Bad RF or bad CPU?

[landmasta]

Hey everyone, broke out the old famicom for the first time in a few months yesterday. I was having problems with the audio. At first it wasn't coming through at all, but after cleaning the contacts and fiddling with it, it managed to come through. Today again I'm getting no sound. I know that sometimes the cpu can corrode and that can take the sound out of games, but if I was able to get sound yesterday is it more likely that I just need a new RF cable?