Old Yamaha soldering can get lousy in my experience.I've got a Yamaha DSP-1000 suround sound amp which is about 10 years old and is diplaying all the problem signs those amps have become notorious for, crackling through the speakers, volume control problems, etc.
Replace caps with polypropylene, and wire with 10 pair telephone cable will give these a birthday.My main speakers are a set of KEF Concerto's I built from a kit back in 1974. They're still good, but they're sounding a little tired.