I had a pretty bad spill on my mid-2012, 13" Macbook Pro about a week ago (just water, but it got on the keyboard and the system shut itself off). Fearing the worst, I did everything I felt I could, dried it out with the "fan trick", opened it up, etc. It eventually powered back up with the battery inside but attaching the MagSafe adapter did not change the status of the battery and indeed the LED indicator light did not turn on. I was initially scared that it would not draw power from the adapter at all, but upon disconnecting the battery the MacBook boots up when the MagSafe is plugged in.
So I do not know where to go from here. I tried some easy things, like resetting the SMC, I tried every possible direction I could find for that (they seem to vary slightly based on who you ask, I definitely tried Apple's official directions). The orange LED light came on the adapter for a few minutes after one such attempt, but as soon as I restarted the computer it returned to not charging. I can confirm that when the battery is plugged in and the MagSafe is plugged in, the MagSafe draws no power (confirmed with a power meter). I think the only confirmed cases I've seen like this on support forums that were solved involved having Apple replace the logic board, which is not really logical from a cost perspective at this point.
I'm wondering exactly which part is messed up. My fear is that it's the logic board, and I just don't really know how to confirm it, but I'd hate to give up just because I don't know a lot about how the circuitry works. My bottom line question is: which piece of hardware would cause this problem to occur (if any)? I've noticed there's a DC-in board separate from the logic board in my disassembly (and looking at the pictures from ifixit) and potentially the cable itself could be problematic somehow, but I'm not sure how to confirm what's wrong or how to test it. Any help is appreciated!
As a note, I'm not going to bother with having Apple fix this, because they will know it's water-damaged and will want to replace the whole logic board. Admittedly that may be the problem, but I'd rather just bite the bullet and get a brand new computer at that point. I'm looking for a smaller fix, if such a fix exists.
Best Answer
After borrowing several different power adapters, I determined there was something inconsistent. The mid-2012 MBPs come with the MagSafe 1 "L" connector power adapter, but the pin layout is the same as the "T" connector models. I tried two of each and the L hasn't been able to charge my battery and the T charges consistently. Each time I made sure to use the right wattage adapter, which is 60W for this model.
I can't explain this, but it's charging now. Leaving this in case anyone else manages to dump water on their Macbook or have it fail in a similar fashion. I'd love to know why it works with only T connector adapters, but I'm guessing this is such a niche question it has not been looked into. I have also determined that in the "Power" section of System Report, it gives full power adapter info (serial number, model, etc.) for the T connector adapters I have used but not for the L connector adapters, so it seems to be an issue with the charge control (middle) pin on the MagSafe.
Long story short, always try another adapter if you have any others available. Switching to a different connector type fixed my issue.