In 1983 my Commodore 64 stopped making sound. I looked at the schematic at the back of the big Commodore Reference and found an op-amp transistor that came out of the SID chip. I figured, hey, that’s a cheap part, might as well try that first. I went to Radio Shack and bought another transistor, and soldered it in.
This was the first motherboard of a computer I fixed.
I’ve been building things in and out of computers ever since.