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LG 32LH500B - No power, no standby

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    #21
    Re: LG 32LH500B - No power, no standby

    Can you see where the Cathode of that Zener diode Z0D5 is connected to which pin of the IC?
    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
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    TV Factory reset codes listing:
    http://www.badcaps.net/forum/showthread.php?t=24809

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      #22
      Re: LG 32LH500B - No power, no standby

      It meters out to BP pin on U0D1 (LNK6777k) The trace for BP goes under the IC directly to Z0D5 and R0D9

      Comment


        #23
        Re: LG 32LH500B - No power, no standby

        Originally posted by JeffJ View Post
        It meters out to BP pin on U0D1 (LNK6777k) The trace for BP goes under the IC directly to Z0D5 and R0D9
        So the resistance reading of that Zener should be about 68K then, correct?
        ZOD5 looks to be for protection on the BP pin in case the internal Voltage regulator shorted of have high leakage which will dump high Voltage from D pin to BP pin.
        I see page 13 of the spec sheet for the BP shutdown threshold current of 8.2ma so if the over current occur it will go into shutdown.
        Last edited by budm; 08-12-2020, 05:27 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


          #24
          Re: LG 32LH500B - No power, no standby

          Originally posted by budm View Post
          So the resistance reading of that Zener should be about 68K then, correct?
          ZOD5 looks to be for protection on the BP pin in case the internal Voltage regulator shorted of have high leakage which will dump high Voltage from D pin to BP pin.
          I see page 13 of the spec sheet for the BP shutdown threshold current of 8.2ma so if the over current occur it will go into shutdown.
          BP to S i tested 68K when it waso ut of circuit, when i test it in circuit it just keeps rising and rising to several hundred K. testing across that zeener gives the same results.

          Should i remove Z0D5 and test BP to S and see what i get then. and also test it out of circuit?

          Comment


            #25
            Re: LG 32LH500B - No power, no standby

            ZOD5 is the added on protection, it is not used in the application circuits as shown in the spec sheet so you can remove it and the circuit should still function without it..
            This is getting to be really interesting since the circuit does not have much at all and the circuit they are using is pretty close to the application circuit, most low cost TV will basically copy the application circuits so they do not have to start from scratch and cost them money.
            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


              #26
              Re: LG 32LH500B - No power, no standby

              SO ive removed Z0D5 and it test fine out of circuit, still get a reading both ways on tis pads. removed R0D9, still get a reading both ways. BP is still at 2.7V so im missing something else in the bp circuit.

              I'll keep digging, welcome to ideas.

              Comment


                #27
                Re: LG 32LH500B - No power, no standby

                Originally posted by JeffJ View Post
                SO ive removed Z0D5 and it test fine out of circuit, still get a reading both ways on tis pads. removed R0D9, still get a reading both ways. BP is still at 2.7V so im missing something else in the bp circuit.

                I'll keep digging, welcome to ideas.
                OK, I need to do more thinking and reading the spec sheet.
                BTW is there any way you can have the Volt meter connected between BP pin and GND so you can monitor the Voltage when you first apply the power to the board?
                You should also check the Voltages on PD, CP, and FB pins for the records then I will look at the spec sheet as to what to be expected on those pins.
                Last edited by budm; 08-12-2020, 06:31 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


                  #28
                  Re: LG 32LH500B - No power, no standby

                  Originally posted by budm View Post
                  OK, I need to do more thinking and reading the spec sheet.
                  BTW is there any way you can have the Volt meter connected between BP pin and GND so you can monitor the Voltage when you first apply the power to the board?
                  Yes their is a way i can do that, I dropped R0D9 on my hardwood floor, and im cursing my self and any one who will listen right now. Not to hard to find another 3kohm resistor though.

                  Removed R2D9 Z0D5 and R0D9 and now BP is 5.7V All 3 seem to test ok (resistors correct values) out of circuit. I removed Z0D5 first, tested, no luck, then R0D9, tested, no luck. then R2D9, Tested saw i fgot 5.7VDC on BP.

                  Oh and here is the kicker.

                  Tv powers on and works with the above two resistors and diode removed..... I am well i dont know what to say now.
                  Last edited by JeffJ; 08-12-2020, 06:37 PM.

                  Comment


                    #29
                    Re: LG 32LH500B - No power, no standby

                    Originally posted by JeffJ View Post
                    Removed R2D9 Z0D5 and R0D9 and now BP is 5.7V

                    and yes their is a way i can do that, I dropped RoD9 on my hardwood floor, and im cursing my self and any one who will listen right now. Not to hard to find another 3kohm resistor though.
                    OK, I need to look at the pictures to see what and how those resistors are connected.
                    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


                      #30
                      Re: LG 32LH500B - No power, no standby

                      Originally posted by budm View Post
                      OK, I need to look at the pictures to see what and how those resistors are connected.
                      DOnt know if you caught my edit on the previous post. Also with R2D9, R0D9 and Z0D5 removed BP to S is 68K now.

                      Comment


                        #31
                        Re: LG 32LH500B - No power, no standby

                        R0D9 (302 = 3K Ohms) looks to be the same function as R9 of the application circuit.
                        R2D9 (470 = 47 Ohms) I cannot tell where it goes to, I can see that one end is connected BP pin.
                        I would put the ZENER and R0D9 back in place and see if it still running, right now the BP 5.7V is supplying by the BP not from AUX winding.
                        I think R2D9 is connected to something on the other end and not allowing the BP to go up.
                        Per spec sheet, BP pin can source current up to 8mA, that means it can maintain 5.7V with load resistance as low as 5.75V/8.2mA = 700 Ohms and still to maintain 5.7V.
                        I think R2D9 (47 Ohms) is the key.
                        Last edited by budm; 08-12-2020, 07:03 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


                          #32
                          Re: LG 32LH500B - No power, no standby

                          Originally posted by budm View Post
                          R0D9 (302 = 3K Ohms) looks to be the same function as R9 of the application circuit.
                          R2D9 (470 = 47 Ohms) I cannot tell where it goes to, I can see that one end is connected BP pin.
                          I would put the ZENER and R0D9 back in place and see if it still running, right now the BP 5.7V is supplying by the BP not from AUX winding.
                          I think R2D9 is connected to something on the other end and not allowing the BP to go up.
                          Ok makes sense, thanks for sticking with this, with me. i'm learning a fair bit. I really appreciate you taking the time.

                          Replacing R0D9 might have ot wait until tomorrow i dont know if i have a 3k resistor, and the other one went off into the ether of my office floor, never to be found again it seems.

                          I will work on figuring out where R2D9 goes so far I've traced it through the board and then back to the top where it goes on a trace under C0D4 450V 68uf capacitor. It seems to come out on the top of the board on the bottom side of C0D1 to R0D6.

                          See attached.
                          Attached Files

                          Comment


                            #33
                            Re: LG 32LH500B - No power, no standby

                            Originally posted by JeffJ View Post
                            Ok makes sense, thanks for sticking with this, with me. i'm learning a fair bit. I really appreciate you taking the time.

                            Replacing R0D9 might have ot wait until tomorrow i dont know if i have a 3k resistor, and the other one went off into the ether of my office floor, never to be found again it seems.

                            I will work on figuring out where R2D9 goes so far I've traced it through the board and then back to the top where it goes on a trace under C0D4 450V 68uf capacitor. It seems to come out on the top of the board on the bottom side of C0D1 to R0D6.

                            See attached.
                            At least we are getting close, it looks like they add something to control the BP pin via R2D9, I am learning too about this IC, this is the first time I deal with this IC P/N.
                            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


                              #34
                              Re: LG 32LH500B - No power, no standby

                              Originally posted by budm View Post
                              At least we are getting close, it looks like they add something to control the BP pin via R2D9, I am learning too about this IC, this is the first time I deal with this IC P/N.
                              So if you see the attached that circuit that R2D9 leads to exits through the diode with the white glue on it through the board aboard and goes to the Anode of D0D1 in the Rectification circuit, the top most diode in the rectification diode array thats closest to C0D1 450V cap.

                              Comment


                                #35
                                Re: LG 32LH500B - No power, no standby

                                https://www.badcaps.net/forum/attach...5&d=1597280341
                                Ah, I did not see that section before, it looks to be for either LOW AC (Brow out) protection circuit or Over Voltage protection, more likely to be for Brown out protection, I suspect those high resistance resistors (marked as 474, connected in series) have drifted into higher value and cause fault brownout shutdown thinking that In coming AC is low when it is rally not.
                                When AC Voltage is low, the regulated power supply will draw more incoming current to maintain the same power output of the power supply.
                                I think we found the cause of the problem. I wish I see the R2D9 and that detection circuit earlier.
                                They use BP pin for shutdown in case of Brownout, since the Transistor connected to R2D9 is not active when no power applied to the board, the resistance reading on BP will be high, but when Transistor is turned on (Brown out) when power up the board, the BP is pulled down through R2D9 to keep BP pin Voltage low.
                                Last edited by budm; 08-12-2020, 07:21 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


                                  #36
                                  Re: LG 32LH500B - No power, no standby

                                  Also R0D6 goes to the Emitter of Q0D1 which my research suggests is a MMBT3906 (bottom right pin of Q0D1 in attached)
                                  Attached Files

                                  Comment


                                    #37
                                    Re: LG 32LH500B - No power, no standby

                                    I update my post 35, check those 474 resistors.
                                    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


                                      #38
                                      Re: LG 32LH500B - No power, no standby

                                      Originally posted by budm View Post
                                      I update my post 35, check those 474 resistors.
                                      All 3 meter out to 470k almost on the button

                                      But what you said makes sense and its got to be something in this areas still. because with R2D9 in place BP is low (2.7V) and also the VDC across C0D1, COD4 and the D pin on the LSK677K is all 154.7V. with R2D9 removed across C0D1, COD4 and the D pin on the LSK677K is 160.7VCD which is proper, so something is pulling it down.
                                      Last edited by JeffJ; 08-12-2020, 07:23 PM.

                                      Comment


                                        #39
                                        Re: LG 32LH500B - No power, no standby

                                        Originally posted by JeffJ View Post
                                        All 3 meter out to 470k almost on the button
                                        Check E-B and E-C junction Voltages of Q0D1(2A).
                                        Z0D6 soldering does not look very good.
                                        Update Q0D1 is PNP so R2D9 connected to the Emitter of Q0D1 makes sense.
                                        Q0D1 has to be off for the BP pin Voltage to rise to 5.7V
                                        Last edited by budm; 08-12-2020, 07:33 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


                                          #40
                                          Re: LG 32LH500B - No power, no standby

                                          Originally posted by budm View Post
                                          Check E-B and E-C junction Voltages of Q0D1(2A).
                                          Z0D6 soldering does not look very good.
                                          Update Q0D1 is PNP so R2D9 connected to the Emitter of Q0D1 makes sense.
                                          Q0D1 has to be off for the BP pin Voltage to rise to 5.7V
                                          Alright, this i will have to do tomorrow I only have a TS100 at home and my air station is at work, and i feel like i should get this back together properly so we can meter Q0D1 out properly to give us answers.


                                          Ill touch up Z0D6 as well

                                          Should i resemble everything or just R2D9?

                                          Comment

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