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Toshiba 32AV500U picture but no backlight

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    #41
    Re: Toshiba 32AV500U picture but no backlight

    Originally posted by TechShui View Post
    Either that, or tape the black probe to the chassis (GND) of the TV, that way you can use one hand for the red probe, and your other hand free for the power switch.
    I alligator clipped it to ground and took readings as I powered it on. Voltages never stabilize but I can see generally where they max out but unfortunately I get 0 bonus points because my DMM isn't a Fluke.
    Originally posted by TechShui View Post
    Umm, aren't the capacitor values marked on there?
    Umm, no. There are probably a dozen or more SMD caps with no markings at all on them. I know their locations in the circuit, just not their values. The two 35v330uf are the only aluminum elect caps on the board and are also the only two with values marked on them or the schematic.

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      #42
      Re: Toshiba 32AV500U picture but no backlight

      I went ahead and tried it or myself.

      I replaced the blown FETs, and the inverter controller IC.

      My results are almost identical, with brief flash of the backlight, but then another 6-7 seconds later the backlight flashes again.

      I straightened out the sync ribbon cable which seemed a little loose, but just made it go crazy, flickering on an off rapidly, and I think I might've burnt the IC again, because it now has image, but no backlight. Back to square one.

      I see the pair of inverters for $45 on eBay
      Considering the hours of time you will save, that's well worth it.

      For the record, desoldering / resoldering the IC was not easy, and I damaged at least one trace removing the old one.

      It's a 32-pin IC, with traces the thickness of a hair, I used a hot-air SMD reflow gun. And still I think a couple of the pins were not making good enough contact with the pads.
      Dakota, if you're not ready to give up, check your soldering work, check the pads if they're cracked, and make sure they're not bridged.

      I wouldn't worry about the caps or the transformers, you're over-analyzing. Just just focus on what countless people have identified as the problem: The FETs and the IC.

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        #43
        Re: Toshiba 32AV500U picture but no backlight

        Same problem for me, 2 shorted mosfets on slave board. Replaced the mosfets and inverter IC. All is working now. Using Chip Quik really helps.

        At first when I hooked it back up I still was not getting backlight. I noticed Inv pin was now getting 5v but the 24v was dropping off. I left and came home a couple hours later to work on it and the backlight just came on.

        Oh also after replacing Mosfets noticed fuse on same board was blown. Did not have a 5a 72v, so I used a 3a 63v fuse from a bad board, do you think that will be ok??

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          #44
          Re: Toshiba 32AV500U picture but no backlight

          Well backlight stayed on for an hour on so then went out again.. Fuse is still good.

          Before I just replace the board, can this be caused by the lower value fuse even though it is not blown??
          Last edited by kevinm34232; 09-29-2012, 06:48 PM.

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            #45
            Re: Toshiba 32AV500U picture but no backlight

            I know this is old but did anyone ever figure out the problem with these slave boards....is it just the fets and ic?

            I just got one for free....and I can see the image on the screen with a flashlight so I know it is the backlight issue. The two fets on the slave board are shorted....i was planning just to replace them, but has anyone resolved this issue?

            thanks

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              #46
              Re: Toshiba 32AV500U picture but no backlight

              I've got a Toshiba 32C3035DB
              The backlight died - two Mosfets on the master board were blown. I replaced all the mosfets on both master and slave, and both driver ICs.
              When I powered it up, the backlight came on for about 2 seconds, then the fuse on the master and one of the MOSFETS blew again.
              Any ideas?

              Comment


                #47
                Re: Toshiba 32AV500U picture but no backlight

                Originally posted by SpiderElectron View Post
                I've got a Toshiba 32C3035DB
                The backlight died - two Mosfets on the master board were blown. I replaced all the mosfets on both master and slave, and both driver ICs.
                When I powered it up, the backlight came on for about 2 seconds, then the fuse on the master and one of the MOSFETS blew again.
                Any ideas?
                Please start a new thread since your Tv is not the same model as the OP.
                Also up load good clear pictures of the whole back side of the TV so we can see all the boards and how they are connected together, and then the pictures of each 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

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                  #48
                  Re: Toshiba 32AV500U picture but no backlight

                  I have the same symptoms as @DakotaKid:
                  A "screaming/hissing" noise coming from the Slave board transformer when the backlights briefly fire up. And after couple of flashes it goes dark.

                  Initially the slave board had two blown FETs and a fuse which I replaced.
                  I did not replace the IC, and I also measure ~23 ohms on both master and slave boards on their secondary transformer windings

                  Upd: Waited a bit longer and blown the same two FETs again

                  Any ideas?
                  Last edited by zape; 01-16-2020, 10:15 PM.

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                    #49
                    Re: Toshiba 32AV500U picture but no backlight

                    Replacing IC, blown FETs and fuse fixed it for me.

                    Comment

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