If you're going to repair electronics, it would be helpful to understand theory as well; it's not just a matter of using tools, but knowing what's going on, too. The Art of Electronics by Paul Horowitz is a book many recommend.
For troubleshooting power audio electronics Rod Elliott (sound-au.com) has a large number of useful articles both on simple theory (no poles and zeros) and on practical matters. Bob Cordell's and/or Doug Self's books on designing power amplifiers are good for a bit more "practical theory" (how the blocks are arranged, what goes wrong with poor design and/or a too-small budget for protection).
I don't have recommendations for radio frequency because I've not spent time with it. The ARRL (Amateur Radio Relay League) has several books that are well regarded, I believe.
Which may be only one factor, or maybe somebody just placed a diode backwards :\
So there can really be some unsung variables that make you think.
Until your hair falls out . . .