I don't know about that. I imagine a good number of quad pieces you run across now days will have some kind of power amp problem. The reason is that when the amp blows on an old piece of gear, people don't want to invest in it, because they think that the unit will not last long before needing something else. However, most of the Japanese quad gear being made at the time was good quality gear in it's general construction. If the unit is well maintained, it will last. I have seen problems with the protection circuit itself, but that is rare. More than likely it's doing it's job, which is to protect your speakers from being fried in the event of a power amp failure. Speakers don't like direct current. The power amps have no capacitor separating the amp and the speaker, so if the amp fries, that relay is your only protection. Incidently, all it takes is just one channel going bad to shut it down. Look for it.
The Quadfather