Sharp LC-40LE550U no backlight

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  • budm
    Badcaps Legend
    • Feb 2010
    • 40746
    • USA

    #21
    Re: Sharp LC-40LE550U no backlight

    The 0.89V is the Vf of the protection diode not the White LED Vf, you need to reverse the probes to read the Vf of the LED which it should be around 2.8- 3V.
    It can also be that your meter does not put out enough Voltage in Diode mode to turn on the White LED.
    It can also be dual LED in one body so the Vf will be around 6V.
    Last edited by budm; 09-15-2016, 01:27 AM.
    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
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    TV Factory reset codes listing:
    http://www.badcaps.net/forum/showthread.php?t=24809

    Comment

    • Markpixley
      Member
      • Aug 2012
      • 37
      • United States

      #22
      Re: Sharp LC-40LE550U no backlight

      Originally posted by budm
      The 0.89V is the Vf of the protection diode not the White LED Vf, you need to reverse the probes to read the Vf of the LED which it should be around 2.8- 3V.
      It can also be that your meter does not put out enough Voltage in Diode mode to turn on the White LED.
      It can also be dual LED in one body so the Vf will be around 6V.
      Thanks for the response, so down that road would it be about as smart to make a simple power supply and test each LED since I have already scratched the surface to diode test them? Just do the 3 volt test and see if they light?

      It seems odd to me that there are 5 distinct strips and 10 power leads, if a single led was out wouldn't that simply stop that strip from working instead of all five strips?

      I am not techy enough but trying...(I actually build vintage tube recording gear so this lower power stuff is all new to me)

      Comment

      • budm
        Badcaps Legend
        • Feb 2010
        • 40746
        • USA

        #23
        Re: Sharp LC-40LE550U no backlight

        If you look at the LED connectors in deatails, you can see that the LED strips are connected in series to form ONE long LED string, if ypu look at the bottom side of the power supply board where the LED connector CN202 PIN 1 (+) is connected to the LED power supply filter cap CL115 positive leg, the pin 1 of CN202 goes to the first LED string ANODE, the negative return goes to CN202 PIN 2 (-) this (-) is then connected to the Anode (CN202 pin 3) of next LED string, and on and on to the fifth string.
        So as you can see, the LED connectors are terminated as series connections for the 5 LED strings, if one goes open circuit then the whole backlights will not be on.
        Pictures provided by shopjimmy.
        Sharp 9JY0940CTJ05000 (FTPL-009) Power Supply Unit.
        http://www.shopjimmy.com/sharp-9jy09...pply-unit.htm#
        Attached Files
        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

        • Markpixley
          Member
          • Aug 2012
          • 37
          • United States

          #24
          Re: Sharp LC-40LE550U no backlight

          Originally posted by budm
          If you look at the LED connectors in deatails, you can see that the LED strips are connected in series to form ONE long LED string, if ypu look at the bottom side of the power supply board where the LED connector CN202 PIN 1 (+) is connected to the LED power supply filter cap CL115 positive leg, the pin 1 of CN202 goes to the first LED string ANODE, the negative return goes to CN202 PIN 2 (-) this (-) is then connected to the Anode (CN202 pin 3) of next LED string, and on and on to the fifth string.
          So as you can see, the LED connectors are terminated as series connections for the 5 LED strings, if one goes open circuit then the whole backlights will not be on.
          Pictures provided by shopjimmy.
          Sharp 9JY0940CTJ05000 (FTPL-009) Power Supply Unit.
          http://www.shopjimmy.com/sharp-9jy09...pply-unit.htm#
          Ahhh very helpful again it takes some of the voodoo out of it...making moire sense Thanks!

          Comment

          • Markpixley
            Member
            • Aug 2012
            • 37
            • United States

            #25
            Re: Sharp LC-40LE550U no backlight

            Originally posted by Markpixley
            I also have another question since i have never seen these before, but what is the clear diode looking fuse item labelled SG105 in the bottom right hand corner of image #2?

            Is it some sort of slow blow fuse and if so is there a way to test it? It seems to connect ground planes on the back of the psu...but I am unfamiliar with it.
            All the other "SG" parts show a continuity test beep, EXCEPT this one in the corner...is this some kind of time delay fuse or capacitor part?

            This one is not giving me any response, Ohm or continuity at all...

            Does "SG" mean surge guard?
            Last edited by Markpixley; 09-15-2016, 08:09 PM.

            Comment

            • budm
              Badcaps Legend
              • Feb 2010
              • 40746
              • USA

              #26
              Re: Sharp LC-40LE550U no backlight

              Surge Arrestor, as you can see, some of them are connected in parallel with the inductor windings so you see very low DCR.
              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

              • Markpixley
                Member
                • Aug 2012
                • 37
                • United States

                #27
                Re: Sharp LC-40LE550U no backlight

                Thanks budm, you have been very helpful...

                So here's where I am at...I used a 12 volt psu and tested all the LED's (based on your suggestion that they are double and 6 volts)...every pair I tested lite up brightly and all my continuity test on the strips seem to be solid...

                Unit power light turns green...I can get it to turn red but it takes a bit...and it usually just flips back to green...

                No back light...at all voltages still as earlier...

                Without being to much of a bother what might be my next course of testing?

                Comment

                • budm
                  Badcaps Legend
                  • Feb 2010
                  • 40746
                  • USA

                  #28
                  Re: Sharp LC-40LE550U no backlight

                  So you can light up each LED strip individually using external power supply.
                  You have 5 LED strips, each strip has 10 LEDs, each LED is rated at 6V, so total Vf is 50 LEDs x 6V = 300V, and you have 329V feeding the strings per post #1 but you never see the LEDs light up at all.
                  It means you have open connection between the 5 set of the LED strings some where, or the LED return through the Power MOSFET is not active.
                  Last edited by budm; 09-16-2016, 12:14 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

                  • budm
                    Badcaps Legend
                    • Feb 2010
                    • 40746
                    • USA

                    #29
                    Re: Sharp LC-40LE550U no backlight

                    What DCV do you have on pin 5 of CN203, that the LED string return line to the PWM Controlled power MOSFET QD101?
                    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

                    • Markpixley
                      Member
                      • Aug 2012
                      • 37
                      • United States

                      #30
                      Re: Sharp LC-40LE550U no backlight

                      76.2 vdc

                      Comment

                      • budm
                        Badcaps Legend
                        • Feb 2010
                        • 40746
                        • USA

                        #31
                        Re: Sharp LC-40LE550U no backlight

                        BTW, what is the P/N of the LED backlights controller IC UD101?
                        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

                        • Markpixley
                          Member
                          • Aug 2012
                          • 37
                          • United States

                          #32
                          Re: Sharp LC-40LE550U no backlight

                          the voltage to Cn202/cn203=

                          1. (+) 340
                          2. (-) 286
                          3. (+) 286
                          4. (-) 233
                          5. (-) 233

                          1. (-) 180
                          2. (+) 180
                          3. (-) 128
                          4 (+) 128
                          5. (-) 77.8

                          Comment

                          • Markpixley
                            Member
                            • Aug 2012
                            • 37
                            • United States

                            #33
                            Re: Sharp LC-40LE550U no backlight

                            Originally posted by budm
                            BTW, what is the P/N of the LED backlights controller IC UD101?
                            Nikos
                            PO425AD
                            WUE900302

                            Comment

                            • budm
                              Badcaps Legend
                              • Feb 2010
                              • 40746
                              • USA

                              #34
                              Re: Sharp LC-40LE550U no backlight

                              Originally posted by Markpixley
                              76.2 vdc
                              OK, so there is no open connection on the LED strings, and you can get all the LEDs in each strip to light up OK.
                              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

                              • Markpixley
                                Member
                                • Aug 2012
                                • 37
                                • United States

                                #35
                                Re: Sharp LC-40LE550U no backlight

                                Originally posted by budm
                                OK, so there is no open connection on the LED strings, and you can get all the LEDs in each strip to light up OK.
                                Correct...now here's a question...

                                The Rich Tek chip (UD101)

                                Pins 13/12 each show 10 volts (led 1/2)
                                Pins 10/9 show no voltage (.004) which would be led 4/3

                                Vin is 12v
                                Fault is 12v

                                Is this chip ONLY being used for two led diagnostics? and pins 10/9 would never be used anyway?

                                Comment

                                • Markpixley
                                  Member
                                  • Aug 2012
                                  • 37
                                  • United States

                                  #36
                                  Re: Sharp LC-40LE550U no backlight

                                  Originally posted by budm
                                  OK, so there is no open connection on the LED strings, and you can get all the LEDs in each strip to light up OK.
                                  Forgive me for being dense (Thick as a brick per Jethro Tull)...

                                  I start with 340 volts and end with 76 but no light...so where in hell is all that voltage going?...if it was open I would not see any voltage at the last pin...

                                  If there is a short...?

                                  Comment

                                  • budm
                                    Badcaps Legend
                                    • Feb 2010
                                    • 40746
                                    • USA

                                    #37
                                    Re: Sharp LC-40LE550U no backlight

                                    Originally posted by Markpixley
                                    the voltage to Cn202/cn203=

                                    1. (+) 340
                                    2. (-) 286
                                    3. (+) 286
                                    4. (-) 233
                                    5. (-) 233

                                    1. (-) 180
                                    2. (+) 180
                                    3. (-) 128
                                    4 (+) 128
                                    5. (-) 77.8
                                    Looking at those reading for the Vf of each string, for example: the first string is 340 - 286 = 54V, so average Vf of each sting is about 52V which is not right since ten 6V LED should be 60V per string.
                                    It looks like the MOSFET QD101 is not being turned on.
                                    I need to look up the spec the IC UD101 to see how it function.
                                    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

                                    • Markpixley
                                      Member
                                      • Aug 2012
                                      • 37
                                      • United States

                                      #38
                                      Re: Sharp LC-40LE550U no backlight

                                      So far the info I have gathered on the niko is it is not schothy or esr, it can maintain up to 800 rds volts on 10v...seems like it goes up to 4 amps 512 pf Ciss typical...

                                      Comment

                                      • Markpixley
                                        Member
                                        • Aug 2012
                                        • 37
                                        • United States

                                        #39
                                        Re: Sharp LC-40LE550U no backlight

                                        Originally posted by budm
                                        Looking at those reading for the Vf of each string, for example: the first string is 340 - 286 = 54V, so average Vf of each sting is about 52V which is not right since ten 6V LED should be 60V per string.
                                        It looks like the MOSFET QD101 is not being turned on.
                                        I need to look up the spec the IC UD101 to see how it function.
                                        Yes its actually a little more each string has eleven led's so the voltage required is 66volts...

                                        Comment

                                        • Markpixley
                                          Member
                                          • Aug 2012
                                          • 37
                                          • United States

                                          #40
                                          Re: Sharp LC-40LE550U no backlight

                                          I flipped the psu over and have it plugged in, powered up and the Mosfet QD101 reads 12.44v bottom leg at left, 14.17v bottom leg right (same as pin 13 on UD101) and 79.2v (same as Cn203 pin 5/bottom rail of led return)

                                          Comment

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