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PHILIPS 42PFL7404 no back-light

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    #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
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    #2
    Re: PHILIPS 42PFL7404 no back-light

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

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      #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...

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        #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

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          #5
          Re: PHILIPS 42PFL7404 no back-light

          Originally posted by re-atari View Post
          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.

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            #6
            Re: PHILIPS 42PFL7404 no back-light

            Originally posted by biogon View Post
            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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