I've got the LMS335 that started acting up after 18 months giving very erratic depth readings intermittently. Spoke to a tech at Lowrance, and they recommended the only easy way to isolate if the problem is in the electronics or the transducer is to try swapping one of them out. If you know someone that has that same unit, try to borrow it for an afternoon and see what happens. If the problem remains, then it's a problem with the transducer. If the problem goes away and you're sure it's not the setup, then the electronics will need to be serviced or replaced.
In my case, I could not find anyone with the same unit, so I bought a new transducer. The ducer would be more likely the piece to fail given the problem I was seeing. To test, just disconnect the mounted one, hook up the new one, drop it over the side and power on the electronics to see if it makes a difference.
John
2120DVSC
