Over time things wear out, that is life. If the receiver is older, the electrical components inside could just be worn out. It might be a small problem, but would not be worth trying to figure out and you'd spend more than what you payed to have it fixed.

You would be better off buying an affordable receiver new for a couple of hundred bucks if that is in your budget.

M80s VP180 4xM22ow 4xM3ic EP600 2xEP350
AnthemAVM60 Outlaw7700 EmoA500 Epson5040UB FluanceRT85