The larger of Apple's MacBook Air laptops featuring dual microphones and 802.11ac Wi-Fi connectivity.

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SMC issue or I/O Board?

I'm working on a water damaged macbook air. It had some artificially sweetened sweet tea spilled on the table around it and it found its way in.

I've thoroughly cleaned the main board, and I have it to where I can boot and use all functionality of the computer with just one catch:

If I connect the flat ribbon connector that goes from the I/O board to the logic board, the computer boots without the LCD backlight and shuts itself off before it gets to the login screen. The charge light never comes on, and the battery won't charge.

If I disconnect that ribbon connector, I can boot the machine all the way to the login screen and log into the computer. The computer has full functionality with the exception of the cooling fan running full tilt, and obviously the audio and other things that rely on that connection don't work. The battery still won't charge.

It seems like an SMC issue, but when the ribbon is not connected the backlight and kb light and all of those features work fine, even the ambient light sensor.

I'm thinking I should try replacing the IO board, but the absolute cheapest I can find it is $30, and if that's not the fix I'd rather save that cash to spend on sending the mobo out to have the SMC repaired.


Upon closer examination I found that one of the pins of the IO board connector was burned off on the IO board side. It just happened to be the 1-Wire pin for the charger control.

My "new" IO board came in today and the computer seems perfect.

Total investment under $200 including the original purchase of the broken computer.

THANK YOU to those who took the time to reply.

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Sounds like you have something damaged here. Hopefully its the I/O board.

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Hey, just another update:

The computer still isn't charging, but with an external display connected and the battery disconnected, i can use it with the io board connected and the fan and processor seems normal. I'm really confused by this set of symptoms. The display backlight and kb backlight are still out as long as the io board is fully connected.

Another issue that may be complicating matters is that the battery is stone dead and may not want to charge even if there wasn't other issues. Unfortunately it sat for a full month between the spill and mt getting to work on it, and that did it no favors.

Im still amazed it works as well as it does.


agree with Dan. sounds like a bad I/O board


I went ahead and ordered a used one. Fingers crossed.

I'm thinking the black screen may be due to a bad hall effect/lid sensor. The fact that it worked almost normally with an external display connected is consistent with the lid sensor shorted in a "closed" state.

I think the battery charging issue may be related, but also complicated by the low charge state of the battery.


Happy to hear you got it working! If this answer answered your question please remember to rate (score) and mark it accepted.


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James will be eternally grateful.
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