Ed Crespy posted an answer for this Garmin GPSMAP 740S GPS Sounder & Chartplotter 010-00835-03:
"Sounds like you have a battery problem not a Electronics Problem. First thing is to solve..."
Ed Crespy posted an answer for this Lowrance HDS 5 Fishfinder GPS Chart Plotter HDS 5 Base US 83 200kHz:
"Sounds like you do not have your transducer connected. You will know it is working if you..."