I know that this thread is old, but I had the same problem too.
Is your TV happens to be a Sharp AQUOS? Because a friend of mine and I have a Sharp AQUOS, old model from 2007-2008-2009ish, before the quattron era (with the silver wave design at the bottom of the tv), and we all had this issue.
When I did upgrade to the 8642HD, the problem was still present, but way less frequent.
Now I still have the same tv, but I use an Onkyo Audio-Video receiver between my PVR and my TV. I no longer have the black screen problem, but sometimes, on very very rare occasion (maybe 3-4 times a year), I lose sound, but this seems to be a receiver problem, since I only have to restart the receiver, not the PVR.