Sharp LC37SB24u won't stay on

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  • jakeklem
    Member
    • Feb 2015
    • 42
    • United States

    #1

    Sharp LC37SB24u won't stay on

    I need some help tracking down an issue with this set. I've found that a few of the CCFL are not lighting, but there are other issues it seems. I have the inverter board disconnected from the PSU. It will power on and I can see (with a flashlight) the menu flicker on the screen, but it only appears for a second. Then one of three things will happen. TV goes dead and I get the green blinking light, it will stay on but no menu, or it turns red then I get the amber light if I try to power it back on.

    voltages on the PSU when it stays on:
    13v: 13v
    BU5v: 5v
    PS_ON: 3v

    Can anyone suggest a starting point on fixing this one?
    Attached Files
  • budm
    Badcaps Legend
    • Feb 2010
    • 40746
    • USA

    #2
    Re: Sharp LC37SB24u won't stay on

    "I've found that a few of the CCFL are not lighting" It will only take one bad CCFL, or bad Inverter transformer or circuit to put the TV in protection mode, so if you know that it has bad CCFL, then you need to replace it or bypass the protection circuit at you own risk.
    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

    • jakeklem
      Member
      • Feb 2015
      • 42
      • United States

      #3
      Re: Sharp LC37SB24u won't stay on

      Does it go into protection mode if the inverter is disconnected?

      Comment

      • budm
        Badcaps Legend
        • Feb 2010
        • 40746
        • USA

        #4
        Re: Sharp LC37SB24u won't stay on

        Originally posted by jakeklem
        Does it go into protection mode if the inverter is disconnected?
        Do you mean the cables going to the inverter board are disconnected or the cables to the lamps?
        It depends on the design.
        You also need to look at the inverter board connectors to see if there are any labels for the pins to tell you what the pin's functions are.
        Last edited by budm; 03-05-2015, 08:04 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

        • jakeklem
          Member
          • Feb 2015
          • 42
          • United States

          #5
          Re: Sharp LC37SB24u won't stay on

          I mean the little bridge between the power board and the inverter is disconnected.
          yes, there is labeling on the inverter board connection from the PSU. see attached picture.

          Getting 64v on the 60v pins.
          Attached Files
          Last edited by jakeklem; 03-05-2015, 08:41 PM.

          Comment

          • CapLeaker
            Leaking Member
            • Dec 2014
            • 7982
            • Canada

            #6
            Re: Sharp LC37SB24u won't stay on

            Looks like we can see only every other pin out, not all of them. There is more behind the connector

            Comment

            • budm
              Badcaps Legend
              • Feb 2010
              • 40746
              • USA

              #7
              Re: Sharp LC37SB24u won't stay on

              Please list all the pin names.
              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

              • jakeklem
                Member
                • Feb 2015
                • 42
                • United States

                #8
                Re: Sharp LC37SB24u won't stay on

                Oops, I missed that. Here it is.
                Attached Files

                Comment

                • jakeklem
                  Member
                  • Feb 2015
                  • 42
                  • United States

                  #9
                  Re: Sharp LC37SB24u won't stay on

                  How might I bypass the protection mode? I want to see if it will stay on without the CCFL.

                  Comment

                  • jakeklem
                    Member
                    • Feb 2015
                    • 42
                    • United States

                    #10
                    Re: Sharp LC37SB24u won't stay on

                    I get voltage after power on until it goes into protection mode. Here is the pin out to the inverter board:

                    GND 0
                    STB 3v
                    OFL 0
                    OSC 0
                    ERR 0
                    REGBRT 0
                    NC 0
                    ADMIN 0
                    NC 0
                    13V 13v
                    GND 0
                    NC 0
                    GND 0
                    GND 0
                    NC 0
                    GND 0
                    no label 0
                    NC 0
                    60v 64v
                    60v 64v
                    60v 64v
                    60v 64v

                    Comment

                    • CapLeaker
                      Leaking Member
                      • Dec 2014
                      • 7982
                      • Canada

                      #11
                      Re: Sharp LC37SB24u won't stay on

                      if you disconnect the inverter from the PSU, does the TV work normal less the back light?

                      Comment

                      • budm
                        Badcaps Legend
                        • Feb 2010
                        • 40746
                        • USA

                        #12
                        Re: Sharp LC37SB24u won't stay on

                        Originally posted by CapLeaker
                        if you disconnect the inverter from the PSU, does the TV work normal less the back light?
                        It does per post 1.
                        I do not see the BL-ON signal pin on that list of the pin out.
                        Also the dim control signals and other signals also showing 0V which do not look right.
                        Last edited by budm; 03-31-2015, 07:05 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

                        • jakeklem
                          Member
                          • Feb 2015
                          • 42
                          • United States

                          #13
                          Re: Sharp LC37SB24u won't stay on

                          Originally posted by CapLeaker
                          if you disconnect the inverter from the PSU, does the TV work normal less the back light?
                          Briefly yes, but it will not stay functional.

                          Comment

                          • jakeklem
                            Member
                            • Feb 2015
                            • 42
                            • United States

                            #14
                            Re: Sharp LC37SB24u won't stay on

                            Originally posted by budm
                            It does per post 1.
                            I do not see the BL-ON signal pin on that list of the pin out.
                            Also the dim control signals and other signals also showing 0V which do not look right.
                            Yes, good observation Bud. I wonder if the pin without a label might be BL-ON.

                            Any ideas for a starting point of what I can test? Is there a way I can fake out the circuit protection to make it act like the inverter is plugged in?

                            I haven't messed with backlights much. What would happen if I remove the ones that are not functioning and power it on?
                            Last edited by jakeklem; 03-31-2015, 10:25 PM.

                            Comment

                            • budm
                              Badcaps Legend
                              • Feb 2010
                              • 40746
                              • USA

                              #15
                              Re: Sharp LC37SB24u won't stay on

                              OK, I look at the inverter board picture at Shopjimmy, I see that it has a rectangular box fuse F7501, and also a bunch of power MOSFETs mounted on the heatsink, so you should check them out to see if any of the MOSFETs is shorted out or not.
                              http://www.shopjimmy.com/sharp-runtk...-inverter.htm#
                              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

                              • budm
                                Badcaps Legend
                                • Feb 2010
                                • 40746
                                • USA

                                #16
                                Re: Sharp LC37SB24u won't stay on

                                OK, this is what I found, I look up the power supply board at Shopjimmy:
                                http://www.shopjimmy.com/sharp-rdenc...upply-unit.htm
                                According to SJ, this power supply board is also used in LC-37D44U (the other 3 models do not have good service manuals for them).
                                So I found the service manual at ELEKTROTANYA:


                                Page 70 show the pinout of the LB connector, the STB (Von) is the BL-ON and you do have 3V there so BL-ON is OK.
                                You said you see blinking LED, so see the manual to see if the code match your blinking LED.
                                It is big manual and I did not have the time to look at everything in details yet.
                                Last edited by budm; 03-31-2015, 11:36 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

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