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Author Topic:   SONAR Transducer Testing, Life Span of Sounders
98expeditionXLT posted 10-11-2011 09:18 PM ET (US)   Profile for 98expeditionXLT  
I have a Garmin GPSmap 498 SONAR with an Airmar P66 dual frequency transducer. The GPS [receiver] works perfectly. On occasion at high speed [the sounder] flashes the same depth for a few minutes, then it recovers. Lately [this malfunction of the sounder] has been more frequent and [occurs] at slower [boat] speeds. When in very shallow water, under 10-feet depth, the sounder display will flash the last depth for a few minutes, then recover, and work fine. But [the water depth] could be down to four-feet by then.

I checked the two connectors and all the pins seem to engage properly. I remove the device from the boat everytime the boat is back on the trailer. I called Garmin today. They are sending me a card with a software update.

I verified the transducer installation, and it has not shifted over five years and is installed according to manufacturer's instructions.

Is there a way of testing a transducer? What is the life expectancy of [SONAR] units?

jimh posted 10-11-2011 10:56 PM ET (US)     Profile for jimh  Send Email to jimh     
I don't know of any procedure or technique for testing a SONAR transducer using ordinarily available test equipment that one might reasonably expect a boater to own.

The life span of a recreational marine sounder is hard to assess. They certainly ought to last ten years, or at least one would hope for ten years. A SONAR transducer might be prone to damage if you operated it when it was not immersed in the water.

kmev posted 10-11-2011 11:38 PM ET (US)     Profile for kmev  Send Email to kmev     
I was experiencing the same [results] with my Garmin 440s. I updated the software, changed all the manual settings to every possible combination, and double-checked the tranducer installation: level with bottom, deep enough, not behind and chines, etc.

I started to think jimh was on to something about running the sonar out of the water (like everytime I enter waypoints while on the trailer), but a search of the Garmin owners manual located no warnings about running the sonar out of the water.

Finally, tonight I figured I would try making small adjustments to the transduder. I tilted the transducer's aft end down one click so that the transducer was no longer lever with the bottom but at a slight angle.

Running the boat tonight I noticed the tranducer kicked up less spay than before, and after running about 10 miles over varying water depths of 3 to 85 feet, it never lost the bottom once. Previously, over that same route, I had to hard restart the unit several times to get the sonar to relocate the bottom.

Perhaps your tranducer got tweaked slightly, but not enough to be noticeable?

98expeditionXLT posted 10-12-2011 06:37 PM ET (US)     Profile for 98expeditionXLT    
Today I checked the connectors and the transducer connector looks good, however the cable connector to the back of the 498 had some corrosion on the +12 V connection. I plan to clean this with some contact cleaner. Is it possible to apply dielectric grease to the two connectors?

I also moved the transducer up slightly on the transom as I was approaching max distance below the hull.

When I spoke with Garmin yesterday, the tech told me that there is no harm running the transducer out of water for short periods of time, however over extended time the crystal could overheat. He suggested that I should be able to feel the pulse or even hear it.

Unfortunately my boating season came to an end last weekend.

jimh posted 10-12-2011 08:50 PM ET (US)     Profile for jimh  Send Email to jimh     
If you suspect a SONAR transducer of failing, one method of testing is to move your SONAR unit to another boat with a known good transducer. If your SONAR unit works fine with a different transducer, you can look more closely at your transducer as the source of the problem. You could also try a different SONAR unit on your boat with your transducer. If the other SONAR produces the same results, this also tends to point to your transducer as the problem.

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