Most electrical/electronic items (radios, TVs, washing machines, ...) used to come with a schematic, or at least a block diagram, inside the device. Similarly, published integrated circuit data sheets contained enough information to understand how the chip worked to a low-level. This changed around the 80s from memory? There wasn't a word for "open source" in electronics, as it was just the unnamed default. It was all paper based, as it predated wide-spread online distribution.

My parents bought a relatively inexpensive television in 1987 and it came with complete schematics, printed out as an addendum to the user manual. I was more excited about those than the TV itself because I had just learned to read schematics from one of the Forrest Mims books at Radio Shack a few months earlier. This was in the US and I am pretty sure it was made by Emerson.

A dumb brand name dryer we got from Home Depot a few years back still has one of these. It was a breath of fresh air to unfold it and pretty quickly determine what part was bad with a multimeter and some high school electronics education.

Some test instruments still come with "theory of operation" documentation. Those are tons of fun to read.