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    Samsung TV - no backlight, except when mainboard disconnected

    Hi,

    I am troubleshooting a Samsung ue48h6400aw. When plugged normally, trying to turn it on leads to blinking power light 7 times and no backlight. If I press buttons I see the corresponding power light flashing (that it acknowledged the action).

    If I unplug the mainboard from the power board and plug in the TV, the backlight turns on.

    Does this mean it's 100% the mainboard and I should replace that? Or it could still be the power board?

    Would appreciate any input, thanks!
    -Gil

    #2
    Re: Samsung TV - no backlight, except when mainboard disconnected

    I've seen bad tcon boards that cause no video and no backlight in H model years. If the TV turns on on and off with no backlight and no video and backlights come on when forced, I would suspect the Tcon before the main board.

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      #3
      Re: Samsung TV - no backlight, except when mainboard disconnected

      Thanks for your reply! Is there some test I could perform to confirm it is the t-con?

      Comment


        #4
        Re: Samsung TV - no backlight, except when mainboard disconnected

        Originally posted by neilc6 View Post
        I've seen bad tcon boards that cause no video and no backlight in H model years. If the TV turns on on and off with no backlight and no video and backlights come on when forced, I would suspect the Tcon before the main board.
        Thanks for your reply! Is there some test I could perform to confirm it is the t-con?

        Sorry for double post.. I couldn't figure out how to delete my reply

        Comment


          #5
          Re: Samsung TV - no backlight, except when mainboard disconnected

          Forcing the backlights on confirms both your backlights and power supply are likely good. If the TV turns on and off, the main board is likely good.

          Second test is to power up the TV with only one side at a time connected between the Tcon board and panel. If one side is good, you have a panel fault on the bad side. If no side is good, tcon is still suspect.

          Comment


            #6
            Re: Samsung TV - no backlight, except when mainboard disconnected

            Originally posted by neilc6 View Post
            Forcing the backlights on confirms both your backlights and power supply are likely good. If the TV turns on and off, the main board is likely good.

            Second test is to power up the TV with only one side at a time connected between the Tcon board and panel. If one side is good, you have a panel fault on the bad side. If no side is good, tcon is still suspect.
            I did this (with the main board also connected I assumed) and if either side is connected, the backlight comes on (but still no display when turning on TV). When both sides are connected, no backlight comes on at all when plugging in.

            I didn't notice any difference in halves of the screen though with either side connected.

            I should order a Tcon then?

            Thanks for your help, I really appreciate it!

            Comment


              #7
              Re: Samsung TV - no backlight, except when mainboard disconnected

              Originally posted by neilc6 View Post
              Forcing the backlights on confirms both your backlights and power supply are likely good. If the TV turns on and off, the main board is likely good.

              Second test is to power up the TV with only one side at a time connected between the Tcon board and panel. If one side is good, you have a panel fault on the bad side. If no side is good, tcon is still suspect.
              New tcon arrived today and didn't fix the problem. Does this mean it has to be the mainboard?

              Comment


                #8
                Re: Samsung TV - no backlight, except when mainboard disconnected

                Hi, Did you solve the problem? I think i might have about the same problem now with my tv. The backlight only comes on if i have the mainboard disconnected.
                as soon as i connect it, no matter if i have one, none, or both sides on the Tcon
                connected it turns off immediately.

                Comment


                  #9
                  Re: Samsung TV - no backlight, except when mainboard disconnected

                  check that the tcon fuse is ok, should show continuity.
                  Last edited by nomoresonys; 10-27-2022, 10:54 AM.

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                    #10
                    Re: Samsung TV - no backlight, except when mainboard disconnected

                    try it with tcon unhooked from mainboard, see if theres any change.

                    Comment


                      #11
                      Re: Samsung TV - no backlight, except when mainboard disconnected

                      Originally posted by nomoresonys View Post
                      try it with tcon unhooked from mainboard, see if theres any change.
                      It does not make a difference. i have noticed that the Ps_on voltage cycles
                      between 0 and 3.3V (on for several seconds and off for a few) any thoughts about that?

                      Comment


                        #12
                        Re: Samsung TV - no backlight, except when mainboard disconnected

                        I think its a mainboard issue, maybe check the voltage regulators on mainboard.

                        Comment


                          #13
                          Re: Samsung TV - no backlight, except when mainboard disconnected

                          some testing there, some voltage regulators are fixed some are not, if not sure which you are dealing with, you can look up the data sheet of the component: https://www.youtube.com/watch?v=ocqnqmBxiqY

                          Comment


                            #14
                            Re: Samsung TV - no backlight, except when mainboard disconnected

                            These Samsung “H” series have a problem with the main board. Usually a diode goes bad and takes the ic next to it out also.

                            Probe diode on main board for shorts

                            Comment


                              #15
                              Re: Samsung TV - no backlight, except when mainboard disconnected

                              ^^+10, hell yeah, do that too.

                              Comment


                                #16
                                Re: Samsung TV - no backlight, except when mainboard disconnected

                                Thank you for the inputs.

                                I found something strange. A component marked with "AA5"
                                Can't find what that is..I also found a couple of shorted resistors around that component. I marked 2 of them in the picture (there are a few more).

                                How do you now what values those should have?
                                Attached Files

                                Comment


                                  #17
                                  Re: Samsung TV - no backlight, except when mainboard disconnected

                                  measure resistors in ohm mode, my meter reads most under 10 ohm resistors as short in continuity mode but they are not, if resistors are in parallel then the resistance will be half the marked value, instructable there for determining values: https://www.instructables.com/Readin...esistor-codes/

                                  Comment


                                    #18
                                    Re: Samsung TV - no backlight, except when mainboard disconnected

                                    i measured i ohm mode. In this case they are not in parallel (i know that formula), they are going to separate legs on that AA5 IC. They are so tiny that it seems like they don't have any numbers on them.

                                    Comment


                                      #19
                                      Re: Samsung TV - no backlight, except when mainboard disconnected

                                      not exactly sure but if all those other tiny resistors dont read short, then you might have found the problem or at least part of it, but how to find their value is a good question if not marked.

                                      Comment


                                        #20
                                        Re: Samsung TV - no backlight, except when mainboard disconnected

                                        Originally posted by Henke View Post
                                        Thank you for the inputs.

                                        I found something strange. A component marked with "AA5"
                                        Can't find what that is..I also found a couple of shorted resistors around that component. I marked 2 of them in the picture (there are a few more).

                                        How do you now what values those should have?
                                        resister never short. they open dead or their value increses.
                                        AA5 ic looks like eeprom 24cxx type.

                                        Comment

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