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PHILIPS 42PFL7404 no back-light

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  • biogon
    New Member
    • Sep 2021
    • 7
    • España
    #1

    PHILIPS 42PFL7404 no back-light

    I have a problem with the back-light on a 12-years-old PHILIPS 42PFL7404 TV with DELTA DPS-298 power supply. Screen time is 11000h. A month ago the image started to flicker slightly and after a minute it turned off, but keeping the audio. It was necessary to disconnect from the line to turn it on again, with the same symptoms (Error code:17). The PSU seems to have all the components and welds fine. For a while I ran it without the back cover and it held up well without shutting down. With a heat fan I looked for the susceptible area and found it in the return circuit and supervision of the power supply (everything related to the zener IC953 and the opto PC901); when warming in for 5 " at 100ºC the same phenomenon occurred and it turned off.
    If anyone has had this problem or experience with this power supply I would appreciate an answer.
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    Last edited by biogon; 09-14-2021, 04:52 AM. Reason: more information
    Tags: None
    • William1967
      Badcaps Veteran
      • Nov 2017
      • 231
      • Netherlands
      #2
      Re: PHILIPS 42PFL7404 no back-light

      Check the 4 capacitors between the transformer and the backlight output cables.

        Comment

        • biogon
          New Member
          • Sep 2021
          • 7
          • España
          #3
          Re: PHILIPS 42PFL7404 no back-light

          Thanks for your answer. I have already checked those 4 HV capacitors and both appearance and value seem correct. These 4 caps according to the scheme are used in the out volt-current-arcs inverter supervision sub-circuits. I have seen PS with caps problems and the look of those capacitors was very bad, but...

            Comment

            • re-atari
              Senior Member
              • Oct 2010
              • 143
              #4
              Re: PHILIPS 42PFL7404 no back-light

              This PSU is used on the 8404 series (42" and larger models) as well. There's an electrolytic cap underneath the tunnelshaped cooling plate, which is known to go bad.
              Not the best place to put an electrolytic cap...

              re-atari

                Comment

                • biogon
                  New Member
                  • Sep 2021
                  • 7
                  • España
                  #5
                  Re: PHILIPS 42PFL7404 no back-light

                  Originally posted by re-atari
                  This PSU is used on the 8404 series (42" and larger models) as well. There's an electrolytic cap underneath the tunnelshaped cooling plate, which is known to go bad.
                  Not the best place to put an electrolytic cap...

                  re-atari
                  But, when the back-light goes off all the other systems work; audio, tuner, IR remote, led signaling...And the error shown is: (Error code:17) -> back-light problem.

                    Comment

                    • biogon
                      New Member
                      • Sep 2021
                      • 7
                      • España
                      #6
                      Re: PHILIPS 42PFL7404 no back-light

                      Originally posted by biogon
                      But, when the back-light goes off all the other systems work; audio, tuner, IR remote, led signaling...And the error shown is: (Error code:17) -> back-light problem.
                      That cap is in the main line input rectifier.

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