I think I've read that
Raymarine are helpful with
advice so maybe call them?
Probably shouldn't go much beyond checking every pin/socket of the connectors at both ends of the scanner cable yourself -
power cable disconnected for
safety.
Not just a quick look but a thorough
inspection with a powerful magnifier - looking for
corrosion or poor contact. Visual scan of boards can sometimes find problems. Heat damage,
corrosion, leaked electrolytics are all fairly easy to spot.
Magnetron seems a strong possibility though.