Gordon, last week I had a similar experience. The screen on my V2 was dark! Since I had a DE with its own working screen I was able to swap parts to held isolate the problem. It turned out to be a bad connection with the flat cable that connect the DSI connector to the video board for the 7 inch display. I have had trouble with those ribbon cables before. They are delicate and I have of course had to remove it several times. The original became very chewed up. I bought a bunch of replacements on eBay in various lengths. One apparently faulty one looked clean suggesting a possible problem with the connector. Now that would be very difficult yo repair. Be careful!
Jack, N6LN
John Terrell, N6LN