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Backlights but no picture - No 12v to Tcon board

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    #41
    Re: Backlights but no picture - No 12v to Tcon board

    Originally posted by budm View Post
    https://www.badcaps.net/forum/attach...2&d=1571874353

    Emitter pin (Top) is connected to R125/C181
    Collector pin (Middle pin) is connected to R126
    Base is the bottom pin.
    Thanks.

    Emitter pin = 0.0v ON, 0.0v OFF
    Collector pin = 11.5v ON, 0.0v OFF
    Base pin = 0.0v ON, 0.0v OFF

    Comment


      #42
      Re: Backlights but no picture - No 12v to Tcon board

      This may be the layout for the smd transistor. The readings given for the base does not appear correct.
      Attached Files
      Willing to help but I'm no expert.

      Comment


        #43
        Re: Backlights but no picture - No 12v to Tcon board

        Originally posted by dick_barton View Post
        This may be the layout for the smd transistor. The readings given for the base does not appear correct.
        Do you mean that the 0v reading on the base pin means that that component is faulty? Or that you think I measured the voltage incorrectly?
        Last edited by Stuckster; 10-24-2019, 04:59 PM.

        Comment


          #44
          Re: Backlights but no picture - No 12v to Tcon board

          Originally posted by Stuckster View Post
          Thanks.

          Emitter pin = 0.0v ON, 0.0v OFF
          Collector pin = 11.5v ON, 0.0v OFF
          Base pin = 0.0v ON, 0.0v OFF
          BASE is not being driven.
          Check the resistance between GND and the Base pin.
          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


            #45
            Re: Backlights but no picture - No 12v to Tcon board

            Originally posted by budm View Post
            BASE is not being driven.
            Check the resistance between GND and the Base pin.
            Resistance between GND and the Base pin is 3.3 measured at 200k Ohms.

            Comment


              #46
              Re: Backlights but no picture - No 12v to Tcon board

              3.3K is not bad.
              Right now you can try removing the LVDS cables from the main board first the try forcing on Q1 by connecting 100 Ohms resistor between GND and Gate pin and see if you will get 12VDC at Drain pin or not.
              https://www.badcaps.net/forum/attach...2&d=1571874353
              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


                #47
                Re: Backlights but no picture - No 12v to Tcon board

                Originally posted by budm View Post
                3.3K is not bad.
                Right now you can try removing the LVDS cables from the main board first the try forcing on Q1 by connecting 100 Ohms resistor between GND and Gate pin and see if you will get 12VDC at Drain pin or not.
                https://www.badcaps.net/forum/attach...2&d=1571874353
                Hmm. I really appreciate your help, but unfortunately I don't have a 100 Ohms resistor, nor the experience to solder components to the board. So this might be getting beyond my abilities.

                Is there some other way to simulate 100 Ohms of resistance between GND and the Gate pin? Possibly using the meter?

                Failing that, how certain are you at this stage that replacing the mainboard would essential fix the TV? And if I put a new mainboard in, from what we have already diagnosed, what is the chance that there could be something feeding back from the PSU or the Tcon and damaging Q1 on the mainboard? Or is that very unlikely?

                Comment


                  #48
                  Re: Backlights but no picture - No 12v to Tcon board

                  Well, if you do not have the ability to solder the component on the main board then how are you going to fix the the board?
                  At this you know that the main board is not sending the 12V to run the T-CON, so there is nothing else you can do but replacing the main board with KNOWN WORKING BOARD.
                  You can take the board to the local repair shop and have them solder in the resistor for you.
                  Q1 is not being turned on by Q2 that is why we are trying to do force on with the resistor to provide the 12V to run the T-CON, if there is no problem with T-CON and other problems with the main board then all the functions of the TV should work, if not then you have more than just 12V to the T-CON board problem, so the only way to find out is to force on Q1 but since you do not know how to solder then it is moot point to do further troubleshooting the board. If force on gets the TV to function then we can use other signal to turn on Q1 instead but that will require board modification which you cannot do.
                  Last edited by budm; 10-24-2019, 10:10 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


                    #49
                    Re: Backlights but no picture - No 12v to Tcon board

                    Originally posted by budm View Post
                    Well, if you do not have the ability to solder the component on the main board then how are you going to fix the the board?
                    At this you know that the main board is not sending the 12V to run the T-CON, so there is nothing else you can do but replacing the main board with KNOWN WORKING BOARD.
                    You can take the board to the local repair shop and have them solder in the resistor for you.
                    Q1 is not being turned on by Q2 that is why we are trying to do force on with the resistor to provide the 12V to run the T-CON, if there is no problem with T-CON and other problems with the main board then all the functions of the TV should work, if not then you have more than just 12V to the T-CON board problem, so the only way to find out is to force on Q1 but since you do not know how to solder then it is moot point to do further troubleshooting the board. If force on gets the TV to function then we can use other signal to turn on Q1 instead but that will require board modification which you cannot do.
                    Hey. My intention from the outset was to diagnose the cause so I could confidently return and replace the faulty board.

                    Is the fix you have suggested a temporary measure for further testing or will it actually fix the problem and if so if I'm able to get it repaired it is it ok to leave it like that permanently?

                    Comment


                      #50
                      Re: Backlights but no picture - No 12v to Tcon board

                      Maybe try there, they indicate that they have 1 mainboard, I don't know anything about them, might want to look their record up: http://a1tv.com.au/TCL.html

                      Comment


                        #51
                        Re: Backlights but no picture - No 12v to Tcon board

                        Originally posted by nomoresonys View Post
                        Maybe try there, they indicate that they have 1 mainboard, I don't know anything about them, might want to look their record up: http://a1tv.com.au/TCL.html
                        Hi. Yeah I have enquired with those guys. They want $355.00 plus $22.00 postage for a new board! Hard to justify on a 4 year old set.

                        I can get a new board off Ebay for around $270, which is still pricey. So I first need to arrange a refund on the faulty board to obtain the funds.

                        Might have to learn how to solder pcbs!

                        Comment


                          #52
                          Re: Backlights but no picture - No 12v to Tcon board

                          Ok, I guess they lied, in their ad it said, we are back in business, all parts are 120 dollars, there at the bottom: http://a1tv.com.au/index.html

                          Comment


                            #53
                            Re: Backlights but no picture - No 12v to Tcon board

                            The board you are working on that's failing to power the Tcon was one you've just bought?
                            The one you've just looked at in post#51 is you feel, too expensive to buy for a 4 year old set?

                            Even though the Tcon is not being powered with the mainboard you already have, do you have sound, can you change channels etc to try and work out if the rest of the mainboard is functioning?

                            Is this your own TV or are you repairing it for someone else?
                            Last edited by dick_barton; 10-25-2019, 11:24 AM.
                            Willing to help but I'm no expert.

                            Comment


                              #54
                              Re: Backlights but no picture - No 12v to Tcon board

                              Post #1 I need to be 100% certain which board is faulty before I outlay money to replace it.
                              But it looks like he did outlay the money to get the replacement board to begin with, but I thought he did not want to spend big money on the board.
                              I have already determined:
                              - Tcon board not receiving any 12V.
                              - Mainboard only outputting 2.6v to audio/speakers
                              - Replacement PCB (no change)
                              - Replacement Tcon board (no change
                              )

                              Bottom line, the replacement board we are troubleshooting is not sending the 12V either.
                              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


                                #55
                                Re: Backlights but no picture - No 12v to Tcon board

                                Originally posted by nomoresonys View Post
                                Ok, I guess they lied, in their ad it said, we are back in business, all parts are 120 dollars, there at the bottom: http://a1tv.com.au/index.html
                                Ha. Yes. When I was googling it took me straight to the page with the part. I never saw the home page. Will have to call them on it and see what they say. Thank you

                                Comment


                                  #56
                                  Re: Backlights but no picture - No 12v to Tcon board

                                  Originally posted by dick_barton View Post
                                  The board you are working on that's failing to power the Tcon was one you've just bought?
                                  The one you've just looked at in post#51 is you feel, too expensive to buy for a 4 year old set?
                                  Hey. No the replacement board I bought was from a private seller and was sold in "used working condition". Was trying to save some $$. Lesson learned I guess.

                                  Originally posted by dick_barton View Post
                                  Even though the Tcon is not being powered with the mainboard you already have, do you have sound, can you change channels etc to try and work out if the rest of the mainboard is functioning?
                                  I can't see a thing on the screen. So I have tried hooking up an external audio source, but I can't tell if it's on the right input. Have tried cycling the source button to no avail.

                                  Originally posted by dick_barton View Post
                                  Is this your own TV or are you repairing it for someone else?
                                  My own TV.

                                  Comment


                                    #57
                                    Re: Backlights but no picture - No 12v to Tcon board

                                    Originally posted by budm View Post
                                    Post #1 I need to be 100% certain which board is faulty before I outlay money to replace it.
                                    But it looks like he did outlay the money to get the replacement board to begin with, but I thought he did not want to spend big money on the board.
                                    I have already determined:
                                    - Tcon board not receiving any 12V.
                                    - Mainboard only outputting 2.6v to audio/speakers
                                    - Replacement PCB (no change)
                                    - Replacement Tcon board (no change
                                    )

                                    Bottom line, the replacement board we are troubleshooting is not sending the 12V either.
                                    Hi Budm. To clarify. The replacement board I first bought was a used board. Was trying to save some money. Unfortunately it didn't work. Now that we have determined fairly conclusively that is faulty (with your generous help) I would like to return the used board so I can buy a new board.

                                    Comment


                                      #58
                                      Re: Backlights but no picture - No 12v to Tcon board

                                      Ended up returning the used board and received a refund through Paypal. Got the TV serviced and new mainboard installed. Repairs are warranted for 3 months. Thanks all for your help.

                                      The moral of this story? Never buy used electronic components unless you can diagnose and repair them!

                                      Comment


                                        #59
                                        Re: Backlights but no picture - No 12v to Tcon board

                                        Thanks for the follow-up on the repair.
                                        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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