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820-2879 - no backlight after i restart the computer.

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  • 820-2879 - no backlight after i restart the computer.

    board was liquid damaged. L9008 was burnt, R9731's pin1 was burnt too, few led returns resistors.
    after repeal and replace, the backlight has come back on with image. but every time i restart the computer, the backlight goes out.

    D9701 pin 1 has 12.46v , pin 2 has 27.54v when backlight is working.
    D9701 pin 1 has 12.52v , pin 2 has 12.5v when backlight stop working.

    PRAM reset. same problem.

    ive replaced led driver twice. i also replaced, lvds connector even tho is good.
    i've tried few lcd panels and new cable already.

    bad boost circuit?

    Sync problem?

    bad smc or mcp?

    reflash the bios didn't solve the problem


    if i wake from sleep, the backlight will turn back on.
    Last edited by Alan.L; 05-16-2017, 01:49 PM.

  • #2
    SMC_LID solid at 3.4V? Voltage on BKL_EN?

    Comment


    • #3
      SMC_LID
      -------------
      3.395v with backlight
      3.395v without backlight


      BKL_EN
      ------------
      3.105v with backlight
      3.110v without backlight


      BKL_PWM
      --------------
      2.952v with backlight
      2.935v without backlight
      Last edited by Alan.L; 05-16-2017, 02:55 PM.

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      • #4
        Seems ok. R0910 is infamous for dying and still sort of working.

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        • #5
          i need to change R0910? im pretty sure i've changed this. ok i'll change it.

          could be the L9701 coil has gone bad?

          reason because i just fixed a macbook air 11" 2011. with no liquid corrosion on the lcd area. it had a similar symptom where sometime backlight doesn't work.
          the measurement on the coil sometime isnt correct and sometime correct. so i changed this coil then backlight now always work,
          Last edited by Alan.L; 05-17-2017, 09:01 AM.

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          • #6
            :/ replacing R0910 and L9701, still no dice. no hope for this board?

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            • #7
              I really have no other solution then to just replace all parts in the BKL circuit. Checking traces too while you have resistors/caps off the board.

              Comment


              • #8
                duke, do you think it has SMC issue. when i have backlight then i press restart then i quickly put a magnet over the sleep sensor, it rebooted and backlight appear

                Comment


                • #9
                  It is possible, but finding a good SMC for this dinosaur will be a nightmare.

                  Comment


                  • #10
                    As long as enable and pwm are present there should be backlight. So i suspect something in the backlight circuit

                    Comment


                    • #11
                      i'll already checked every resistors and traces and even replaced some components that looked good. i dont have smc for this board. i give up and move on to something else.

                      Comment


                      • #12
                        Why would this be an SMC issue? Enable and PWM is present so there should be backlight.

                        Comment


                        • #13
                          because backlight still work if i put a magnet over the sensor and restart

                          Comment


                          • #14
                            So? It just cycles the enable and would clear any fault conditions the backlight IC may have encountered.

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                            • #15
                              its ok duke. i no longer have this laptop. i dont want to spend any more time on it.

                              Comment

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