Usually the instrument goes bad (because it has electronic and working parts in it), but sending units, fixed in epoxy, don't (but can). The best thing to do is to send them both back, but make sure it is not just a power problem (like you are not getting power to the instrument). And, to answer your original question......no, you cannot use a new Ray Marine instrument with your old Datamarine transducer. They are calibrated to match.