'01 Venture Warner Bros. Edition

Hello all.
 
I just bought an '01 Venture  on Friday from a dealership, and got the extended warrnaty to boot.
Went to let the kids watch a tape Saturday night, and I'm getting a white streaking screen.  Also get the same screen when plugging in a portable gaming system.  Audio is fine for both inputs.  I went to troubleshoot is last night after the kids went to bed, and the darn thing worked.  I went to use it today again, and same white streaking screen.
 
I popped the AV input jack cover off, and re-seated the large cable (kind of looks like a computer parallel cable), and it's still not working.  Since the sound is working OK on both inputs, I'm assuming it's either a control box or video screen issue.  Does anyone have input as to any history with these components, or any further troubleshooting I can do?
 
I know this is a specialty piece that most dealerships don't have experience with, that's why I'm trying to get as much info before I take it back next week.
 
I can just hear the dealership now..."Well it worked when we tested it."
 
Thanks in advance for any input.
 
Matt