ISO belles 350A reference schematic

Looking for schematics for my Belles 350A Reference.

Has a hum thru the speakers and loud popping sound when powering off.

David Belles will not give up the schematics nor offer any tips on the cause. Just wants to sell me a new amp or send mine in.

I have several friends who do repairs and have a good idea, however, need the schematics.

I would appreciate any help.