In the software world, I find the best way to learn how a piece of software works is to download and read the source code. Does this translate well to the hardware world (i.e. repairing a broken piece of hardware)
The equivalent, in my opinion, is taking a working peace of hardware and have somebody (or a detailed manual) explaining to you how it works. The software-equivalent of "repairing a broken peace of hardware" would be chasing a bug in a program from poorly documented source code someone else wrote. Poorly documented, because most commercial hardware is lacking vital information in its documentation, if there is any publicly available. I thing I learned most from reading design-logs, watching teardowns all supplemented by courses and lots of practical tinkering.
I'd say a good beginners project for you is not repairing things, but augmenting household items:
- Fixing your toilet light with a motion detector
- Adding a morse-code door buzzer/opener to the intercom of your apartment
- Adding temperature control to your water heater so you can have perfect 80°C water for black tea
- Building PC-controlled led-lighting for your work area
- Switching power for your printer, scanner, external hardrive and sound system via USB on you computer
- 4 button keyboard as foot mat with capacitive touch sensors to control your pc's audio player
You get the gist...