Samsung LN46B750 power issue

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  • dbruts
    Member
    • Nov 2013
    • 18
    • United States

    #1

    Samsung LN46B750 power issue

    There was a surge through the HDMI cable that fried the main assembly board resulting in a completely dead unit when plugged in. I ordered a replacement and installed. Now when powered, the standby light flashes quickly, but the screen does not turn on. When i unplug the power supply and the main board, the backlight turns on. I thought this might be a power issue so i also purchased power supply board. There are no bulging or cracked capacitors on either of the boards. After installing this, the standby light continues to flash very quickly. I have a voltmeter and feel comfortable testing. I do not have the ability to test the capacitors though. Any help would be greatly appreciated.

    I have tested the pins on the cable from the power supply to the main board. Results are:
    1 (POW ON/OFF) 4.37V
    2 (H_Sync) 0-4.99 switching
    3 (STB 5.3V)
    4 (GND) 5.17
    5 (GND) 5.17
    6 (GND) 5.17
    7 (13Vs) -7.59
    8 (13Vs) -7.59
    9 (GND) 5.15
    10 (GND) 5.20
    11 (GND) 5.20
    12 (GND) 5.20
    13 (5.3V) 0
    14 (5.3V) 0
    15 (5.3V) 0
    16 (5.3V) 0
    17 (GND) 5.19
    18 (GND) 5.19
    19 (13Vm) -7.58
    20 (GND) 5.20
    21 (13Vm) -7.58
    22 (13Vm) -7.57
    23 (INV ON/OFF) 0.06
    24 (NC) -0.03
    25 (E-PWM) -0.03
    26 (GND) 5.17
    27 (DET_SV) -0.03
    28 (GND) 5.17
    29 (GND) 5.15
    30 (GND) 5.17

    Other information:
    • When everything connected and plugged in, there is no lights on the ethernet plug in.
    • Red standby light flashes sold red for 4 seconds then 5 quick flashes and a one second red light then 12 quick flashes then repeat
    • I have read resetting the EEPROM may help, but have not found any schematics to identify where the EEPROM chip is on the main board (BN94-02585C)
    • When ordering an assembly board, I was sent an "alternate" part that is supposed to be interchangeable. when the part was plugged in, the tv powered on, but was unresponsive from remote control commands. I was able to see white noise, the sound worked, and i could change channels and volume. Input would not work and I was unable to reach any service menu (mute -> 1 -> 8 -> 2 -> Power)
    Last edited by dbruts; 12-06-2013, 09:47 PM. Reason: More info
  • budm
    Badcaps Legend
    • Feb 2010
    • 40746
    • USA

    #2
    Re: Samsung LN46B750 power issue

    "When i unplug the power supply and the main board, the backlight turns on." That is how you test to see if the power supply, backlights inveter circuits are good or not, in this case, it is good otherwise the backlights will not be on.
    1 (POW ON/OFF) 4.37V Main board is sending the correct Power supply on signal.
    23 (INV ON/OFF) 0.06. The main board is not sending out the backlights on signal, so this is bad.

    "28 (GND) 5.17
    29 (GND) 5.15
    30 (GND) 5.17"
    These cannot not be right. What do you use for ground ref. point?
    Where did you get the main board from? Right now it is not sending out the correct signals.
    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

    • dbruts
      Member
      • Nov 2013
      • 18
      • United States

      #3
      Re: Samsung LN46B750 power issue

      Originally posted by budm
      "
      23 (INV ON/OFF) 0.06. The main board is not sending out the backlights on signal, so this is bad.
      To test, i unplugged the cord from the power supply to the main board and tested the cable at the main board end. when the cord is unplugged, it appears there should be no power going to the main board which then connects to the T-CON board, speakers, and remote control receiver. Does the 0.06 reading mean there is a signal being sent, but because the main board does not send anything back, the main board is bad?
      Originally posted by budm
      "
      "28 (GND) 5.17
      29 (GND) 5.15
      30 (GND) 5.17"
      These cannot not be right. What do you use for ground ref. point?
      Where did you get the main board from? Right now it is not sending out the correct signals.
      I am unsure what you mean by ground ref. point. I am testing with pin 3 which is the (STB 5.3V) pin. I purchased the main board from HDTVPartstore. I was going to purchase from ShopJimmy (which everyone seems to recommend), but they were out of stock. Thank you again for your help and patience.

      I have also added a couple updates to the main post

      Comment

      • dbruts
        Member
        • Nov 2013
        • 18
        • United States

        #4
        Re: Samsung LN46B750 power issue

        I am also using a Voltmeter set at 20 (DC line over three dots) for all tests.

        Comment

        • dbruts
          Member
          • Nov 2013
          • 18
          • United States

          #5
          Re: Samsung LN46B750 power issue

          Should I be testing with the cable plugged in from the power supply to the main board?

          Comment

          • budm
            Badcaps Legend
            • Feb 2010
            • 40746
            • USA

            #6
            Re: Samsung LN46B750 power issue

            OK, let start with this test; disconnect the cable between the main board and the power supply board, if the backlights come on when you plug the power cord into the outlet, that means the power supply and inverter circuits are OK.
            Can we also get the good pictures of the back side of the TV so we can see how all the boards are connected?
            "When ordering an assembly board, I was sent an "alternate" part that is supposed to be interchangeable." This does not sound good.
            BTW: What is the power supply board P/N. BN44-XXXXX?
            Last edited by budm; 12-06-2013, 10:57 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

            • dbruts
              Member
              • Nov 2013
              • 18
              • United States

              #7
              Re: Samsung LN46B750 power issue






              If you need any other images let me know.

              http://imgur.com/8AhJHhQ
              http://imgur.com/mekoI5c
              http://imgur.com/8AhJHhQ
              http://imgur.com/qDtSXGg
              Last edited by dbruts; 12-06-2013, 11:06 PM. Reason: Images did not appear so including link

              Comment

              • dbruts
                Member
                • Nov 2013
                • 18
                • United States

                #8
                Re: Samsung LN46B750 power issue

                When i remove the cable between the main board and the power supply, the backlight does turn on.
                "When ordering an assembly board, I was sent an "alternate" part that is supposed to be interchangeable." This does not sound good.
                BTW: What is the power supply board P/N. BN44-XXXXX?
                I have a main board with part #BN94-02585C. I ordered from partstore and was shipped a replacement piece that they said was a "substitute" part.
                Attached Files

                Comment

                • dbruts
                  Member
                  • Nov 2013
                  • 18
                  • United States

                  #9
                  Re: Samsung LN46B750 power issue

                  Close up of main board. I also returned the main board that I received and purchased a board that matches.
                  Attached Files
                  Last edited by dbruts; 12-06-2013, 11:28 PM.

                  Comment

                  • budm
                    Badcaps Legend
                    • Feb 2010
                    • 40746
                    • USA

                    #10
                    Re: Samsung LN46B750 power issue

                    OK, your power supply board and the inverter circuit are OK, so your new board is not working, but since the TV was hit with the surge we are not 100% sure if something else is good or not.
                    What is the P/N of the power supply board so we can verify all the output voltages of the power supply. T-CON board will also need to be checked.
                    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

                    • dbruts
                      Member
                      • Nov 2013
                      • 18
                      • United States

                      #11
                      Re: Samsung LN46B750 power issue

                      P/N of power supply board is BN44-00266A
                      Attached Files

                      Comment

                      • dbruts
                        Member
                        • Nov 2013
                        • 18
                        • United States

                        #12
                        Re: Samsung LN46B750 power issue

                        I will have to reposition the tv in order to get at the T-CON board.

                        Comment

                        • budm
                          Badcaps Legend
                          • Feb 2010
                          • 40746
                          • USA

                          #13
                          Re: Samsung LN46B750 power issue

                          So right now you have the correct main board installed?
                          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

                          • dbruts
                            Member
                            • Nov 2013
                            • 18
                            • United States

                            #14
                            Re: Samsung LN46B750 power issue

                            Yes. It was the replacement with matching codes BN94-02585C

                            Comment

                            • dbruts
                              Member
                              • Nov 2013
                              • 18
                              • United States

                              #15
                              Re: Samsung LN46B750 power issue

                              T-CON board images
                              Attached Files

                              Comment

                              • budm
                                Badcaps Legend
                                • Feb 2010
                                • 40746
                                • USA

                                #16
                                Re: Samsung LN46B750 power issue

                                OK, right now we know that we do have 5.3VSTBY, now we need to verify that the power supply does have 5.3V and 13V at CN801 connector, still leave the plug off the CN801 to the main 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

                                • dbruts
                                  Member
                                  • Nov 2013
                                  • 18
                                  • United States

                                  #17
                                  Re: Samsung LN46B750 power issue

                                  Sorry I am a little confused. When I took the readings, I tested like the layout in the image. Is the other image a close up of the CN801 to be tested?
                                  Attached Files
                                  Last edited by dbruts; 12-07-2013, 12:20 AM.

                                  Comment

                                  • budm
                                    Badcaps Legend
                                    • Feb 2010
                                    • 40746
                                    • USA

                                    #18
                                    Re: Samsung LN46B750 power issue

                                    OK, you can test with the connector still attached to the power supply board cn801, or without the connector in place but more chance of probe slipping.
                                    The black probe of the meter will be connected to the metal chassis. then using the red probe to check each pin and report the readings.
                                    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

                                    • dbruts
                                      Member
                                      • Nov 2013
                                      • 18
                                      • United States

                                      #19
                                      Re: Samsung LN46B750 power issue

                                      Testing like image.

                                      1 (POW ON/OFF) .8
                                      2 (H_Sync) 0
                                      3 (STB 5.3V) 5.21
                                      4 (GND) 0
                                      5 (GND) 0
                                      6 (GND) 0
                                      7 (13Vs) 12.78
                                      8 (13Vs) 12.78
                                      9 (GND) 0
                                      10 (GND) 0
                                      11 (GND) 0
                                      12 (GND) 0
                                      13 (5.3V) 5.21
                                      14 (5.3V) 5.21
                                      15 (5.3V) 5.21
                                      16 (5.3V) 5.21
                                      17 (GND) 0
                                      18 (GND) 0
                                      19 (13Vm) 12.78
                                      20 (GND) 0
                                      21 (13Vm) 12.78
                                      22 (13Vm) 12.78
                                      23 (INV ON/OFF) 5.12
                                      24 (NC) 0
                                      25 (E-PWM) 4.68
                                      26 (GND) 0
                                      27 (DET_SV) 5.16
                                      28 (GND) 0
                                      29 (GND) 0
                                      30 (GND) 0
                                      Attached Files

                                      Comment

                                      • budm
                                        Badcaps Legend
                                        • Feb 2010
                                        • 40746
                                        • USA

                                        #20
                                        Re: Samsung LN46B750 power issue

                                        Good, the power supply is OK.
                                        Put connectors back in place, but remove the cables between the T-CON and the main board to see if the TV will power up with different LED blinking code.
                                        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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