Navman 3100s Depth Sounder faulty

dtynan

dtynan

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As the subject says, the boat has a Navman 3100s depth sounder installed by the previous owner. It was working until recently when the boat was lifted out, power-washed and antifouled (and surveyed). Now the device just either shows "--" or some off-the-charts depth. I pulled the transducer, hoping they'd antifouled it (they had, a bit) but cleaning it didn't help. I've had a look at behind the panel and there's nothing obvious. I know my way around electronics so I'm thinking of sticking an oscilloscope on the coax between the transducer and the display. I'm expecting a DC voltage to power what looks to be a smart sensor, and an AC modulation representing the out/return? Has anyone ever looked at that signal on this or any other depth sounder? At this point, I'm trying to decide if it's the transducer or the display. Given that it was working before the lift-out would suggest the transducer, and I can find one on eBay for around $227 (plus shipping and duties) but I'd rather not throw good money after bad if it turns out to be the display. The other option would be to just replace it with a Raymarine/Garmin/Nasa unit but I'm guessing the through-hole is a different size, and I'm not planning to lift the boat again until October. So, here are my questions, please?

1. Is Navman/Northstar still in business? I can't find a website.
2. Is it even possible to get a schematic for one of these things?
3. What should I expect in terms of a signal on the coax - I'm guessing the 40kHz or 400kHz echo, and then the response?
4. Do these transducers use a standardised hole/tube? Can I swap out the transducer for a Raymarine/Nasa unit without a lift-out and hole drill?

Finally, at the risk of invoking a flame war, would you go Raymarine/Garmin or Nasa Clipper? I'd come down on the side of Raymarine, but those babies ain't cheap! My old boat had a Nasa depth and log, and they worked just fine.

If it's any help, the previous owner also installed the Navman log and wind speed units.
 
I fitted one of these from new on previous boat for Navman bidata. I got the model with the "better" transducer - which was an Airmar provided with the appropriate plug for Navman. Not a smart sensor type though. So hole size I had to make was standard 50mm/2".
Navman went some years ago - but sort of carried on by Plastimo as AdvanSea - and I think their transducer is compatible (I think it's the same model no, I will try and check). I also fitted the Navman digital wind. I might have PDFs of the manuals.
Having said all that I would check the connections very thoroughly first.
 
Hey, thanks for that! That's really useful. I did find manuals online, and have the originals on board. I did check the wiring but there's no harm in pulling out the display unit again and double-checking. I guess it's a justification for always choosing more common units. If it were a Raymarine or Nasa unit, I could borrow a transducer and see how the display works. Or vice versa.
 
It's the single function unit. One of three (speed, wind, depth in that order). The B&G chart plotter seems to support an NMEA sensor but that seems to come in at around £500 and I want to see the depth on the panel above the companionway, so I'd also need some sort of remote display. From what I can tell, that would come in at another 400 or 500 quid/euro/dollars/whatever. On top of that, Murphy will ensure that the transducer won't fit in the Navman tube. I presume your chart plotter is in the cockpit? Mine is at the chart table. If it isn't, how do you check your depth while at the helm?

I think the conclusion I'm reaching is to just buy the AdvanSea transducer (or a Navman one if I can find it) as I really need depth for an upcoming trip and won't have a chance to lift the boat beforehand.
 
It may be the display unit screen. It's a common problem with these. I've repaired all 3 of my navman units with this fault.
The zebra strip is a bit too short so the circuit board doesn't make a good contact with the lcd.
Either fit taller zebra strip or add a packer between the screen and the case.
 
dtynan said:
I think the conclusion I'm reaching is to just buy the AdvanSea transducer (or a Navman one if I can find it) as I really need depth for an upcoming trip and won't have a chance to lift the boat beforehand.
Click to expand...

If you do go this route remember they were marketed as NothStar in the USA which could help expand your search.
 
Older transducers and NASA ones are usually 150kHz and more recent ones are 200kHz, or sometimes 50/200kHz. A lot of manufacturers used Airmar transducers and you might be able to locate the type here:
Airmar
The site is down at the moment but from memory it gives cross references and wiring diagrams.
If you can find a transducer of the correct frequency you can test it in air. Just point it at 90deg to a hard flat surface such as a pane of glass and the reading will be about 5 times too large (relative speed of sound in water and air)
 
If it is a faulty transducer they don't have to be mounted through the hull. They seem to work just as well bonded inside the hull with sikaflex or similar.
Use one big smooth blob and push the transducer down onto it to avoid trapping air bubbles under it.
 
Last edited:
The Navman uses a 200kHz transducer. From new they offered two through hull versions (at least one of these was Airmar) and an in hull puck.
 
I have the older Navman Depth D100 which still was fine in June, but gave a week later --- or one of three fixed readouts. In the end, I replaced the large (470 µF) capacitor, which generates the pulse. Works again.
 
I bought a replacement transducer on eBay. I haven't been to the boat yet, but if anyone is vaguely interested, I'll let you know how I get on. Interestingly, the replacement is a solid, through-hull unit which would need me to lift the boat to install it. The existing transducer can be removed from the tube but the replacement can't. Seeing as I'm planning to go sailing through Orca country pretty soon and I'm planning to hug the 20 metre contour, I will see if the replacement works if mounted internally or if it comes to it, hanging over the side! I'll also pull the existing cable and see if I can find something stupid/obvious. I didn't the last time, but who knows?
 
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