I am going to assume (I don't like that word!!!) that is has the snap in base? If so make sure that nothing is bent, pins...brackets..etc etc in the bracket. Make sure everything is connected securely. That's where I'd start.
no turns out the guy before me had the wrong transducers on the boat it has a 4 pin transducer and the head unit has a 2 pin connection.. anyone ever had this happen trying to upgrade your transducer is there a replacment cable? any help wud be great..thx