Troubleshooting LG Plasma

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  • DanFen
    Badcaps Veteran
    • Apr 2017
    • 201
    • Malta

    #21
    Re: Troubleshooting LG Plasma

    So I guess the next step is to remove all IGBTs/FETs that resulted as bad in the continuity test and test them individually?

    Comment

    • zape
      Senior Member
      • Jul 2017
      • 176
      • USA

      #22
      Re: Troubleshooting LG Plasma

      IGBTs might be connected in a parallel so you'd want to remove one by one and test out of circuit until you find that the board is no longer shorted.

      Comment

      • DanFen
        Badcaps Veteran
        • Apr 2017
        • 201
        • Malta

        #23
        Re: Troubleshooting LG Plasma

        Thanks I'm attaching a diagram with those that are shorted (marked with a C). I couldn't successfully read the part numbers of some of them.

        I've already removed the bad RJP63K2 and according to a previous post, it seems to be good. I did it like so:
        Continuity between Drain & Source: no continuity (and I am guessing this is good?).

        Then I've tested the On/Off state by charging the capacitor. I did this with the multi-meter by:

        1. Holding the negative on the Source, and touching the Gate with the positive lead.
        2. Then I moved the positive lead onto the Drain to test and got no connection.

        Just want to make sure that the above testing method is correct for all the shorted components?

        Originally posted by zape
        IGBTs might be connected in a parallel so you'd want to remove one by one and test out of circuit until you find that the board is no longer shorted.
        Attached Files
        Last edited by DanFen; 03-29-2020, 02:51 PM.

        Comment

        • zape
          Senior Member
          • Jul 2017
          • 176
          • USA

          #24
          Re: Troubleshooting LG Plasma

          The testing method is correct, if the IGBT measured shorted in circuit but looks good when out of circuit this means there is another IGBT or some other failed component.
          Look at the traces to see what else could be the reason for the short.

          Comment

          • DanFen
            Badcaps Veteran
            • Apr 2017
            • 201
            • Malta

            #25
            Re: Troubleshooting LG Plasma

            Thanks Is the testing of Mosfets and Rectifiers the same? Cause as you can see from the drawn diagram there is only one IGBT that is shorted, and from what I could find, these work a little bit different to Mosfets and Rectifiers.

            Originally posted by zape
            The testing method is correct, if the IGBT measured shorted in circuit but looks good when out of circuit this means there is another IGBT or some other failed component.
            Look at the traces to see what else could be the reason for the short.

            Comment

            • DanFen
              Badcaps Veteran
              • Apr 2017
              • 201
              • Malta

              #26
              Re: Troubleshooting LG Plasma

              So I got all of those which I found were shorted out of the board. I must say that I never had such difficulty with desoldering components out like I had with these!

              Some feet of these components have a round circle around them, what does it mean?

              What is the best way to proceed from here?
              Attached Files

              Comment

              • DanFen
                Badcaps Veteran
                • Apr 2017
                • 201
                • Malta

                #27
                Re: Troubleshooting LG Plasma

                So following that, I've checked diodes for short (in diode more + beep), and found 2 that "are shorted". I'm attaching 3 photos showing these diodes (one of the photos is a full view of the board).
                Attached Files

                Comment

                • tvtimmy
                  Badcaps Legend
                  • Mar 2015
                  • 1160
                  • usa

                  #28
                  Re: Troubleshooting LG Plasma

                  Do the diodes have 3 legs? If so, the outer ones are connected and they will beep or read short. Test them center to an outer then center to the other outer.

                  Comment

                  • DanFen
                    Badcaps Veteran
                    • Apr 2017
                    • 201
                    • Malta

                    #29
                    Re: Troubleshooting LG Plasma

                    No the ones I've checked are 2 legged. I've pointed them out on the photos.

                    Originally posted by tvtimmy
                    Do the diodes have 3 legs? If so, the outer ones are connected and they will beep or read short. Test them center to an outer then center to the other outer.

                    Comment

                    • tvtimmy
                      Badcaps Legend
                      • Mar 2015
                      • 1160
                      • usa

                      #30
                      Re: Troubleshooting LG Plasma

                      Unsolder 1 leg and test again. Capacitors can cause funky readings.

                      Comment

                      • DanFen
                        Badcaps Veteran
                        • Apr 2017
                        • 201
                        • Malta

                        #31
                        Re: Troubleshooting LG Plasma

                        You're correct, removed one of them and it measured correctly.

                        But the other didn't, there's continuity from negative to positive, and reading when set to to diode mode shows 0.002.

                        Now this is a funny one (or funny because I've never seen it), cause the Cathode side has a long leg which seems to be connected to some other component which I am not able to see (it's hidden under the heatsink). I'm attaching an image.

                        Originally posted by tvtimmy
                        Unsolder 1 leg and test again. Capacitors can cause funky readings.
                        Attached Files

                        Comment

                        • tvtimmy
                          Badcaps Legend
                          • Mar 2015
                          • 1160
                          • usa

                          #32
                          Re: Troubleshooting LG Plasma

                          Did you lift one leg of the one with the bad reading too?

                          Comment

                          • DanFen
                            Badcaps Veteran
                            • Apr 2017
                            • 201
                            • Malta

                            #33
                            Re: Troubleshooting LG Plasma

                            I've actually removed it altogether.

                            Originally posted by tvtimmy
                            Did you lift one leg of the one with the bad reading too?

                            Comment

                            • DanFen
                              Badcaps Veteran
                              • Apr 2017
                              • 201
                              • Malta

                              #34
                              Re: Troubleshooting LG Plasma

                              The problem is, the markings on it are so faint I can't read them.

                              EDIT: I think it says UF4007

                              Comment

                              • DanFen
                                Badcaps Veteran
                                • Apr 2017
                                • 201
                                • Malta

                                #35
                                Re: Troubleshooting LG Plasma

                                I've ordered this diode, although I am not sure what else I can check I haven't individually checked the rectifiers/fets I've removed though.

                                Comment

                                • DanFen
                                  Badcaps Veteran
                                  • Apr 2017
                                  • 201
                                  • Malta

                                  #36
                                  Re: Troubleshooting LG Plasma

                                  Why do I still have continuity on the IGBT / FETs / Rectifer connectors (holes) on the board even with the components out of the board (although not all of them have this)? I also noticed that 2 of the 3 holes of these components are covered in metal, the other is just a hole.
                                  Last edited by DanFen; 04-06-2020, 12:04 PM.

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                                  • DanFen
                                    Badcaps Veteran
                                    • Apr 2017
                                    • 201
                                    • Malta

                                    #37
                                    Re: Troubleshooting LG Plasma

                                    Tested the Mosfets and the IGBTs that had short in circuit, and the Rectifiers as well.

                                    Mosfets and IGBTs were tested in the same method, i.e. tested on and off state.
                                    Rectifiers were tested like normal diodes, got 0.4 reading on the good ones.

                                    Does this make sense? I also wonder if I should get the other 4 that are still on the board and test?
                                    Attached Files

                                    Comment

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