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    Samsung UN50F6300AF No Backlights

    I was given this 50" Samsung to fix by a friend. It has a standby led which is on when plugging set in. After powering up by manual switch, led blinks for a while then shuts off. Power supply shuts down shortly thereafter. There is never any indication of backlights. If I repeat this process, I can see an image using the flashlight method before the unit shuts down. I am pretty sure it is the backlight leds. I removed the back, disconnected the main cable from the power supply and see no BL activity. Normally at this point, I would set off on disassembling the display and testing the strings with a tester. But, I would like to learn of an approach to see what is going on in there before doing that. I am sure it can be done and I see a legend next to the backlight connector which is trying to tell me something. Would someone please teach me what I can do using this connector? I feel voltages with the cable connected and disconnected should tell a story and also I think maybe a tester could be applied to individual strings at that connector. I might be able to disassemble the display and trace everything back and figure out what I am seeing, but I would like another approach. Thanks.
    Attached Files

    #2
    Re: Samsung UN50F6300AF No Backlights

    Measure the DCV on the back light connector. It should ramp up and then back down. If that isn't happening, disconnect the back lights from the PSU and check again. IF you still haven't gotten anything out of the LED connector, there is something wrong with the PSU.

    Comment


      #3
      Re: Samsung UN50F6300AF No Backlights

      What's the markings on this power supply board? What do the labels say? This would help us ID the components on the power board and how the LED circuit is.

      Looking on shopjimmy.com --> Is this BN44-00612B what your power board looks like? https://www.shopjimmy.com/samsung-bn...upply-unit.htm

      If that is it, the output on Channel 1 is 219V@245mA; Channel 2 is 274V @245mA.

      1) With the TV off, put a probe across "1+" to chassis ground. Turn on the TV. Observe if the DMM increases at all. If not, then there may be a short to GND on the LED strips themselves. If the voltage rises to 219V or higher, the LED strip is likely open somewhere (one or more blown LEDs).

      2) Repeat with 2+, 3+, 4+ to chassis GND.

      3) With the TV off, disconnect the LED strip from the power board. put a probe across "1+" to chassis ground. Turn on the TV. Just like before, observe if the DMM increases at all. If it does, the LED strip is at fault.

      4) Repeat with 2+, 3+, 4+ to chassis GND.
      -Thomas
      I'm a hardware engineer focused on networking equipment for my day job. I void warranties and fix consumer electronics for fun.

      Comment


        #4
        Re: Samsung UN50F6300AF No Backlights

        Thanks for the replies. I will get some pictures of the entire board, the answers to your questions and the results of your tests.

        Comment


          #5
          Re: Samsung UN50F6300AF No Backlights

          If you search your power supply part number, BN44-00621B, RJ has posted a schematic for a similar board with the same LED connector. Looks like there are 4 strings 4-/4+,3-/3+,2-/2+,1-/1+. 1&2 and 3&4 are connected in series on the connector and powered as two separate circuits. You can put your LED tester across the 4 and compare voltages. Search the LED strips for your model and multiply the number of LEDS x 2.7V for expected voltage.
          Last edited by neilc6; 03-28-2020, 02:06 PM.

          Comment


            #6
            Re: Samsung UN50F6300AF No Backlights

            Hello. My PSU is BN44-00612B and is the Shop-Jimmy board. I have included photos of my board and neilc6 (RJs) schematic.

            Per CapLeaker and noth82's post, I checked the voltages on 1+, 2+, 3+ and 4+ as shown below:

            OFF with LEDs connected
            1+ near 0 VDC
            2+ near 0 VDC
            3+ near 0 VDC
            4+ near 0 VDC

            ON with LEDs connected
            1+ 408 VDC
            2+ .3 VDC
            3+ 440 VDC
            4+ 440 VDC

            OFF with LEDs disconnected
            1+ near 0 VDC
            2+ near 0 VDC
            3+ near 0 VDC
            4+ near 0 VDC

            ON with LEDs disconnected
            1+ near 0 VDC
            2+ near 0 VDC
            3+ 440 VDC
            4+ 440 VDC

            I tried a few times and hope this is accurate and tells you something.

            Neilc6 - Thanks for the location of the schematic. I didn't get your post till I got to work and will run your tests also when I get back to the TV.
            Attached Files

            Comment


              #7
              Re: Samsung UN50F6300AF No Backlights

              Thanks.

              I think you have a open LED in the first string - you see 408V going into CH1+, but nothing on CH2+.

              Do you have an LED tester? If you do, you can confirm the issue is between CH1+ and CH1-.
              Last edited by ngth82; 03-28-2020, 07:48 PM.
              -Thomas
              I'm a hardware engineer focused on networking equipment for my day job. I void warranties and fix consumer electronics for fun.

              Comment


                #8
                Re: Samsung UN50F6300AF No Backlights

                Thanks ngth82. I do have an led tester and will try that when I get home. This is currently a gray area for me. If there is an open led on string 1 and string 2 is in series with string 1, will the leds before the open one light up and nothing thereafter? And what would you expect if you had a shorted led? Would the rest of the string(s) light up except the shorted led? In the past when I have the display open and test the strips, I guess I haven't paid much attention to what actually happens. I guess I am just overjoyed to find a bad one after all that work! And when I do get all the strings working, what voltages should there be at 1+, 2+, 3+ and 4+ with the power on and the leds connected and disconnected? And how do you know what voltage should be present? The legend by the connector says open .245 VDC and short .22V. What does that mean? This is all excellent information for me and I appreciate your help. I was always the one in class who asked all the stupid questions.

                Thanks.

                Comment


                  #9
                  Re: Samsung UN50F6300AF No Backlights

                  The connector has four strings 1+/-, 2+/-, 3+/- and 4+/-... on the power board, 1+/- and 2+/- are combined together as Channel 1... then 3+/- and 4+/- combined together as Channel 2. Look at page 3 of the schematics "DRIVER_POWER_1_A" and "DRIVER_POWER_1_B"

                  The current thought is that the LED strips that are fed in to 1+/- has an open (so it won't light up when tested... and that the LED strips that are fed into 2+/- works (should light up when tested).


                  The strips connected to 3+/- and 4+/- should also work (test to make sure).


                  Look at the PCB markings on the supply board under "output rating" -- It says "CH1 219V @ 245mA" "CH2 274V @ 245mA"

                  There are likely more LEDs on CH2 than CH1.

                  Strip 1+/- and 2+/- should each see no more than ~110V each when working
                  Strip 3+/- and 4+/- should each see no more than ~137V each when working.
                  -Thomas
                  I'm a hardware engineer focused on networking equipment for my day job. I void warranties and fix consumer electronics for fun.

                  Comment


                    #10
                    Re: Samsung UN50F6300AF No Backlights

                    Are you sure you count the pins correctly?
                    You also did not report any (-) pins.
                    Your reports do not look right:
                    ON with LEDs connected
                    1+ 408 VDC
                    2+ .3 VDC
                    3+ 440 VDC
                    4+ 440 VDC

                    ON with LEDs disconnected
                    1+ near 0 VDC driven by LED power supply A so it cannot be 0V.
                    2+ near 0 VDC
                    3+ 440 VDC
                    4+ 440 VDC this not right either.
                    According to the schematic, the LED connector pin out:
                    LED strings 1 and 2 are connected in series to form one large string driven by LED power supply A
                    Pin 12 (1+ Anode of string #1) is connected to the LED power supply A output.
                    Pin 11 (1- which is Cathode of string #1) is connected to Pin 10 (2+ which is the Anode of string #2).
                    Pin 9 (2- which is the Cathode of string #2) is connected to return circuit for LED power supply A.

                    LED strings 3 and 4 are connected in series to form one large string driven by LED power supply B
                    Pin 6 (3+ Anode of string #3) is connected to the LED power supply B output.
                    Pin 5 (3- which is Cathode of string #3) is connected to Pin 4 (4+ which is the Anode of string #4).
                    Pin 3 (4- which is the Cathode of string #4) is connected to return circuit for LED power supply B.
                    Last edited by budm; 03-28-2020, 08:58 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


                      #11
                      Re: Samsung UN50F6300AF No Backlights

                      Hello budm. I will recheck the numbers and also add the - pins. I have another question, but I will research a bit and run it by you later. Thanks.

                      Comment


                        #12
                        Re: Samsung UN50F6300AF No Backlights

                        I am totally confused. I understand why budm has problems with my values, because now understanding a bit more, I do too. But the problem remains as I checked them over and over and I am still getting the exact same thing. I am getting 440V on 3+ and 4+ with LEDs connected or disconnected which in my understanding is nearly impossible. Also with the cable to LEDs disconnected and probing the empty connector pins on the PS board, I get 2.4 ohms between pins 6 and 4 which are 3+ and 4+ which again can't be possible. Unless, the problem is not the LEDs but the PS or both.

                        I didn't get around to testing the back lights from the PS connector. But I bet at least some of them will work.

                        Maybe tomorrow things might be clearer and I can figure out what I am doing wrong.

                        Comment


                          #13
                          Re: Samsung UN50F6300AF No Backlights

                          Are you sure you count the pins correctly?
                          Pictures provided by SHOPJIMMY.
                          What is the resistance between Pin 4 (4 +) and Pin 5 (3-)?
                          Your meter probes resistance is 2.4 Ohms?
                          Attached Files
                          Last edited by budm; 03-29-2020, 11:35 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


                            #14
                            Re: Samsung UN50F6300AF No Backlights

                            OK, from the back of the board as shown, resistance between pins 4 and 5 is 0 ohms. From the back also, the resistance between pins 4 and 6 is 2.4 ohms. This is with nothing connected to the board. Note: my board and SJ photo are not the same as far as traces and components.

                            Comment


                              #15
                              Re: Samsung UN50F6300AF No Backlights

                              Originally posted by MEB View Post
                              OK, from the back of the board as shown, resistance between pins 4 and 5 is 0 ohms. From the back also, the resistance between pins 4 and 6 is 2.4 ohms. This is with nothing connected to the board. Note: my board and SJ photo are not the same as far as traces and components.
                              Huh? A 612b is a 612b. Its just that the SJ's picture is 180 degrees the other way, that's all. I don't see any other components.

                              Comment


                                #16
                                Re: Samsung UN50F6300AF No Backlights

                                In post #6, OP confirmed the board is a BN44-00612B. Can you confirm this is what your board looks like? https://www.shopjimmy.com/samsung-bn...pply-unit.htm#

                                Budm -
                                Where did you get the photo from post #13? It looks different than the OP board from SJ.
                                -Thomas
                                I'm a hardware engineer focused on networking equipment for my day job. I void warranties and fix consumer electronics for fun.

                                Comment


                                  #17
                                  Re: Samsung UN50F6300AF No Backlights

                                  So much confusion in this thread. If you have a tester, put it across the 4 pairs of wires going to the strips and compare the voltages. You will know for sure if you have an open string or not.

                                  Comment


                                    #18
                                    Re: Samsung UN50F6300AF No Backlights

                                    Here are the 2 photos I am comparing. I can see the connector pin out is the same but little else. Maybe budm was just trying to show me the connector and not necessarily the surrounding board.
                                    Attached Files

                                    Comment


                                      #19
                                      Re: Samsung UN50F6300AF No Backlights

                                      Originally posted by neilc6 View Post
                                      so much confusion in this thread. If you have a tester, put it across the 4 pairs of wires going to the strips and compare the voltages. You will know for sure if you have an open string or not.
                                      +1
                                      -Thomas
                                      I'm a hardware engineer focused on networking equipment for my day job. I void warranties and fix consumer electronics for fun.

                                      Comment


                                        #20
                                        Re: Samsung UN50F6300AF No Backlights

                                        Originally posted by ngth82 View Post
                                        In post #6, OP confirmed the board is a BN44-00612B. Can you confirm this is what your board looks like? https://www.shopjimmy.com/samsung-bn...pply-unit.htm#

                                        Budm -
                                        Where did you get the photo from post #13? It looks different than the OP board from SJ.
                                        OK, I see where I screw up reading post #6, the board is 612b, the schematic is for 645A, so the picture I sue for ref. is for 645A.
                                        Now I have to look at 612B board pictures instead.
                                        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

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