What would be the possible reasons for the Bass, Treble, and Balance knobs not functioning on a receiver. I have recently sold my unit and the person who purchased it mentioned that the knobs don't do anything. I mentioned to him to perform a system reset to clear all input and speaker level settings (reference calibration and small/large). I know when the receiver left my house, front and rear channels were set to small thus sending my LFE to the sub channel. Would this disable the Bass knob? I can't think of a reason the other knobs wouldn't work. Any ideas? Anyone ever run into this before?