As far as i know Lowrance have got a no open machine policy. Meaning that they wont fix it. but replace if still under warranty. and sometimes offer you a new unit at a well discounted price if not.
I might be wrong about this but i know as Willem said they provide great Customer service. So they do stay your best bet. unless you know a very good electronics shop that can replace blown components. Thing is to find out what caused it in the first place.
Replacing my broken garmin with a lowrance this weekend.
Regards
Malboer