TV LG 65UM7470PSA Display Doesn't Turn On

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  • ekronz
    New Member
    • Feb 2022
    • 5
    • UK
    #1

    TV LG 65UM7470PSA Display Doesn't Turn On

    Hello, people.

    My TV has gone bad about a month ago. At first it wasn't turning on from the standby state, so I replaced the mainboard. (The mainboard has a humming to it, but I believe it is normal Coil Whinning)

    Now... With the new mainboard it does turn on, however, my display isn't working properly, It doesn't turn on when I turn the TV on.

    I measured the Power-On voltage on the P201 connector, it has ok voltage when in standby (0V, according to specification), however when I turn the TV on it should have 3V+. The other pins that has voltage on the P201 should be 7.8V on standby and 13.2V when the tv is on. However, they all keep the same voltage at 7.8V, regardless of the TV state.

    Also measured the voltages across the mainboard. When it is on the Power-On voltage goes to 3.3V (which is right), however the other voltages stay at 7.8V (as if it was at standby mode)

    After checking the above, I went and measured the LED Power connector. The LED+ is measuring something around 300 and the LED- something around 130V. Also, something strange happens! When I connect the probe to the LED- the backlight turns on, is it normal?

    Finally I checked the voltage in the "green" component (check picture, I believe it is a voltage regulator) and it measured 30~40V.

    Now I'm thinking... Do I need a new powerboard? Did my LED Strips gone bad? I don't know what else to test.

    Please Help!

    Thank you all, in advance.

    Last edited by ekronz; 02-06-2022, 01:05 PM.
    Tags: None
    • CapLeaker
      Leaking Member
      • Dec 2014
      • 8215
      • Canada
      #2
      Re: TV LG 65UM7470PSA Display Doesn't Turn On

      Measure all pins with your DMM and post the pin name with the voltages measured with the TV on and off.

        Comment

        • Diah
          Badcaps Legend
          • Feb 2013
          • 6397
          • Germany
          #3
          Re: TV LG 65UM7470PSA Display Doesn't Turn On

          Originally posted by ekronz
          Hello, people.

          My TV has gone bad about a month ago. At first it wasn't turning on from the standby state, so I replaced the mainboard. (The mainboard has a humming to it, but I believe it is normal Coil Whinning)
          this TV it may smarter rather than user,, you are going to toast PCB and MB.
          changing MB not easy task if it is not 100& same series

            Comment

            • R_J
              Badcaps Legend
              • Jun 2012
              • 9557
              • Canada
              #4
              Re: TV LG 65UM7470PSA Display Doesn't Turn On

              Measure the voltage across C611 (main filter) Post this voltage in standby and when power-on

                Comment

                • ekronz
                  New Member
                  • Feb 2022
                  • 5
                  • UK
                  #5
                  Re: TV LG 65UM7470PSA Display Doesn't Turn On

                  Originally posted by CapLeaker
                  Measure all pins with your DMM and post the pin name with the voltages measured with the TV on and off.
                  On P201?

                    Comment

                    • ekronz
                      New Member
                      • Feb 2022
                      • 5
                      • UK
                      #6
                      Re: TV LG 65UM7470PSA Display Doesn't Turn On

                      Originally posted by Diah
                      this TV it may smarter rather than user,, you are going to toast PCB and MB.
                      changing MB not easy task if it is not 100& same series
                      I checked serial numbers, model, rev etc. It's the same board 100%

                      Also, the noise only appears when the TV is on

                        Comment

                        • ekronz
                          New Member
                          • Feb 2022
                          • 5
                          • UK
                          #7
                          Re: TV LG 65UM7470PSA Display Doesn't Turn On

                          Originally posted by R_J
                          Measure the voltage across C611 (main filter) Post this voltage in standby and when power-on
                          around 390V when Standby, around 380V when On

                            Comment

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