Can anyone that owns a CZ-20 give me some tips on pinpointing in the water? I had problems with my unit and had to have it repaired. They had to replace much of it with CZ-21 parts. That is fine but I can not seem to pinpoint when I'm in the water. I can get a signal but trying to actually find the target is hit and miss for me. I've tried doing this in shallow water with different coins and even a ring and I do fine but when I get in deeper water and I can't see the bottom..... I am at a loss. Anyone?