Wondering if there is anyone with more iMac internal knowledge than I or an authorized repair shop. I have an iMac 12,2 that's been having issues. It suddenly began to randomly restart and I have no idea what the issue is. And I mean it's TOTALLY random. It can work for an hour or two and be fine, and other times it will be used for less than five minutes and restart, only to restart in five minutes or an hour later. When it restarts, there is no restart message and it goes straight to the login screen. It also does not make a report of the restart. I've tried clean installs, installing older OS's, booting from an external HDD, run the AHT, run memtest, removed all four 8GB RAM chips and tested each in each slot, installed the OS on separate internal drives (I had previously installed an SSD and a HDD at separate times years prior) and nothing seems to work. I took it to Apple and they said it was an issue with the drives. The the Apple tech merged the two drives into a fusion drive and said it was working fine now. I took it home and it restarted with ten minutes. I called the Apple tech and he basically said take it to an authorized repair shop, because it's too old for them to work on it at the Apple Store(?). Anyway, I took it to a local, well known, and well thought of (even by me) authorized repair shop. It passes every test. They retried many of the things I did above and after a few weeks came to the conclusion it was the logic board. They replaced it with a new one, and and that did not work because it still randomly restarted on them. Now they have no idea what it could be. As a last ditch effort they're going to test the graphics card and I suggested testing the power supply also, which they said they would. Anyway, anyone in MacRumors world have any ideas?