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Samsung UN55H8000AFXZA No Backlight, LED Strips OK

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    Samsung UN55H8000AFXZA No Backlight, LED Strips OK

    TV show image with the help of a flashlight but no backlight. I can confirm that all led are OK.

    CNL802A
    TV OFF
    0v

    TV ON
    Pin 11 and 12: 16v
    All others: 0v

    CNL802B
    TV OFF
    0V

    TV ON
    Pin 9 and 10: 16v
    All others: 0v
    Attached Files

    #2
    Re: Samsung UN55H8000AFXZA No Backlight, LED Strips OK

    1) Do you get backlights if the cable between the power supply board and the main board is not connected?
    2) What did you use for ground for the meter when you measure 16V on the + pins?
    3) What are the Voltages of each pin of the connector of the power supply that goes to the main board? Notes: measurement is done with all cables in place and you need to put down the pin name for each pin so we can easily see what you have on each pin..
    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


      #3
      Re: Samsung UN55H8000AFXZA No Backlight, LED Strips OK

      1- Not backlight with the cable disconnected.
      2- TV Chassis
      3-

      2 SD: 0.3v
      4 STT: 0.2v
      6 DATA: 0.1v
      8 VSYNC_IN: 3.2v
      10,12 LD: 3.2v
      14 BLUONOFF: 4.97v
      16 PWRONOFF: 3.3v
      18,20 GND:
      22 Vamp: 12.68v
      24 GND:

      1 LD: 3.28v
      3 CLK: 1.69v
      5 CONT: 0.07v
      7 GND:
      9,11,13,15,17 A13V: 12.68v
      19 GND:
      21,23 V AMP: 12.68v

      Comment


        #4
        Re: Samsung UN55H8000AFXZA No Backlight, LED Strips OK

        Monitor the voltage between chassis ground and J816 when the tv is first turned on, What is the voltage?

        Comment


          #5
          Re: Samsung UN55H8000AFXZA No Backlight, LED Strips OK

          J816: 16.2v

          Comment


            #6
            Re: Samsung UN55H8000AFXZA No Backlight, LED Strips OK

            J876, J864: 16.2v

            Comment


              #7
              Re: Samsung UN55H8000AFXZA No Backlight, LED Strips OK

              That voltage is low, What is the voltage across one of the main filter caps, CP811S or CP812S ? If this voltage is about 385vdc then the pfc circuit is working ok.
              Last edited by R_J; 03-06-2020, 08:17 PM.

              Comment


                #8
                Re: Samsung UN55H8000AFXZA No Backlight, LED Strips OK

                CP811S: 387v remember I can see image in the dark screen

                Comment


                  #9
                  Re: Samsung UN55H8000AFXZA No Backlight, LED Strips OK

                  What is the power supply board P/N? BN44-?????
                  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


                    #10
                    Re: Samsung UN55H8000AFXZA No Backlight, LED Strips OK

                    Originally posted by alfredomfr1 View Post
                    CP811S: 387v remember I can see image in the dark screen
                    I know that, but if the pfc was not working properly the led boost circuit would not be getting full voltage.
                    It seems like the problem is that the Led voltage is not being boosted to 34v. This could be caused by a bad led in one of the strings causing the led controller to shut down. 1 bad led in any of the 16 strings could cause the issue.

                    Comment


                      #11
                      Re: Samsung UN55H8000AFXZA No Backlight, LED Strips OK

                      Bn44-00740a

                      Comment


                        #12
                        Re: Samsung UN55H8000AFXZA No Backlight, LED Strips OK

                        R_J I already open the screen and tested all the LED

                        Comment


                          #13
                          Re: Samsung UN55H8000AFXZA No Backlight, LED Strips OK

                          And how did you test all the led's?
                          You tested all the led's in all 16 seperate strings?

                          Comment


                            #14
                            Re: Samsung UN55H8000AFXZA No Backlight, LED Strips OK

                            With my led tester, every string same voltage: 30v

                            Comment


                              #15
                              Re: Samsung UN55H8000AFXZA No Backlight, LED Strips OK

                              Check the fets Q9951 & Q9952, and the gate drive resistors, this is the led boost circuit, what is the number on the controller IC995?
                              Last edited by R_J; 03-06-2020, 08:53 PM.

                              Comment


                                #16
                                Re: Samsung UN55H8000AFXZA No Backlight, LED Strips OK

                                I will check the FETs tomorrow, thanks to budm and R_J for your help.

                                Comment


                                  #17
                                  Re: Samsung UN55H8000AFXZA No Backlight, LED Strips OK

                                  not sure what power supply this is in this video but maybe worth a watch
                                  https://www.youtube.com/watch?v=2BCdAz0xE70

                                  Comment


                                    #18
                                    Re: Samsung UN55H8000AFXZA No Backlight, LED Strips OK

                                    Q9951 and Q9952 OK, R9988 and R9958 OK
                                    IC 9951: NCP1034DG
                                    10k R9972 and R9973 are OK when tested out but R9973 only read 68 ohm in the circuit. All components on the picture are OK
                                    Attached Files

                                    Comment


                                      #19
                                      Re: Samsung UN55H8000AFXZA No Backlight, LED Strips OK

                                      https://cdn.badcaps-static.com/pdfs/...2b3c1b8a2d.pdf
                                      Start checking to see if the IC has the VCC for it to run.
                                      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


                                        #20
                                        Re: Samsung UN55H8000AFXZA No Backlight, LED Strips OK

                                        VCC: 11.92v
                                        FET Q9951 Gate: 76v
                                        FET Q9952 Gate: 16.7v

                                        Comment

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