Unfortunately as sleek as Mac's are. They have thier flaws and thats their rep on parts. Its meh at best. At least we have a great site like IFixIt that is there for the consumer. I couldnt imagine shelling out big bucks for this old of a mac.
Well taking apart the IMAC isnt too bad. It deffienetly took paitence and making a gameplan. I made a plastic card to bend to slide the two fingers in the back to free the casing. that was probably the hardest part. After that slowly lift from the bottom pulling towards you. This will allow you to access and remove the screen. Also want to remember that the IMAC has the mic and camera that needs disconnected before the front case comes off. Once thats done t8 and t5 bits and be careful uplggine the different plugins from the screen. Two to the left and one main one that needs the t5 bit tow screws hold in the plugin. Powersupply is on the top left. The hardest part was getting the main cord unpluuged. Once unplugged hold onto the female end. I made this misktake and it slid under the logic board. If this happens verry carefully use precison standard screwdrivers and slowly pinch it to the new power supply. Secure with the 4 t8 screws and reassemble. I didnt find the video for my exact mac. However its fairly similar.
Job was about 20 minutes total just. I really took my time.
Make sure you hold onto the female end of the power supply plugin. Its not fun digging it out it it slides under the logic board.