BENQ FP91G+ problem

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  • simke
    New Member
    • Jan 2014
    • 5
    • Croatia

    #1

    BENQ FP91G+ problem

    I have problem with BENQ FP91G+ lcd monitor.Monitor won't to power up.
    When I plug in power cord in monitor I hear quiet whistling from back of the monitor,when i press power button on monitor whistling stops,screen is on for a moment with Benq logo and then turn off.Any help would be much appreciated.Thanks.
    Attached Files
  • Davi.p
    Hobbist
    • Sep 2009
    • 4261
    • Italy - Milan

    #2
    Re: BENQ FP91G+ problem

    Is a well known fault, search the forum for the keys "Benq FP71g" or "C5707"

    Comment

    • selldoor
      Slow Learner
      • Dec 2010
      • 7870

      #3
      Re: BENQ FP91G+ problem

      or just "FP91G"
      see here
      https://www.badcaps.net/forum/showth...ighlight=FP91g
      Please upload pictures using attachment function when ask for help on the repair
      http://www.badcaps.net/forum/showthread.php?t=39740

      Comment

      • budm
        Badcaps Legend
        • Feb 2010
        • 40746
        • USA

        #4
        Re: BENQ FP91G+ problem

        Check the C5707 transistors, solder joints on the transistors and inverter transformers. Check the black fuse PFxxx, it should be less than 1 Ohm.
        Attached Files
        Last edited by budm; 01-13-2014, 05:32 PM.
        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

        • mejohn
          New Member
          • Mar 2015
          • 8
          • germany

          #5
          Re: BENQ FP91G+ problem

          I got a very similar problem and exactly the same board! If I switch the monitor on, the green led lights up and for a fraction of a second I see the blue benq label on the monitor. Then the monitor is dead again.
          I already checked the black fuse PF801 and the LDO regulator on the logic board, there I measured to voltages 3.3V and 1.8V.
          I couldn't find the C5707, please give me a hint. The capacitors all look very good, none is curved or vented.

          Comment

          • budm
            Badcaps Legend
            • Feb 2010
            • 40746
            • USA

            #6
            Re: BENQ FP91G+ problem

            Just to be sure, you need to upload good clear pictures of YOUR board for us to look at.
            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

            • mejohn
              New Member
              • Mar 2015
              • 8
              • germany

              #7
              Re: BENQ FP91G+ problem

              Originally posted by budm
              Just to be sure, you need to upload good clear pictures of YOUR board for us to look at.
              Here you are. If you want specific pictures, please don't hesitate to ask.
              Attached Files
              Last edited by mejohn; 03-05-2015, 12:16 PM.

              Comment

              • budm
                Badcaps Legend
                • Feb 2010
                • 40746
                • USA

                #8
                Re: BENQ FP91G+ problem

                "I couldn't find the C5707"
                Q808, 809, 815, 816.
                These boards are know for having lots of bad solder joints in the inverter section (transformer legs, transistor legs, cap legs etc), and bad tuning caps (grey rectangular caps, lose its capacitance).
                Last edited by budm; 03-05-2015, 12:57 PM.
                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

                • Lumberjack777
                  Badcaps Veteran
                  • Dec 2010
                  • 464

                  #9
                  Re: BENQ FP91G+ problem

                  If I might add budm - I'd also check Q812 & Q805. I've had one of them go on occassion.

                  And resolder those transformer legs etc, as budm said, or it will happen again.

                  Here's a typical repair kit for similar models. http://www.ebay.com/itm/REPAIR-KIT-E...item54042beafc

                  Comment

                  • mejohn
                    New Member
                    • Mar 2015
                    • 8
                    • germany

                    #10
                    Re: BENQ FP91G+ problem

                    I checked all components including the mosfets (Q805, Q812) and found that two C5707 are gone (Q808 and Q809). In approximately 4-6 weeks I get the parts from china and I am going to post the result.

                    Thank you very much!

                    Comment

                    • mejohn
                      New Member
                      • Mar 2015
                      • 8
                      • germany

                      #11
                      Re: BENQ FP91G+ problem

                      Success! After replacing the two faulty c5706 and resoldering a lot of legs the monitor works fine again.

                      Comment

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