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    eax55357701 repair

    Have a LG 37lh40 with a bad power supply EAX55357701/32 board. tv tries to light back lights but can't - cycles forever. took power board out and bench tested. has 5V, jumper pwr on to 5v and 12V good, 20V good. Have a second power board - it turns on tv - works perfectly, I have checked all caps (ESR), looked for bad solder, checked all xsistors, and no luck, anybody have any experience with these power supply boards ? thanks
    Attached Files
    Last edited by ajshoe; 10-09-2019, 05:44 PM.

    #2
    Re: eax55357701 repair

    also observed main board green led flashes fast with bad power supply bd. with good power board in - main board green led is on solid.

    Comment


      #3
      Re: eax55357701 repair

      Have you checked the dc voltage across the two legs of the 450V 68uF capacitors on both power supplies to see if there is a difference.
      Willing to help but I'm no expert.

      Comment


        #4
        Re: eax55357701 repair

        Originally posted by dick_barton View Post
        have you checked the dc voltage across the two legs of the 450v 68uf capacitors on both power supplies to see if there is a difference.
        +10

        Comment


          #5
          Re: eax55357701 repair

          Out of town til weds.i will test that & Report back next week. Thanks

          Comment


            #6
            Re: eax55357701 repair

            tested both boards - broken board has 162V across C611 (68UF 450V cap) with plug in. with PWR_ON HI = 385V.
            good board has 162V across C611 (68UF 450V cap) with plug in. with PWR_ON HI = 377V.
            all fuses good. seems like a bad solder joint but don't see any

            Comment


              #7
              Re: eax55357701 repair

              So one board powers everything OK. The original has all the voltages when tested but doesn't light up the lamps.
              Check the On/Off voltage at pin 14 of IC301 (BD9215F) which should be 3V to enable the lamp driver circuits.
              Attached Files
              Last edited by dick_barton; 10-16-2019, 10:04 AM.
              Willing to help but I'm no expert.

              Comment


                #8
                Re: eax55357701 repair

                So does the backlights try to come on at all when using the bad board?
                Did you check inverter transformers winding resistances and compared them to the working board?
                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: eax55357701 repair

                  put small wire on ic301 pin 14 - never moves off 0 volts. I had a good ground (used GRD on main connector - P201). assume the IC301 turns on inv lights (ON/OFF) ? have bad IC301 ?

                  windings resistance across output of inv xformer were: good board - 22.9 ohms each output - total across both 46.8 ohms
                  bad board - 26.7 ohms across both - 50.9 ohms

                  symptoms of set were that it would gradually take longer and longer to turn on (red led indicator on front bottom of set would turn solid blue led). It finally stopped turning on (led front bottom indicator never turns blue - stays red).

                  seems like main board is telling it to shut down. going to check voltages again on bad board in set.
                  Last edited by ajshoe; 10-16-2019, 11:03 AM.

                  Comment


                    #10
                    Re: eax55357701 repair

                    bad power supply board in set: turn power switch on - 12V varies between 8v and 12v, 20V varies between 9v and 14v. hitting the on/off button on side of set seems to do nothing - same voltage swings.

                    Comment


                      #11
                      Re: eax55357701 repair

                      In your first post you say
                      took power board out and bench tested. has 5V, jumper pwr on to 5v and 12V good, 20V good."
                      Now you say the voltages on the bad power supply are varying?

                      On the bad board what voltage do you have at Fuse F501 when you power up out of standby.
                      Last edited by dick_barton; 10-16-2019, 11:28 AM.
                      Willing to help but I'm no expert.

                      Comment


                        #12
                        Re: eax55357701 repair

                        earlier posts I was checking and reading voltages on bench. I tested them again on bench - they are correct and constant. The last posts were tested with bad power board in tv. I then plugged in set and then turned power switch on. took readings that I posted - voltages are varying. I thinking now that the power supply can't supply enough current on 12V. Can I load test the 12V and 20V line ?

                        also - I ohmed the pin 14 to inv on/off - it is good - 1K ohms on both boards
                        Last edited by ajshoe; 10-16-2019, 01:17 PM.

                        Comment


                          #13
                          Re: eax55357701 repair

                          The board only has one power transformer (LLM-001) to provide always on 5V Standby and the switched 12V, 20V, so you are indicating that the 12V and the 20V are not stable, so are you sure that the 5V Standby is stable since is generated by the same power transformer LLM-001 when connected back in the TV.
                          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


                            #14
                            Re: eax55357701 repair

                            checked 5V - when power switch is turned on - 5V varies between 4.94V and 5.12V about every 3 seconds. hitting the on/off button on side of set just makes 5V cycle again between 4.94V and 5.12V

                            Comment


                              #15
                              Re: eax55357701 repair

                              Is the variation of the 5V in sync with the variation of the 12V/20V?
                              May be try heating the power supply board with hair dryer to see all the Voltages will become steady or not.
                              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: eax55357701 repair

                                heated power board while monitoring 5V - got the cycling to 5.02V to 5.12V. saw the backlight come on for second or two. only happened once. think variation is in sync with 5V, 12V, 20V supplies
                                Last edited by ajshoe; 10-16-2019, 02:29 PM.

                                Comment


                                  #17
                                  Re: eax55357701 repair

                                  believe I've found problem. IC201 and IC202 (AS431AN - shunt diode) seem bad - going to get new ones.

                                  Comment


                                    #18
                                    Re: eax55357701 repair

                                    local electronic store gave me lm431 as a sub. checked the diode out - don't think its compatible with as431an. looks like its configured backwards. anybody know of a acceptable sub ?

                                    Comment


                                      #19
                                      Re: eax55357701 repair

                                      installed new lm431 - to92 - made lm431 work. installed board and now have solid 5 volts. 12V and 20V come up but cycles to 0 about every 5 secs.
                                      DC voltage at F501 is 377V but cycles to 250V every 5 seconds. observing IC301 pin14 inv on/off - never goes to 3V
                                      Last edited by ajshoe; 10-18-2019, 10:07 AM.

                                      Comment


                                        #20
                                        Re: eax55357701 repair

                                        It sounds like the PS-ON is going on and off.
                                        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

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