Metals used in circuits can react with oxygen. It's a common and natural reaction and can cause connection problems, but the process is reversible with deoxidizing sprays which can improve the sound quality of your amplifier.
Remove the two screws on both sides of the receiver. Keep these and the rest of the screws in a safe place.
Remove the top screw on the back panel.
Slide off the case to expose the internal components of the receiver.
Carefully wipe the circuit board and its components to remove any dust.
Lightly spray the circuit board with DeoxIT.
Lightly spray the input and output connectors with DeoxIT on the inside of the back panel.