chuck it in the bin and buy a complete new unit that would be my advice....i know that sounds a bit harsh, but by the time you have it checked or repaired that money would be better put towards the cost of a new unit, if your happy with model then buy one exactly the same, fit the new transducer to the new unit, check it's working correctly the try the old one, ok you may end up with 2 fully working units but ones a spare......just my view on it