot side?
                                      Attached Files

                                      Comment


                                        #20
                                        Re: TCL 65S517 No Backlight, Picture and Sound OK

                                        you can do measure on QW3 /4 if there voltage.. be sure only to use HOT area GND probe

                                        Comment

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