LG 26LE5300 Boot Loop after power surge hit

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  • Chaks
    Senior Member
    • Sep 2015
    • 115
    • India

    #1

    LG 26LE5300 Boot Loop after power surge hit

    I have a LG 26le5300 that gets stuck at boot logo after automatically rebooting for 4 or 5 times when switched on.
    I suspect some blown components (see image in red and yellow markings on the pcb image and also on the pcb schematic image) in this area, the P channel MOSFET A03407 (Q7501). The voltage reading Vgs should be 10.8 for a 24 volt input bu I get +24.03 volts between Gate and Source. And -24.0 Volts between Gate and Drain. Measured with multi meter's Red lead on Gate and black lead on source and drain respectively.
    Please help:
    Attached Files
  • Chaks
    Senior Member
    • Sep 2015
    • 115
    • India

    #2
    Re: LG 26LE5300 Boot Loop after power surge hit

    Can anyone please help me with the main board PCB of lg TV 26le5300. I want to compare my PCB with an actual working PCB to see if any components are missing on the PCB. Is there any complete service manual for the TV . please help.
    Image of both sides of working PCB is what I need at least.
    Last edited by Chaks; 12-16-2018, 03:52 AM.

    Comment

    • nomoresonys
      Badcaps Legend
      • Jan 2013
      • 12085
      • U.S.

      #3
      Re: LG 26LE5300 Boot Loop after power surge hit

      Try heating sections of the mainboard with a hairdryer, see if it stays on if no results try heating some capacitors on powerboard.

      Comment

      • Chaks
        Senior Member
        • Sep 2015
        • 115
        • India

        #4
        Re: LG 26LE5300 Boot Loop after power surge hit

        Q7502 2sc3052 npn transistor has the following readings.
        Base +lead to emitter -lead = 0.6v
        Base +lead to collector -lead =0.6v
        Emitter +lead to base -lead =over limit
        Collector +lead to base -lead = over limit

        Collector +lead to emitter -lead = 0.98 volts
        Emitter +lead to collector -lead = 0.68 volts

        POWER DET circuit:

        IC 7509 ( ncp 803 sn293)

        Pin 3 vcc to ground of PCB is 3.5 volts
        Resistance between pin vcc and reset pin 2 is 100k ohms
        The TV resets when pin 1 gnd or pin 2 reset is touched by multimeter leads pos or neg.

        IC 7510 (ncp 803 sn293)
        Pin vcc to ground of PCB is 0.9 volts
        Pin 3 vcc to gnd pin 1 is 1.9 volts
        Resistance between vcc and reset pin is 355k ohms
        Pin 1 gnd and pin 2 reset pin (+lead) is 3.6 volts
        Reset pin to ground of PCB is 1.2 volts

        Is there anything faulty here? Power-det circuit is on page 35 of the service manual.
        Last edited by Chaks; 12-18-2018, 01:01 AM.

        Comment

        • budm
          Badcaps Legend
          • Feb 2010
          • 40746
          • USA

          #5
          Re: LG 26LE5300 Boot Loop after power surge hit

          https://www.badcaps.net/forum/attach...6&d=1544886413
          For Q7501 (P-ch) the GATE Voltage has to be about 3 ~4 V < Source Voltage, you need to use circuit GND to verify the Voltages.
          What Voltage do you have on that POWER_ON pin?
          Q7500 has to be turned on by POWER_ON control Voltage for Q7501 to be on.
          We also need pictures that show how all the boards are connected together.
          Last edited by budm; 12-18-2018, 11:04 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

          • Chaks
            Senior Member
            • Sep 2015
            • 115
            • India

            #6
            Re: LG 26LE5300 Boot Loop after power surge hit

            I get the Vgs 10.8 volts on the a03407A G-S but only for a couple of seconds. The +15 Volts control chart in the service manual page 35.
            I checked all the voltages as per the service manual charts on page 35. There are two areas Power-Det and 24-volt->15 volt chart where the readings does not match.
            in power detect IC7510 vcc pin is not reading +3.5_ST but the IC7509 vcc pin measures +3.5_ST.
            The other issue is that in 24-volt->15 volt control chart. the R7540 reads 32k Ohms only. the other resistors are ok and as per smd code/markings.The Capacitor 7522 has turned darkbrown seems over heated or about to die but but measures ok.Or it may be already dead. these 2 components along with Q7502 in the first chart in page 35 are abnormal. I will post an image of the pcb along with test voltages below.
            Attached Files
            Last edited by Chaks; 12-18-2018, 12:05 PM.

            Comment

            • Chaks
              Senior Member
              • Sep 2015
              • 115
              • India

              #7
              Re: LG 26LE5300 Boot Loop after power surge hit

              Additional PCB Images
              Attached Files

              Comment

              • budm
                Badcaps Legend
                • Feb 2010
                • 40746
                • USA

                #8
                Re: LG 26LE5300 Boot Loop after power surge hit

                So what is the answer for this one: What Voltage do you have on that POWER_ON pin?
                https://www.badcaps.net/forum/attach...6&d=1544886413
                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

                • Chaks
                  Senior Member
                  • Sep 2015
                  • 115
                  • India

                  #9
                  Re: LG 26LE5300 Boot Loop after power surge hit

                  Here are the readings of the Q7500, Q7501 , Q7502, orientation as they appear in on the PCB. Thanks a lot for your time sir
                  Attached Files

                  Comment

                  • budm
                    Badcaps Legend
                    • Feb 2010
                    • 40746
                    • USA

                    #10
                    Re: LG 26LE5300 Boot Loop after power surge hit

                    So you do have 24V with reference to GND Source and also at Drain pin of Q7501, so what is wrong with that? That is what it should have when it is turned on.
                    BTW, you do know how to read schematic, correct? And you do understand how Transistor and MOSFET work, correct?
                    I still do not understand why you have to make other measurement that are not reference to GND, no need to do that right now.
                    Last edited by budm; 12-18-2018, 05:57 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

                    • Chaks
                      Senior Member
                      • Sep 2015
                      • 115
                      • India

                      #11
                      Re: LG 26LE5300 Boot Loop after power surge hit

                      Should I not worry about this
                      https://www.badcaps.net/forum/attach...0&d=1545156295
                      Is this normal?

                      Comment

                      • Biruslapio
                        Badcaps Veteran
                        • Nov 2013
                        • 552
                        • Brasil

                        #12
                        Re: LG 26LE5300 Boot Loop after power surge hit

                        Resistors are almost always in parallel with a lot of things in the circuit,especially main boards,it's not a problem if they read less than their rated resistance,but more,for example this 120k reading 200k,that would mean it is defective.
                        These capacitors if not reading 0 OHM are probably good,sometimes they are in parallel with some processor silicon which measures kinda low resistance(5 OHMs or more generally).

                        Comment

                        • Chaks
                          Senior Member
                          • Sep 2015
                          • 115
                          • India

                          #13
                          Re: LG 26LE5300 Boot Loop after power surge hit

                          When the TV is connected to the ac using adapter the standb red led is ON and the optical output on the back of the tv usually glows red but in my case the optical output on my TV is off. The optical lack J1103's vcc pin does not have power. That's why I suspect that some part of the PCB is not getting power which is supposed to be there even when the TV in on standby mode. There is power in the USB ports of the TV.. In most of the TV's I have seen the standby led and the optical jack are red.In the present case it is not. That's what I am trying to first get the optical jack power up.

                          Comment

                          • Chaks
                            Senior Member
                            • Sep 2015
                            • 115
                            • India

                            #14
                            Re: LG 26LE5300 Boot Loop after power surge hit

                            Can I use test points (TP) / JP to trouble shoot further. Can someone help me.

                            Comment

                            • Chaks
                              Senior Member
                              • Sep 2015
                              • 115
                              • India

                              #15
                              Re: LG 26LE5300 Boot Loop after power surge hit

                              LG LOGO is displayed before or after the microprocessor lg engine lge101d is active .? Anyone has information on this.
                              Last edited by Chaks; 12-20-2018, 01:04 AM.

                              Comment

                              • Chaks
                                Senior Member
                                • Sep 2015
                                • 115
                                • India

                                #16
                                Re: LG 26LE5300 Boot Loop after power surge hit

                                Referring to the connector P7501
                                ... the Pin 14 is at 3.3 volts when the TV is switched on (blue std_by light) this pin is Error_Out (output) to IC LGE 101D Error_Out (input at gpio 41).

                                This Pin 14 is at 3.3 volts even when the P7501 connector is not connected to the LCD_PANEL.

                                Pin 14 is at 0.9 volts when the tv is in std_by red light mode.
                                Pin 13 is at 1.03 volts when the tv is in std_by red light mode.

                                When the tv is completely off the Pin 14 to pcb Gnd measures 5.0Mega Ohms.

                                Is this also normal. I have attached the pcb as well as schema for reference.
                                Attached Files

                                Comment

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