Follow all of your cables and check your connections. Raymarine uses a SeaTalk system to communicate between all of your electronics, (VHF, GPS, Sonar Unit, SmartCraft, etc) It is usually located behind the panel at your right knee when standing at helm. That is also where your sonar module is that the transducer plugs in to. These units fail and cause all sorts of electronics communication issues. Disconnect each cable and reconnect it, sometimes this will do the trick - but don't count on it.
Your system is older than 10 years, so Raymarine will no longer support it. They won't even discuss it. If you want to rule out the transducer, many marinas / electronics dealers will send you a loaner to hook up and drop overboard as a test. We messed with ours, band aiding it for 2 seasons and after having a reputable Raymarine service tech trouble shoot it, we finally gave in and put in a new Garmin 7600 System. Pricey, but boy is it sweet. I could not believe all of the wiring and modules the installer pulled out. The new system, 3 cables - power / radar / transducer and a splice into SmartCraft and VHF.
