Hi - I have a 15-year-old Luxman analog receiver that I want to use in my den. It operates and sounds great, except when I turn the balance knob. Turning it creates crackling from both speakers. Sometimes the speaker or speakers cut out completely. I have isolated the problem to turning the balance knob. I imagine that I must have a dirty contact inside the receiver. If this is, in fact, the case, how do I clean it? Or, if I am wrong in my assessment, I would like to hear other suggestions. Thanks!