Power Supply replacement iMac 27" Mid 2010
There was a horrible electrical arcing/buzzing sound emanating from inside the top left corner area. It varied in intensity with screen brightness and optical drive activity, leading me to believe it was the power supply at fault. My new power supply arrived quickly and was well packaged.
My first attempt to simultaneously lift the lcd and remove connecters proved to be too difficult. I enlisted a helper to hold up the lcd which made it quite a lot easier. The display data connector has some very fragile plastic parts on either side of it. I managed to break one of these off with no effort. Luckily the connector seated just fine without it. Everything went back together very quickly and now is back to being completely silent. The iFixit guides were very detailed and completely invaluable.
I suppose one could fashion a couple dowels of the proper lengths to be used to prop up the lcd while removing and attaching connectors, but another person is a great help. Also, one must exercise great care when squeezing the arms of the display data connector- the plastic parts are super fragile. Lastly, the power supply from iFixit looked quite different from the one pulled from my iMac. It shared the same power output ratings printed on the circuit board, was the same shape and had the same connectors. It was from a different manufacturer than the original and all of its discreet parts were in an entirely different configuration. This caused me some initial concern, but it functions just fine.