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Panasonic TX-55CX400B backlights flashing on and off

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    Panasonic TX-55CX400B backlights flashing on and off

    Hi peeps, have a Panasonic TX-55CX400B here, guy I got it from said he tried to turn it on other day, and no backlights.

    When I received it last night, I plugged it in, and it came straight on and appeared to be working fine, so knowing this would only be temporary, I left it running for a good few hours, and they eventually went off. I tried turning it off and back on again, and this time the backlights started flashing at a steady continuous pace. So I turned it off and left it overnight as it was getting late.
    This morning when I turned it on, same problem, backlights flashing, so I stripped it down and tested the LEDs and 1 was dead. So changed the dead LED, thinking that would solve the problem, but it hasnt.
    So now even with the bad LED replaced, turn it on, and backlights flash in a constant uniform manor, only difference now is, they are all illuminated. Also you can hear a noise from the powerboard, that runs in time with backlights flashing. However if I unplug the backlights from the powerboard, and switch on, this doesnt happen, it comes on and holds steady.

    Ive included a pic of underside of PCB, cant see any dry joints etc, but I have included a close up of a section of the board that caught my eye, just would like peoples opinions on that section please?

    Anyone came accross this before? Or could point me in the direction of where to start with diagnostics now please?
    Attached Files
    Last edited by Bloopeta; 12-04-2019, 01:59 AM.

    #2
    Re: Panasonic TX-55CX400B backlights flashing on and off

    The joints in the R551 area look a little funky??

    Comment


      #3
      Re: Panasonic TX-55CX400B backlights flashing on and off

      That cap by C514 looks a little suspicious.

      Comment


        #4
        Re: Panasonic TX-55CX400B backlights flashing on and off

        Check all your diodes.

        Comment


          #5
          Re: Panasonic TX-55CX400B backlights flashing on and off

          Do you have backlight tester?
          If you do, what is the Vf of each LED string?
          BTW, the bad LED, was it shorted or open?
          Last edited by budm; 12-04-2019, 11:23 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


            #6
            Re: Panasonic TX-55CX400B backlights flashing on and off

            Originally posted by budm View Post
            Do you have backlight tester?
            If you do, what is the Vf of each LED string?
            BTW, the bad LED, was it shorted or open?
            Ive ordered one a couple of weeks ago, bit still hasnt arrived yet

            And the bad LED was shorted
            Last edited by Bloopeta; 12-04-2019, 12:55 PM.

            Comment


              #7
              Re: Panasonic TX-55CX400B backlights flashing on and off

              Originally posted by nomoresonys View Post
              Check all your diodes.
              Ive tested all diodes with DMM, and this one D516 is raising suspicion, on diode test mode its reading 020 both ways :/ and beeping both ways.
              Attached Files

              Comment


                #8
                Re: Panasonic TX-55CX400B backlights flashing on and off

                Cane we see the bottom side of the board so we can see how that diode is connected in the circuit.
                Try lifting one leg off the board and re-test the diode.
                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


                  #9
                  Re: Panasonic TX-55CX400B backlights flashing on and off

                  Originally posted by budm View Post
                  Cane we see the bottom side of the board so we can see how that diode is connected in the circuit.
                  Try lifting one leg off the board and re-test the diode.
                  Here are the pics, ill lift a leg and retest and report back
                  Attached Files

                  Comment


                    #10
                    Re: Panasonic TX-55CX400B backlights flashing on and off

                    That diode is part of RCD (Resistor/Capacitor/Diode) Snubber network.
                    The solder joint on the leg of the cap that is connected to the Cathode of that diode D516 has ring around the joint, that should be re-soldered, look at other solder joints as well for that kind ring forming on component legs.
                    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: Panasonic TX-55CX400B backlights flashing on and off

                      Originally posted by budm View Post
                      That diode is part of RCD (Resistor/Capacitor/Diode) Snubber network.
                      The solder joint on the leg of the cap that is connected to the Cathode of that diode D516 has ring around the joint, that should be re-soldered, look at other solder joints as well for that kind ring forming on component legs.
                      I have lifted 1 leg of said diode, and getting the same reading as before, 020 and beeping both ways. So that will need replacing?

                      Comment


                        #12
                        Re: Panasonic TX-55CX400B backlights flashing on and off

                        What are the numbers printed on it?
                        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


                          #13
                          Re: Panasonic TX-55CX400B backlights flashing on and off

                          Originally posted by budm View Post
                          What are the numbers printed on it?
                          HER207

                          I have replaced it, resoldered the area you pointes out, and went over board and touch up any points that looked remotely like needed it, and hey presto, we have functioning backlights! Gonna leave it now as its 23.27pm here, and ill get it all resembled in the moring.

                          Comment


                            #14
                            Re: Panasonic TX-55CX400B backlights flashing on and off

                            Backlights working but sometimes the backlight will go off
                            17ips20 low voltages across most caps
                            Led voltages upon turning on the tv will jump to 155 volts but does not drop
                            Led - 10v led + 155v led - 10v led + 155v
                            Any help please
                            Last edited by sordids999; 04-25-2020, 12:15 PM.

                            Comment


                              #15
                              Re: Panasonic TX-55CX400B backlights flashing on and off

                              Pictures of the psu
                              Attached Files

                              Comment


                                #16
                                Re: Panasonic TX-55CX400B backlights flashing on and off

                                Sorry hopefully better pictures
                                Attached Files

                                Comment


                                  #17
                                  Re: Panasonic TX-55CX400B backlights flashing on and off

                                  Possibly an intermittent LED in the backlight. Did you try turning down the backlight level? Not sure if that model has local dimming as well.

                                  Comment


                                    #18
                                    Re: Panasonic TX-55CX400B backlights flashing on and off

                                    The strange part is if I swap the 17ips20 which as you can see in the picture has taken alot of heat in the top right with another 17ips20 but slightly different I'm now getting a dark patch in the middle of the screen so its possibly pointing to a bad led inside the screen
                                    It's a shame because I cant find any new sets of these leds anywhere

                                    Comment


                                      #19
                                      Re: Panasonic TX-55CX400B backlights flashing on and off

                                      Hi guys sorry jump on this thread but it's the only one with my TV
                                      (Tx-55cx400b)
                                      I'm waiting for a few bits to arrive to test properly, the screen was blank so I've done the strip down and checked and I have 3leds out (fingers crossed that is the only fault)
                                      But whilst I'm waiting for items to arrive I've just remembered that some of the spacers/risers/standoffs where brittle and broke so I'm now looking for those, but what the 🤬 are they called🤔 (see pic) please help me.....
                                      Attached Files

                                      Comment


                                        #20
                                        Re: Panasonic TX-55CX400B backlights flashing on and off

                                        Where have they broken ? If its just the attaching lugs i just use dab of hot glue for sticking them down.

                                        Comment

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