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820-3437 powers on, no backlight and no green light

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  • 820-3437 powers on, no backlight and no green light

    I have a water damaged 820-3437 that powers on, there is backlight for a sec then it turns off and also there is no green light. I have replaced LP8550 already and also ran a trace from ball 5 on LP7701 to pin 1 of C7796 because I thought I had a bad feedback trace. (Any suggestions on an easier way to measure for a bad trace besides continunity mode from eah side of the board would be great). After that I still have backlight for only a sec and I am still getting 8.5V on backlight circuit. Please help!!
    Last edited by Puevig reven; 07-09-2016, 12:16 AM.

  • #2
    If you have backlight for a second it could be because of the SMC_LID signal is pulled down.

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    • Puevig reven
      Puevig reven commented
      Editing a comment
      How does SMC_LID get pulled down?? OR how do I fix this??

  • #3
    Flatcable, IO board or connectors in that order.

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    • Puevig reven
      Puevig reven commented
      Editing a comment
      I have tried these already

  • #4
    It normally gets pulled down when you close the lid. The sensor is in the lio board thats why duke says you should try with another one. But if thats not the case then in more rare situations it could also be the trackpad (or ipd connector/cable) or SMC or C4835.

    But start by measuring SMC_LID to check if its high or low to see if it is because of this or not.
    Last edited by Sykulski; 07-09-2016, 06:56 PM.

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    • #5
      Could be crap in the touchpad connector also or crap in the IO board connector. I bet SMC_LID is pulled low and that is the only place that goes.

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      • #6
        Last time I had this issue, backlight for a split second, SMC_lid was between the high and low levels (2.1v), SMC itself was shorting the signal. (Yes the worse case)
        My trackpad and keyboard were not properly working, except with external monitor plugged in.
        SMC replacement solved the issue.

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