No backlight on Toshiba 42HL67US LCD

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  • SurrealMustard
    Badcaps Veteran
    • Jan 2015
    • 486
    • The United States of America

    #1

    No backlight on Toshiba 42HL67US LCD

    I'm looking at this 42" Toshiba 42HL67US "Regza" LCD and it appears to power up and produce audio, but the backlight is not coming on. Using the flashlight trick, I can see the outline of the "no signal" box on the screen, so I'm pretty sure we've got video.

    What would be the best strategy for getting to the bottom of this? It's one of the older models (circa 2007), so everything is on separate boards and it has what appear to be two inverters instead of one.
    Attached Files
  • budm
    Badcaps Legend
    • Feb 2010
    • 40746
    • USA

    #2
    Re: No backlight on Toshiba 42HL67US LCD

    I would find out if you do have 24VDC on the power supply board to run the inverter boards or not, if it does then check to see if the inverter board is getting the BL-ON from the main board or not.
    If you look at the back or the front of the TV in the dark room, do you see the backlights eve flash on for seconds?
    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

    • SurrealMustard
      Badcaps Veteran
      • Jan 2015
      • 486
      • The United States of America

      #3
      Power supply strong

      Originally posted by budm
      I would find out if you do have 24VDC on the power supply board to run the inverter boards or not, if it does then check to see if the inverter board is getting the BL-ON from the main board or not.
      If you look at the back or the front of the TV in the dark room, do you see the backlights eve flash on for seconds?
      As far as I can tell, the backlight doesn't come on even for a moment. Looking more closely at the power supply board, I did find a "24v_Inv" on one of the connectors, and it was delivering a strong 24 volts. Would this indicate a possible problem with the inverter?

      Comment

      • ReeceyBurger123
        Never Give Up !
        • May 2014
        • 7325
        • Britain

        #4
        Re: No backlight on Toshiba 42HL67US LCD

        Yes an inverter fault, I have seen these inverters with shorted mosfets. Take the covers of the inverters off and get us some images please.
        Please Do Not PM My Page Asking For Help Badcaps Is The Place For Advise, Page Linked For Business Reasons Only. Anyone Doing So Will Be Banned Instantly !

        https://www.facebook.com/Telford-Tel...7894576335359/

        Comment

        • SurrealMustard
          Badcaps Veteran
          • Jan 2015
          • 486
          • The United States of America

          #5
          Update

          Originally posted by ReeceyBurger123
          Yes an inverter fault, I have seen these inverters with shorted mosfets. Take the covers of the inverters off and get us some images please.
          I got the covers off and am attaching images to the post. Is there a way to test the MOSFET on both boards with a multimeter to determine which one is bad?

          Originally posted by roseawebs
          I always afraid to open any device. I always think, it could be more damage by me. But here seeing all people try to solve opening their device like this.
          However, our toshiba tv also stop to work and i cannot solve this.
          Feel free to join us for the repair!
          Attached Files

          Comment

          • dick_barton
            Badcaps Legend
            • Aug 2015
            • 6642
            • Wales

            #6
            Re: No backlight on Toshiba 42HL67US LCD

            You have a fuse on one of the boards marked F2. You may have more so you need to check them out with your meter set to ohms and ensure that they are short circuit.
            The mosfets can also be checked with the meter set to diode mode and check between the 3 pins (1-2,1-3,2,-3) that you have no short circuit.
            All checks carried out with set disconnected.
            Willing to help but I'm no expert.

            Comment

            • dick_barton
              Badcaps Legend
              • Aug 2015
              • 6642
              • Wales

              #7
              Re: No backlight on Toshiba 42HL67US LCD

              I think the 4 pin devices with tabs are dual mosfets and you will need to check that there are no short circuits between any of the pins on each of them as ReeceyBurger123 has said.
              Attached Files
              Willing to help but I'm no expert.

              Comment

              • budm
                Badcaps Legend
                • Feb 2010
                • 40746
                • USA

                #8
                Re: No backlight on Toshiba 42HL67US LCD

                Lots of fuses on that board F1~F6.
                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

                • orinoco8
                  Member
                  • Jan 2016
                  • 26
                  • USA

                  #9
                  Re: No backlight on Toshiba 42HL67US LCD

                  Check the input signal of DIM into power board. If this is active, you got a faulty main board that is telling power board not to turn on back light.

                  You can force backlight to stay on by connecting INV output from main board into DIM input of power board. Can't see them clearly from the first picture you uploaded. Usually it's pin 15 and 16 of the cable between main board and power board.

                  Comment

                  • budm
                    Badcaps Legend
                    • Feb 2010
                    • 40746
                    • USA

                    #10
                    Re: No backlight on Toshiba 42HL67US LCD

                    We still do not know if we have BL_ON signal or not either.
                    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

                    • SurrealMustard
                      Badcaps Veteran
                      • Jan 2015
                      • 486
                      • The United States of America

                      #11
                      Follow-up

                      Originally posted by dick_barton
                      I think the 4 pin devices with tabs are dual mosfets and you will need to check that there are no short circuits between any of the pins on each of them as ReeceyBurger123 has said.
                      All checked out. No shorts.

                      Originally posted by budm
                      Lots of fuses on that board F1~F6.
                      All that were present checked out.

                      Originally posted by orinoco8
                      Check the input signal of DIM into power board. If this is active, you got a faulty main board that is telling power board not to turn on back light.

                      You can force backlight to stay on by connecting INV output from main board into DIM input of power board. Can't see them clearly from the first picture you uploaded. Usually it's pin 15 and 16 of the cable between main board and power board.
                      I found 24v_INV, but not a DIM. Is it possible that it is identified as something else on this model?

                      Originally posted by budm
                      We still do not know if we have BL_ON signal or not either.
                      Where would the place to test that be?

                      Comment

                      • dick_barton
                        Badcaps Legend
                        • Aug 2015
                        • 6642
                        • Wales

                        #12
                        Re: No backlight on Toshiba 42HL67US LCD

                        Can you post a clear photo of the legend written alongside these two connectors.
                        Attached Files
                        Willing to help but I'm no expert.

                        Comment

                        • Alastair E
                          Chief Womble
                          • Mar 2013
                          • 1963
                          • U.K.

                          #13
                          Re: No backlight on Toshiba 42HL67US LCD

                          Are these not the sets with the strange switching-regulators on that brown board that give trouble....?
                          TELEFIX

                          How PLASMA SCREENS WORK, X-SUS and Y-SUS what they do--
                          http://www.irf.com/technical-info/appnotes/an-1088.pdf
                          PLEASE DO NOT EMAIL ME PRIVATELY FOR REPAIR ADVICE. QUESTIONS BELONG ON THE FORUM!

                          Comment

                          • SurrealMustard
                            Badcaps Veteran
                            • Jan 2015
                            • 486
                            • The United States of America

                            #14
                            progress

                            Originally posted by dick_barton
                            Can you post a clear photo of the legend written alongside these two connectors.
                            Yes. It will appear in the attachments section.

                            Originally posted by Alastair E
                            Are these not the sets with the strange switching-regulators on that brown board that give trouble....?
                            Your guess is as good as mine. Can they be tested with a multimeter?
                            Attached Files

                            Comment

                            • dick_barton
                              Badcaps Legend
                              • Aug 2015
                              • 6642
                              • Wales

                              #15
                              Re: No backlight on Toshiba 42HL67US LCD

                              So the two connectors do not appear to provide any further useful information. Was looking to see if there was a Dim or something similar printed on the board but not on those two connectors.

                              Maybe it's on the brown circuit board?

                              Edit
                              Do you have all the voltages given on the connectors of the brown board or are any missing.
                              Last edited by dick_barton; 06-04-2016, 08:34 AM.
                              Willing to help but I'm no expert.

                              Comment

                              • budm
                                Badcaps Legend
                                • Feb 2010
                                • 40746
                                • USA

                                #16
                                Re: No backlight on Toshiba 42HL67US LCD

                                You have two inverter boards, both of them are the same? It is not likely that both inverters are bad at the same time.
                                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

                                • dick_barton
                                  Badcaps Legend
                                  • Aug 2015
                                  • 6642
                                  • Wales

                                  #17
                                  Re: No backlight on Toshiba 42HL67US LCD

                                  Originally posted by Alastair E
                                  Are these not the sets with the strange switching-regulators on that brown board that give trouble....?
                                  SurrealMustard, what regulators are on this board which Alastair has mentioned?
                                  Willing to help but I'm no expert.

                                  Comment

                                  • SurrealMustard
                                    Badcaps Veteran
                                    • Jan 2015
                                    • 486
                                    • The United States of America

                                    #18
                                    measurements and details

                                    Originally posted by dick_barton
                                    Maybe it's on the brown circuit board?

                                    Edit
                                    Do you have all the voltages given on the connectors of the brown board or are any missing.
                                    A picture of the connectors is attached to this post as reference. The measured voltages are as follows (going from top to bottom):

                                    11.6
                                    ground
                                    6.4
                                    ground
                                    24
                                    ground

                                    5
                                    ground
                                    3.2
                                    ground
                                    29.1
                                    47.7
                                    20.6
                                    ground

                                    They seem in spec for the most part to me. Can you spot anything off about those values?

                                    Originally posted by budm
                                    You have two inverter boards, both of them are the same? It is not likely that both inverters are bad at the same time.
                                    They are very similar, but one is billed as the "master" and the other the "slave". They are different enough to not have the same model number.

                                    Originally posted by dick_barton
                                    SurrealMustard, what regulators are on this board which Alastair has mentioned?
                                    I'm not entirely sure to be honest.
                                    Attached Files

                                    Comment

                                    • budm
                                      Badcaps Legend
                                      • Feb 2010
                                      • 40746
                                      • USA

                                      #19
                                      Re: No backlight on Toshiba 42HL67US LCD

                                      Check the DCV on those 4 pads of the Master Inverter board when TV is powered on.
                                      BTW, you are 100% sure that ALL the fuses on the master and slave boards are all good?
                                      Pictures provided by shopjimmy.
                                      Attached Files
                                      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

                                      • dick_barton
                                        Badcaps Legend
                                        • Aug 2015
                                        • 6642
                                        • Wales

                                        #20
                                        Re: measurements and details

                                        Originally posted by SurrealMustard
                                        A picture of the connectors is attached to this post as reference. The measured voltages are as follows (going from top to bottom):

                                        11.6
                                        ground
                                        6.4
                                        ground
                                        24
                                        ground


                                        5...........................5.1V
                                        ground...................GND
                                        3.2........................POW_SIG
                                        ground...................Audio_VCC
                                        29.1......................GND_A
                                        47.7......................40V
                                        20.6......................18V
                                        ground...................GND


                                        They seem in spec for the most part to me. Can you spot anything off about those values?
                                        The readings in red do not match up with the connector legend. Audio_VCC and GND_A may be switched.
                                        Last edited by dick_barton; 06-04-2016, 02:12 PM.
                                        Willing to help but I'm no expert.

                                        Comment

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