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Philips 47PFL8404 H / 12, chassis Q548.1ELA

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    Philips 47PFL8404 H / 12, chassis Q548.1ELA

    Hello everybody,

    I have a Philips LCD TV model 47PFL8404 H / 12, chassis Q548.1ELA.
    My TV has the following problem: TV starts, in a fraction of a second gets a picture and a backlight. The image and the backlight go out immediately. After a few seconds the TV gets the picture again and loses it. So a few times at the start. After a few unsuccessful launches, the image and the backlight no longer come. My TV has a normal sound. Problem is in the power supply - inverter defective. ( „Delta“ DPS-298CP-A )
    PSU checked, I've replaced all four of the high voltage capacitors at the output of the inverter transformers with new ones. I have also replaced IC702 = DDA003A and IC3 = DDA005, without success. I also checked the neon lights in the backlight in the panel. Everything is right. The TV still behaves the same way!
    For suggestions, I would be grateful!

    #2
    Re: Philips 47PFL8404 H / 12, chassis Q548.1ELA

    Hello,

    Do you have a photo of the power supply and also, do you get weird sparking and buzzing sounds when powering your TV?

    The 4 capacitors you've replaced (C731, C709, C734 and C705), how did they originally look like? Were they burnt up and had dark brown green color? And did you replace them with the exact same type 33pF 6kV (C709, C705) and 47pF 6kV (C731, C734)?

    I actually own the 37 inch version of the same television with the same power supply and, unfortunately, with the similar issue.
    While mine doesn't have any leaking capacitor, I've discovered that the diode at D909 has gone bad. It has a high deviation in its forward Voltage compared to the manufacturer's datasheet. The type is 1N5408G and for good measure I also will be replacing D907 diode, SB2100, as well as the Q901, 2SK4101 (K4101) MOSFET. My reasoning for replacing them is because those high voltage capacitors usually don't go bad on their own and when asking around I learned that some of these diodes usually start to deviate from spec and affect other components.

    At the moment of posting I've ordered these diodes and mosfet and they will be shipped from Germany within next week, so I can prove if my theory holds any water..

    So yeah, if I were you, I would test all diodes in the power supply and see if they're functioning properly.

    Comment


      #3
      Re: Philips 47PFL8404 H / 12, chassis Q548.1ELA

      What voltage do you get using diode test on D907 D911?

      Comment


        #4
        Re: Philips 47PFL8404 H / 12, chassis Q548.1ELA

        How did you check the ccfl lamps in the panel? You may have a bad inverter transformer, there are two, check the resistance of the secondaries and compare them to each other.
        Last edited by R_J; 03-21-2019, 03:22 PM.

        Comment


          #5
          Re: Philips 47PFL8404 H / 12, chassis Q548.1ELA

          When I was waiting for the parts to arrive I took these pictures that I included in the attachments. As you can see its the DPS-298CP-1A.
          Yesterday I replaced these components: Q901, D907 and D909.

          @otoluk, While my motherboard doesn't have a D911 it does however have a D907. The original D907, the SB2100, I measured around 175mV using diode test and compared to data sheet it should be around 330mV. Guess I replaced a part that would cause a lot of headache in the near future.

          @R_J, I guess you're right. Replacing these components I mentioned before didn't fix the backlight. It still does flick 0.3 second on before turning off. Do you have an idea how to get to the CCFL inverter? Is it sandwiched inside with the CCFL tubes inside the LCD screen or is it the rather big transformer on the top right corner just before the 4 blue filter capacitors?
          Attached Files
          Last edited by Elitebook; 03-28-2019, 05:15 PM. Reason: typos

          Comment


            #6
            Re: Philips 47PFL8404 H / 12, chassis Q548.1ELA

            T301 is the inverter transformer (large double transformer) There are two seperate outputs. BUT each line supplies more than one ccfl inside the panel, so there will be some kind of distibution board inside the panel. and it only take one bad lamp to cause the backligt circuit to shut down in protection.
            Also note that even though there are two leads going to CN3, they are connected together, and the same with CN2, both leads are connected together so there must be some wiring inside the panel that connects the returns of the ccfl's
            And to check the resistance on the transformer secondaries, check the resistance between 5 & 6 and compare it to 7 & 8, they should read close to the same resistance.
            Last edited by R_J; 03-28-2019, 05:49 PM.

            Comment


              #7
              Re: Philips 47PFL8404 H / 12, chassis Q548.1ELA

              I'm back after a long hiatus. I did tear down the TV even more and now I did access the CCFL distribution board. The pictures do show some discoloration on the PCB, but I don't exactly know if they're either caused by heat or manufacturing.
              I'll try to take those tubes out one by one and see if that makes any difference.

              https://imgur.com/a/gYNIvdM

              Comment


                #8
                Re: Philips 47PFL8404 H / 12, chassis Q548.1ELA

                You should be able to power up the tv without the lcd panel connected and see which ccfl's are lighting or not. If the plastic holding the tubes has become hard, it might be hard to remove the ccfl without breaking them

                Comment


                  #9
                  Re: Philips 47PFL8404 H / 12, chassis Q548.1ELA

                  The plastic holding mounts for the tubes have indeed become very brittle. The CCFL's do power on and off very fast about two or three times when I power up the TV.
                  Is there a way to remove the tubes without breaking them?

                  Comment


                    #10
                    Re: Philips 47PFL8404 H / 12, chassis Q548.1ELA

                    Hard to see in picture, do any of the tubes have a blackened looking end compared to the rest? How did the resistance test of transformer secondaries go? as always BE CAREFUL when working on HOT/DEADLY side of powerboard or inverter board.
                    Last edited by nomoresonys; 08-16-2019, 04:56 PM.

                    Comment


                      #11
                      Re: Philips 47PFL8404 H / 12, chassis Q548.1ELA

                      Maybe check the board for bad/cold solder joints, take a close look at the transformer solder joints.

                      Comment


                        #12
                        Re: Philips 47PFL8404 H / 12, chassis Q548.1ELA

                        Do ALL the tube light up and at about the same brightness? if they do they are likely ok and should'nt be causing the shutdown. I would not try removing them, if you break one you will need to find replacements, and there may not be a need to remove them if something else is at fault.
                        They look like they are soldered into the pc board at the ends, so they would be hard to remove anyway, check that the solder connections are good.
                        Last edited by R_J; 08-16-2019, 09:19 PM.

                        Comment


                          #13
                          Re: Philips 47PFL8404 H / 12, chassis Q548.1ELA

                          Originally posted by nomoresonys View Post
                          Hard to see in picture, do any of the tubes have a blackened looking end compared to the rest? How did the resistance test of transformer secondaries go? as always BE CAREFUL when working on HOT/DEADLY side of powerboard or inverter board.
                          So I should measure it without desoldering it from the board first?
                          Last edited by Elitebook; 08-17-2019, 07:44 AM.

                          Comment


                            #14
                            Re: Philips 47PFL8404 H / 12, chassis Q548.1ELA

                            Yes. remember it's resistance testing, which means the tv will be UNPLUGGED from power.
                            Last edited by nomoresonys; 08-17-2019, 09:47 AM.

                            Comment


                              #15
                              Re: Philips 47PFL8404 H / 12, chassis Q548.1ELA

                              Maybe check youtube for resistance testing tv transformers, if needed.

                              Comment


                                #16
                                Re: Philips 47PFL8404 H / 12, chassis Q548.1ELA

                                Put the ohm meter on its lowest scale, like 100 ohms scale as opposed to 100K ohms scale.

                                A transformer consists of 3 or more coils of wire. 2 yellow wires for example represents the leads of one coil. 2 brown wires represents the leads of another coil. You can do a quick test for each winding for an open while the transformer is still connected in a circuit. Assuming you're using a cheap inaccurate ohm meter. Look for a reading of somewhere between one and about 10 ohms. If any winding reads higher than 10 ohms you have probably found a bad transformer. Unless you didn't get a good connection to the coil leads with your test leads. Always check at least 3 times before you draw a conclusion.
                                Last edited by nomoresonys; 08-17-2019, 10:03 AM.

                                Comment


                                  #17
                                  Re: Philips 47PFL8404 H / 12, chassis Q548.1ELA

                                  Allright, I did test the transformer on both the hot and cold side. I've included this picture. The numbers are in Ohms. Black number is tested while off and green when TV is turned on. I measured it according to the drawing, I hope that its clear enough to decipher.

                                  I've shot this video of how the CCFL tubes are behaving as a good measure.

                                  https://www.youtube.com/watch?v=RFMnuZQOqfk


                                  Edit:

                                  I have to add that the cold side trafo on bottom right doesn't show any resistance from its legs. Might be that the transformer has a break inside, ie open circuit. I guess I have to desolder it to verify.
                                  Attached Files
                                  Last edited by Elitebook; 08-18-2019, 11:43 AM.

                                  Comment


                                    #18
                                    Re: Philips 47PFL8404 H / 12, chassis Q548.1ELA

                                    You don't check resistance with power on. The one secondary between 7 & 8 seems open.
                                    5 & 6 is one secondary, 7 & 8 is the other
                                    See post #6
                                    Last edited by R_J; 08-18-2019, 12:12 PM.

                                    Comment


                                      #19
                                      Re: Philips 47PFL8404 H / 12, chassis Q548.1ELA

                                      I put unplugged in capital letters, post 14.

                                      Comment


                                        #20
                                        Re: Philips 47PFL8404 H / 12, chassis Q548.1ELA

                                        Originally posted by R_J View Post
                                        You don't check resistance with power on. The one secondary between 7 & 8 seems open.
                                        5 & 6 is one secondary, 7 & 8 is the other
                                        See post #6
                                        Looking at T301 secondary side only 10 & 9 are connected instead of 5 & 6. For its neighbor 6 & 5 are connected instead of 7 & 8. I did measure it again, this time correctly.

                                        For post #6:
                                        About CN3 and CN2 connectors, only the pin in the middle has a wire plugged in it, the outer two are un-utilized. Looking at the distribution board it has only one wire going into them.
                                        From what I'm understanding the only connection these two distribution boards, the Left and Right one, make is between the CCFL tubes as pictured in the attachment. As what you've stated previously, only one of the two secondaries are giving me a readout.

                                        @R_J & @nomoresonys About the powering it on while testing the resistance part, yes what I did is stupid and very dangerous mistake.
                                        Attached Files
                                        Last edited by Elitebook; 08-18-2019, 01:22 PM.

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