Thanks for the input!
Putting the cable on the return and sends jacks has already helped sort out the difficulty with my clean channel. I've been playing for about an hour without interruption. It's funny how simple a solution can be.
The lead channel however is still not functioning even after trying all the tricks that I've read so far. What's more the news about the possibility of blown power caps is quite distressing given my current budget. Is there any way for a person without previous experience to pinpoint and fix these kinds of problems? I've downloaded the schematic from the internet, but I understand only the part where it says input.. :? Could anybody reccommend a good book to read for getting involved with the electronics?