[mythtv-users] Black screen on watch TV. What to check?

[mark]

I can capture video fine from /dev/video0 but cannot get the watch TV  
in Myth to work.  What can I check?
I have checked all my settings in mythth-setup ( capture card, tuner  
etc... ) and mythfrontend looks fine too.
It dies after about 20 seconds and only shows a black screen.

Some areas to check would e appreciated.  Things to try.... etc...

Thank you