About 7 years later the fan started coming on and going off so back to a local shop with great reviews. I was told the power caps were dying.
The low voltage suppy had drifted from its + and/or - 15 volts and this causes the problem you noted. Mine does this and every few years it is just a matter of tweaking the pot to get proper operation again. In fact, it is doing it now, and I need to get it out of the entertainment console to do it (PITA)!
When I had my Marantz in the shop, I noted this to the tech and he said if it is that unoften, just deox it and see how long it goes.

