There is a diagnostic option on the E80 that will tell you the input voltage. That maybe the problem. We had the same problem, but first Raymarine
said it was a problem with the unit and replaced the entire unit (so there must have been some problems). Later we replaced the converter (12v to 12v) that was installed to keep the voltage steady and now it works fine.
There is also a new software
update that you can install yourself, but I have not done that yet.