In my flat a weeks ago, the neutral wire failed. Almost 380 V, went trought my electrical installation burning many things, one of them, damm! was the IMAC. Suddenly started to exit fume from inside the computer. I crossed my finger and I expected only the Power supply was damaged. I succeded.
As a read in your wonderful manual, step by step, took me two hours to finish it.
A magnetic screwdriver is mandatory to remove the screen holding screws ( 4 ).