1. Hey, labeledy! Better late than never, eh? I take your avatar as the requisite photo and do hereby declare,
@labeledbass, you are now member #1232 in the Fender Rumble Club. Welcome!
B. It could be a corroded FX Return switch, which cuts off the signal from the preamp to the power amp. Try an instrument cable from the FX Send directly to the FX Return. If that makes it work, then just turn it off and run the cable plug in&out of the FX Return jack several times to knock the corrosion off that switch. A not too common, but often overlooked, problem.
III. If that doesn't do anything, then all I can say is take it to an Authorized Fender Service Center. It may cost a few bucks, but they can do a much better cleanup and straighten up than most users can.
Hope this helps, label. Please keep your Rumbling brothers & sisters updated so that we all may . . . .
Rumble On!
.