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Keyboard or Logic Board or Something Else?

My son's MacBook Air started acting funny and then died completely. Apple store verified that the liquid sensors were activated, even though my son swears he did not spill anything into the MBA. I removed the bottom plate, and there does not seem to be any visible spill residue. I have not done a complete teardown.

Symptoms:

  • pressing power button does nothing
  • when connecting magsafe - led on magsafe connector starts green, then after a few seconds goes amber. If I leave it connected for a few days, it DOES NOT go green again
  • reset of smc toggles magsafe led to green - then it reverts to amber
  • system can boot if I bypass the SMC as follows:
    • disconnect battery connector
    • hold down power button
    • connect magsafe
    • release power button

When I boot by bypassing the SMC, the keyboard and trackpad do not work, but a USB keyboard and mouse do work. The system boots to OSX, display looks normal, and i can access the network - everything works. If I select "restart", system will reboot as expected.

What should I check next or replace? If the SMC reset using keys on the keyboard does toggle the magsafe led, then some of the keys must be working - so the keyboard must not be completely dead. Is there any way to debug further?

Thanks for any insight.

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Find out which sensors were activated to see if just the upper case has been shorted out or if the ones on the logic board were also activated.

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There is a red dot (activated sensor) on the main logic board right below the wireless card. Is there a diagram (and identifying list) of these sensors that I could refer to? Even if ALL the sensors were activated, does that necessarily mean that the component doesn't work?

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Replaced the logic board... but there is NO DIFFERENCE in the behavior. The macbook behaves in EXACTLY the way as before with the new logic board: smc reset toggles the light on the magsafe... bypassing the magsafe boots - keyboard and trackpad dont respomd. The sensors on the battery were fine. What next?

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More debug: if i disconnect the trackpad cable from the logic board, the system boots... and when it comes up, keypad and trackpad (obviously) do not work. Sensor dot on IC on trackpad IS red.

Did i waste my time (and money) replacing the logic board?

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And a final update: I removed and re-attached the trackpad and keyboard ribbon cables from the trackpad logic board. Now everything works - system boots, keyboard and trackpad work, battery charges. So i'm not sure i could have diagnosed this down to a "re-seat the keyboard ribbon cable" from the onset, but at least the macbook is functioning now.

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It's the logic board.

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Please back up this diagnosis with logic.

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bcarb será eternamente grato(a).
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