Yes you can upgrade a weak old Core Duo iMac into a decent performing modern machine that will support the latest Mac OS and if your interested, allow you to program for the iPhone and iPad.
Note: this isn’t for the faint hearted and later when I have more time I will revise this posting with more detail and I will break out the images from the gallery or add captions to the gallery photos to give a better understanding of what is going on in each photo.
The first thing you need to do it open up the iMac, I really wish I would have read how to do this before attempting it on my own because there are two metal levers inside of the front bezel which you need to press to allow the bezel to release. I thought it was just being stubborn and since the metal is so thin I ended up bending it and eventually had to remove the metal framework to get the bezel to fit flush. This is the only thing that holds the top half of the bezel to the iMac so if you pull on the top near the webcam you will see it separate from the case.
After you remove the front bezel and place it to the side you will need to work on the LCD but first carefully remove the black heat-shield which is made up of a paper foil type of material. This stuff is very important and if it’s not replaced in the fashion it was removed you will likely damage one part or more from overheating. I have seen screens damaged and power supplies fail when this stuff isn’t replaced because not only does it block heat from reaching specific components but it also redirects the hot air up and out the back vents.
Once this is all done and you have removed the LCD and placed to the side safely you can work on getting the main board out, if your only upgrading your hard drive you can stop here and swap it out. The processor is on the back of the main board so you will need to completely remove it from the case but don’t worry the worst is behind you at this point and removing the main board is actually quite easy. When the heat-sink is removed you will see the main CPU and GPU on the back of the board, removing the CPU from the socket is no different from removing it from a common laptop socket. You can replace the CPU with any Core Duo or Core 2 Duo which runs on the same FSB (Front Side Bus) as the stock piece. Unfortunately even after replacing the CPU with a true 64bit Core 2 Duo the iMac will still run in 32 bit mode and there is no way to force it into 64 bit mode. This is a problem because it limits the memory so don’t bother buying 8GB of ram because the system wont even boot. In fact if memory serves me correctly the max was a measly 2GB. One thing that was really deceiving is when I installed a 2GB stick in the system it booted up just fine, normally this means that the system will take 4GB because the only time you will see a maximum memory limit that applies to either a single slot or dual slots is when it’s imposed in the BIOS or in this case the UEFI. I know this because the chipset used on the board does in fact support 4GB of memory and if one slot will boot with a 2GB stick than that means the max is the maximum of each slot combined unless there is a limit imposed somewhere else. Shame on Apple for never releasing an update to fix this, but one thing you can count on Apple for is figuring out a way to make the old products useless to force users into buying the new products. In all the big brands that I know of, Apple is the #1 offender of this practice.
OK so now that we have the CPU and hard drive upgraded the last thing is to put it all back together the way it came apart and install the memory, boot it up, cross fingers.