Depth Sounder
I had the same problem with my depth sounder and went through the whole gamut of possibilities. First I tried adjusting the settings inside the sounder. Then I pulled the transducer and cleaned it thinking that it may be fouled. I sent the unit in to the manufacturer who was kind enough to bench test it and tell me that there was nothing wrong with the unit. They even sent me a new transducer to use in case the depth sounder still didn't work right. I replaced the old transducer and still it worked intermittently. Last season someone suggested a spray used by electronics technicians to clean and dry parts in assemblies like a depth sounder. He gave me a can of the stuff, I sprayed it into the back of the unit and the problem disappeared. I sprayed it into the works behind the knotmeter for good measure and everything works fine. The original source of the problem was a faulty gasket on the instrument face on the outside of the cabin bulkhead which allowed a small amount of water to leak into the depth sounder. I can't remember the name of the product, but I'll bet someone out there would know or you could go to some place like Radio Shack and find it.
