Hi. I bought a second hand due, it has a slight annoying problem hopefully somebody can help me with. I can be watching it fine for as long as I want with no problems if I don't change channel. If I have been watching it for a while and change channel I get black screen, if I restart cam it stays the same. Once I do a restart it comes on again. It does not do it all the time. Does anybody know what might be causing this?