Not long after my CARDiac,, my dad brought home an Apple ][+, which came with a schematic that revealed the inner workings of the machine in ways that I found visually striking, if significantly less accessible than the CARDiac:
(For me, at least. For the legendary hardware hacker Andrew "bunnie" Huang, it was the start of a journey that turned him into one of the world's virtuoso reverse-engineers and science communicators):