Problems With Humminbird 788ci

[Blackhawk19]

The last 3 times out my unit has started to lock up all of a sudden on 1.2'. Everything else on the unit works fine, this may last 2 min or 15 min. I've turned of the unit and restarted but it still shows 1.2', I've even pulled the transducer out of the water, it's on the trolling motor and it still reads the same depth while it's laying flat on the boat. I called Humminbird yesterday but the tech guy didn't really have any idea. I'm hoping someone on hear might have an idea, my wife just thinks I'm having problems so I can get a new DI unit Doh Any help would be appreciated.

I really like the product but this is the second unit I've had problems with. Had a 565 that would stay fogged up for have the morning so you couldn't read it and now this. This unit is 2yrs old but until 6 months ago I was using the transducer from the 565 (they're the same) so the transducer I'm using is only six months old.