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Phillips 47pfl7403d/27 backlight goes off after a while, works after power cycling

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    #1

    Phillips 47pfl7403d/27 backlight goes off after a while, works after power cycling

    Ugh, the last set I worked on was a Magnavox, then an RCA, and now this POS Phillips. Everything else about the set works fine. It loses backlight after a period of time after being turned on. If you haven't used the set in a while, it takes longer for it to lose backlight. Also, if you turn it off and turn it back on after it's lost power, it will stay on for a bit, sometimes not needing another power cycling.

    I think it's an inverter issue, but there is no inverter board like most older sets, and it is integrated onto the power board. My pics aren't very good, but here are some images from the web that illustrate it perfectly:

    http://i.ytimg.com/vi/zbRSssOxIjQ/maxresdefault.jpg"]whole TV with back removed

    Power supply / Inverter

    This seems to be a fairly common problem, but I couldn't find mention of a solution anywhere. Any idea where to start? Or should I pull caps and test them, etc? Some folks have mentioned poor soldering connections and flexing the board will bring back the backlight, but no dice for me with that.

    Cheers, Alex
    Last edited by withalligators; 09-02-2014, 02:22 PM.
    Tags: None
    #2
    Re: Phillips 47pfl7403d/27 backlight goes off after a while, works after power cyclin

    bump

    Comment

      #3
      Re: Phillips 47pfl7403d/27 backlight goes off after a while, works after power cyclin

      I have a Phillips 47PFL7403/F7. The two Large main capacitors on the power supply board are bulging and hot.
      TV Symptoms are: TV turns on and plays for several minutes normally. Then the picture disappears but the sound remains.
      Have you heard of this problem before ?
      I am hoping that replacing the largest main high voltage capacitors 450v 150uf Panasonic Series TS-ED capacitors I think, (in the center of the PS PCB) will correct the issue,
      I hope its not the inverter board also.
      All other capacitors look normal.

      I am a tech and only need any advice you can provide. I have not seen this specific TV problem on a LCD Phillips before. I rarely see Phillips TV's.
      Not sure if I have one problem or two.
      Anyone else has had experience with this issue please reply.
      MRGCAV@gmail.com
      Milwaukee Wisconsin.

      Lets compare notes.

      Comment

        #4
        Re: Phillips 47pfl7403d/27 backlight goes off after a while, works after power cyclin

        Dang, I must have missed or not gotten the email notification that you posted here. I was out of the country for a while, and am about to start work on this thing. Have you had luck getting it up and running? I am tempted to just replace all the caps and see how that works.

        Comment

          #5
          Re: Phillips 47pfl7403d/27 backlight goes off after a while, works after power cyclin

          Do up some voltage measurements when the tv is working ok, and then again after the backlight quits.

          Comment

            #6
            Re: Phillips 47pfl7403d/27 backlight goes off after a while, works after power cyclin

            Well damn. Poking around on teh board while it was hot, I accidentally bridged the top two legs on PC201. TV shut off, now when I press power, relay clicks, nothing happens.
            Readings I got before I screwed it up:
            +12V 12.15
            +12V 12.16
            GND1 -0.01
            GND1 -0.01
            BL_ON/OFF 3.01
            DIM 3.47
            BOOST 1.47
            ANL/PWM -0.02

            On this link PC201 is bottom center of the board, spanning the black line that divides the inverter section of the board from the PSU section of the board. I bridged the two legs in the inverter side.

            Any advice? TV is probably only worth 150-175 on a good day.

            Comment

              #7
              Re: Phillips 47pfl7403d/27 backlight goes off after a while, works after power cyclin

              And what for voltages are you getting now?

              Comment

                #8
                Re: Phillips 47pfl7403d/27 backlight goes off after a while, works after power cyclin

                Well, I let it sit for a bit unplugged, and now it turns on again. I guess I will wait for the back lights to cut off to get some readings. I'm just getting the aforementioned pins. Is there anything else I should be looking at?

                Skimming through ebay, there are several different repair kits for sale. Many are offering the various mosfets as a fix. Some are for a few capacitors, and some are for some 7 pin ICs. Should I be looking at the mosfets? I can't even find the ICs they sell anywhere on the board.

                Comment

                  #9
                  Re: Phillips 47pfl7403d/27 backlight goes off after a while, works after power cyclin

                  Before you buy anything, disconnect the main board and force the PSU on and measure voltages on all the pins.

                  Comment

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