Are You Familiar With This Bridge Circuit?
I believe you have come across such circuit (bridge rectifier circuit and how it works) especially when you study any basic electronic course or reading any theory books on electronics. It is good to understand the circuit/diagram but in the actual repair one have to know about how to accurately test the circuit or component be it off board or on board. A guy who is good in electronic theory could reason with you about how all the current flows in the circuit and etc but when comes to testing the bridge rectifier they are stuck.
So if you really wants to be good in electronic repair make yourself good in testing electronic components and of course understanding how the circuit works would be an added advantage for you.