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Yet another BenQ FP71G+

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    #1

    Yet another BenQ FP71G+

    I have this BenQ which had classic issue with shorted C5707s.

    So I replaced all 4 C5707s and corresponding capacitors (22k160), and resoldered everything, especially inverter components.

    Now, it has classic 2 seconds to black: shows image, BL shuts off, LED stays green, and I can see image with a flashlight.

    I have 15,8V passing PF 801, and reaching Q805 and Q812, but NOT reaching C5707s.

    The only possible issue I can think of:
    One FU 9024N was shorted (Q805), and since I couldn't grab one, I replaced it with FQU 11P06, so now I have one of each on board (Q805 and Q812)


    (not my board, bud identical)
    Attached Files
    stay classy
    Tags: None
    #2
    Re: Yet another BenQ FP71G+

    maybe the tubes are bad.

    also check the blue ceramic output caps.

    Comment

      #3
      Re: Yet another BenQ FP71G+

      Sure thing.
      So, if the tube ignites for the 2 seconds, than shuts down, it still can be bad?
      stay classy

      Comment

        #4
        Re: Yet another BenQ FP71G+

        What resistance do you get on the PF 801? >1 Ohms?

        'I have 15,8V passing PF 801, and reaching Q805 and Q812, but NOT reaching C5707s." So not reaching ALL 4 C5707?
        The Voltage must have reached the C5707 (2 per Oscillator) Royer oscillators setup otherwise you will not get the lamps to even flash on for seconds.
        You need test lamps to help narrowing down the problem.
        https://www.badcaps.net/forum/showthread.php?t=19987
        BTW, if Q805 shorted out, the the Inverter in that section will run at full lamp brightness.
        Attached Files
        Last edited by budm; 06-30-2016, 09:04 AM.
        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

          #5
          Re: Yet another BenQ FP71G+

          Originally posted by budm View Post
          What resistance do you get on the PF 801? >1 Ohms?
          In my case, PF801 is a jumper, I'll post my picture later.

          Originally posted by budm View Post
          The Voltage must have reached the C5707 (2 per Oscillator) Royer oscillators setup otherwise you will not get the lamps to even flash on for seconds..
          As usual you are correct. I think voltage gets to C5707s and drops very fast.

          Originally posted by budm View Post
          You need test lamps to help narrowing down the problem.
          Yes, that is a handy tool. Will make one and post results.

          Originally posted by budm View Post
          BTW, if Q805 shorted out, the the Inverter in that section will run at full lamp brightness.
          I thought it fries the C5707 when shorted, since my burned a couple of times.
          Guess something else fried them.
          stay classy

          Comment

            #6
            Re: Yet another BenQ FP71G+

            After some playing with BenQ, i found out this:
            If I lower the brightness enough, it will work normally and stay on forever.

            If I put the brightness up (somewhere around 80 out of 100) it shuts down the BL.

            Is this problem with some component not withstanding higher current?

            What measurement could narrow it down?
            stay classy

            Comment

              #7
              Re: Yet another BenQ FP71G+

              You either have something in the inverter dropping out or one of the wires to the CCFLs is weak and arcs at higher current. I would test the lamps with another inverter if possible.
              Originally posted by PeteS in CA
              Remember that by the time consequences of a short-sighted decision are experienced, the idiot who made the bad decision may have already been promoted or moved on to a better job at another company.
              A working TV? How boring!

              Comment

                #8
                Re: Yet another BenQ FP71G+

                Originally posted by Joe Black View Post
                After some playing with BenQ, i found out this:
                If I lower the brightness enough, it will work normally and stay on forever.

                If I put the brightness up (somewhere around 80 out of 100) it shuts down the BL.
                I have the same problem with this monitor. If I lower the brightness down to 35, it stays on and works indefinitely. If I up the brightness, it goes 2 seconds to black.

                Given it is only a 17 inch monitor and I have several spare, I just use it like so. The amount of effort and since I already ruined/broke a ccfl in a previous attempt, once this monitor dies, it goes to the recycle center. I'll save the power and logic board.
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                Comment

                  #9
                  Re: Yet another BenQ FP71G+

                  Originally posted by retiredcaps View Post
                  Given it is only a 17 inch monitor and I have several spare, I just use it like so. The amount of effort and since I already ruined/broke a ccfl in a previous attempt, once this monitor dies, it goes to the recycle center. I'll save the power and logic board.
                  Totally reasonable. BUT, I just love to repair electronics.

                  If only I knew how to
                  stay classy

                  Comment

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