My Lowrance depth finder that I bought used for $50 won't turn off. It will turn on, but I have to turn it off by turning off the main power switch on the dash of my boat.

I have not called Lowrance, but I know that if the thing won't turn off, it won't be long before I go out and it won't turn on. Just bought it and put it on last summer, but it was used in the original box.

Has anyone ever sent one in for a repair, or is it even worth it? Any opinions welcome. Thanks. GTT