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Russell H.
Russell H., Service Tech
Category: GPS
Satisfied Customers: 10777
Experience:  8+ years of professional experience
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I have just purchased a second hand boat with a Garmin gps

Customer Question

i have just purchased a second hand boat with a Garmin gps map 751xs when using the depth sounder, the unit is unable to provide a depth reading( fixes on one depth and the number flashes). The unit will also not display sea floor image, the screen is completely blue with no sea floor image. The transducer appears to be ok and connected to the unit properly. Is there anything you can advise that I do thank you Jason.
Submitted: 1 year ago.
Category: GPS
Expert:  Russell H. replied 1 year ago.

Hi, thank you for contacting My name is Russell. I will do my best to provide the right answer to your question.

What transducer do you have, working with the Garmin, and has it ever worked in your experience (I realize the boat is second-hand, so maybe it never has worked in your experience) ?

(With that information, I ought to be able to give you a good answer to this question. Please Reply letting me know. Thanks.)

Customer: replied 1 year ago.
The unit has never worked in my experience. The transducer is a AIRMAR and the model is TM150M
Expert:  Russell H. replied 1 year ago.

The capability of the transducer for sonar, depends upon whether it also has a (big, black, squared-off) CHIRP sonar module in the circuit. (Otherwise known as a Lowrance SonarHub, or similar device/box.)

Actually, on further research, it may be this GPSMAP doesn't need a 'black box' to get CHIRP sonar, with this transducer.

The only question in my mind is, does a Lowrance transducer work well with a Garmin device? In this case there's no reason to believe it *doesn't* - yet - since you do get some readings of some sort even now.

It's more likely that the connection has become slightly dirtied. Corrosion is a constant enemy of electronics and metals in any maritime or water-going context, especially in salt-water or brackish waters.

Trace the connection from the Garmin to the transducer (transom-mounted). See if the wires/cables are at all damaged, severely bent, or even slightly cut, anywhere along the entire length. (And see whether there's a 'black box' involved, en-route.)

Power Off the system.

Then disconnect the connections to the transducer from the Garmin, one at a time only! and scrub both sides of each connection with a clean dry brush for 30 seconds or so, then wipe down both sides with a clean dry rag cloth until the metal shines, and re-connect firmly, then on to the next connector, and proceed similarly.

(Also check the transom mount of the Airmar transducer.)

Then power On the system, and try it again.

Customer: replied 1 year ago.
I will check the cable in daylight tomorrow, however as it is a new boat to me I am not 100% sure if it has a sonar module does this Garmin sounder need this module to work correctly
Expert:  Russell H. replied 1 year ago.

Not necessarily needed, no. The Garmin model you have is 'independently CHIRP capable'.

Let me know how it goes. Thanks.

Customer: replied 1 year ago.
Hi, just checked the transducer cable and all appears ok (no cuts or damage to the cable). As the cable is so long a small proportion of it was coiled up neatly under the dash. There is no "black box"/sonar module integrated, purely the transducer/transducer cable which plugs into the back of the head unit. The head unit appeared to work fine other than the sonar component. It gives GPS coordinates, spread etc. if I unplug the transducer cable from the head unit when powered up it comes up saying it has lost connection with the transducer which I assume is good and shows the head unit is working ok. Do you think it could possibly be a faulty transducer?
Expert:  Russell H. replied 1 year ago.

Did you try the scrub-with-brush and wipe-with-cloth on the connectors for the cable to the transducer, also?

If you did and it still obstinately doesn't work, then it could be a defective transducer. Taking it to a shop (where they can test it by putting it into a busket of water, to some extent, hooked up to another device or display) and having it tested would make sure of the diagnosis.

If you need recommendations or listings to a local shop that could do testing on it, let me know your local zip code please.