I’ve just replaced an FCV-620 model with a new 628. According to Furuno techs, the transducer from the previous unit (Airmar P66) is compatible with the 628. However, after attaching wiring and powering the unit up (only for a few seconds), I’m getting no depth reading, only - - - - . Furuno says not to be concerned, it will show the depth when it’s in the water. Is this consistent with what your seeing on similar units?