Worked for 10 years and all of a sudden after about 2 hours of use started to alarm. No indication of alarm. Immediately switched off unit. Turned on ok and few minutes will alarm and cannot be shut off at (on/off) knob. Disconnected power cable to shut off unit. Next day, tried again, same scenario - ok for 2 hrs and then started to alarm. Anyone has any idea. Wiring and cables ok. Transducer has hairline crack but that was there since day one. I do not have the manual anymore. Is it worth it to fix?