BTW, one of the neat things about the BBC Micro is that they shipped with a complete circuit diagram for the main board in the back of the manual.
They provide a small but complete schematic of the C64 in the back of the thick ring-bound manual that came with that system, too.
For that matter, you could buy Technical Reference manuals for the IBM-PC product lines and many of us have them. It has schematics of the mainboard and all the IBM-brand expansion boards, along with commented source code listings for the BIOS and the BIOS extensions on expansion boards.
Providing lots of information about the hardware used to be a priority. Not just for repair, but so that programmers could get right down to the signal paths and I/O scheme.