Phihips 47pfl5704d / f7 Back light not working

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  • cwolford
    Member
    • Mar 2017
    • 46
    • USA

    #1

    Phihips 47pfl5704d / f7 Back light not working

    Phihips 47pfl5704d / f7 Back light not working

    When it turns on it has a low glow on right and left side of the screen. Like the lights are trying to come on. Then it goes black.

    With a flash light I can see menu, av, etc.

    With the back off, you press power button a green led come on near the cpu.

    It stays on if I leave tv on.

    No signs of bad caps, busted / cracked IC, or missing IC legs

    There is one resistor that looks suspect , although I cannot read its value as it 5th band is black.

    I think the psu has the backlight inverter built in.

    The photos posted are top and bottom of the PSU.

    This old post I found https://www.badcaps.net/forum/showth...=47pfl5704d+f7

    About me:
    Have Computer repair knowledge, car repair knowledge, some electrical engineering knowledge not a lot not in school atm. Only have access to my tools.

    Please assume I don't know how to test a part, it has been a while since a played with IC.

    I know resistors have to be out of circuit to test.
    I know ac / dc
    I know ohms / amps / volts / ground / continuity
    I have replaced SMD by hand it's a pain.coun
    I have replaced through the hole components
    Don't remember how to test diodes / caps / relays.
    Don't remember what how to test or how they function MOV/mosfet
    Forgot stuff about using dmm oL vs o.oo ect. I will need a quick brush up, if i cant remember i will ask.

    Tools:
    All kinds of hand tools
    Hakko soldering station fx-888 + other soldering tools
    DMM : uni-t UT61E
    analogue multimeter
    Sparkfun arduino invetor kit
    Old PC PSU willing to use for benchtop psu
    Attached Files
  • cwolford
    Member
    • Mar 2017
    • 46
    • USA

    #2
    Re: Phihips 47pfl5704d / f7 Back light not working

    Bottom photos and one more of the top.


    I can take more photos of what ever area if they are not clear enough. Will work on getting better photos anyway.

    I can put back in to do volt test too. Looking for what to do now, also maybe guide me through why you think i need to test xyz. I want to learn as i go thanks.
    Attached Files
    Last edited by cwolford; 03-02-2017, 08:41 PM.

    Comment

    • dskall
      Badcaps Legend
      • Oct 2016
      • 2905
      • usa

      #3
      Re: Phihips 47pfl5704d / f7 Back light not working

      You might want to look at this post https://www.badcaps.net/forum/showth...er+testing+cfl
      I assume no responsibility for any stupid suggestions I might post.

      Comment

      • cwolford
        Member
        • Mar 2017
        • 46
        • USA

        #4
        Re: Phihips 47pfl5704d / f7 Back light not working

        This would tell me if it was bad psu or back light right? I assume that the back lights connectors are the 2 (2 wire ) connectors that run to the LCD pannle from the PSU.

        The connector on the PSU have 3 pin But the Connectors only use 2. See photo.


        EDIT
        TO any one: The resistor with the spot on it, that might be bad, that i dont know how to read. Its is located between heat sink 2 and 3. I labeled them at some point.
        Attached Files
        Last edited by cwolford; 03-02-2017, 09:48 PM.

        Comment

        • dick_barton
          Badcaps Legend
          • Aug 2015
          • 6642
          • Wales

          #5
          Re: Phihips 47pfl5704d / f7 Back light not working

          Originally posted by cwolford
          The resistor with the spot on it, that might be bad, that i dont know how to read. Its is located between heat sink 2 and 3. I labeled them at some point.
          Try and take a clear photo of it showing its colours and also what you meter reads when you measure it.
          Willing to help but I'm no expert.

          Comment

          • dick_barton
            Badcaps Legend
            • Aug 2015
            • 6642
            • Wales

            #6
            Re: Phihips 47pfl5704d / f7 Back light not working

            What DC voltages do you have on DIM & BL_ON/OFF (pic5, Post #2) when you power up out of standby.
            Willing to help but I'm no expert.

            Comment

            • cwolford
              Member
              • Mar 2017
              • 46
              • USA

              #7
              Re: Phihips 47pfl5704d / f7 Back light not working

              Originally posted by dick_barton
              Try and take a clear photo of it showing its colours and also what you meter reads when you measure it.
              5 band resistor brown blue blue gold black

              I will remove it after i use the dmm on the psu to get the volts you want. Then I will use the DMM on it.

              I posted a better photo of it in the first post, i Added the one on the 2nd as it shows the spot better.

              https://www.badcaps.net/forum/attach...9&d=1488508394

              Comment

              • cwolford
                Member
                • Mar 2017
                • 46
                • USA

                #8
                Re: Phihips 47pfl5704d / f7 Back light not working

                Originally posted by dick_barton
                What DC voltages do you have on DIM & BL_ON/OFF (pic5, Post #2) when you power up out of standby.
                Dim volt readings:
                power on ~3.3v then jumps to ~14v Then settles at ~1.68v

                BL_ON/OFF power on:
                it spikes some times But always settles at ~3.17v
                Power on 3 times. The spike is like less than second.
                1st time ~5v
                2nd time no spike just ~3v
                3rd time ~10v

                So if i ground Bl_ON/Off The side of the tv light up but dont kick on. IT was an accident

                Comment

                • CapLeaker
                  Leaking Member
                  • Dec 2014
                  • 7972
                  • Canada

                  #9
                  Re: Phihips 47pfl5704d / f7 Back light not working

                  If you get BLon at 10V DC, there is something totally wrong, because you only have 5V STBY. So either there is a measurement error or your batteries in your DMM are low.

                  The BLon comes from the main board. Shorting that to ground is not good at all. That's another way of kissing the main board good bye.

                  Comment

                  • cwolford
                    Member
                    • Mar 2017
                    • 46
                    • USA

                    #10
                    Re: Phihips 47pfl5704d / f7 Back light not working

                    Originally posted by CapLeaker
                    If you get BLon at 10V DC, there is something totally wrong, because you only have 5V STBY. So either there is a measurement error or your batteries in your DMM are low.

                    The BLon comes from the main board. Shorting that to ground is not good at all. That's another way of kissing the main board good bye.
                    If you look at the board, my probe slipped off and hit the ground right next to it.

                    I tested it like 5 or 6 times and It only hit that high number once.

                    it was for a split sec as soon as it powered on, I wish i could log it with a better dmm, but it may be just my dmm not able to take reading fast enough.

                    Comment

                    • cwolford
                      Member
                      • Mar 2017
                      • 46
                      • USA

                      #11
                      Re: Phihips 47pfl5704d / f7 Back light not working

                      the resistor i don't know the value of measured 0.29 ohms
                      5 band resistor brown blue blue gold black
                      or red grey grey gold black

                      The two in the middle look shine not sure if blue are grey. Too the eye they look the same color. In photo they look different.

                      the first one could be red or brown not sure.

                      I dont know what to do about the black at the end tho.
                      Attached Files
                      Last edited by cwolford; 03-03-2017, 08:15 PM.

                      Comment

                      • budm
                        Badcaps Legend
                        • Feb 2010
                        • 40746
                        • USA

                        #12
                        Re: Phihips 47pfl5704d / f7 Back light not working

                        You reading the resistance of the meter leads + the resistance of the resistor, it looks like 0.18 Ohms resistor, so it is OK.
                        Never stop learning
                        Basic LCD TV and Monitor troubleshooting guides.
                        http://www.badcaps.net/forum/showthr...956#post305956

                        Voltage Regulator (LDO) testing:
                        http://www.badcaps.net/forum/showthr...999#post300999

                        Inverter testing using old CFL:
                        http://www.badcaps.net/forum/showthr...er+testing+cfl

                        Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                        http://s807.photobucket.com/user/budm/library/

                        TV Factory reset codes listing:
                        http://www.badcaps.net/forum/showthread.php?t=24809

                        Comment

                        • budm
                          Badcaps Legend
                          • Feb 2010
                          • 40746
                          • USA

                          #13
                          Re: Phihips 47pfl5704d / f7 Back light not working

                          Originally posted by cwolford
                          the resistor i don't know the value of measured 0.29 ohms
                          5 band resistor brown blue blue gold black
                          or red grey grey gold black

                          The two in the middle look shine not sure if blue are grey. Too the eye they look the same color. In photo they look different.

                          the first one could be red or brown not sure.

                          I dont know what to do about the black at the end tho.
                          That R517 is the Source resistor for the power MOSFET Q501 which drives the power transformer T501 for the 12V and +VAMP power supply. So if you do have +12VDC at the connector then that power supply section is working.

                          This looks like your power supply:
                          Philips 272217100692 Power Supply / Backlight Inverter
                          http://www.shopjimmy.com/catalogsear.../?q=47pfl5704d

                          Pictures provided by shopjimmy.
                          So if you look at the TV in the dark, do you see the backlights even flash on for seconds?
                          Attached Files
                          Never stop learning
                          Basic LCD TV and Monitor troubleshooting guides.
                          http://www.badcaps.net/forum/showthr...956#post305956

                          Voltage Regulator (LDO) testing:
                          http://www.badcaps.net/forum/showthr...999#post300999

                          Inverter testing using old CFL:
                          http://www.badcaps.net/forum/showthr...er+testing+cfl

                          Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                          http://s807.photobucket.com/user/budm/library/

                          TV Factory reset codes listing:
                          http://www.badcaps.net/forum/showthread.php?t=24809

                          Comment

                          • cwolford
                            Member
                            • Mar 2017
                            • 46
                            • USA

                            #14
                            Re: Phihips 47pfl5704d / f7 Back light not working

                            Yes there is an 4 inch glow up and down the left and right side.
                            Last edited by cwolford; 03-03-2017, 09:24 PM.

                            Comment

                            • budm
                              Badcaps Legend
                              • Feb 2010
                              • 40746
                              • USA

                              #15
                              Re: Phihips 47pfl5704d / f7 Back light not working

                              Are you getting about 380~400 VDC between the two legs of either one of the two 450vdc main filter caps laying on its side when TV is turned on?
                              It sounds like the inverter is running but not putting out enough high Voltage to light up the whole length of the lamps., it may be inverter transformer too.
                              Is there any sign of over heated inverter transformer T701? Look real close on top and bottom side of the board where the inverter transformer is.
                              Last edited by budm; 03-03-2017, 09:43 PM.
                              Never stop learning
                              Basic LCD TV and Monitor troubleshooting guides.
                              http://www.badcaps.net/forum/showthr...956#post305956

                              Voltage Regulator (LDO) testing:
                              http://www.badcaps.net/forum/showthr...999#post300999

                              Inverter testing using old CFL:
                              http://www.badcaps.net/forum/showthr...er+testing+cfl

                              Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                              http://s807.photobucket.com/user/budm/library/

                              TV Factory reset codes listing:
                              http://www.badcaps.net/forum/showthread.php?t=24809

                              Comment

                              • cwolford
                                Member
                                • Mar 2017
                                • 46
                                • USA

                                #16
                                Re: Phihips 47pfl5704d / f7 Back light not working

                                I want to make damn sure I do this right. That's high voltage. Am I probing ground and a leg of the cap or using both legs. And ground as in metal frame.

                                Comment

                                • cwolford
                                  Member
                                  • Mar 2017
                                  • 46
                                  • USA

                                  #17
                                  Re: Phihips 47pfl5704d / f7 Back light not working

                                  Between the legs of each cap its 398 to 400v

                                  I don't know what to look for in the transformer but it does not look melted or discolored.

                                  Comment

                                  • cwolford
                                    Member
                                    • Mar 2017
                                    • 46
                                    • USA

                                    #18
                                    Re: Phihips 47pfl5704d / f7 Back light not working

                                    "it does use CCFL and it has circuit board inside the panel with Balancer cap for each tube," should I tear it down and look a the balancer caps?

                                    Comment

                                    • cwolford
                                      Member
                                      • Mar 2017
                                      • 46
                                      • USA

                                      #19
                                      Re: Phihips 47pfl5704d / f7 Back light not working

                                      I would like to check the inverter transformer, but not sure I can if these are the right specs it is to give out:
                                      Min. Type. Max
                                      VBL 1150 1350 1550 VRMS

                                      I don't think my dmm can read that it's to high. Any input?

                                      Comment

                                      • CapLeaker
                                        Leaking Member
                                        • Dec 2014
                                        • 7972
                                        • Canada

                                        #20
                                        Re: Phihips 47pfl5704d / f7 Back light not working

                                        You could measure that with a high voltage probe no problem. But not everyone has this. Could be a bad transformer, bad caps, cold solder joint etc.

                                        Comment

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