When the display starts to show you a picture then blanks out, does the display still stay powered on..? I would inspect both the connections on the Dome/Assy and connector on the Display for signs of corrosion, and condition of the Interconnect Cable.
You still might need to send the unit is service to correct the problem.
You might also check the reed relay/switch in the scanner. There are several things that can cause your symptoms. As deep blue say, you might need to have a dealer check it or send it in.