Ordering SMD LED for backlight

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  • Diah
    Badcaps Legend
    • Feb 2013
    • 6355
    • Germany

    #21
    Re: Ordering SMD LED for backlight

    Originally posted by budm
    Please look at the VF/If chart of the LG spec I provided.
    here dear friend what i am talking on.. the main roll always with TV Back light LED we need to take care on these facts.
    how much we have on One LED
    1- Forward Current (IF )
    2- Pulse Forward Current (IFp)
    3- Reverse Current (IR): uA
    4- Reverse Voltage (VR): V (mA)
    5- Power Dissipation (PD) W most 1w
    6- Operating Temperature (Topr):
    7- Storage Temperature (Tstg: always = (Topr)
    8- Soldering Temperature Tsld):

    the LG sheet was refer to Double chip. Single one had other way for measurement and sheet dialogue.

    look on the first photo OP posted the label. 6V all in one line 50 pieces socket type with each 2 wires. ( its one line PSU out )

    the second label photo nothings special as we do know size and type but it tell us that this type had 100 lu. this is not always described on the strips label. as each manufacture use its own way to described .

    the subject become interesting. so i find its not bad we discusses it here ..

    i would like to add one Facts that the critical point always to LED Backlight the starting from cold start the tv.

    PSU will give the high level after it receive the BL_ON signal untill the firmware come in place to reduce the current. ( this why many TV manufacture didn't install main switch to the AC Line. so TV remain in STB.

    other manufacture ( Most Chinese brand ) they add the control part at the eeprom start up script to sent BL-ON under value control. this we can find it when we log in SM. and under LED back light section. we will find the way it work. for example Hisense they had most always the BL value range like 0-20-50-80-100
    where 0=0, 20=30, 50=80, 80=90 , 100=100,
    in short words it mean user put the BL in setting of 50. but in fact its 80.

    such TV sets which work on this script add to boot eeprom suffer always corrupted firmware or damage SPI Flash. so other manufacture they make the SMD LED can handle this high power at start on. better than they will face other problem with MB or firmware or boot .bin driver.
    Last edited by Diah; 01-31-2019, 12:11 PM.

    Comment

    • Mcologist
      Member
      • Jan 2019
      • 20
      • Canada

      #22
      Re: Ordering SMD LED for backlight

      Here are the photos
      Attached Files

      Comment

      • Mcologist
        Member
        • Jan 2019
        • 20
        • Canada

        #23
        Re: Ordering SMD LED for backlight

        Hey Budm thanks for all the help, My meter in diode mode shows nothing (.0L) and it only lights the LED's up very faintly.
        The LED power connections are the two on the top right.
        I have some 6v LED's in just to get it going to test. measuring the LED's while everything is on I get 2.9v on all of the original LED's.
        The 6v that I have in are 5000k color temp but appear very yellow next to the originals which look very blue, What color temp are backlight LED's usually?

        Comment

        • budm
          Badcaps Legend
          • Feb 2010
          • 40746
          • USA

          #24
          Re: Ordering SMD LED for backlight

          "measuring the LED's while everything is on I get 2.9v on all of the original LED's. "
          You're 100% sure that it only shows about 2.9V on each original LED's? Are they lit up brightly? How about the 6V LED you put in, what does it show? 5 something Volts?
          Last edited by budm; 02-04-2019, 10:02 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

          • Mcologist
            Member
            • Jan 2019
            • 20
            • Canada

            #25
            Re: Ordering SMD LED for backlight

            Yes it is bright and I put the screen back on to check how much a difference the color made and it has great picture minus the yellow spots

            Comment

            • Mcologist
              Member
              • Jan 2019
              • 20
              • Canada

              #26
              Re: Ordering SMD LED for backlight

              yes it is 2.9v on original ones and just under 6v on the test ones

              Comment

              • budm
                Badcaps Legend
                • Feb 2010
                • 40746
                • USA

                #27
                Re: Ordering SMD LED for backlight

                Well, that means your LED are 3V not 6V (Dual-LED) type, that is why I insist you to take the reading to verify.
                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

                • Mcologist
                  Member
                  • Jan 2019
                  • 20
                  • Canada

                  #28
                  Re: Ordering SMD LED for backlight

                  agreed but Diah seemed so sure he was correct :P also without working LED's would it be safe to jumper over the burnt out ones to get the rest powered in order to measure?

                  Comment

                  • budm
                    Badcaps Legend
                    • Feb 2010
                    • 40746
                    • USA

                    #29
                    Re: Ordering SMD LED for backlight

                    That is why I suggest you to do the test, it does not take much work to verify, that is what I always do, verify and verify. But what do I know about LED's?
                    Fifty 6V LED'S, that means the total Vf will be about 300V.
                    When you bypass the LED, the PWM Controlled MOSFET that maintains the constant current will have to dissipate more heat, you can bypass it but I would not do it permanently, for taking measurement is OK.
                    Last edited by budm; 02-04-2019, 11:40 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

                    • Diah
                      Badcaps Legend
                      • Feb 2013
                      • 6355
                      • Germany

                      #30
                      Re: Ordering SMD LED for backlight

                      Originally posted by budm
                      Well, that means your LED are 3V not 6V (Dual-LED) type, that is why I insist you to take the reading to verify.
                      after he replaced his new LED and test the old one while the TV was on he write it said 2.9V

                      is this mean 0.1 the tolerance if we use 3V LED? how about the first start up- and we do know the reading go high then go down ..

                      i write 4.7 V. but all who sell are just seller.. the yellow he have now just the effect of color temperature

                      Comment

                      • budm
                        Badcaps Legend
                        • Feb 2010
                        • 40746
                        • USA

                        #31
                        Re: Ordering SMD LED for backlight

                        Since we do not have the VF/If graph of his LED and we do not know how much current is in the circuit right now 2.9V may be about right, Vf is also affected by the Temperature. I would expect Vf of his LED will be higher may around 3 ~ 3.1V at full rated current.
                        The so call 3V LED is the Typ. rating spec that why they give you the graph so when you design the drive circuit you will know what to expect at the required current.
                        If you look at the printed spec for Typ. Vf, is at rated test current and at 25c. See #5 Electro -Optical Characteristics page 7 for example. The max rating is 200mA but the test is done at 150mA.
                        So from LG spec sheet, the Vf is 6.36V typ. @150mA @Ta of 25c. and it matched the graph on page 12, good manufacturers will provide the graphs.
                        If OP want to look at details of the LED, he can do the Vf/If plot and see what he has, that is one of my many job responsible when I was working for Fairchild.
                        Last edited by budm; 02-05-2019, 02:59 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

                          #32
                          Re: Ordering SMD LED for backlight

                          Here is LG 5152 spec for single LED.
                          Max If = 200mA
                          Vf @ 65mA, Ta 25c = 2.70min, max 3.0V, so out of the batch some may be 2.7V some may be 3.0V, and some are in between.
                          Per Graph on page 10, @150mA Vf =3.18V
                          Attached Files
                          Last edited by budm; 02-05-2019, 02:53 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

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