LG 55UB850V doesn’t turn on

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  • tehmatix
    Senior Member
    • Nov 2012
    • 174
    • UK
    #1

    LG 55UB850V doesn’t turn on

    Hi,
    The red led flashing continuously.
    I checked the power supply board and found 3.5V fluctuating down and up
    I replaced the capacitors and the voltage , 3.5V still varying
    On bridge rectifier 320V
    Attached Files
    Tags: None
    • Diah
      Badcaps Legend
      • Feb 2013
      • 6357
      • Germany
      #2
      Re: LG 55UB850V doesn't turn on

      disconect the main boards from PWB and check yours STB 3.5V stable or not !

        Comment

        • tehmatix
          Senior Member
          • Nov 2012
          • 174
          • UK
          #3
          Re: LG 55UB850V doesn't turn on

          I disconnected from main board and it does the same thing

            Comment

            • Diah
              Badcaps Legend
              • Feb 2013
              • 6357
              • Germany
              #4
              Re: LG 55UB850V doesn't turn on

              check your replacment capacitors if the legs - + correct or one faulty / stock one.

                Comment

                • nomoresonys
                  Badcaps Legend
                  • Jan 2013
                  • 12129
                  • U.S.
                  #5
                  Re: LG 55UB850V doesn't turn on

                  hit the ones you didn't change out with a hairdryer for a couple minutes, see if the voltage gets stable for a bit.

                    Comment

                    • nomoresonys
                      Badcaps Legend
                      • Jan 2013
                      • 12129
                      • U.S.
                      #6
                      Re: LG 55UB850V doesn't turn on

                      I test simple things first, including all diodes and resistors on top of board and all solder joints, look very closely at the solder joints, reflow any that look suspect, careful not to bridge any, examples of bad joints there if needed: https://www.google.com/search?q=bad+...ih=607&dpr=1.5

                        Comment

                        • nomoresonys
                          Badcaps Legend
                          • Jan 2013
                          • 12129
                          • U.S.
                          #7
                          Re: LG 55UB850V doesn't turn on

                          If those things check out, check the diodes and transistors on the heatsinks, youtube is your friend for transistor testing.

                            Comment

                            • tehmatix
                              Senior Member
                              • Nov 2012
                              • 174
                              • UK
                              #8
                              Re: LG 55UB850V doesn't turn on

                              Hi,
                              I re-soldered pads and checked the diodes and capacitors. 3,5V it still variable.
                              On pin 7 at ICE3BR4765J , Vcc voltage is variable. I think the optocupler on FB pin is damage. I will change it and I will come back latter

                                Comment

                                • nomoresonys
                                  Badcaps Legend
                                  • Jan 2013
                                  • 12129
                                  • U.S.
                                  #9
                                  Re: LG 55UB850V doesn't turn on

                                  Did you try post #5.

                                    Comment

                                    • tehmatix
                                      Senior Member
                                      • Nov 2012
                                      • 174
                                      • UK
                                      #10
                                      Re: LG 55UB850V doesn't turn on

                                      No, I didn't tried to heat the board/components

                                        Comment

                                        • nomoresonys
                                          Badcaps Legend
                                          • Jan 2013
                                          • 12129
                                          • U.S.
                                          #11
                                          Re: LG 55UB850V doesn't turn on

                                          And...no hairdryer?

                                            Comment

                                            • tehmatix
                                              Senior Member
                                              • Nov 2012
                                              • 174
                                              • UK
                                              #12
                                              Re: LG 55UB850V doesn't turn on

                                              Yes, hairdryer no effects
                                              Optpcoupler changed no effects
                                              Output diode for 3,5V changed no effects
                                              Moving forward I replaced the entire 3.5V psi with an external one:
                                              - red led stay on solid
                                              - when press button on remote control on main board those 2 leds flashing one , tv doesn’t turn on, front red led turn on
                                              - no other aux voltage 12v or 24v or backlight
                                              I suspect a software glitch caused by 3.5V pulses

                                                Comment

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