FAN7547 not operating?

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  • Behemot
    Badcaps Legend
    • Dec 2009
    • 4845
    • CZ

    #1

    FAN7547 not operating?

    I got 715G1643-1 board from Fujitsu Siemens P17-2. The owner changed some caps, there was blasted zener diode between +5 and +13,5 V (?). I replaced it and still have no backlight, image is present using lamp.

    According to datasheet, if there is no voltage present (this pin is not connected here) on pin 4 (Dimming Mode Selection), it should operate in PWM range, but there is 2,76 V constant voltage without any ripple on pin coming from signal board, making 1,06 V on the Vds pin of the IC itself. I guess I can count that as 1 V 100% brightness?

    However, there is definitelly no 200 Hz ripple on OSC pin, see attachement, there are some hundreds of kHz. The same is on COMP (Error Amplifier Output) pin.

    I have aprox. 13,6 V on Vcc1 this one is directly connected with the appropriate voltage rail) but nothing on Vcc.

    Lamps are not the problem, I have tested different 17'' lamps without any luck. Secondaries of both transformers seem to be OK, all transistors and foil cap in the inverter power section is OK. All ceramics on the output measure OK.
    Attached Files
    Less jewellery, more gold into electrotech industry! Half of the computer problems is caused by bad contacts

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  • bammbammfran
    Badcaps Veteran
    • Apr 2014
    • 476
    • USA

    #2
    Re: FAN7547 not operating?

    I believe that the fan7547 won't turn on without vcc
    Did you try tracing back the vcc line

    any voltage on the softstart pin 10 ?

    Comment

    • budm
      Badcaps Legend
      • Feb 2010
      • 40746
      • USA

      #3
      Re: FAN7547 not operating?

      This is the example application circuit, see if the VCC is switched through some kind of transistor.
      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

      • Behemot
        Badcaps Legend
        • Dec 2009
        • 4845
        • CZ

        #4
        Re: FAN7547 not operating?

        There is something, will check tomorrow, I have it in my shop. So there indeed should be aprox. 13,6 volts on both Vcc pins, right?
        Less jewellery, more gold into electrotech industry! Half of the computer problems is caused by bad contacts

        Exclusive caps, meters and more!
        Hardware Insights - power supply reviews and more!

        Comment

        • budm
          Badcaps Legend
          • Feb 2010
          • 40746
          • USA

          #5
          Re: FAN7547 not operating?

          "So there indeed should be aprox. 13,6 volts on both Vcc pins, right?" Yes. i have a feeling you are missing the drive signal to turn on the switch for the VCC.
          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

          • Behemot
            Badcaps Legend
            • Dec 2009
            • 4845
            • CZ

            #6
            Re: FAN7547 not operating?

            There is one more pin coming from signal board which is 0 V, that may be it…
            Less jewellery, more gold into electrotech industry! Half of the computer problems is caused by bad contacts

            Exclusive caps, meters and more!
            Hardware Insights - power supply reviews and more!

            Comment

            • Behemot
              Badcaps Legend
              • Dec 2009
              • 4845
              • CZ

              #7
              Re: FAN7547 not operating?

              Man screw this, you would not think about that. The owner already opened it for initial recapping, probably bent the pin on signal board connector which was supposed to turn the IC on. I've bent it back, contact is OK and backlight is operating

              This is second time, first time there was some Lenovo wide panel which had broken connector for button board. It had no earth so the signal could not go low. I think he has talent for breaking connectors
              Last edited by Behemot; 06-10-2014, 07:06 AM.
              Less jewellery, more gold into electrotech industry! Half of the computer problems is caused by bad contacts

              Exclusive caps, meters and more!
              Hardware Insights - power supply reviews and more!

              Comment

              • bammbammfran
                Badcaps Veteran
                • Apr 2014
                • 476
                • USA

                #8
                Re: FAN7547 not operating?

                A good clear picture of the bottom of the power supply board might help

                Comment

                • Behemot
                  Badcaps Legend
                  • Dec 2009
                  • 4845
                  • CZ

                  #9
                  Re: FAN7547 not operating?

                  No need anymore, the pin which turns on the controller IC is in conductive state once again and it works, see the previous post
                  Less jewellery, more gold into electrotech industry! Half of the computer problems is caused by bad contacts

                  Exclusive caps, meters and more!
                  Hardware Insights - power supply reviews and more!

                  Comment

                  • budm
                    Badcaps Legend
                    • Feb 2010
                    • 40746
                    • USA

                    #10
                    Re: FAN7547 not operating?

                    That pin is probably the BL_ON (INVR_ON) pin.
                    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

                    • Behemot
                      Badcaps Legend
                      • Dec 2009
                      • 4845
                      • CZ

                      #11
                      Re: FAN7547 not operating?

                      There is no marking on any of the boards but yeah usually something like that…
                      Less jewellery, more gold into electrotech industry! Half of the computer problems is caused by bad contacts

                      Exclusive caps, meters and more!
                      Hardware Insights - power supply reviews and more!

                      Comment

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