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bn44-00264c - CCFL emulation

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    bn44-00264c - CCFL emulation

    hi there,

    I am fixing a SAMSUNG le40b530p7w. It has 2/3 lamps which are acting up. This leads to the inverter (bn44-00264c) shutting off entire backlight after several minutes. I ruled out inverter issue - the PFC_OUT voltage is stable 390V, so are 13V & 5.3V. ICs are getting the power etc. When the backlight is shut off, these voltages stay.

    I do not want to disable protect feature completely, but rather 'emulate' these fussy CCFLs.

    I tried to replace the CCFLs with capacitors - tried 22pf, 47pf, 47*2pf.
    unfortunately the backlight goes after a second or two.

    How could that be achieved?

    BD9893 datasheet: http://dalincom.ru/datasheet/BD9893F.pdf
    BN44-00264c: https://archive.org/details/Samsung_BN44-00264C

    #2
    Re: bn44-00264c - CCFL emulation

    Not that I recommend doing this, but disabling the protection circuit on the inverter will do the trick.

    Comment


      #3
      Re: bn44-00264c - CCFL emulation

      Capacitors are not suitable, the best way is to trick the single lamp current control, to avoid current consumption, but leaving circuit as is, lamp must be replaced with resistor, must read panel datasheet and seen current/voltage of lamp, not at startup but normal use..

      Comment


        #4
        Re: bn44-00264c - CCFL emulation

        i used to sub in known good tubes for testing

        Comment


          #5
          Re: bn44-00264c - CCFL emulation

          he don't want to test..

          Comment


            #6
            Re: bn44-00264c - CCFL emulation

            Thanks for the responses guys.
            I know it is the faulty bulbs since when removed, backlight goes after a second and with the redish/flickering ones in, it might go on for hours. And I do not have any good bulbs for replacement, hence the quest

            I tried to change the sensing circuitry and unfortunately failed.

            The over/under voltage protections do not seem to be kicking in (PR_1 / VS / OVP).
            It seems what's left is the current feedback based on fb_1 and fb_2 lines but I do not understand how could it measure current if this feedback is only based on Z7/Z8 lamps?
            (the faulty bulbs are not on this pair).

            What's worse is when I had a number of cables hooked up to measure the voltages during operation, one of them shorted and fried BS9893 chip...doh
            Last edited by cruiser_; 11-17-2021, 05:32 AM.

            Comment


              #7
              Re: bn44-00264c - CCFL emulation

              why don't asked my advice?

              Comment


                #8
                Re: bn44-00264c - CCFL emulation

                I do this in parallel

                I ordered 100k 20W resistors, along with BS9893.
                Still, for my own educational benefit, I would like to understand which part of protection kicks in.

                Comment


                  #9
                  Re: bn44-00264c - CCFL emulation

                  With no ccfl connected the voltage will be high, so it is likely the over voltage protection is shutting down the drive.
                  You may be able to disconnect one of the diodes ie: DI806 ~ DI812 for the bad lamp.
                  If the bad ccfl is connected to TI802s pins 3, then it could be fault with the FB line tripping the circuit.
                  Last edited by R_J; 11-19-2021, 12:51 PM.

                  Comment


                    #10
                    Re: bn44-00264c - CCFL emulation

                    thanks R_J,
                    i made sure the bad CCFL was not on that circuit that provides feedback.
                    What is the purpose of DI806-812 diodes? I thought they only provided some sort of 'back current' protection?

                    Comment

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