I need some advice on something I did w/my 2 Humminbirds. I have a 997C SI Combo NVB (bought in 2009) on my console and a 898C SI Combo (bought in 2012) on my trolling motor. By the end of last year's fishing season, it wasn't hard to notice that when making changes on my map screen (say changing the zoom or the depth of shallow water, etc.) how fast the 898 is. So this year I decidedthat since both units use the same hi def transducers, I'd just switch the units and leave the transducers and cables as is. I've been out fishing twice so far and noticed that when the fish alarm sounds off detecting a fish in the area, no fish appear on the 2D sonar. I'd like input as to whether switching just the units to different transducers, would that make any difference in either or both units operating correctly. I'm wondering if I should just call Humminbird and see about shipping them in to be checked over. Any ideas and/or thoughts?