A couple of years ago on this forum a topic entitled "Denon 1909 loses audio and video for a second" was posted. Being a newbie I have the same question.....after about six minutes the picture on my TV screen starts to "snow-up" and then goes black. When it goes black and the sound also quits. After about four minutes of this the picture and sound come back and everything is fine! I had a Comcast feed and switched to U-verse and the same thing is happening. What did anyone learn from the past discussion?
Is the cable box and receiver connected by HDMI? If so, it's probably a "Handshake" problem. Try using component cables (red, blue, & green) for video, and optical or digital coax for audio, and see if that doesn't clear up the problem.