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LG LED TV Model 42LE5300 not switching on

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    LG LED TV Model 42LE5300 not switching on

    Hi Guys,
    I have another unit that's beating me up here.

    This set starts up and is in standby mode. Upon pressing the power button the set makes a relay clicking sound and then the on board "piezo speaker" which sounds when pressing any of the on board buttons starts making a long beeping sound. In the mean time the secondary voltages (those that should start up when pressing the power button) do not come up.
    This is my findings so far.

    1. When adding a 680 ohm resistor from +3.5V rail to the "Power ON" pin to force PSU secondary voltages on my PFC circuit does work because my mains smoothing cap voltage goes from 330VDC to 393VDC.
    2. The power supply section responsible to generate the secondary voltages is operated by a L6599D. I scoped the gate drive pulses on switch on and i could briefly see some square waves but it shut down.
    3. I then checked all secondary diodes for short. Only thing i saw was the Schottky diode is leaky in reverse bias but that's normal.
    4. I replaced L6599D with no difference
    5. I checked opto coupler and zener on the feedback circuit and found no fault. There is however a SMD chip with a marking "438" which is 3 pin and might be a SMD type KIA431, not sure could not test.
    I have added pictures as needed to assist you in your diagnosis.
    All tests above were done without the main connected and PSU forced on.
    Attached Files

    #2
    Re: LG LED TV Model 42LE5300 not switching on

    I have added the PSU to main plug voltages whilst all boards connected and wrote down both standby and power on voltages
    Attached Files

    Comment


      #3
      Re: LG LED TV Model 42LE5300 not switching on

      Any help would be greatly appreciated.

      Comment


        #4
        Re: LG LED TV Model 42LE5300 not switching on

        looks like i will be forced to order the complete power supply. 51 Views and no response must mean a real head scratcher.

        Comment


          #5
          Re: LG LED TV Model 42LE5300 not switching on

          .
          Last edited by nomoresonys; 02-11-2019, 10:55 AM.

          Comment


            #6
            Re: LG LED TV Model 42LE5300 not switching on

            So PS-ON is present (3.38V) and the PFC Boosted Voltage is also present, correct?
            But the rest of the power supplies come on. So all the fuses on the board are good?
            You also do not have DRV-ON (BL-ON), Dim controls.
            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


              #7
              Re: LG LED TV Model 42LE5300 not switching on

              Hi Budm, yes the PS-ON and boosted voltage is correct (PFC = 390V). I dont get the other voltages that are 12V, 20V etc coming from those two transformers that look identical.
              There are 3 fuses all measuring correct.
              I do not get the DRV-ON from the main (perhaps as a result that the 12V does not start up to feed the main???)

              Comment


                #8
                Re: LG LED TV Model 42LE5300 not switching on

                PS-On signal is response for turning on the PFC, the switched 12V, etc. so we need to find out why those two large power transformers are not being driven.
                Is the L6599D getting the VCC Voltage to run?
                What Voltages do you have on Q102, 103 pins?
                Is R219 OK?
                Is C114 OK?
                Also check the resistance of R115 ~118 which are for Line sense on pin 7 of the IC that monitor the PFC Voltage, it will shutdown the IC if it thinks that PFC Voltage is too low, but isnce your PFC Voltage is OK but the resistors have drifted up in value then that will cause the problem, look at the spec sheet of the IC as to how pin 7 functions and what Voltage it should have on that pin.

                LG EAY60803201 (YP42LPBL) Power Supply Unit.
                Pictures provided by shopjimmy.
                Attached Files
                Last edited by budm; 02-12-2019, 12:13 AM.
                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


                  #9
                  Re: LG LED TV Model 42LE5300 not switching on

                  Looks like C256 and R259 have heat damage?
                  Last edited by captainKKK; 02-12-2019, 04:06 PM.

                  Comment


                    #10
                    Re: LG LED TV Model 42LE5300 not switching on

                    Originally posted by budm View Post
                    PS-On signal is response for turning on the PFC, the switched 12V, etc. so we need to find out why those two large power transformers are not being driven.
                    Is the L6599D getting the VCC Voltage to run?
                    What Voltages do you have on Q102, 103 pins?
                    Is R219 OK?
                    Is C114 OK?
                    Also check the resistance of R115 ~118 which are for Line sense on pin 7 of the IC that monitor the PFC Voltage, it will shutdown the IC if it thinks that PFC Voltage is too low, but isnce your PFC Voltage is OK but the resistors have drifted up in value then that will cause the problem, look at the spec sheet of the IC as to how pin 7 functions and what Voltage it should have on that pin.

                    LG EAY60803201 (YP42LPBL) Power Supply Unit.
                    Pictures provided by shopjimmy.
                    I will check this afternoon and get back to you. Thanks.

                    Comment


                      #11
                      Re: LG LED TV Model 42LE5300 not switching on

                      Originally posted by captainKKK View Post
                      Looks like C256 and R259 have heat damage?
                      Thanks CaptainKKK will check those two components as well this afternoon.

                      Comment


                        #12
                        Re: LG LED TV Model 42LE5300 not switching on

                        Originally posted by captainKKK View Post
                        Looks like C256 and R259 have heat damage?
                        Hi CaptainKKK,
                        Cap C256 is a 47uf 25V cap measuring 48uf and ESR of 0.5 ohms
                        R259 is a 10 ohm and measures 10 ohms. Some of these resistors have a dark background color, even on the shopjimmy photo of the same PSU they are darker.

                        Comment


                          #13
                          Re: LG LED TV Model 42LE5300 not switching on

                          Originally posted by budm View Post
                          PS-On signal is response for turning on the PFC, the switched 12V, etc. so we need to find out why those two large power transformers are not being driven.
                          Is the L6599D getting the VCC Voltage to run?
                          What Voltages do you have on Q102, 103 pins?
                          Is R219 OK?
                          Is C114 OK?
                          Also check the resistance of R115 ~118 which are for Line sense on pin 7 of the IC that monitor the PFC Voltage, it will shutdown the IC if it thinks that PFC Voltage is too low, but isnce your PFC Voltage is OK but the resistors have drifted up in value then that will cause the problem, look at the spec sheet of the IC as to how pin 7 functions and what Voltage it should have on that pin.

                          LG EAY60803201 (YP42LPBL) Power Supply Unit.
                          Pictures provided by shopjimmy.

                          Hello Budm, i checked the following,

                          1. Is the L6599D getting the VCC Voltage to run? Yes 13V on the VCC pin.
                          2. Resistors R115~R118 each measure 1 Mohm as indicated on resistor.
                          3. What Voltages do you have on Q102, 103 pins?
                          Q102 G = 0V, D=390V, S = 0V
                          Q103 G = 0V, D = 0V, S = 0V
                          4. Is R219 OK? Its a 1 Mohm res measures ok.
                          5. Is C114 OK? Bingo...................... Measuring in the picofarads.
                          This is a 203J 800V cap. I assume 20nf @ 800V. I need to find a replacement
                          and i am wondering if this will be the only fault. Anything else i must check for? The mosfets measure fine. If i trigger them the Drain - Source goes short and if i Short all three legs then Drain - Source goes open circuit.

                          Thank you for your guidance thus far.
                          Awaiting your response before i put in this cap.

                          Comment


                            #14
                            Re: LG LED TV Model 42LE5300 not switching on

                            Just an update...
                            I put two 10nf 2kv caps in parallel and wiggled them in so that they fit and voila... The set is working and on test.
                            Thanks Budm, i am so chuffed about this repair. That cap has no signs of failure.

                            Comment


                              #15
                              Re: LG LED TV Model 42LE5300 not switching on

                              Glad to hear, that dc blocking/coupling cap is one of the commonly fail cap in that circuit.
                              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


                                #16
                                Re: LG LED TV Model 42LE5300 not switching on

                                Glad to hear your TV is now working after replacing that bad capacitor C114.

                                In case anyone else finds it useful, I wanted to mention that I had resistor R103 (3 ohm, big black rectangle) fail open on one LG power board I worked on with no power.

                                L6599 IC is also a good candidate to check/replace.
                                Attached Files

                                Comment


                                  #17
                                  Re: LG LED TV Model 42LE5300 not switching on

                                  That R103 (in series with TH101) will go open circuit if the bypass relay RL102 is bad, I.E. bad contact, so it is not bypassed by the relay.
                                  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


                                    #18
                                    Re: LG LED TV Model 42LE5300 not switching on

                                    Originally posted by budm View Post
                                    That R103 (in series with TH101) will go open circuit if the bypass relay RL102 is bad, I.E. bad contact, so it is not bypassed by the relay.
                                    Hi BudM:

                                    Thanks for weighing in. I have no idea what it was for, but R103 was completely open (not 3 ohms) so I replaced it and a few other components. I don't know if R103 being open would prevent the TV turning on, but it was part of my troubleshooting.

                                    What is the purpose of the bypass relay?
                                    Last edited by Unspun01; 02-13-2019, 04:35 PM.

                                    Comment


                                      #19
                                      Re: LG LED TV Model 42LE5300 not switching on

                                      The resistor and the TH (NTC) are for inrush current limiting when TV is first on and they need to be bypassed by the relay once the TV is on, if they are not bypassed then resistor and NTC will run hot, that resistor has built-in thermal fuse and it will go open circuit if it gets too hot. You can verify if the relay contacts are goo or not by taking the AC Voltage reading between the two legs of the Resistor and the TH, it should be 0 VAC if the relay is working. This also common problem with Sharp TV's also.
                                      Last edited by budm; 02-13-2019, 04:47 PM.
                                      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


                                        #20
                                        Re: LG LED TV Model 42LE5300 not switching on

                                        Would R103 prevent the TV from turning on? It was bad, but it was not the only part I replaced so I don't remember if it was a cause, or collateral...

                                        Comment

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