I recomend a there should be a specific forum for equipment malfunctions, but here goes.

The reverb on my Fender Princeton 65 isn't working, and when I turn it up past 5 I get a weird rumbley noise, almost like a thunderstorm far away. I get that noise, but I don't get any reverb.
I bought it used at a pawn shop but the reverb didn't work then either. One of my friends did some stuff with the wires (While it was on, wasn't that bright) and got the reverb working.

Recently though I noticed it wasn't working, so and any specific thing I should do to fix it?
BTW, If i can't get an answer here, ill probably bring it in somewhere, but it'd be easier and cheaper if its a DIY.