If I bypass the issue by going through to display, it gives a bottom picture, but the units for depth which are set as metric, show as imperial in the image i.e. in about 30 m of water, it shows about 80 feet. It was working fine at the start of the day before this. Any advice welcome.  

No suitable repair places where I am so could be time to upgrade if not a simple fix.

Connected to Airmar P66