Chosen Solution
Hi everyone. I have a water damaged (tea) MacBook Air that was dead as a doorknob. No light on the MagSafe, no fan or anything. A visual inspection of the logic board (820-3437-B) showed no classical water damage (corrosion) but the backlight diode (D7701) was literally blown off the board (replaced). The LVDS connector however is in excellent condition. I also found a burnt pin on the I/O Flex (821-1722-A), which I repaired. So after all of this, the Green MagSafe light comes on and then turns orange to show that the battery is charging. Voltage Rails: PP3V3_G3H measures 3.4V PPBUS_G3H measures 8.6V The SO, S3 & S5 rails are present. Despite all of this, the computer will not power on so I’m starting to think it is a keyboard issue but I’m reluctant to order an expensive replacement upper case just to test. Is there any way to test (or circumvent) this keyboard? Do you have any other troubleshooting ideas? @mayer @oldturkey03 @danj @reecee @rany EDIT 2017-05-30 Thanks everyone for the help. I goit the MBA fully booted and started configuring it. @reecee nailed it with having me probe ALL_SYS_PWRGD and I found a U1950 Dual AND Gate IC that had a cold (or corroded) solder joint. I replaced it and the MBA booted!
The last issue is getting it to switch from AC to battery without shutting down. I have created a new question (Shuts down when disconnected from AC)
This model will boot when the charger is plugged in, if you are getting no fan spin but the S0 rails are present, check ALL_SYS_PWRGD to see if this is present (and the signals U1950 produces for the PCH). Plug the charger in with literally nothing except the I/O board plugged in. If the CPU is not getting hot, it is likely this signal or another signal for the CPU is missing, check out U7200 too. Likely has been messed with before, so check for any clues on the board indicating past water damage (brown probe points, flux residue, etc). I won’t repeat everything mentioned in the other answers, pretty much covers it and you have got the basics down from doing iPhone board repair. Good luck :)
First clean the board, even if you cont “see” anything doesn’t meanie’s not there. How to Correctly clean corrosion from a MacBook Pro logic board. I aslo have a question, what end of the flex cable was damaged? Logicboard end or I/O end? There is no reason to buy an entire uppercase, we always opt for keyboard only replacements, they are a much better value and are easy to install. https://www.ebay.com/p/?iid=301134821626…
I would disconnect everything, plug in fan, MagSafe DC in, genuine 60W adapter, and see if fan spins. Then start adding elements until something comes up. Also G3H 8.6V tested present on both sides of the fuse? Also, the blown diode, did you test both pads for resistance to ground? And for continuity to the next component in line?
Try for a spontaneous boot. Dis connect the battery and magsafe, Then hook the battery back up to the logic board. As soon as you connect the mag-Safe, you should get a boot.
Those are where the power on pads are.
