I recently sent my F-75 to Fisher to have a problem fixed. I was detecting one day, no problems. Then decided to go in the water about a foot deep. I was only in the water a couple minutes and came back out. The detector started making all of these random sounds and would not detect anything. I thought some water got in the coil somehow. I sent it in telling them what I just stated, a couple weeks later got it back. I noticed it had the same coil on it. The paper stated that the coil was retuned, a washer replaced and a new toggle. It works fine now. So a big shout out to the Fisher folks for fixing my F-75! It was still in warranty.