Thanks for responding. I'm thinking the same. The first time I called them, they told me to run the updates and see whether that would solve the problem. It didn't. I called back and explained that I had the mainboard switched out, and they told me that that should have solved the problem. I'm explaining to them that I'm still experiencing this issue.
I'm using the TV less, in the hopes that that will help in some way, but I'm emailing Sharp later today. We'll see what happens. (edit: When I emailed, I got a failure msg., saying that "user is over quota"). Sigh.