LG 43LJ594V PS pulsing. TV won't go to stby

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  • edugimeno
    Badcaps Veteran
    • May 2017
    • 568
    • Spain
    #1

    LG 43LJ594V PS pulsing. TV won't go to stby

    Hi There!
    I just got this TV set. It won't even light up the st-by led.

    I opened the set and the PS is model LGP43DJ-17F1.

    Only 2 secondary voltages: 13,2V for main and 68V for BL

    BL capacitor gets steady 90V (but at this time the voltage is not latched onto the BL strips, so it sees it open)

    13,2V capacitors get 7,8->8v pulsing a little.

    All this both with connectors to main & BL and without them, no change
    I hace checked all diodes on board and they all test OK (on board) both in forward (0,4-0,6v) and reverse (open). Also no SMD diodes & mosfets in back side show continuity between their legs

    I can't find the schematic for this board.
    Can anyone figure out where to look first?

    Thanks

    Attached pics of PS board
    Attached Files
    Tags: None
    • edugimeno
      Badcaps Veteran
      • May 2017
      • 568
      • Spain
      #2
      Re: LG 43LJ594V PS pulsing. TV won't go to stby

      Uh... according to the attached document, it looks like 7.8-8v is correct when TV is OFF...

      Maybe that's because this TV doesn't have a standalone 5v_stby voltage and maybe it lowers the mains voltage while off

      Does it make sense? Why is the stby led off?

      Thanks
      Attached Files

        Comment

        • lotas
          Badcaps Legend
          • Jan 2016
          • 4479
          • Russia
          #3
          Re: LG 43LJ594V PS pulsing. TV won't go to stby

          LG 43LJ594V Service manual.
          Attached Files

            Comment

            • nomoresonys
              Badcaps Legend
              • Jan 2013
              • 12082
              • U.S.
              #4
              Re: LG 43LJ594V PS pulsing. TV won't go to stby

              DO the first test there in your attachment, Forcing smps on with a jig.

                Comment

                • edugimeno
                  Badcaps Veteran
                  • May 2017
                  • 568
                  • Spain
                  #5
                  Re: LG 43LJ594V PS pulsing. TV won't go to stby

                  Ok I got some updates today

                  I checked the PS board with the suggested method in my previously attached PDF. 3v to PWR_ON and "13v" voltage rises from 7.8V (meaning STBY in this setup) to 13V (meaning full ON).

                  Then applied 3v to DRV_ON as well and got 159V on BL socket, exactly the expected voltage from specs PDF

                  Also I plugged the LED strips into its socket and this voltage was ok to light up the backlight (although very blueish, so these will need replacing sooner or later)

                  So I call the PS board GOOD. I put it back into the set to test again.

                  Same symptom, no stby led on, still I clicked on the front panel button and tried the remote PWR_ON and nothing changed, no BL, no 13V (still 7.8v).

                  So this sounds like a bad MAIN board? (attached pics from MAIN) What are my chances that I buy a new one and it works? I also tried with all the other wiring in MAIN board disconnected (SPKRs and LVDS to tcon) and nothing changed

                  Is there any chance that the small board inside the remote IR sensor/push switch could be the issue? How can I test this? I don't want to pay for a new main board and have any risk on not being the issue...

                  Thanks!
                  Attached Files

                    Comment

                    • edugimeno
                      Badcaps Veteran
                      • May 2017
                      • 568
                      • Spain
                      #6
                      Re: LG 43LJ594V PS pulsing. TV won't go to stby

                      Let me add something myself...
                      Provided this PS only generates one single voltage to the main board, it is expected that the main board has several sub power supplies
                      If the stby led doesn't even power up, this probably means the sub PS that provides voltage for the stby led is dead or shorted out. Does this make sense?
                      Would it be easy to find out where to start to look at?

                      Thanks!

                        Comment

                        • CapLeaker
                          Leaking Member
                          • Dec 2014
                          • 8020
                          • Canada
                          #7
                          Re: LG 43LJ594V PS pulsing. TV won't go to stby

                          Kind of. VSB is generated on the PSU. So make sure the PSU is generating VSB. That goes either directly or through a buck regulator to the main IC on the main board.. Most of the TV’s I repaired with this issue ended up with the problem being on the main IC.

                            Comment

                            • edugimeno
                              Badcaps Veteran
                              • May 2017
                              • 568
                              • Spain
                              #8
                              Re: LG 43LJ594V PS pulsing. TV won't go to stby

                              This PS is a bit different than other I've seen. It only has one output. This output generates either 7.8V when in Stbdy (off) to keep the IR and other stuff alive, and then switches to 13V when ON to power on everything else. I checked this switching with PS_ON hi and lo and it works perfect.

                              So all goes on this single PS output.

                              I can see a bunch of other dc-dc converters on the main board. Is it worth to try to diagnose them all and see if any of them is faulty?

                                Comment

                                • ReeceyBurger123
                                  Never Give Up !
                                  • May 2014
                                  • 7325
                                  • Britain
                                  #9
                                  Re: LG 43LJ594V PS pulsing. TV won't go to stby

                                  Originally posted by edugimeno
                                  This PS is a bit different than other I've seen. It only has one output. This output generates either 7.8V when in Stbdy (off) to keep the IR and other stuff alive, and then switches to 13V when ON to power on everything else. I checked this switching with PS_ON hi and lo and it works perfect.

                                  So all goes on this single PS output.

                                  I can see a bunch of other dc-dc converters on the main board. Is it worth to try to diagnose them all and see if any of them is faulty?
                                  See if there's shorts to gnd, I've had this board with mlccs short.
                                  Please Do Not PM My Page Asking For Help Badcaps Is The Place For Advise, Page Linked For Business Reasons Only. Anyone Doing So Will Be Banned Instantly !

                                  https://www.facebook.com/Telford-Tel...7894576335359/

                                    Comment

                                    • edugimeno
                                      Badcaps Veteran
                                      • May 2017
                                      • 568
                                      • Spain
                                      #10
                                      Re: LG 43LJ594V PS pulsing. TV won't go to stby

                                      Originally posted by ReeceyBurger123
                                      See if there's shorts to gnd, I've had this board with mlccs short.
                                      Ok that seems easy to test, will check that tonight
                                      Thanks

                                        Comment

                                        • edugimeno
                                          Badcaps Veteran
                                          • May 2017
                                          • 568
                                          • Spain
                                          #11
                                          Re: LG 43LJ594V PS pulsing. TV won't go to stby

                                          Ok I checked the main board ok. Found no shorted caps, but I'm starting a new thread for this as the subject changed...

                                          https://www.badcaps.net/forum/showthread.php?p=1238940

                                            Comment

                                            • edugimeno
                                              Badcaps Veteran
                                              • May 2017
                                              • 568
                                              • Spain
                                              #12
                                              Re: LG 43LJ594V PS pulsing. TV won't go to stby

                                              TV has been fixed, there was a fried choke very close to the socket from PS board, in the +13V line, that was feeding a shorted to GND capacitor.

                                              All good now, thanks everyone

                                                Comment

                                                • Diah
                                                  Badcaps Legend
                                                  • Feb 2013
                                                  • 6346
                                                  • Germany
                                                  #13
                                                  Re: LG 43LJ594V PS pulsing. TV won't go to stby

                                                  good job- the credit to @ReeceyBurger123 who pointed to same fault

                                                    Comment

                                                    • edugimeno
                                                      Badcaps Veteran
                                                      • May 2017
                                                      • 568
                                                      • Spain
                                                      #14
                                                      Re: LG 43LJ594V PS pulsing. TV won't go to stby

                                                      Exactly, but the short was "hidden" due to a tinitiny blown choke...I was about to order a new main board for this TV. I still have to replace the led strips as they have the blue-tint-of-death... (C) LG

                                                        Comment

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