Anybody's 501 keep blacking out?

I have a 501 showroom unit that keeps blacking out every so often and I see it showing up on my recordings. I am curious if anybody's else was doing it or if it just my receiver going back. This makes the fourth one I have had in about a year. I have used a different dish and different wire to make sure it was not that, but thats not the issue. I am asking what the problem could be and how I could have this fixed.