Sharp LC-55N620CU PSU 192020 help ID'ing a transistor

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  • DXseekerMO
    Badcaps Legend
    • Feb 2018
    • 1119
    • US

    #1

    Sharp LC-55N620CU PSU 192020 help ID'ing a transistor

    I'm working on the stand-by portion of a HiSense/Sharp power supply #192020. I found a transistor blown apart to the point I can only read a couple numbers. Can anyone help me ID this?
    Attached Files
    Last edited by DXseekerMO; 03-01-2019, 03:11 PM.
    They call me......."threadkiller"
  • linksys1127
    Senior Member
    • Sep 2016
    • 121
    • United States

    #2
    Re: Sharp LC-55N620CU PSU 192020 help ID'ing a transistor

    I happen to have one of these on hand. GB1 is the marking. Here's the picture.
    Attached Files

    Comment

    • DXseekerMO
      Badcaps Legend
      • Feb 2018
      • 1119
      • US

      #3
      Re: Sharp LC-55N620CU PSU 192020 help ID'ing a transistor

      Originally posted by linksys1127
      I happen to have one of these on hand. GB1 is the marking. Here's the picture.
      Shout out to linksys1127 and Hernando MS! Thank you for posting that, super stoked up you had that board!

      The placement of this and the other transistor in the circuit makes me wonder if the over voltage event originated on the main board?

      Thank you, I appreciate it!
      They call me......."threadkiller"

      Comment

      • linksys1127
        Senior Member
        • Sep 2016
        • 121
        • United States

        #4
        Re: Sharp LC-55N620CU PSU 192020 help ID'ing a transistor

        Glad I could give back! Good luck with your repair!

        Comment

        • budm
          Badcaps Legend
          • Feb 2010
          • 40746
          • USA

          #5
          Re: Sharp LC-55N620CU PSU 192020 help ID'ing a transistor

          https://www.shopjimmy.com/sharp-1920...led-board.htm#

          It is on the cold side, that section looks to be something to do with driving those two Opto N881, 891.
          Is it tested bad?
          Are you not getting the 12V and 18V standby Voltages?
          Last edited by budm; 03-01-2019, 05:25 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

          • DXseekerMO
            Badcaps Legend
            • Feb 2018
            • 1119
            • US

            #6
            Re: Sharp LC-55N620CU PSU 192020 help ID'ing a transistor

            Originally posted by budm
            https://www.shopjimmy.com/sharp-1920...led-board.htm#

            It is on the cold side.
            Is it tested bad?
            Yes it's on the cold side and it does test bad.
            They call me......."threadkiller"

            Comment

            • budm
              Badcaps Legend
              • Feb 2010
              • 40746
              • USA

              #7
              Re: Sharp LC-55N620CU PSU 192020 help ID'ing a transistor

              Are you not getting the 12V and 18V standby Voltages?
              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

              • DXseekerMO
                Badcaps Legend
                • Feb 2018
                • 1119
                • US

                #8
                Re: Sharp LC-55N620CU PSU 192020 help ID'ing a transistor

                Correct, no stand-by. There is voltage on the hot side tho. Only issue I saw on the hot side was up and down voltage on the rectifier diode, DC side.
                Last edited by DXseekerMO; 03-01-2019, 05:31 PM.
                They call me......."threadkiller"

                Comment

                • budm
                  Badcaps Legend
                  • Feb 2010
                  • 40746
                  • USA

                  #9
                  Re: Sharp LC-55N620CU PSU 192020 help ID'ing a transistor

                  Originally posted by DXseekerMO
                  Correct, no stand-by. There is voltage on the hot side tho. Only issue I saw on the hot side was up and down voltage on the rectifier diode, DC side.
                  Please clarify, are you saying the DC Voltage on the main filter cap is going up and down?
                  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

                  • DXseekerMO
                    Badcaps Legend
                    • Feb 2018
                    • 1119
                    • US

                    #10
                    Re: Sharp LC-55N620CU PSU 192020 help ID'ing a transistor

                    Main cap voltage across is solid at 166V, but when I check directly across the DC side of the rectifier diode the voltage goes from 166v down to about 142V repeatedly.

                    Red probe on + side and black probe on - checked directly on the DC side of the rectifier diode pins
                    Last edited by DXseekerMO; 03-01-2019, 06:53 PM.
                    They call me......."threadkiller"

                    Comment

                    • DXseekerMO
                      Badcaps Legend
                      • Feb 2018
                      • 1119
                      • US

                      #11
                      Re: Sharp LC-55N620CU PSU 192020 help ID'ing a transistor

                      Originally posted by linksys1127
                      Glad I could give back! Good luck with your repair!
                      Thank you!
                      They call me......."threadkiller"

                      Comment

                      • budm
                        Badcaps Legend
                        • Feb 2010
                        • 40746
                        • USA

                        #12
                        Re: Sharp LC-55N620CU PSU 192020 help ID'ing a transistor

                        Originally posted by DXseekerMO
                        Main cap voltage across is solid at 166V, but when I check directly across the DC side of the rectifier diode the voltage goes from 166v down to about 142V repeatedly.

                        Red probe on + side and black probe on - checked directly on the DC side of the rectifier diode pins
                        The DC Voltage at the +/- leg of the rectifer bridge is pulsing dc since there is no filter cap, the + of the rectifier is fed to the anode of diode VD804, the cathode is the connected to the + leg of the filter cap.
                        So 166V steady if is fine for running the standby power supply section.
                        Is R818 OK? It should be less than 1 Ohm.
                        P/N of the SMPS IC N834?
                        Did you remove that transistor off board and tested it? Is it shorted between E and C pins?
                        Last edited by budm; 03-01-2019, 07:10 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

                        • DXseekerMO
                          Badcaps Legend
                          • Feb 2018
                          • 1119
                          • US

                          #13
                          Re: Sharp LC-55N620CU PSU 192020 help ID'ing a transistor

                          Originally posted by budm
                          The DC Voltage at the +/- leg of the rectifer bridge is pulsing dc since there is no filter cap, the + of the rectifier is fed to the anode of diode VD804, the cathode is the connected to the + leg of the filter cap.
                          So 166V steady if is fine for running the standby power supply section.
                          Is R818 OK? It should be less than 1 Ohm.
                          P/N of the SMPS IC N834?
                          Did you remove that transistor off board and tested it? Is it shorted between E and C pins?
                          R818 checks less than 1ohm

                          N834 is 1271A, believed to be NCP1271, datasheet attached

                          I was unable to conclusively find a datasheet for either of those transistors. I'm having a hard time turning a the numbers on them in to a part number so I an get the right sheet.

                          The 1P transistor is directly short on the top center and lower left pins

                          EDIT/ADD: I checked the components near N834 and all appear to check OK in-circuit. The IC itself is not shorted to ground and ground is not shorted to any other pins
                          Attached Files
                          Last edited by DXseekerMO; 03-01-2019, 07:44 PM.
                          They call me......."threadkiller"

                          Comment

                          • R_J
                            Badcaps Legend
                            • Jun 2012
                            • 9515
                            • Canada

                            #14
                            Re: Sharp LC-55N620CU PSU 192020 help ID'ing a transistor

                            That GB1 is a TL431 reference ic
                            Using hot ground, check if you have VCC on N834 pin 6, Also check for aprox +160v on pin 8. Then check the base of V812, it should have +16 volts (VZ810 is a 16v zener)
                            Last edited by R_J; 03-01-2019, 09:01 PM.

                            Comment

                            • budm
                              Badcaps Legend
                              • Feb 2010
                              • 40746
                              • USA

                              #15
                              Re: Sharp LC-55N620CU PSU 192020 help ID'ing a transistor

                              RJ, great info.
                              Last edited by budm; 03-01-2019, 08:51 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

                              • DXseekerMO
                                Badcaps Legend
                                • Feb 2018
                                • 1119
                                • US

                                #16
                                Re: Sharp LC-55N620CU PSU 192020 help ID'ing a transistor

                                Originally posted by R_J
                                That GB1 is a TL431 reference ic
                                Thank you R_J, how did you translate the number on the IC to the number you gave me?

                                Originally posted by budm
                                RJ, great info.
                                Agreed, for sure!
                                They call me......."threadkiller"

                                Comment

                                • DXseekerMO
                                  Badcaps Legend
                                  • Feb 2018
                                  • 1119
                                  • US

                                  #17
                                  Re: Sharp LC-55N620CU PSU 192020 help ID'ing a transistor

                                  Originally posted by R_J
                                  That GB1 is a TL431 reference ic
                                  Using hot ground, check if you have VCC on N834 pin 6, Also check for aprox +160v on pin 8. Then check the base of V812, it should have +16 volts (VZ810 is a 16v zener)
                                  N834:

                                  PIN6 is 6.6v to 11.1v up and down
                                  PIN8 checks just like across the rectifier diode, about 144v to 161v

                                  Base of 812:

                                  6.7 to 6.8v, up and down rhythmically
                                  They call me......."threadkiller"

                                  Comment

                                  • R_J
                                    Badcaps Legend
                                    • Jun 2012
                                    • 9515
                                    • Canada

                                    #18
                                    Re: Sharp LC-55N620CU PSU 192020 help ID'ing a transistor

                                    Check R801,R887,R803, Are you sure that was the base of V812 you checked? AC3 comes from the + of the bridge rectifier.
                                    maybe check all 3 pins of V812
                                    See if this helps
                                    Attached Files
                                    Last edited by R_J; 03-01-2019, 09:49 PM.

                                    Comment

                                    • DXseekerMO
                                      Badcaps Legend
                                      • Feb 2018
                                      • 1119
                                      • US

                                      #19
                                      Re: Sharp LC-55N620CU PSU 192020 help ID'ing a transistor

                                      Originally posted by R_J
                                      Check R801,R887,R803, Are you sure that was the base of V812 you checked? AC3 comes from the + of the bridge rectifier.
                                      maybe check all 3 pins of V812
                                      See if this helps

                                      I am sure I checked the base of V812, verified with the datasheet. The other two pins of V812 check at 6.2v

                                      R801 = 628K in one direction and about 852K in the other
                                      R887 = 632K in one direction and about 852K in the other
                                      R803 = 628K in one direction and about 750K in the other


                                      EDIT/ADD: The schematic above shows R803 as 270K resistor. The one installed on my board has the numbers 684 on it, same as R801 & 807.

                                      After that series of resistors the test point has 6.8v and is mostly stable. At the first resistor that comes directly from the + of the bridge rectifier the voltage is up and down from 141V to 165V.
                                      Last edited by DXseekerMO; 03-01-2019, 10:34 PM.
                                      They call me......."threadkiller"

                                      Comment

                                      • R_J
                                        Badcaps Legend
                                        • Jun 2012
                                        • 9515
                                        • Canada

                                        #20
                                        Re: Sharp LC-55N620CU PSU 192020 help ID'ing a transistor

                                        Have you replaced N851 ? If it is still in circuit and shorted, it could be shutting down the power supply by turning on the optocpupler. If you don't have sot23-3 find a to-92 style and use it for now, most smps use them.

                                        "PIN6 is 6.6v to 11.1v up and down" That tells me the ic's startup cell is working, the ic should pulse the fet's gate and the fet should drive the transformer, this will give you the +20 volts on C819, so check that R821 & R823 are ok.
                                        Also check that you have +160 on the V807 Fet
                                        Last edited by R_J; 03-01-2019, 10:56 PM.

                                        Comment

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