I have a Twentieth Anniversary Macintosh that needs the power supply replaced, but I can't figure out how to open the base unit, especially without damaging its case. There's no give at all between the shell and the unit inside. I acquired it this way, knowing the repair it needed, and the TAM is reportedly in working order other than the power supply, although idle for years. I'm just not sure how to get started. Any tips from someone with TAM experience?