If you find a piece of vintage gear from the 90s, Elektor often published "service-level" deep dives or similar circuit designs that help in troubleshooting.
Relive a Golden Era of Electronics: The Elektor Magazine 1990–1999 DVD ISO elektor magazine dvd 19901999 iso
The DVD ISO (a digital image of the original archive disc) typically contains a decade’s worth of magazines in a searchable PDF format. Key features often include: If you find a piece of vintage gear
If you manage to get your hands on this archive, keep an eye out for these "hall of fame" projects: A staple of high-end DIY audio. elektor magazine dvd 19901999 iso