NEWS FLASH for MacBook Air users with 3 Beeps at startup!!!
On a hunch, as I have noticed my MacBook Air has overheated in the past, I opened mine up to check the THERMAL PASTE. Made no sense that DRAM of any sort would fail after 15 months. When I got down to the logic board, I inspected the 8 visible 1 gigabit chips visible. The solder joints appeared pristine. Nothing else appeared burned, fractured, loose or disconnected. I then removed the heatsink I found the thermal paste dried and hardened! I carefully removed all of the old paste and then applied new high quality thermal paste. I then reassembled the machine. Rebooted and NO 3 beeps! Once again, my MacBook Air appears to be working perfectly.
Therefore, if you have recently had a MacBook Air exhibit the 3 beep boot failure, strongly consider checking your thermal paste. WARNING: You should do this ONLY you are an experienced repair person, and only if your computer is already out of warranty.
FYI: I've been building, repairing and modding computers since 1987.
Hope this helps some people,
John
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=== Update (11/28/2010) ===
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UPDATE: THERMAL PASTE
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Having now had to do this repair twice, I am beginning to suspect that environmental conditions (temperature, ambient humidity) are directly affecting thermal paste on the Macbook Air (as least the Rev C).
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Please let me explain, as I do not think there is anything inherently wrong with this model. Each time I have run into the 3 beep scenario, it has occurred after the MacBook Air has been exposed to extremes in temperature. Specifically, it has been left out in the center console of my 2007 Tundra when it has been very cold (10º F to 20º F). Although this area of the pickup truck should be insulated (you would think, as this console is specifically marketed pitching it as a place to store your notebook computer), it seems to not be so. That and the fact that the MacBook Air is so thin, and there is no real thermal insulator between the case and the logic board. My thinking is that the paste contracts and/or dries out when exposed to extremely cold temperature. If the former is true, then when it warms up it could potentially fail by cracking, or even pulling away from the surface it is adhered to. Likewise this could occur as it contracts, or if it gets dried out. Anyone out there with material science engineering experience with thermal paste, input would be greatly appreciated.
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Bottomline is that each time I've had the 3 beep scenario, twice now and after machine being on (sleeping, cover closed), being exposed to a significant temperature drop, when I open it up and replace the paste, it works again. CAUTION: the paste itself is not at all easy to work with, and can make a real mess. It especially loves hydrophillic substances like your fingers. And MORE IMPORTANTLY, if you fail to put the thermal paste on properly, you are in for a potential disaster. Although I think Apple has engineered a fail safe for this by preventing the boot sequence, resulting in the 3 beeps (misleadingly indicating RAM failure), I wouldn't want to be the one finding a fire igniting my Air! Just to respond to the memory seating issue, there is none. As others have pointed out, it is soldered (using SMD -tiny 'surface mount' - chips) to the logic board).
NEWS FLASH for MacBook Air users with 3 Beeps at startup!!!
On a hunch, as I have noticed my MacBook Air has overheated in the past, I opened mine up to check the THERMAL PASTE. Made no sense that DRAM of any sort would fail after 15 months. When I got down to the logic board, I inspected the 8 visible 1 gigabit chips visible. The solder joints appeared pristine. Nothing else appeared burned, fractured, loose or disconnected. I then removed the heatsink I found the thermal paste dried and hardened! I carefully removed all of the old paste and then applied new high quality thermal paste. I then reassembled the machine. Rebooted and NO 3 beeps! Once again, my MacBook Air appears to be working perfectly.
Therefore, if you have recently had a MacBook Air exhibit the 3 beep boot failure, strongly consider checking your thermal paste. WARNING: You should do this ONLY you are an experienced repair person, and only if your computer is already out of warranty.
FYI: I've been building, repairing and modding computers since 1987.
Hope this helps some people,
John