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820-2327 A1278 2008 no backlight and picture

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  • 820-2327 A1278 2008 no backlight and picture

    backlght chip area bit water damaged, no too bad, i replaced the chip, the lcd connector, fuse, the laptop works with ext monitor.

    The lcd is not recognised,

    Q9807 2. pin is high 3.3V which means that the backlight is not enabled by SMC, so the quiestion why it doesn recognise the LCD?

  • #2
    "no backlight and picture"
    Clarify that please; missing image too?
    If has image, then LCD is recognized and problem is only backlight related.
    If no image, then check voltage for J9000, pins 2/3, 4, 5, 6.
    Be sure all the traces of J9000 are OK.
    Also check solders and integrity of nearest components.


    • #3
      i got new cable and screen, replaced the lcd connector on the board, there is picture but no backlight

      replaced the backlight chip too

      i think the issue could be the SMC

      Q9807 pin 2 is 3.3V pin 5 is 0V
      Q9806 pin 3 is 12V which i think should be less than 12V to open, its a PNP transistor

      so Q9806 pin 1-2-5-6 is zero, the whole backlight circuit is not powered


      • #4
        Q9807 needs 3V at pin 5 too.
        Only then Q9806 can drive voltage to L9701, through R9730.
        LVDS_IG_BKL_ON comes from MCP79, not from SMC.
        Tied pin 3/Q9807 to ground and check for backlight...


        • #5
          i soldered a cable between 1 and 3 pin of Q9807, now the reading for U 9701:
          1 0
          2 0
          3 12
          4 5
          5 4.3
          6 0
          7 0
          8 4
          9 0
          10 0.18
          11 0.25
          12 0.22
          13 0
          14 0
          15 0
          16 0.31
          17 0
          18 0
          19 0
          20 3.7


          • #6


            • #7
              are awas water damaaged, had to run cable between R9723 and chip,


              • #8
                Check if all traces are OK; especially passing holes to other side.
                Also check all resistors arount U9701.
                Did you try known good LCD assembly?


                • #9
                  yes, before there was no picture and no backlight, now there is picture and no backlight, the original lcd cable had corrosion or burn on the 2 pins where the lcd main power goes in, i think the original screen backlight is shorted also

                  i dunno, do u see something on the picture i uploaded?

                  i will try another backlight chip maybe, it gets the power but wont boost the 12V to higher voltage (it supposed to be 35V??)


                  • #10
                    R9724 doesn't look too good; seems to have damaged terminal.
                    Nothing was connected to pin 9/U9701?
                    Last edited by 2informaticos; 02-12-2019, 06:34 AM.


                    • #11
                      R9723 1.2M ohm resistor was corroded, the voltage divider did not work, i dont have the same donor board, so i found a 1M resistor, not 1.2M, now there is backlight and picture, but i think only every second LED is on in the backlight so the bottom of the screen has those patches of dark , tried other screen same issue, but it is usable now.

                      Is the board controlling the LED `s oin the screen? the lcd voltage is 26V now


                      • #12
                        Backlight voltage is correct now; aprox 25V for all A1278.
                        Check if all LED return resistors are good.


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