John Morley

My 20" white Intel iMac has the same problem. It's definitely temperature related and it doesn't appear if I boot up in safe mode so I suspect it has something to do with the graphics acceleration, which is disabled in safe mode. So I'm in agreement with those who believe it's the GPU that's faulty. If Dylan can run Windows XP from Bootcamp without seeing the fault, maybe XP isn't using graphics acceleration. Is there a way of starting Mac OS X in normal mode but without the graphics acceleration? Suppose I temporarily (or permanently) moved the relevant .kext file?

The SODIMMs don't need to be low voltage DDR3L (i.e. 1.35 volt). In fact Apple recommends (https://support.apple.com/en-gb/HT202593) regular 1.5 volt DDR3 and most late 2012 Mac Minis were shipped with it. So is Crucial wrong? The truth is that either will work.

Answering my own question, the clips re-engage when the lower case is correctly positioned. You can help them by gently pressing the lower case with your thumbs midway along the two short sides. When everything is correctly aligned the eight screw holes line up.

Yes. You can replace it with another optical drive, replace it with an adapter containing a hard disk or leave the space empty if you wish. Obviously you would lose functionality but you would save a little weight.

Do the retaining clips have to be re-engaged when replacing the lower case?

Note that it has to be 1.5 volt DDR3 RAM, not 1.35 volt DDR3L.