How do I actually learn about PCB Repair and fault finding?

[RethaKoch]

I already run a small repair business fixing controllers and consoles however I dont really know any of the theory behind what I'm doing. All I really do is basic mods and port swaps.
I dont use anything like a multimeter or oscilloscope to do fault finding as I have no clue how but I have some specialized equipment like a hakko desoldering iron.
My business is already profitable doing basic repairs but I want to have a real fundamental understanding of what im doing so I can move on to more advanced pieces of tech.
Even a formal education wouldn't be out of the question but if I can't teach my self why pay for the education?
Any advice on where and how to get started in greatly appreciated.

[sitinsurgent]

I was in a similar spot a while back, doing small fixes without really knowing the deeper electronics side of things. What helped me was starting with the absolute basics, like learning what voltage, current, and resistance actually mean, and then slowly getting comfortable with a multimeter by just testing batteries or simple circuits. Once you get used to that, fault finding on boards feels less intimidating. Watching repair videos where people explain what they’re measuring also makes a big difference, because you see the theory applied in practice.