Laptop backlight issue

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  • stevo1210
    Badcaps Legend
    • Oct 2006
    • 4156
    • Australia
    #1

    Laptop backlight issue

    I've been having this problem with my Toshiba P25 laptop recently. The screen backlight won't come on at times. There's a standby switch around the left corner of the palmrest towards the screen. Basically it is a switch that once pressed the backlight turns off and when released the backlight turns on If the backjlight doesn't come on and I jam that up and down a few times the backlight comes on and works.... I have a feeling this may be a dirty switch? Am I correct in saying this?

    Thanks.
    Don't find love, let love find you. That's why its called falling in love, because you don't force yourself to fall, you just fall. - Anonymous
    Tags: None
    • NxB
      Badcaps Legend
      • Feb 2009
      • 1595
      #2
      Re: Laptop backlight issue

      Could be. Or the little switch that turns off your screen when you close it. Some microswitches you have to actually replace. Once you take them apart its harder to get them back together than just soldering on a new one.

        Comment

        • stevo1210
          Badcaps Legend
          • Oct 2006
          • 4156
          • Australia
          #3
          Re: Laptop backlight issue

          I'm wondering if the screen cable is busted or not? cause in addition to the backlight issue, the screen sometimes goes fuzzy and it goes back to normal once you tap the area where the cable connector is located. Re-plugging that screen cable solves the issues for maybe a few days and then it does it again...
          Don't find love, let love find you. That's why its called falling in love, because you don't force yourself to fall, you just fall. - Anonymous

            Comment

            • ratdude747
              Black Sheep
              • Nov 2008
              • 17136
              • USA
              #4
              Re: Laptop backlight issue

              since the backlight control signal is likely on the video cord, that might be it.
              sigpic

              (Insert witty quote here)

                Comment

                • pentium
                  Badcaps Legend
                  • Mar 2006
                  • 2778
                  • Canada
                  #5
                  Re: Laptop backlight issue

                  Try replacing the switch.
                  If that fails, try replacing the inverter.
                  Find Nedry!


                  Check the Vending machines!!

                  <----Computer says I need more beer.

                    Comment

                    • stevo1210
                      Badcaps Legend
                      • Oct 2006
                      • 4156
                      • Australia
                      #6
                      Re: Laptop backlight issue

                      Originally posted by ratdude747
                      since the backlight control signal is likely on the video cord, that might be it.
                      i have a gut feeling that might be the case.
                      Don't find love, let love find you. That's why its called falling in love, because you don't force yourself to fall, you just fall. - Anonymous

                        Comment

                        • PCBONEZ
                          Grumpy Old Fart
                          • Aug 2005
                          • 10661
                          • USA
                          #7
                          Re: Laptop backlight issue

                          Do you have a single cable to the screen from the chassis or two+?
                          Mann-Made Global Warming.
                          - We should be more concerned about the Intellectual Climate.
                          -
                          Be who you are and say what you feel, because those who mind don't matter and those who matter don't mind.
                          - Dr Seuss
                          -
                          You can teach a man to fish and feed him for life, but if he can't handle sushi you must also teach him to cook.
                          -

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                            • Krankshaft
                              Badcaps Legend
                              • Jan 2007
                              • 2328
                              • USA
                              #8
                              Re: Laptop backlight issue

                              Yank the battery and check the switch with a continuity tester for intermittent operation.

                              The backlight and video signal harness are usually kept separate to prevent interference.

                              To turn the backlight on there is usually a separate BL ON input to the inverter that voltage is applied over.

                              The backlight VCC and GND are always connected when 5 volts for example or possibly VCC switched by a transistor (voltage varies by inverter) is applied to BL ON the inverter starts.

                              Backlight brightness is controlled with another separate inverter input a variable voltage from 0-5 volts for example controls the brightness no input 0V allows full brightness.

                              I'm making a few generalizations but laptop inverters are surprisingly similar to each other only varying a bit in circuit design and in size due to the size bulbs they drive.
                              Last edited by Krankshaft; 12-02-2010, 01:36 PM.
                              Elements of the past and the future combining to make something not quite as good as either.

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