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phillips 19PFL3505D/F7 turns on then off

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    #1

    phillips 19PFL3505D/F7 turns on then off


    this is the power supply i check the fuse good the transistor k3994 is good diodes too are good. some diodes show low voltage .234 and .176 reading what i do know they should be .5 to .7 i take them out of circuit and they measures the same .234 and .176 is this signified are bad......well i just replace them and still doing same thing wont turn on, what it does goes on and logo comes for a sec and then Tv goes off. so what i think there is a coming voltage, but there's something stopping from turning on..... and y try disconnecting lamps and i see the logo come on and then off doing the same thing.... anyone here for help....someone had a problem with this kind of sets of small Tvs.
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    #2
    Re: phillips 19PFL3505D/F7 turns on then off

    Which diodes are they? Dxxx? Where in circuit are they?

    A low forward voltage around 0.2v indicates they could be Schottky diodes. What is the part number of the diodes?

    Or do you get that low voltage in both directions? If yes, they are probably shorted.

    Please provide photos of YOUR board, not a stock photo, and show which diodes you checked and which ones you changed.


    Also, have you checked all the output voltages from the power supply? Do they all come up? Do any turn off after the TV shuts off by itself?

    When the TV goes off, does it still have the Power LED lit or does that go off too?
    "Tantalum for the brave, Solid Aluminium for the wise, Wet Electrolytic for the adventurous"
    -David VanHorn

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      #3
      Re: phillips 19PFL3505D/F7 turns on then off




      The arrow is were the .2 voltage is in just one direction I desoldering one side from board for precise reading. I I think they should be from .3 to .7......I change them for other diodes and still doing the same thing on and in a sec goes off, I can see when logo comes on and rapidly goes off completely.
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        #4
        Re: phillips 19PFL3505D/F7 turns on then off

        Any clues????

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          #5
          Re: phillips 19PFL3505D/F7 turns on then off

          It's hard to say because you have not given all the information I asked for. For a start, you need to tell us:

          1) What is the part number on the diodes you measured as 0.2v? - What is written on the diodes?
          2) What do you get if you measure the old diodes both ways out of circuit?
          3) What do all the voltage rails coming from the PSU do when the TV is powered on and then after it shuts off?
          4) Can you provide better photos of this board? Show both sides, show the ribbon connectors and anything that is printed near them. Get them in focus and not blurry so we can actually read them.
          "Tantalum for the brave, Solid Aluminium for the wise, Wet Electrolytic for the adventurous"
          -David VanHorn

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            #6
            Re: phillips 19PFL3505D/F7 turns on then off

            One diode is schottky sb140 it measures .167 out of circuit..sb360 schottky it measures .150 out of circuit. 3pha20 schottky measures .217. At diode reading with test multimeter.

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              #7
              Re: phillips 19PFL3505D/F7 turns on then off

              How is normal measure should be on this types of schottky diodes.....silicon diodes are from .4 to .7 think if am right.

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                #8
                Re: phillips 19PFL3505D/F7 turns on then off

                A low forward voltage is normal for a Schottky diode.
                Yes, a standard silicon diode will show about 0.55v on the meter.

                Bear in mind the voltage drop will be higher when the diode is operating at full load in circuit, but with the very small current from your multimeter in diode test, the forward voltage will be quite small.

                It sounds like the diodes you changed were OK, and if they were bad, then it should have fixed the problem.


                At this point it would help greatly if you can find out what all the voltage rails are doing during power up and fault condition. Do you know where to check the voltages? Have you tried to find a schematic?
                "Tantalum for the brave, Solid Aluminium for the wise, Wet Electrolytic for the adventurous"
                -David VanHorn

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                  #9
                  Re: phillips 19PFL3505D/F7 turns on then off

                  I haven't check the schematics. The power supply has a all+3.3v whice I do get

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                    #10
                    Re: phillips 19PFL3505D/F7 turns on then off







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                      #11
                      Re: phillips 19PFL3505D/F7 turns on then off

                      OK that's good. Does all+3.3v stay at 3.3v the whole time during power on and shutdown?

                      There are other rails too like +31v, LCD+13v, +7.0v that I can see marked. You need to check all these too.
                      "Tantalum for the brave, Solid Aluminium for the wise, Wet Electrolytic for the adventurous"
                      -David VanHorn

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