TCL 32A12H TV no backlight

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  • dicky96
    Sun Seeker
    • Mar 2017
    • 1825
    • Spain

    #1

    TCL 32A12H TV no backlight

    Hi guys

    My latest repair is this TCL 32A12LH TV, which looks like something that has been thrown together with various bits of off the shelf..... errr...stuff

    I have no back light - It's got 24V from the PSU board to the inverter therefore looks like the SMPS is running.

    There are two other wires from PSU to inverter one has 4.8V on it, the other 2.4V. Had a look on my scope. no logic signals or pwm on them but there does seem to be a considerable (excessive?) amount of ripple - see pic (this is the 2.4V on 1V/cm DC).

    Could anyone tell me what signal/voltage should I see on those 4.8v/2.4v lines to activate the inverter?

    Cheers
    Rich
    Attached Files
    Last edited by dicky96; 05-09-2017, 04:09 PM.
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  • budm
    Badcaps Legend
    • Feb 2010
    • 40746
    • USA

    #2
    Re: TCL 32A12H TV no backlight

    Did you remove the metal off the then inverter board to check the fuses and the caps yet.
    One signal is BL-ON, another one is for Dimming.
    BTW, is that SAMSUNG LCD panel?
    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

    • dicky96
      Sun Seeker
      • Mar 2017
      • 1825
      • Spain

      #3
      Re: TCL 32A12H TV no backlight

      Got the metal off - the 7A fuse on 24V rail near the power connector is OK

      Can't spot any other fuses

      The two electrolytic caps are not happy bunnies!

      I first thought one of these had been replaced before at some time as they are very similar values but different makes, but the glue holding them to the PCB looks the same on both so i guess they are both original?

      I don't suppose anything special needed here? - they are just connected from the 24V rail to 0V in parallel

      No shorts around the four STU432S Fets, but then if there was I would have expected a blown fuse.

      A quick check shows the STU432S are connected in pairs in some sort of parallel arrangement - The source of one pair going to 0V and the drain of the other pair going to 24V

      The driver chip is an OZ9966SN - I am struggling to find a proper datasheet for this, just this image http://www.datasheet4u.com/pdf/OZ9966SN-pdf/1093178 which at least gives some info.

      The screen is a samsung
      Attached Files
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      Comment

      • dick_barton
        Badcaps Legend
        • Aug 2015
        • 6642
        • Wales

        #4
        Re: TCL 32A12H TV no backlight

        Those two electrolytics are in desperate need of changing and I'd do that straight away.
        Willing to help but I'm no expert.

        Comment

        • dicky96
          Sun Seeker
          • Mar 2017
          • 1825
          • Spain

          #5
          Re: TCL 32A12H TV no backlight

          Unfortunately the only suitable replacements I had here were pulls off an old PSU or something. They looked OK on cap and esr meters. They were a bit too big to get the metal screen back on the inverter pcb but I guessed they would be OK for test purposes so I tacked them in place.

          Once I did that the 24V would come on for a few seconds then go off again. Sometimes I would hear a noise like a relay click just after power up.

          I was trying to get my scope on the two signal wires to see if it is trying to strike the inverter but the 24V was not staying present long enough. then after several attempts the 24V did come on for some seconds, and while I was looking at the signal lines one of the replacement caps popped quite spectacularly!

          I guess it wasn't as OK as I thought. Have got to go back to UK next week anyway so will order some new replacements as the bar this TV belongs to are not urgently needing it.

          There's nothing special about the original caps is there other than being small enough diameter to fit under the pcb sheild?

          NXH 35V 470uF SAM YOUNG (M)/105C
          Rubicon 35V 390uF ZLH T0918 105C PET

          Had a quick look at the electrolytics on the output side of the main SMPS and they all look OK visibly
          Last edited by dicky96; 05-10-2017, 08:14 AM.
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          Comment

          • budm
            Badcaps Legend
            • Feb 2010
            • 40746
            • USA

            #6
            Re: TCL 32A12H TV no backlight

            I would at least recap the caps for the 24V on the power supply board too 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

              #7
              Re: TCL 32A12H TV no backlight

              +1 That would be a wise move to do so at the same time.
              Willing to help but I'm no expert.

              Comment

              • dicky96
                Sun Seeker
                • Mar 2017
                • 1825
                • Spain

                #8
                Re: TCL 32A12H TV no backlight

                I think that is excellent advice. Will do. Cheers.
                Follow me on YouTube
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                Comment

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

                  #9
                  Re: TCL 32A12H TV no backlight

                  Also bad cap on the mb I noticed
                  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

                  • budm
                    Badcaps Legend
                    • Feb 2010
                    • 40746
                    • USA

                    #10
                    Re: TCL 32A12H TV no backlight

                    Originally posted by ReeceyBurger123
                    Also bad cap on the mb I noticed
                    I just notice that too, it has black stuff on top and the top is domed.
                    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

                    • dicky96
                      Sun Seeker
                      • Mar 2017
                      • 1825
                      • Spain

                      #11
                      Re: TCL 32A12H TV no backlight

                      I replaced the 470uF 35V cap on the inverter board again and also the domed 1000uF 16V cap that was spotted on the main board Interestingly that one read OK on my ESR meter but only 100uF on my cap meter.

                      Anyway with the three caps replaced the TV now powers up.

                      Cheers guys
                      Follow me on YouTube
                      ------------------
                      Learn Electronics Repair
                      https://www.youtube.com/channel/UCFX...R8UZ2vg/videos

                      Comment

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