Panasonic TX-L37E3B Green light but nothing else..

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  • sickboy
    Senior Member
    • Jun 2015
    • 86
    • UK

    #1

    Panasonic TX-L37E3B Green light but nothing else..

    Hello everyone.
    So I have this Panasonic TX-L37E3B which when switched on, the green LED flashes rapidly for 2 or 3 seconds, then stays on. No picture and no backlight at all. I can't determine if there's any sound.
    I immediately thought it will be a bad backlight LED so stripped the screen down, but the backlight strip is not like the Vestel ones I'm used to. It's on one aluminium strip at the bottom of the screen. I have a backlight tester but the strip seems more complicated, with 3 wires connecting at each side. I've tested each individual LED and they all work. While the TV is switched on there is zero voltage at the strips however. I cannot test voltage at the exact moment of switch on (I need an extra pair of hands!)
    Does anyone have experience of this model or this fault?
    Attached Files
  • Diah
    Badcaps Legend
    • Feb 2013
    • 6355
    • Germany

    #2
    Re: Panasonic TX-L37E3B Green light but nothing else..

    1- Panasonic always suffer from bad LED back light socket due temperature they mild or the solder will be out of work. take the plate out and inspect the socket first
    if the socket OK. then you have open Zinner Diode on one of the groups which will not forward currents to next LED, need to test them all one by one as diode test. when you change the probe Red black at test it should read diode. and when you reserve the probe it should lid on lightly
    Last edited by Diah; 06-13-2019, 08:29 AM.

    Comment

    • sickboy
      Senior Member
      • Jun 2015
      • 86
      • UK

      #3
      Re: Panasonic TX-L37E3B Green light but nothing else..

      Thank you, do you mean the sockets on the LED strip?

      Comment

      • Diah
        Badcaps Legend
        • Feb 2013
        • 6355
        • Germany

        #4
        Re: Panasonic TX-L37E3B Green light but nothing else..

        Originally posted by sickboy
        Thank you, do you mean the sockets on the LED strip?
        yes

        Comment

        • budm
          Badcaps Legend
          • Feb 2010
          • 40746
          • USA

          #5
          Re: Panasonic TX-L37E3B Green light but nothing else..

          https://www.badcaps.net/forum/attach...3&d=1560434141
          You have 4 strings of LED's, One red wire for 4 blue wires for 4 LED strings, same for another set, so the test each string you will remove the connector from the LED driver board then put red probe on red wire and Black probe on each blue wire of the LED set, the do the same for the second set of the LED's.
          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

          • sickboy
            Senior Member
            • Jun 2015
            • 86
            • UK

            #6
            Re: Panasonic TX-L37E3B Green light but nothing else..

            Thanks guys.
            I've resoldered the plugs on the LED strip Diah but still the same problem unfortunately.

            Budm, thank you for the info. Using the backlight tester, all 4 strings of LEDs operate correctly with no fault shown. It looks as if my fault lies further back possibly? I'll try and rig something up so that I can monitor the backlight voltage at switch-on.

            Comment

            • budm
              Badcaps Legend
              • Feb 2010
              • 40746
              • USA

              #7
              Re: Panasonic TX-L37E3B Green light but nothing else..

              You have two set of 4-String, so 8 LED strings total.
              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

              • sickboy
                Senior Member
                • Jun 2015
                • 86
                • UK

                #8
                Re: Panasonic TX-L37E3B Green light but nothing else..

                Yes sorry Budm, I meant 4 strings each side. I've just managed to get back to this TV and the first thing I did was test for voltage on the LED plug at switch on and there is none at all, with the plug in or out there are zero volts. I wish I tried that before stripping the screen down lol, lesson learnt.
                Checking around on the small LED driver board it does have a 24v supply, not sure what other voltages should be there though. One electrolytic cap has a voltage rating of 160v but this remains at a steady 24v across it when switching on so clearly somewthing amiss.
                These LED driver boards are really cheap on ebay so I might buy one, but would prefer to get the fault to component level if possible?

                Comment

                • budm
                  Badcaps Legend
                  • Feb 2010
                  • 40746
                  • USA

                  #9
                  Re: Panasonic TX-L37E3B Green light but nothing else..

                  https://www.badcaps.net/forum/attach...3&d=1560434141
                  The 24V is the feeding Voltage to the boost converter circuits (you can see the two inductor 470C printed on top and associate MOSFET's and that LED driver IC. The output should be over 100V when BL-ON signal is present.
                  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

                  • sickboy
                    Senior Member
                    • Jun 2015
                    • 86
                    • UK

                    #10
                    Re: Panasonic TX-L37E3B Green light but nothing else..

                    Happy to report this is now fixed. The annoying thing though was that I needn't have even removed a single screw - never mind disassembling the screen!
                    Someone on another forum pointed me in the direction of a PDF file which described the TV being locked up due to "changes in the way EPG data is now being broadcast".
                    The fix was to power the TV on at the mains while holding the channel up button on rear of the set.
                    I'll try and link the PDF shortly for future forum users. Thanks for everyone's time who tried to help!

                    Comment

                    • sickboy
                      Senior Member
                      • Jun 2015
                      • 86
                      • UK

                      #11
                      Re: Panasonic TX-L37E3B Green light but nothing else..

                      Panasonic EPG lockout.

                      We have had a number of reported cases of the TV being locked up, i.e. not operating normally.
                      We believe that this is due to the changes in the way EPG data is now being broadcast and
                      found that this primarily affects units produced between 2011 to 2013, and occurs if the
                      TV is left in standby overnight.

                      In order to recover normal operation of the TV, please follow the steps below.
                      (Note: It may not be necessary to carry out all steps, e.g. if TV recovers after
                      step 1 you do not need to carry out steps 2 and 3).

                      Firstly switch off the mains supply and disconnect the aerial from the TV.

                      1) Press and hold the power button located on the unit (not the remote control)
                      and switch on mains supply whilst holding the power button until the unit powers up.

                      Or

                      2) Switch on mains supply, then press and hold the program up button (+) on the side
                      of the unit, until the unit powers up.

                      Or

                      3) Switch on mains supply, press and hold the power button on the unit until the unit powers up.

                      Once the TV has powered up, re-connect the aerial input.

                      To prevent, this phenomenon re-occurring, we advise the following steps are carried out:

                      A) Carry out a shipping mode on the unit and retune stations.
                      B) Turn Off New Station Found function.
                      C) Turn Off New Software Update.
                      D) It is recommended to power off completely and NOT to leave the unit in standby overnight.
                      Last edited by sickboy; 06-15-2019, 08:06 AM.

                      Comment

                      • nomoresonys
                        Badcaps Legend
                        • Jan 2013
                        • 12099
                        • U.S.

                        #12
                        Re: Panasonic TX-L37E3B Green light but nothing else..

                        Nice fix, thanks for sharing.

                        Comment

                        • budm
                          Badcaps Legend
                          • Feb 2010
                          • 40746
                          • USA

                          #13
                          Re: Panasonic TX-L37E3B Green light but nothing else..

                          So basically, the broadcaster can screw up lot of people TV's out there.
                          https://www.theregister.co.uk/2014/0..._freetime_epg/
                          I am surprise that it can screw up the TV that bad, but if you only use TV for games or DVD only then you are safe from the screw up.
                          Do you have the link to that web site?
                          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

                          • sickboy
                            Senior Member
                            • Jun 2015
                            • 86
                            • UK

                            #14
                            Re: Panasonic TX-L37E3B Green light but nothing else..

                            Originally posted by budm
                            Do you have the link to that web site?
                            It was basically just a link to a pdf file stored on another TV repair forum (and wasn’t accessible unless you were a member of that forum). I didn’t want to risk breaking any forum rules here so instead I copy and pasted the full text of the original pdf above.

                            Presumably Panasonic must’ve given themselves quite a headache with this EPG glitch on older sets. I’m surprised they didn’t foresee it since it seems they played a role in developing the newer EPG data themselves.
                            Last edited by sickboy; 06-15-2019, 06:39 PM.

                            Comment

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