General question about CCFL backlight

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  • rtstorm
    Badcaps Veteran
    • Feb 2012
    • 971
    • Croatia

    #1

    General question about CCFL backlight

    Hello, i have one small monitor that have 2 CCFL backlight. Problem is that lamps wont turn on. Tha monitor use external psu with 12V.

    I check caps and thay are ok, the inverter board receive 12V but when starting that it drop to 10.8V

    I test lamp with external ccfl tester one by one and they turn on.

    How can i be shure that lamp are ok or defective?

    Interesting thing is when i connect 3rd lamp (external lamp) to the existing two they all turn on and stay on for 10 seconds and then turn off again.

    I think that lamps are bad but how can be sure? What is normal lamp current?
    ...the quieter you become the more you are able to hear...
  • Joe Black
    eager to learn
    • Sep 2015
    • 173
    • southeastern europe

    #2
    Re: General question about CCFL backlight

    Well, neighbour, since your lamps turn on eventually, they are obviously good.

    You have a bad inverter. Post pictures of your board(s)...

    You would typically search for shorted transistors, check transformators drivers, and transformators themselves... Of course, caps as always...
    Last edited by Joe Black; 06-26-2016, 02:09 PM.
    stay classy

    Comment

    • stj
      Great Sage 齊天大聖
      • Dec 2009
      • 30934
      • Albion

      #3
      Re: General question about CCFL backlight

      your psu is weak - the 12v should not drop.
      if the invertor draws too much current it should blow the onboard fuse.

      check your psu.

      Comment

      • rtstorm
        Badcaps Veteran
        • Feb 2012
        • 971
        • Croatia

        #4
        Re: General question about CCFL backlight

        I have external PSU, i can increse the voltage up to 30V

        I will try with 15-16V
        ...the quieter you become the more you are able to hear...

        Comment

        • rtstorm
          Badcaps Veteran
          • Feb 2012
          • 971
          • Croatia

          #5
          Re: General question about CCFL backlight

          Well i increse voltage to 14V and backlight working

          I do not understand how 12V is not enought when the monitor have a label on backside tjat say 12V input
          ...the quieter you become the more you are able to hear...

          Comment

          • stj
            Great Sage 齊天大聖
            • Dec 2009
            • 30934
            • Albion

            #6
            Re: General question about CCFL backlight

            12v is not the problem, your not feeding enough amps.

            Comment

            • rtstorm
              Badcaps Veteran
              • Feb 2012
              • 971
              • Croatia

              #7
              Re: General question about CCFL backlight

              Hmm but my Power supply have 3A rail. When i set oitput to 12V and backlight try to turn on the monitor pull 1.4A and then drop to 0.6A

              But when set to 14V monitor pull 1.6A and stay on, does not make sense to me.
              ...the quieter you become the more you are able to hear...

              Comment

              • stj
                Great Sage 齊天大聖
                • Dec 2009
                • 30934
                • Albion

                #8
                Re: General question about CCFL backlight

                sorry, but if a 3a suppy drops to 10.8 when you give it a 1.6A load then something is not right - either a connector or the psu is not doing it's job.

                if you set the psu to 14v is it still 14v at the invertor when running, or are you still seeing a 1.2v drop?

                Comment

                • rtstorm
                  Badcaps Veteran
                  • Feb 2012
                  • 971
                  • Croatia

                  #9
                  Re: General question about CCFL backlight

                  When i set psu to 14V i have 13.5V on inverter in stand by and when turn on LCD it drop to 11.5V
                  ...the quieter you become the more you are able to hear...

                  Comment

                  • stj
                    Great Sage 齊天大聖
                    • Dec 2009
                    • 30934
                    • Albion

                    #10
                    Re: General question about CCFL backlight

                    then check the voltage at the psu, because you need to trace the drop.

                    Comment

                    • budm
                      Badcaps Legend
                      • Feb 2010
                      • 40746
                      • USA

                      #11
                      Re: General question about CCFL backlight

                      Are you using SMPS regulated 12V (4A TYP.) power supply?
                      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

                      • stj
                        Great Sage 齊天大聖
                        • Dec 2009
                        • 30934
                        • Albion

                        #12
                        Re: General question about CCFL backlight

                        it sounds like he's using a lab supply

                        Comment

                        • rtstorm
                          Badcaps Veteran
                          • Feb 2012
                          • 971
                          • Croatia

                          #13
                          Re: General question about CCFL backlight

                          Yes i am using lab power supply
                          ...the quieter you become the more you are able to hear...

                          Comment

                          • stj
                            Great Sage 齊天大聖
                            • Dec 2009
                            • 30934
                            • Albion

                            #14
                            Re: General question about CCFL backlight

                            are you seeing the voltdrop on the psu terminals?

                            Comment

                            • rtstorm
                              Badcaps Veteran
                              • Feb 2012
                              • 971
                              • Croatia

                              #15
                              Re: General question about CCFL backlight

                              I will check but i think not.
                              ...the quieter you become the more you are able to hear...

                              Comment

                              • jiroy
                                Badcaps Legend
                                • Jun 2016
                                • 2416
                                • Lebanon

                                #16
                                Re: General question about CCFL backlight

                                If this small monitor is for desktops use only , you can always take 12 volts directly from the desktop PSU . Most of those PS provide 10 A at 12 volts .

                                Less headaches concerning monitors power supplies .

                                Comment

                                • rtstorm
                                  Badcaps Veteran
                                  • Feb 2012
                                  • 971
                                  • Croatia

                                  #17
                                  Re: General question about CCFL backlight

                                  Well i check there is no voltage drop on my lab power supply
                                  ...the quieter you become the more you are able to hear...

                                  Comment

                                  • rtstorm
                                    Badcaps Veteran
                                    • Feb 2012
                                    • 971
                                    • Croatia

                                    #18
                                    Re: General question about CCFL backlight

                                    Here is the picture of main board and inverter
                                    Attached Files
                                    Last edited by rtstorm; 06-27-2016, 04:24 PM.
                                    ...the quieter you become the more you are able to hear...

                                    Comment

                                    • budm
                                      Badcaps Legend
                                      • Feb 2010
                                      • 40746
                                      • USA

                                      #19
                                      Re: General question about CCFL backlight

                                      I think you lab power supply does not capability to handle the in inrush current otherwise you will not see the Voltage drops like that.
                                      Last edited by budm; 06-27-2016, 04:29 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

                                      • stj
                                        Great Sage 齊天大聖
                                        • Dec 2009
                                        • 30934
                                        • Albion

                                        #20
                                        Re: General question about CCFL backlight

                                        it's probably the wires, those croc clips and the wires they are clipped on are not suitable.

                                        Comment

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