I realize my original post is old, but wanted to update because I found an inexpensive fix.
A helpful fellow sailor posted this video:
YouTube - Repairing Navman 3100 sailing instrument Display
Basically do exactly what he says.
It took me three attempts before I found a surplus LCD screen that had a large enough connector to do the job. Still, total cost was $25 to fix two instruments that would have been more like $1,000 to replace.