I'm a casual mac user, not an expert. I call BS on replacing a chip. I believe the worst case is you have to completely wipe the machine and reinstall the OS, a bit time consuming because it's downloaded over the internet. There's not good progress feedback, and the machine appears to have crashed several times during the process. If you read the info linked in the previous posts, some sites give an undocumented way to get into a password reset tool, but since you're adopting the machine maybe you'd be better off erasing it anyway. Apple has an official procedure for doing this. I wonder if this tech knows what it would take to change a chip in the imac? The only way in is to remove the screen that's attached with adhesive. Not impossible, but nothing close to opening up the case on a PC. These things were meant to never be opened up.
