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.