Or if you want to be REALLY C&C, learn too love mono!

My 314 had one channel that was very occasionally out - part of the reason it was $35. After a bit of warm up and a few firm pats it would come back on line. After that would just leave it on as long as practical.
Unless your technically inclined and enjoy tinkering, sometimes its best to either cope or move on. It's a bargain basement NAD after all, not some trophy Macintosh. This is about cheap and cheerful, not cheap and tearful.
Let your daughter pick up the tab on the next one. That should be a cheap and cheerful life lesson. You break dad's things, you pay for it.