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LG 47" 47LN570Y Can I switch PSUs of same Series ?

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    LG 47" 47LN570Y Can I switch PSUs of same Series ?

    No joy with LG 47" 47LN570Y.
    Was hoping for a quick BackLight ( BL) repair in order to get back to another job.

    On start : BL blips. Image OK. BL Strips OK (Led Tester on each) . i.e LED Driver issue. All PSU Caps look OK.

    2 Quick questions :

    first : With no BL connected , should there be output V on the PSU BL connector ? ( something I finally realized I need to clarify )

    2nd : I got PSU of 42LN570Y , it is smaller. Main's connector identical EAX64905(3)501 ( 42 has 3 not 5) : I upload photo of the important info with them. Do you think it can be used instead? ( I will repair the board of the 47" later)

    Thank you
    Attached Files
    Last edited by Ancient1; 01-18-2022, 08:22 AM.

    #2
    Re: Can I switch PSUs of same Series ?

    You likely still have a backlight issue. Your tester only puts out 10-20mA while your TV runs around 300mA. Record the flash of backlights with the panel off and go frame by frame and you should see a few LEDs not lighting up. Intermittent LEDs can also have fluctuating voltages which can trigger the shutdown. Replace all the strips with NEW. PS for a 42 vs 47 TV will have different trigger voltages for shutdown since the number of LEDs is different.

    Comment


      #3
      Re: Can I switch PSUs of same Series ?

      Thank you

      I lighted each of the 6 strips (12 sections ) with my LED Tester ( it raises the V slowly) : They ALL lighted up, though one LED was a late bloomer.
      The Dilemma is of course, to get a definite answer that it isn't a board issue.

      I guess the board will not output the BL V without a load ?

      Comment


        #4
        Re: Can I switch PSUs of same Series ?

        Originally posted by Ancient1 View Post
        Thank you

        I lighted each of the 6 strips (12 sections ) with my LED Tester ( it raises the V slowly) : They ALL lighted up, though one LED was a late bloomer.
        The Dilemma is of course, to get a definite answer that it isn't a board issue.

        I guess the board will not output the BL V without a load ?
        The LED Driver IC upon the Main Board has a feedback circuit built into it that monitors the return voltage from the backlight string. If it isn't within a very specific range the IC will shut down the LED driver portion of the Main Board and you will see no voltage.

        Try monitoring the voltage on one pair of the LED output at the Power Supply. Unplug the TV, attach the leads of the voltmeter to + and - that are next to one another and while plugging the TV in monitor the voltage. If you see a voltage flash that drops back to 0 the LED driver is working. If you see no voltage then turn the TV on while monitoring the voltage. If you get a voltage flash that drops back to 0 the LED driver is good.

        The fact you get a backlight flash when you turn the TV on is proof the LED driver portion of the Main Board is working. Furthermore it only takes 64/1000 of a second for the LED driver to determine there's a problem in the LED strings and turn off the LED driver portion of the PS. The late bloomer LED won't light within that time so the LED Driver IC won't get the proper return voltage in that time and will shut down the LED Driver on the PS.

        LG TVs of this era are notorious for cooking the backlights resulting in the symptoms you are seeing.
        They call me......."threadkiller"

        Comment


          #5
          Re: Can I switch PSUs of same Series ?

          DXseekerMO

          You're the MAN. Detailed explanation with the DOs and DON'Ts : Just what the doctor ordered THANK YOU

          I do see proper LOGO for a brief moment. So that settles it all.

          I am familiar with that brief flash of the Backlight of course. But usually there's a dark, non working LED. Here , ALL (eventually) light up, hence my (now resolved ) dilemma

          I am thinking now on creating a bypass to that slow LED . I expect BL to work.
          I do have old/spare LEDs to choose a right size LED ( not the Lens ) and I can of course compare the light, and if I find one I can cut the strip, solder it after removing ( and isolating ) the slow LED . What do you think ?

          Comment


            #6
            Re: LG 47" 47LN570Y Can I switch PSUs of same Series ?

            Using LED Tester :
            High Current setting : All LEDs light up . (device shows : 42mA. ) = confusion
            Low Current setting : 2 LEDs do NOT light up. ( device shows : 5.5mA. ) = all clear

            Comment


              #7
              Re: LG 47" 47LN570Y Can I switch PSUs of same Series ?

              2 LEDs replaced ( stacking method)
              BL lights up properly

              Diagnosis correct

              Thanks

              Comment


                #8
                Re: LG 47" 47LN570Y Can I switch PSUs of same Series ?

                LN series strips are very inexpensive on Aliexpress $20 to $25 USD. All the LEDs have wear and the remaining ones will likely fail in the future. Just replace them all with NEW as I mentioned before. I don't bother repairing individual LEDs If I can find new strips at a reasonable price.
                Last edited by neilc6; 01-21-2022, 03:47 PM.

                Comment


                  #9
                  Re: LG 47" 47LN570Y Can I switch PSUs of same Series ?

                  neilc6
                  I know, once a certain period passes , the likelihood of failure rises , hence if two are burnt , it could be a sign their time is up.
                  However, the 2 LEDs I replaced were not burnt. ALL worked with the LED Tester on High Current. They didn't light up with low current setting. Their reaction time was slower ? , causing the Driver to shut down.
                  I thought about replacing them all.. but I have a mixed feeling about this.. Maybe their time isn't up yet
                  I think I'll inform the buyer, that if he has BL issue he should pay for a new set. This might happen after 1 year
                  dilemma..

                  Even cheaper than $20 . Buying
                  Last edited by Ancient1; 01-22-2022, 02:51 AM.

                  Comment


                    #10
                    Re: LG 47" 47LN570Y Can I switch PSUs of same Series ?

                    I received the new LED Strip set

                    But discovered the Panel got broken. Looks like it slipped out of place since I didn't fasten it in its place as I should have

                    Attached Files

                    Comment


                      #11
                      Re: LG 47" 47LN570Y Can I switch PSUs of same Series ?

                      So easy for lcd panels to get damaged like this, i did the same on my first backlight repair job. Luckily as you know all the boards work you could sell them on if you wanted.

                      Comment


                        #12
                        Re: LG 47" 47LN570Y Can I switch PSUs of same Series ?

                        Sadly its my 2nd panel I break.
                        I was extremely careful with this one, but what I've learned from this is that they are not designed the same. In this TV , you can see the little bump in the plastic near the edge ? It would look well seated if you look at the middle of the frame. AND, it slipped a bit , since I should have used , and screwed, the metal frames around as they are meant to keep it in place.
                        Lesson : Always reassemble the Panel in Frame properly , even if you know you'll reopen later on. don't be lazy !

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