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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?

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I'm assuming that you have performed the SMC reset and PRAM reset. Have you tried replacing just the battery?

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Yes, I have tried replacing the battery. Interestingly after I swapped out the battery I pulled out the AC while it was running and it stayed on for a few seconds before losing power again, and now it is doing the same thing.

Interestingly system info shows the correct ratings on both batteries, the batteries both charged and showed correct percentages. It just won't run while it's on battery.

의 답변

Eee, dead logic board? That's an expensive repair.

Also, have you tried the DC-in board?

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Yep, that was part that was heavily damaged (someone ripped out part of it with a dremel or something) and was the first thing I replaced. See my post edit, I was able to get it to work by bypassing the SMC. It's been running on battery for a few minutes with no problems. Do you know if it's possible to force a reflash of the SMC?

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As far as I've heard, you can replace the SMC chip itself, but you can't reflash the SMC data. I'm not sure where you would get that chip (iFixit doesn't offer it) or where the instructions are to do such a repair, but if you're comfortable with soldering, I'm fairly sure there are instructions on the internet. Rock on.

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That's certainly a possibility but I wouldn't rule out a reflash since apple can push out SMC firmware updates in OS installers and app store packages. I'll have to look into it more. I imagine finding an SMC chip that is flashed with apple's firmware would be quite difficult, failing just buying another logic board and swapping the chips.

EDIT: Found this: https://discussions.apple.com/thread/485...

I will try and report back. Hopefully if I solve this what ever turns out to be the solution can help someone else if they have the same problem!

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1. Make sure that everything is plugged in. It's entirely possible that a cord could just slip out from the outlet while you're working. If power is present to the monitor and other peripherals, yet there is no power to your computer, there is likely something wrong with your power supply.

2. Hit the power button. The most obvious clue is that the system will do absolutely nothing when you hit the power button. If there is no sound and no monitor activity of any kind, the power supply has probably died. While this can also be caused by a faulty switch, it is usually the result of a burned-out power supply.

3. Look at when your computer boots up. Noticeable changes in how long it takes for your computer to boot up and shutdown, as well as spontaneous rebooting, could be a sign that something is wrong.

4. Check for beeps. If the system makes rapid, short beeps repeatedly and does not boot when you try to get it to, this could be linked to the power supply.

5. Observe any computer failures. If there are system startup failures or lockups, memory errors, HDD file system corruption or USB power issues, this is often directly related to your power supply.

6. Check the fan in your computer. If the fan in your computer is failing to spin, it could lead to overheating and smoke in the system, all of which can cause a failed power supply.

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