Fixing a power issue
So I bought a broken (turned out to be water damaged) Macbook air 13" late 2010 off ebay with the goal of fixing it up and either keeping it or reselling it. I get a lot of enjoyment out of projects like this so I'll do that every so often.
After thoroughly cleaning the logic board with IPA I am able to get the thing to boot consistently. However, it will only work off of the power adapter and not the battery. The magsafe light is working properly, I've cleared the SMC and PRAM multiple times and the battery charges.
When I try to power on with the battery the fan will spin up, start to slow down, then the machine will shut off. It will then turn back on after about a second and do the same thing until I finally plug the AC power in, then the screen turns on and it will boot. If the machine is running and I unplug the AC, the screen will shut off, the fan will speed up to max and then it will just sit there until I hold down the power button to make it turn off again. Every so often it will do this even with the AC still plugged in.
I'm fairly competent with electronics and reflow soldering, so is there any specific component(s) that I could look at, test, or replace on the logic board that might be causing this problem? Or is it pretty much unsolvable and requires me to replace the entire logic board? Thanks in advance!
EDIT: It appears that unplugging the battery, bypassing the SMC and booting on AC power, plugging in the battery and then unplugging the AC, it will run. So it looks like an SMC problem. So let me ask this: is it possible to force a reflash of the SMC?
EDIT 2: Flashed SMC, problem is still present. Downgraded SMC firmware, same problem. Any other ideas?
Testing across 2 diodes near the battery connector, the voltage across them is ~16V with AC power and only ~8V when it's trying to start on battery. Maybe there's a boost converter in there that's blown?