Hello! Long time speaker builder going amp technician!

Hello! I have been building speakers for a long time. I have some engineering education, have build electrostatic speakers, some simple circuits like that. However I want to learn how to fully repair amplifiers.

I will be starting with the following

Anthem PVA-7
sherwood receiver
some plate amps for subs
jolida fx=10
crown k2
blue circle bc-2

Hopefully you guys can point me at some good guides, and how to approach some of these that dont have schematics or service manuals.
Cheers!