M421VT LED Screen Color Distortion

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  • dfang
    Member
    • Feb 2013
    • 39
    • USA

    #21
    Re: M421VT LED Screen Color Distortion

    It looks like the PS has now failed...The only dc voltage at main connector is the two 5.2vdc,,,no 12vdc,no 24vdc.....What the heck happened ? I only removed the shield on the main board..
    Attached Files

    Comment

    • newtothis
      Badcaps Legend
      • Mar 2013
      • 1556
      • england

      #22
      Re: M421VT LED Screen Color Distortion

      Originally posted by dfang
      It looks like the PS has now failed...The only dc voltage at main connector is the two 5.2vdc,,,no 12vdc,no 24vdc.....What the heck happened ? I only removed the shield on the main board..
      Ok one will be 5v standby voltage, Is there a voltage legend near that connector?

      Will be looking for something like PS_ON and we need to jump 5v Standby to PS_ON with a ~500ohm resistor. The other voltages will most likely come up and its actually the mainboard not sending the PS_ON signal.

      Can try reinstalling the shield on the main and trying again... May be that the shield carries a ground.

      Either way by the seems of it there is a fault or bad connection at the main IC... It is most likely going to be a BGA chipset as they are most prone to thermal failure.
      Last edited by newtothis; 04-20-2015, 03:22 PM.

      Comment

      • dfang
        Member
        • Feb 2013
        • 39
        • USA

        #23
        Re: M421VT LED Screen Color Distortion

        Originally posted by newtothis
        Ok one will be 5v standby voltage, Is there a voltage legend near that connector?

        Will be looking for something like PS_ON and we need to jump 5v Standby to PS_ON with a ~500ohm resistor. The other voltages will most likely come up and its actually the mainboard not sending the PS_ON signal.

        Can try reinstalling the shield on the main and trying again... May be that the shield carries a ground.

        Either way by the seems of it there is a fault or bad connection at the main IC... It is most likely going to be a BGA chipset as they are most prone to thermal failure.
        I reinstalled the heat shield,,no good result..Now trying to dig up a 500ohm resistor.. There is a voltage legend near the PS connector with PS_ON,,(see one of my last pic's)..Will jump one of the 5.2volt terminals with PS_ON..at the PS connector and man the fire extinguisher..

        Comment

        • newtothis
          Badcaps Legend
          • Mar 2013
          • 1556
          • england

          #24
          Re: M421VT LED Screen Color Distortion

          Remove the connector from the Main and use the resistor on the end of the connector, I have a feeling we will see all the voltages rise

          Comment

          • budm
            Badcaps Legend
            • Feb 2010
            • 40746
            • USA

            #25
            Re: M421VT LED Screen Color Distortion

            It may have used the metal shield as the conductor path between two GND plane, you can see that the legs of shield are connected to big copper plane. Or you may have damaged the traces or through hole plating (for the top and the bottom side of the board copper traces) for the legs of the shield.
            Last edited by budm; 04-20-2015, 05:18 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

            • newtothis
              Badcaps Legend
              • Mar 2013
              • 1556
              • england

              #26
              Re: M421VT LED Screen Color Distortion

              Originally posted by budm
              It may have used the metal shield as the conductor path between two GND plane, you can see that the legs of shield are connected to big copper plane. Or you may have damaged the traces or through hole plating (for the top and the bottom side of the board copper traces) for the legs of the shield.
              Yeah noticed the planes hence suggested replacing the shield as it may carry the ground.

              Got a feeling its going to be a BGA IC mindya causing the initial fault. Gonna be tricky to remedy without the tools

              Comment

              • budm
                Badcaps Legend
                • Feb 2010
                • 40746
                • USA

                #27
                Re: M421VT LED Screen Color Distortion

                Or while removing the shield and flexed the board, what ever bad BGA connections it has it could have gone bad completely.
                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

                • newtothis
                  Badcaps Legend
                  • Mar 2013
                  • 1556
                  • england

                  #28
                  Re: M421VT LED Screen Color Distortion

                  Originally posted by budm
                  Or while removing the shield and flexed the board, what ever bad BGA connections it has it could have gone bad completely.
                  Also something I was thinking.

                  OP do you have a hot air rework station at all? I can try and guide you through reflowing the BGA if needed.
                  Last edited by newtothis; 04-20-2015, 08:17 PM.

                  Comment

                  • dfang
                    Member
                    • Feb 2013
                    • 39
                    • USA

                    #29
                    Re: M421VT LED Screen Color Distortion

                    Originally posted by newtothis
                    Remove the connector from the Main and use the resistor on the end of the connector, I have a feeling we will see all the voltages rise
                    You mean disconnect the main connector and jump 5.2 vdc and PS_ON wires with a resistor at that connector ? Will a 765 ohm resistor work ? If not I will find something else..

                    Comment

                    • newtothis
                      Badcaps Legend
                      • Mar 2013
                      • 1556
                      • england

                      #30
                      Re: M421VT LED Screen Color Distortion

                      Yes that will work fine, Plug the resistor into the end of the cable that goes to the PSU with it disconnected at main. I think the voltages will all come up, If they do I think me and budm are right in thinking bad BGA connections

                      Comment

                      • dfang
                        Member
                        • Feb 2013
                        • 39
                        • USA

                        #31
                        Re: M421VT LED Screen Color Distortion

                        Originally posted by budm
                        It may have used the metal shield as the conductor path between two GND plane, you can see that the legs of shield are connected to big copper plane. Or you may have damaged the traces or through hole plating (for the top and the bottom side of the board copper traces) for the legs of the shield.
                        You know Budm,,I think the copper traces or plating may have been damaged due to excessive heat trying to remove that shield and the shield indeed may play a ground roll on the board circuitry..I noticed around one of the holes for a shield leg kind of buggered up due to removal efforts..

                        Comment

                        • newtothis
                          Badcaps Legend
                          • Mar 2013
                          • 1556
                          • england

                          #32
                          Re: M421VT LED Screen Color Distortion

                          Can you provide a picture of the damage, I am still thinking the BGA needs doing

                          Comment

                          • dfang
                            Member
                            • Feb 2013
                            • 39
                            • USA

                            #33
                            Re: M421VT LED Screen Color Distortion

                            Originally posted by newtothis
                            Can you provide a picture of the damage, I am still thinking the BGA needs doing
                            I need to remove shield again,,I'll provide pic when I get it removed..

                            Comment

                            • dfang
                              Member
                              • Feb 2013
                              • 39
                              • USA

                              #34
                              Re: M421VT LED Screen Color Distortion

                              Ok,,got shield back off,,man I should put a zipper on this shield..

                              I don't see anything obvious but got to thinking,,,could have put too much heat on the board with heat gun and unsoldered some electronic parts...
                              Attached Files

                              Comment

                              • tom66
                                EVs Rule
                                • Apr 2011
                                • 32560
                                • UK

                                #35
                                Re: M421VT LED Screen Color Distortion

                                Looks fine to me - the soldermask (green protective ink layer) is damaged, but that is not critical to the function of the board. Copper is still intact.
                                Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
                                For service manual, schematic, boardview (board view), datasheet, cad - use our search.

                                Comment

                                • dfang
                                  Member
                                  • Feb 2013
                                  • 39
                                  • USA

                                  #36
                                  Re: M421VT LED Screen Color Distortion

                                  Originally posted by newtothis
                                  Yes that will work fine, Plug the resistor into the end of the cable that goes to the PSU with it disconnected at main. I think the voltages will all come up, If they do I think me and budm are right in thinking bad BGA connections
                                  Ok,,with resistor jumped at main board connector,,PS Voltages are now:
                                  ON-OFF=0vdc
                                  DIM=3.28vdc
                                  12v=2.52vdc
                                  12v=2.53vdc
                                  GND=0vdc
                                  GND=0vdc
                                  GND=0vdc
                                  24v=0vdc
                                  24v=0vdc
                                  5.2v=5.14vdc
                                  5.2v=5.14vdc
                                  ACD=0vdc
                                  I would like to have a known good main to try...

                                  Comment

                                  • newtothis
                                    Badcaps Legend
                                    • Mar 2013
                                    • 1556
                                    • england

                                    #37
                                    Re: M421VT LED Screen Color Distortion

                                    Originally posted by dfang
                                    Ok,,with resistor jumped at main board connector,,PS Voltages are now:
                                    ON-OFF=0vdc
                                    DIM=3.28vdc
                                    12v=2.52vdc
                                    12v=2.53vdc
                                    GND=0vdc
                                    GND=0vdc
                                    GND=0vdc
                                    24v=0vdc
                                    24v=0vdc
                                    5.2v=5.14vdc
                                    5.2v=5.14vdc
                                    ACD=0vdc
                                    I would like to have a known good main to try...
                                    Can you confirm settings and what ground you are using for the tests please, Those are way off. Also check your meter battery

                                    ***EDIT*** Actually your 5v is correct so can't be meter or testing method, Has to be a PSU fault ***


                                    So we now face a faulty PSU and Main! :/

                                    Ok my view is that the BGA connections are bad causing your initial symptoms, This has a good chance at being sorted with a reflow.. So now onto troubleshooting the PSU...

                                    Can you force the PSU on again and also use another resistor to the ON/OFF pin, This should boot the voltages for the Backlights
                                    Last edited by newtothis; 04-21-2015, 03:06 PM.

                                    Comment

                                    • dfang
                                      Member
                                      • Feb 2013
                                      • 39
                                      • USA

                                      #38
                                      Re: M421VT LED Screen Color Distortion

                                      Originally posted by newtothis
                                      Can you confirm settings and what ground you are using for the tests please, Those are way off. Also check your meter battery

                                      ***EDIT*** Actually your 5v is correct so can't be meter or testing method, Has to be a PSU fault ***


                                      So we now face a faulty PSU and Main! :/

                                      Ok my view is that the BGA connections are bad causing your initial symptoms, This has a good chance at being sorted with a reflow.. So now onto troubleshooting the PSU...

                                      Can you force the PSU on again and also use another resistor to the ON/OFF pin, This should boot the voltages for the Backlights
                                      Force PSU on again ? You mean jump with resistor at main board connector as before ? Use another resistor from where to ON/OFF pin ? STBY 5.2v ?

                                      Comment

                                      • newtothis
                                        Badcaps Legend
                                        • Mar 2013
                                        • 1556
                                        • england

                                        #39
                                        Re: M421VT LED Screen Color Distortion

                                        Onto the other 5v will do it.

                                        So yes we are forcing the psu on and also forcing the backlight voltages on, This way everything "should" be on and we can see what voltages you are getting

                                        Comment

                                        • dfang
                                          Member
                                          • Feb 2013
                                          • 39
                                          • USA

                                          #40
                                          Re: M421VT LED Screen Color Distortion

                                          Originally posted by newtothis
                                          Onto the other 5v will do it.

                                          So yes we are forcing the psu on and also forcing the backlight voltages on, This way everything "should" be on and we can see what voltages you are getting
                                          Will attack it tomorrow,,I'm learning a lot...
                                          Thanks for the help from you all...

                                          Comment

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