Sound and picture but no backlight

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  • JCdes
    Senior Member
    • Feb 2013
    • 91
    • USA

    #61
    Re: Sound and picture but no backlight

    Top side
    Attached Files

    Comment

    • budm
      Badcaps Legend
      • Feb 2010
      • 40746
      • USA

      #62
      Re: Sound and picture but no backlight

      There should be printing on the body of Q201.
      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

      • JCdes
        Senior Member
        • Feb 2013
        • 91
        • USA

        #63
        Re: Sound and picture but no backlight

        A couple of posts back I said theres no voltage at gnd

        Comment

        • JCdes
          Senior Member
          • Feb 2013
          • 91
          • USA

          #64
          Re: Sound and picture but no backlight

          D669 I think...

          Comment

          • Topcat
            The Boss Stooge
            • Oct 2003
            • 16954
            • United States

            #65
            Re: Sound and picture but no backlight

            The argument has been removed, do not resume it.
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            Comment

            • JCdes
              Senior Member
              • Feb 2013
              • 91
              • USA

              #66
              Re: Sound and picture but no backlight

              Originally posted by budm
              There should be printing on the body of Q201.
              D669A is the part#

              Comment

              • dick_barton
                Badcaps Legend
                • Aug 2015
                • 6642
                • Wales

                #67
                Re: Sound and picture but no backlight

                They look like transistors. Data sheet.
                http://www.datasheetq.com/datasheet-.../Iscsemi/D669A
                Willing to help but I'm no expert.

                Comment

                • JCdes
                  Senior Member
                  • Feb 2013
                  • 91
                  • USA

                  #68
                  Re: Sound and picture but no backlight

                  I noticed there's 0v at d204

                  Comment

                  • dick_barton
                    Badcaps Legend
                    • Aug 2015
                    • 6642
                    • Wales

                    #69
                    Re: Sound and picture but no backlight

                    Have you check D204 with your meter set to diode mode?

                    JP8 whicjh is a 0 ohm resistor is on the other side of the board close to this diode. I would check that it hasn't gone open circiut.
                    I would check all the 0 ohm resistor in that area
                    Last edited by dick_barton; 12-20-2020, 10:47 AM.
                    Willing to help but I'm no expert.

                    Comment

                    • JCdes
                      Senior Member
                      • Feb 2013
                      • 91
                      • USA

                      #70
                      Re: Sound and picture but no backlight

                      Will do right away

                      Comment

                      • JCdes
                        Senior Member
                        • Feb 2013
                        • 91
                        • USA

                        #71
                        Re: Sound and picture but no backlight

                        Jp8, jp5, jp16 are all ok...

                        Comment

                        • JCdes
                          Senior Member
                          • Feb 2013
                          • 91
                          • USA

                          #72
                          Re: Sound and picture but no backlight

                          Got continuity both ways on d204 but then all resistors underneath do connect them. I would have to pull it out tomorrow to test it.

                          Comment

                          • budm
                            Badcaps Legend
                            • Feb 2010
                            • 40746
                            • USA

                            #73
                            Re: Sound and picture but no backlight

                            D204 has a bunch of low Ohms (2R20) resistors connected in parallel with it so it will show conduction in both directions.
                            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

                            • budm
                              Badcaps Legend
                              • Feb 2010
                              • 40746
                              • USA

                              #74
                              Re: Sound and picture but no backlight

                              BTW, are you getting the 380 ~ 400 VDC PFC Boosted Voltage on main filter cap EC101 ( measured between the two legs) when TV is turned on?
                              What are the Voltage rating of the caps EC11/12/201/202?
                              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

                              • budm
                                Badcaps Legend
                                • Feb 2010
                                • 40746
                                • USA

                                #75
                                Re: Sound and picture but no backlight

                                Originally posted by dick_barton
                                They look like transistors. Data sheet.
                                http://www.datasheetq.com/datasheet-.../Iscsemi/D669A
                                They are too cheap to use the typical MOSFET for the PWM control of the constant control (LOW side control).
                                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

                                • JCdes
                                  Senior Member
                                  • Feb 2013
                                  • 91
                                  • USA

                                  #76
                                  Re: Sound and picture but no backlight

                                  Originally posted by budm
                                  BTW, are you getting the 380 ~ 400 VDC PFC Boosted Voltage on main filter cap EC101 ( measured between the two legs) when TV is turned on?
                                  What are the Voltage rating of the caps EC11/12/201/202?
                                  For ec101 I'm getting 376v, ec11 and 12 are 100uf 100v... 201 and 202 are 47uf 160v.

                                  Comment

                                  • budm
                                    Badcaps Legend
                                    • Feb 2010
                                    • 40746
                                    • USA

                                    #77
                                    Re: Sound and picture but no backlight

                                    Originally posted by JCdes
                                    For ec101 I'm getting 376v, ec11 and 12 are 100uf 100v... 201 and 202 are 47uf 160v.
                                    OK, the PFC Boost Voltage is working.

                                    Next, meter set to 20Vdc, all connectors in place, black probe on the chassis, red probe on 1 of 3 pins of Q201 at a time then turn the TV on while watching the meter to see how high it goes up to then turn off the TV then repeat the same test on the other 2 pin of Q201.
                                    BTW, look at the spec sheet, post #67, of the Transistor so you can see which pin is Base and Emitter, middle pin is Collector (Connected to the Cathode of the LED string). Emitter is connected to resistor R244 (5R10), the other end of the resistor is then connected to circuit ground via D204//with resistors (R246/A, 247/A, 248/A) to complete the current path for the LED string, as you can see, the Cathode of the LED strings are not connected directly to circuit ground so if the transistors are not turned on then the LED strings will not light up.
                                    R212 (1K) is connected to the FB pin 5 of the IC to monitor the Vdrops on D204//with resistors (R246/A, 247/A, 248/A) for maintaining the constant current through the LED strings.
                                    BTW, what is wattage of the 100 Ohms resistor you have? We can use that to bypass the Cathode return of one of the LED string to circuit ground via 100 Ohms resistor just to find out if the LED string will try to come on or not.
                                    Last edited by budm; 12-20-2020, 07:52 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

                                    • JCdes
                                      Senior Member
                                      • Feb 2013
                                      • 91
                                      • USA

                                      #78
                                      Re: Sound and picture but no backlight

                                      I get 0 on pin 1, 0 on pin 2 and .64 on pin 3. Nothing changes when I turn it on. I can check the wattage on the resistors I got tomorrow.
                                      Last edited by JCdes; 12-20-2020, 08:00 PM.

                                      Comment

                                      • budm
                                        Badcaps Legend
                                        • Feb 2010
                                        • 40746
                                        • USA

                                        #79
                                        Re: Sound and picture but no backlight

                                        Originally posted by JCdes
                                        I get 0 on pin 1, 0 on pin 2 and .64 on pin 3. Nothing changes when I turn it on.
                                        0.64V on pin 3 (Base) is on border line of Bias Voltage to run it on since the Emitter is connected to the Diode to ground.
                                        Can you put the 100 Ohms resistor to the middle (Collector) pin of Q201 or on the LED connector pin that goes to the middle pin of Q201, the other end of the resistor will be connected to the circuit ground (chassis), you should see the one of the LED string try to come on, just watch out for the resistor may be over heated but it is just for testing only. Do not leave the TV on for too long.
                                        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

                                        • JCdes
                                          Senior Member
                                          • Feb 2013
                                          • 91
                                          • USA

                                          #80
                                          Re: Sound and picture but no backlight

                                          I can do that tomorrow. I got all the tools and goodies in my hobby shack outside the house. I'll do it and report back tomorrow. I really appreciate all the help. Resistor to center leg and to chassis right?

                                          Comment

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