I can not seem to get my fish finder to work correctly. Hopefully someone can point me in the right direction. I have a BBFF1 fish finder networked to one RDP-149 and two RDP-148s. My transducer is a B258 thru-hull. All equipment was installed new in 2007. Here is what I have noticed. In shallow water (50 feet) in 200Khz mode if I have unit set to auto/fishing mode I will read correct depth but will not get any marks for fish or bait, just a blue screen between bottom and surface. In manual tuning I read correct depth but at 0 gain screen is half full of green clutter and increasing gain to 5 all clutter. This will happen even with boat stopped with generator and both engines off as well as other electronics and radios turned off to eliminate noise. I have a 60 mile run to fishing grounds and when I am running out I will set unit to auto/fishing and dual frequency. I will read correct depth even at 25 knots on the way then start trolling. When I get to around 600 feet of water it stops reading bottom and displays something around 5 feet the rest of the day until I return to shallow water again coming home. Once I get back to 100 feet or so it starts reading correct depth again. I have tried stopping the boat and turning off all accessories, generator and both engines in deeper water (800 feet)too. Still no correct depth. It just says 3 to 5 feet in either 200 or 50 kHz. Changing to manual 50 kHz does not help. However if I turn all my electronics off then back on in 800 feet of water it will read correct depth for a few minutes then back to 3 to 5 feet. While it is reading the correct depth in auto mode never any marks, just all blue screen. In manual mode the screen is full of clutter with gain at 0. Any help would be appreciated. Thanks.