Hello all, a few months back my iMac "shut down" by itself (as if there was a power shortage) and it would not power up again. I brought the iMac to a local authorized dealer (not an Apple Store) and after a costly diagnosis, I was told the it was a motherboard failure and that it needed to be replaced (costing around 800$). I had no intention of paying that much for repairs on an iMac so a friend of mine simply changed the "power supply" and now it works good as new. Is it possible I was almost subject to fraud? Can an iMac run with a defective motherboard? Can a store even run tests on a motherboard with a defective power supply? I'm not familiar with the technical aspects of it all but my friend said the motherboard looked intact and that the iMac "seemed" as though it had never been opened since its production. Is that possible? Any opinion is welcome, thank you!