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I have an a120 MFD and 4 x i70s instrument heads running successfully since installation in April 2017. Recently I have been getting false depth readings flickering down to zero and staying there for a while (30 seconds or so) then returning to expected readings. This is replicated on the MFD. This has been happening in open water (3 to 30 metres) when there is no turbulence from passing traffic.
I see from the forum there isn’t a check I can perform on the depth transducer other than running an independent transducer as a comparison.
After consulting the forum for similar problems I have unplugged the clear cable from the depth transducer in the itc5 (as suggested to someone else) in case I have interference. I am waiting to test the effectiveness of this on a longer run.

This morning after switching on the instruments I had 3 dashes for depth, speed, wind speed, and no wind indictator arrow, the only readings I had were cog and sog from the gps. After about 5 minutes I motored for a couple of minutes to a mooring and the readings came back up.
I have done a check again since and the instruments are all reading again soon after turning the system on.

So, at the moment I have all readings available, the depth is showing as anticipated subject to a longer test for the depth. However, given the 3 dashes readings this morning I am beginning to suspect an intermittent problem with the ITC5.

Apart from sending back the itc5 for testing (which would be very limiting as we live aboard) do you have any suggestions?

We are currently in Long Island Sound.

Many thanks.

Hello Bob,

It's unlikely that an ITC5 fault would stop it communicating on the network intermittently (a network comms fault would almost certainly be permanent.) What's more likely the cause there is something network-related, like a bit of corrosion on the STNG cabling going to the ITC5, or someone having incorrectly connected the ITC5 on the end of a spur cable instead of part of a backbone, and then getting having moisture or extra terminators in the 'spare' blue backbone sockets (ITC5 should never be connected just off a white spur cable; there should only every be 2 terminators in any NMEA2000 system, putting extra ones in will cause all sorts of unpredictable network comms problems; any empty STNG socket is just asking for condensation to start bridging pins, causing data corruption and corrosion.)

Re. the false depth readings, we sometimes get this sort of report in instances where the transducer is fairly close to the keel, so that the sounder's getting an echo from the fringe of the beam from the keel itself. If this is stronger than the bottom echo (maybe soft bottom, turbid water, high heel angle, deeper water etc.) then this can be treated as the real depth by the ITC5. This is one reason why I personally now recommend our installers here in Australia to fit fishfinder depth transducers connected to the MFD rather than an ITC5 - more power, more diagnostic capability in the instance of a problem, and a graphical image of what you're anchoring over, for a similar price to an instrument depth transducer.

Thanks Tom.

I seriously doubt it is the location of the transducer - that hasn’t changed in 17 years and I haven’t been getting variable readings of this nature until now (in open, clean water, 3 to 30 metres depth, sandy bottom, no heeling as under engine and no turbulence from traffic).

My itc5 is part of the backbone and there are two terminators only in the system which has been working properly for 15 months.

I mentioned I read on the forum that disconnecting the clear wire from the transducer could solve the problem and I had done this. However, I had NOT insulated the disconnected terminal which I think might have been touching bare pin for an unused transducer and creating the 3 dashes.

I have now insulated the disconnected wire and for the time being at least all is functioning correctly.


Ok, let's see how you go from there.
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