There's a YouTube channel with excrutiatingly in-depth Amiga repairs: https://www.youtube.com/user/RetroGameModz/videos

He goes down to the circuit level, including within microchips, identifies problems with all kinds of tools including spectrum analysers, and shows off some (to me) amazing soldering skills.

Here's a four hour (I kid you not) video of the repair of an Amiga CD32: https://www.youtube.com/watch?v=lZK3Rmerg1I