iMac turns itself off

Yes, that is so.

I purchased my iMac online in August with 8GB of memory installed. I started having the shutdowns in September, and finally sent it in for repair at an Apple Authorized Service Provider in November (my iMac has one year warranty). They spent three weeks checking my computer, couldn’t find anything wrong, but replaced the power supply unit. When it came home, it shut down after 15 minutes of starting it up. So, I sent it back to the repair in December, and I mentioned the “RAM problem discussed on the net” to the repair technician, but they replaced the power supply unit again. I got it back, and this time it shut down after 24 hours. At that point, I got “suspicious” of how Apple was handling this problem. So, I took the advice of the collective wisdom on the Internet and switched the factory-installed RAMs (mine were Micron) to Samsung RAMs, and lo and behold, my iMac is running like a wonder-machine as it should be.

On a different forum, it has been speculated that the problem is the failure of the RAM companies to comply with the Apple specifications based on Samsung, and therefore, Apple is unwilling to admit that there is any problem (I don’t blame them for taking that stance). But I don’t know why they are still (as of January 2011) telling people that the shutdowns are caused by faulty power supply unit or logic board, and keep on replacing the innards of the machine with no effect, while it is so easy to tell people to switch out the RAMs. I think there may be some legal or corporate concerns rather than technological one, but this is getting into the realm of pure conjecture which is perhaps not appropriate here.

Meantime, my gut-level advice is, do the RAM switch, and call Apple only after if that doesn’t work. The normal practice is to call Apple, have them take a look and do the repair, and do the RAM switch if Apple cannot fix it.