Scanning Sonar Issue

Our procedure while the boat has been sitting in Hawaii is to exercise all the systems to keep things operational and identify and fix any problems before its time to depart for Alaska. In the process, we started to get an error when initializing our Furuno Scanning Sonar in January. On start up, the unit goes thru a self test and during the test, it displayed a warning that there was a training error.

Keeping it simple, there are several servo motors that control the rotation and angle of the transducer when the unit is scanning. Training refers to the positioning of the transducer horizontally (0 to 360 degrees). On start up, the stepper motor is commanded to move to a home position so the unit knows how the transducer is pointed. A training error meant that the unit was not detecting that the transducer had moved to that home position.

With lots of help from Steve Bradburn (Furuno USA), we worked thru all the simple things first. Diagnostics, looking for loose cables or plugs, obvious damage to circuit boards et al. While we were optimistic, Steve told us up front that the most likely problem was damage to the sound dome which would have permitted salt water to enter the unit and destroy the inner workings. The following picture of the sound dome gives a better idea of what we are talking about.


Having eliminated all the simple (and inexpensive) possible problems, the next step was to order in a spare sound dome. Once the replacement was in hand, we plugged the replacement in on a temporary basis and the problem disappeared. Time to replace the sound dome and examine the failed one for issues.

Again, with Steve Bradburn’s help and some clever thinking on the part of Steve Parsons and the tech from Oceantronics (authorized Furuno distributor and service company in Hawaii), the old sound dome was removed, the new one was installed, and our CH270 Scanning Sonar was back in business.

Time for diagnostics. There was no obvious damage to the old sound dome, the seals were completely intact, and the special oil used inside the housing showed no signs of contamination.




When we tried to turn the sonar head, it was clear that something had gone seriously wrong with the training stepper motor. Without any sign of water intrusion or external damage to the sound dome, the simple conclusion is that the stepper motor had suffered a premature failure.

The unit at that the time of the failure was approximately 2.5 years old – just outside the normal two year Furuno warranty. Since the failure was unrelated to any damage to the unit, we prevailed upon Steve Bradburn to see what he might be able to do from a warranty perspective.

At that juncture, we learned thru Steve Bradburn that each Furuno company (i.e. Furuno USA) is afforded a warranty allowance by the Japanese parent company which is included in the price paid by each Furuno company pays for equipment. That warranty allowance is in lieu of any reimbursement for the direct cost of a warranty repair from Furuno Japan.

In our case, the original unit was purchased thru ENL in New Zealand. they in turn purchased it from a company in Australia. When the Australian company (who was afforded the warranty allowance from the parent when they bought the unit and sold it to ENL) was advised of the issue, we were told that it was outside the warranty period and no claim would be honored.

We are most appreciative of the assistance we received from Steve and Furuno USA and agree that it really isn’t their issue since they didn’t sell us the unit. In point of fact, Furuno USA could have simply told us to go deal with ENL or the company in Australia and left us to figure things out for ourselves (fortunately they didn’t).

I have asked Steve if there might be something that Furuno Japan might be willing to do here. The total bill for the repair including parts and labor came to over $5600. If there had been damage to the unit, that is one thing but a premature failure is another.

On a cautionary note to others, watch where you buy your gear – it does have implications down the road if there are warranty issues. Will keep everyone advised as to where this all goes.

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4 Responses to Scanning Sonar Issue

  1. My experience with sonar domes is limited to ones you can walk around in, but I sympathize with your plight. Can you replace the stepper motor, or is it integral to the unit? I understand the logic of each engineering compromise, but for that complex a device, repair seems a better choice than swap and pray.

    • myironlady says:

      Hi Patrick

      Can’t walk around in this one. Frankly, a repair might have worked but we had to get a new sound dome in to see precisely what the problem was with the old one (external circuit boards, the dome itself and, if the dome, what the issue was). At that juncture, all the labor dollars had been spent. Sending the old one back for repair would have incurred both dollars to fix it (if it could be fixed) and then more labor to reinstall it. We are short on time with our departure looming first few weeks in May and we need that sonar for AK. Our call was to replace the dome and then try to work with Furuno on a warranty replacement.


  2. Stan says:

    I have replaced many stepper motors on the CH250’s. This seems to be a common point of failure. The part was about $100US.

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