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How to identify why my MacBook Air won't turn on

Hey guys,

After having completely removed the logic board from my MacBook Air (13', mid 2012), washed it and re-assembled the components (following a water damage), I managed to turn it on, and it worked normally.

However, since I switched it off, it is impossible to turn it on again. The battery is fully charged, the Magsafe led is green, but I don't hear any noise from the inside, so the ventilators don't seem to work. I also reset the SMC, but it didn't change anything.

So, before I throw it to the trash, I would like to try to identify the problem, i.e. the component which is working bad or not working, and possibly replace it.

To sum up, I'm looking for a complete procedure which is able to determine if each component get power, and if this component "seems to be able to work", by using basic electronics tools (as multimeter).

Thanks a lot !

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I'm afraid there's not such a unique step by step procedure for everyone. You need to use your brain, schematics, board view and at least a multimeter to go through all Macbook's power lines and identify where the problem might be.

In case the board doesn't work inside the macbook, first thing try if it does when outside the mac, in order to rule out possible shorts present in other machine components.

If it doesn't and you have a green light from the charger you can avoid checking the onewire circuit and jump straight to PPBUS. From there, you have to check all power lines, voltage and current sensing until you find some hint.

Since yours was a liquid spill on the board look for burnt components or the likes with a good light source and some magnification, you'll probably find some visible hints to start with.

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12 Comments:

Thanks for your reply. However, I'm a beginner in electronics, and so I struggle to understand all what you explained me. Can you please reply to these basic questions:

- What do you mean by 'when outside the mac'?

- What does PPBUS mean?

- How can I visualize the board schematics? I found a .pdf file concerning the correct version of my macbook, but doesn't it exist .sch and .brd files ? Wouldn't it be easier to work with such files? Where can I find these files and which software can I use to read them?

Thank you !

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- Outside the Mac means just that, removing the logic board from the machine or isolate it by disconnecting every possible connector from the board except the power board which is necessary. If it starts this way reattach the various parts one by one until you spot what could be faulty and replace accordingly.

- PPBUS is one of the main power lines in a Mac, you can see that in the schematic you found.

- .brd files are not made readily available by Apple. You'll have to explore the net with patience to find the one relevant to your machine. Together with the board view you will find a viewer enclosed or you can download Openboardview, a beautiful piece of multiplatform software for the purpose.

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Thanks for these infos. I removed the logic board and the power board, connected them together and plugged the magsafe. But how can I make the macbook start and check if it actually starts ?

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You'll find on the board its code, something like 820-xxxx. With that you can google for power pads, two solder pads to be shorted and simulate power button pressing

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Ok, I found the power pads. But how do I know whether it starts?

One more thing: once the logic and the power boards are outside of the mac and isolated from the other components, the magsafe led stays faded when I connect the magsafe, while it was green when I connected it to the complete system. Is it normal?

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This might sound kind of weird but see if it will boot without the track pad connected. It can control the SMC so if it is damaged it can be constantly sending the reset SMC command therefor preventing the system from booting.

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Thanks for your reply. I tried by only connecting the power + logic boards, the magsafe and a fan (to check if it actually starts) and I started it by using the power pads, but it seems that it doesn't start, since the fan doesn't turn on.

Is there more reliable way to check if the macbook really starts?

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Not that I know of.

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Sylvain will be eternally grateful.
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