Thanks to all of you for your help. I think I have it figured out. I’ll probably be shopping for a new HDS unit.

Thanks for all the helpful info. I’ve gotten so far. To clarify my current setup, this is what I have going. I have the the HDS 10M at the console. It is connected via ethernet to LSSI-the LSSI transducer is at the transom of my boat. I am also running a skimmer transducer 50/200khz at the transom. The skimmer transducer is fed all the way to the bow to an HDS 8 and shared back to the HDS 10M via ethernet. I have no problem seeing structure scan on both units. What I can’t get, unless I am plugged into the transducer on my terrova in the bow is 2D sonar from the skimmer transducer. I am wondering if I need the NEP-1 expansion port, or if I have this networked incorrectly, I am thinking also of the switch to be able to go between the skimmer transducer at the transom and the transducer off the terrova at the bow, to see 2D sonar. Initially, I was able to see 2D sonar at the HDS 10M, then I replaced a broken transducer. I think I need to go into a setup menu and choose the model of transducer to make it work. Hope all of this confuses the issue more!?