One stick good, two sticks bad
Q I have a problem on my 27-inch iMac that is driving me crazy. Three weeks ago I suddenly had a kernel panic and the iMac crashed. At first I thought it was a software problem, but after rebooting it continued to crash every few minutes regardless of what apps I had open at the time. I have reinstalled Yosemite, but that hasn’t made any difference. Then I remembered something you have said in these pages and tried taking out one of the RAM sticks. With just one installed the system runs fine (although slower, obviously). And it doesn’t matter which one I use – either one on its own is fine. Both together cause kernel panics inside of ten minutes from booting up. How is this possible? Mark Hardwick
A There are really only two possibilities: either there is some strange conflict that causes this particular combination of RAM modules to fail when both are installed, or there is a fault on the motherboard. The second option could be something as simple as a faulty contact on one of the RAM sockets. Turn your iMac off, remove the RAM and make sure there is no fluff caught in the sockets. Then check none of the little gold contacts are bent or out of line with the others. You can also try dipping a cotton bud in vodka or gin and using it to swab the connectors. If that doesn’t help, try replacing both RAM sticks with a known good pair. 8GB should cost under £50 from www.crucial.com.
Faulty RAM sockets could be a cause of random kernel panics, so check that they're clean and fluff-free.