I have a Tracker ID Sixty Humminbird depth finder (in dash/console model) and when I turn it on it spins around like it is trying to read the depth but no red dot/lamp shows up on the round display to show me the depth? It appears to be working but no red dot/lamp shows the depth? Any idea what is going on? The depth finder is 15 years old so it may just be worn out? Any help/suggestions is appreciated. THANKS!