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    #1

    Sharp LC-40LE550U no backlight

    This TV powers on and off and I can see the floating screen saver very faintly with a flashlight.

    I've measure voltages and here is what I've found

    CN201

    1 - 3.25VDC
    2 - NC
    3 - 112mVDC
    4 - 3.19VDC
    5 - GND
    6 - GND
    7 - GND
    8 - GND
    9 - 12.45VDC
    10 - 12.45VDC
    11 - 12.45VDC
    12 - 12.45VDC
    13 - 375mVDC and rising???
    14 - 3.18VDC
    15 - 0.67VDC
    16 - NC


    CN202

    1 - 329VDC
    2 - GND
    3 - 275VDC
    4 - GND
    5 - 221VDC


    CN203

    1 - GND
    2 - 168VDC
    3 - GND
    4 - 116VDC
    5 - GND
    Attached Files
    Last edited by krygods; 10-08-2015, 11:13 PM.
    Tags: None
    #2
    Re: Sharp LC-40LE550U no backlight

    Originally posted by krygods View Post
    CN201
    3 - 112mVDC
    14 - 3.18VDC
    It would make things easier for us if you put the description of each pin next to the readings.

    CN201

    pin 3 - ACD
    pin 14 - BL_ON

    On most sets, BL_ON (backlight on) going high (> 3) means turn on. On some sets, it might be the opposite.

    ACD might be AC Detect. On some sets, ACD high might be needed to turn on. Or it could be the opposite.

    When the TV is in standby mode, what is the voltage of pins 3 and 14? When turned on what is the voltage of 3 and 14? When the set is turned off, what is the voltage of 3 and 14?

    Wow, 329V DC into the LEDs. Nearly a 55 to 52 volt drop between each strip of LEDs. At least it has decent 47uF 450V cap there.
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      #3
      Re: Sharp LC-40LE550U no backlight

      Originally posted by krygods View Post
      13 - 375mVDC and rising???
      pin 13 is NC. The 357mV reading is just your multimeter on high impedance with some ghost readings. NC is probably not connected to ground otherwise you would get 0V.
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        #4
        Re: Sharp LC-40LE550U no backlight

        Originally posted by krygods View Post
        This TV powers on and off and I can see the floating screen saver very faintly with a flashlight.
        If the TV is in a very dark room, do the LED backlights flash even for a brief time?
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          #5
          Re: Sharp LC-40LE550U no backlight

          Hmm, from

          https://www.sharpusa.com/ForHome/Hom...C40LE550U.aspx

          4 million: 1 dynamic contrast ratio

          Without even seeing the TV, I think I will call

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            #6
            Re: Sharp LC-40LE550U no backlight

            BTW, what is the marking in IC UD101, just right of 47uF 450V cap?
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              #7
              Re: Sharp LC-40LE550U no backlight

              P/N for UD101 is RT8300

              Comment

                #8
                Re: Sharp LC-40LE550U no backlight

                disassembled the panel to test the leds, found bad solder joints on one the of the connectors that join the two separate strips into one long strip. turned it on and the leds blinded me.
                Last edited by krygods; 10-09-2015, 03:55 AM.

                Comment

                  #9
                  Re: Sharp LC-40LE550U no backlight

                  perfect!

                  Comment

                    #10
                    Re: Sharp LC-40LE550U no backlight

                    So how many LEDs are in one strip? 4 LED strips?
                    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

                      #11
                      Re: Sharp LC-40LE550U no backlight

                      I believe it was 10 LEDs per strip 5 strips

                      Comment

                        #12
                        Re: Sharp LC-40LE550U no backlight

                        crazy thing is that four out of 5 led strips are mounted to the panel casing which is plastic, only the second strip from the top is mounted on a strip of metal. I was under the assumption that the LED strips needed to be mounted to metal which acts as a heatsink?

                        Comment

                          #13
                          Re: Sharp LC-40LE550U no backlight

                          They should have good thermal management, I would set the BACKLIGHTS LEVEL (not the brightness/contrast) to as low as you can so the LEDs will run cooler and extend the life of the LEDs.
                          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

                            #14
                            Re: Sharp LC-40LE550U no backlight

                            ok cool, i'll go ahead and set it to a comfortable low level before it goes to a new home.

                            Comment

                              #15
                              Re: Sharp LC-40LE550U no backlight

                              Originally posted by krygods View Post
                              P/N for UD101 is RT8300
                              The datasheet for the above has a FLT pin which detects open/short LED. Monitoring this pin for it going low points you to the LEDs as being suspect.
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                              If you are new to this forum, we can help a lot more if you please post clear focused pictures (max resolution 2000x2000 and 2MB) of your boards using the manage attachments button so they are hosted here. Information and picture clarity compositions should look like this post.

                              We respectfully ask that you make some time and effort to read some of the guides available for basic troubleshooting. After you have read through them, then ask clarification questions or report your findings.

                              Please do not post inline and offsite as they slow down the loading of pages.

                              --- end sig file ---

                              Comment

                                #16
                                Re: Sharp LC-40LE550U no backlight

                                So I have the same problem, found two of the led connectors that needed resoldering...still no backlight...my voltages on CN202 CN203 are all pretty solid (with the exception of voltage dropping to 80 volts at the bottom of CN 203) (which is quite a swing if you ask me from 329v to 80v)...at any rate...

                                Checking UD101...pin 6 is the fault...I get 12 volts on Vin and 12 volts on Fault which seems to point to the leds again...also now that I've re soldered the leds I do get 10v on both pin 13/12 (led 1/2) but zero volts on pins 10/9 (led 4/3)...any idea what I should see there or do I go back and take the panel apart yet again and search through the led connectors...really cheaply designed solder joints for the connectors...not much effort to knock them loose...

                                Comment

                                  #17
                                  Re: Sharp LC-40LE550U no backlight

                                  You are seeing the Voltage to the LED swings all the way up to 329V because there is no load due to open circuit (either by bad connector or the LED has open circuit, when the circuit see that high Voltage that is above the normal operating level then the over Voltage shutdown kicks in then it drops down to 80V which is the Voltage that is fed into the Boost converter circuit to drive the LED strings.
                                  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

                                    #18
                                    Re: Sharp LC-40LE550U no backlight

                                    Originally posted by budm View Post
                                    You are seeing the Voltage to the LED swings all the way up to 329V because there is no load due to open circuit (either by bad connector or the LED has open circuit, when the circuit see that high Voltage that is above the normal operating level then the over Voltage shutdown kicks in then it drops down to 80V which is the Voltage that is fed into the Boost converter circuit to drive the LED strings.
                                    Ahhh thank you, back into the panel to check it will let you know what I find...great forum by the way!

                                    Comment

                                      #19
                                      Re: Sharp LC-40LE550U no backlight

                                      Ok I have physically checked each and every LED with a diode test they all gave me OL one direction and .889 the other, I also checked each and every connection with a continuity test and everything came back ok...

                                      Voltage with reference to ground (negative clip on metal ground Meter set to DC) goes from 340, 286, 233, 180, 128...there are 5 strips with 11 led's each...

                                      But no back light...is it possible that this unit needs some kind of factory reset since it did have a faulty connection on one LED strip?

                                      Would the UD101 go into LED fault and need to be reset somehow? Thanks in advance...

                                      Comment

                                        #20
                                        Re: Sharp LC-40LE550U no backlight

                                        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.

                                        Comment

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