Furuno Radar Problem - Help !!

[Greg4cocokai]

My problem:
Half way thru our current 5 yr cruise our radar (Furuno Navnet 1833c) has decided it only wants to work when it wants to!.. Underway, It always comes on, but after a while the echo/return gets segmented and shortly thereafter goes to a blank screen. I first thought it was water getting into the cables during squalls, NO. I've been up the mast twice to tighten/check the set screws on the motor/gears, NO. It's gear driven, mo belt. Now one person says it's a grounding problem and my elec. guru in the states says it is the motor, something about how it syncronizes the signal. I'm in a marina now (I avoid at all costs!) and have had the unit on for 48 hrs and all is fine. As soon as I head out, it will quit!!!

Any help will be surely appreciated.

Cheers to all, Greg
Townesville, Aus.
Thailand by Dec.