Tuesday, April 26, 2016

Icom M506 NMEA 2000 issues

[Updated 24-Feb-2017]

I've been sitting on this issue for about a year hoping for a fix from Icom, but nothing seems forthcoming, so it's time to post anyway.  I prefer to post problems along with their solutions, but most of the time that's not possible.  At a bare minimum, I try to give the vendor ample time to respond.

The bottom line is that I can't recommend anything except the simplest version of the M506 with no N2K and no AIS since the N2K interface is fundamentally broken.

The M506 is one of Icom's newest marine VHF radios and is available in several different configuration.  They choices are:

VHF, No NMEA 2000, No AIS Receiver
VHF, NMEA 2000, No AIS Receiver
VHF, NMEA 2000, Receiver

I picked the model with NMEA 2000, but no AIS.  My primary navigation data was all on N2K at the time so that made sense.  The VHF could pick up GPS info from N2K enabling DSC emergency calling, and it could transmit incoming DSC alerts to my charting software to show the location of a distress call.  These are all important safety features.  Below is a picture of two of them side by side on my overhead dash.

Two side-by-side M506 VHFs

As radios go, these are really, really good.  Incredible clarity, noise cancellation, the ability to play back recent reception, etc.  I've been very happy with Icom radios, and these are no exception, except for the N2K interface on the M506.  That's a disaster.

The first sign of trouble was that when getting underway, I would power on all sorts of things, and within a few seconds alarms would be going off on other devices indicating a loss of GPS signal.  The errors would clear on their own and not recur until the next time I got underway.  It took me quite a while to figure out that it was the VHFs that were causing it.

After many hours of traces and decoding messages, I finally saw what was happening.  The twist is that it takes two M506s on the same N2K bus to cause the problem.  Each one stimulates the bug in the other.

For those interested, here's what happens.  Otherwise skip over this numbered section:
  1. VHF 1 powers on.
  2. To figure out what GPSs are on the N2K bus, the M506 sends out a broadcast request for the GPS message.  Devices that can send that message do so, and other devices decline.  Through this, the M506 figures out what GPSs are available, or so it thinks.
  3. VHF 2 powers on
  4. VHF 2 sends out the same broadcast request for the GPS message.
  5. VHF 1, hearing the request, responds with the GPS message.  This is where the train skips the tracks.  The VHF is a VHF, not a GPS.  The GPS message it sends contains blank GPS information, but it still sends the message.
  6. VHF 2 hears the response from VHF 1 and concludes that it's a valid GPS source even though it isn't.
  7. Other devices on the network also hear the GPS message from VHF 1, think it is a higher priority GPS than the one they are currently using, and dutifully switch to the higher priority GPS.  But the joke's on them because the GPS message from VHF 1 was blank, and it doesn't send any more if them.
  8. Other devices finally figure out that there is no good GPS data coming from VHF 1 (duh) and switch back to the GPS they were using before.  But this disruption is enough to set off alarms on the AIS transceiver and Coastal Explorer.
  9. Now, just to add insult to injury, VHF 1 sees that the bus has reconfigured when VHF 2 powered on, and it once again sends out its broadcast request for GPS messages.  VHF 2 hears the request and responds with a blank GPS message just as VHF 1 did earlier.  Everything blinks and alarms again, then finally settles down.
  10. Because both VHFs have sent out this silly GPS message, everyone else on the bus thinks they are a valid GPS sources.  If you look through the menus in Coastal Explorer, the Furuno NavPilot, or either of the VHFs, they all list the M506s as possible and valid GPS sources even though they clearly are not.   How messed up is that?
To break the chain, you need to take one of the two M506s off the N2K bus.  Then each never sends an erroneous response to its counterpart's erroneous request.   This is how I have been running for about the past year, with one VHF on N2K and the other on 0183.  Once I broke this cycle, I never got another lost GPS alarm on anything.

Demonstrating the problem is very simple.  All you need are two M506s on the same N2K bus.  Power both on, then work through the menus to select which GPS you want the VHF to use.  On each you will see the other M506 as an eligible GPS source, when of course it isn't.

M506 main screen

Page to select N2K sources for GPS and AIS

How can the M506 be a GPS source when it's a VHF?

But wait, there is more.  Look back two pictures and you will see where you can select which AIS source you want the M506 is display on its own screen.  Well, that has the exact same problem.  Both my VHFs show the other as a valid and eligible AIS source even though neither of them has AIS.

So, great VHF, but don't waste your money on anything but the simplest, 0183 version of the product.

In closing, let me also add that I have updated both VHFs to the latest FW (V1.004).  That helped with some other problems, but does not fix any of what I have reported.  Icom also provided me with V1.005 to try, but no joy.  It didn't address the issues.  So don't waste your time and money sending your M506 back to Icom for updates - at least not at this time because they don't fix these problems.

[Update as of 24-Feb-2017]

Last fall (2016) ICOM came out with new firmware for the M506, but it doesn't fix the problems reported here.  The new Firmware is V1.1 for the main VHF, and V1.006 for the UX-232 module which is the NMEA 2000 interface.

And last summer (2016) I discovered that having two M506 VHFs on the same N2K network isn't the only way to stimulate the problem.  A single M506 plus a Furuno TZT2 chart plotter does it too.  Check out the photo below where the TZT2 seems to think that the M506 is a valid data source for all sorts of crazy data.  Drift, pitch and roll, rudder, rate of turn, atmospheric pressure?  Really?


  1. I can see how this would be intensely frustrating but boats just have one VHF. Is there any reason you'd disqualify the NMEA2K/AIS version if it's going to live all by itself on the network?

  2. Sorry, mean to say "most boats"

  3. You are right, and thanks for pointing that out. I think that's why nobody has complained about this. But I hear over and over again about people's systems doing "weird" things, and this is a great example of one, and its root cause.

    But, before you run out and buy an M506 with NMEA 2000, read the next blog post.....there's more.

  4. Thanks for clarifying and I look forward to the next post. The Standard Horizon equivalent VHF is attractive with integrated GPS and AIS but unfortunately SH doesn't do N2K on anything. I guess you can't have it all...

  5. We've just added an ICOM M506 N2K to a very small backbone (Garmin 7610xsv, Garmin GNX20 4" display, Fusion UD-650).

    As soon as we turn the ICOM on it causes the GNX20 to freeze. Can't even power off the GNX20. Pulling the N2K cable and reattach - GNX20 freezes immediately. Turn off the ICOM, pull/reattach GNX20 N2K cable and the GNX20 works.

    I've replaced the N2K cable for the ICOM - no change. Also changed the T connector for my GNX20 - no change.

    Preparing to take the ICOM off N2K and use NMEA0183.

  6. Wow, that sucks. I don't have any direct experience with Garmin products, so haven't seen this one, but I'm sure others will be thankful to know.

    Have you confirmed that the M506 is running the latest firmware? V1.1 for the VHF, and 1.006 for the UX-232 NMEA 2000 interface? They did make some improvements, but it's still severely broken.

    Another heads up. Do you have a model with AIS? If so, be aware that the AIS only works over the NMEA 2000 interface. It does not work over the NMEA 0183 interface. This has bitten quite a few people. If you have an AIS model and the N2K interface doesn't work acceptably, which it doesn't seem to, I'd suggest returning it for a refund.

    The only way ICOM will get the message is if people start returning these pieces of junk. Personally, I've switched to Standard Horizon.

  7. Last November I built a network for a customer of a Garmin 7612xsv, Garmin 7610, Actisense EMU-1, using his existing Furuno FI50 (wind, N2K), Furuno RD30 Multi (N183), Simrad autopilot (J300x & AP20), & KVH-M7 Sat-TV rcvr. I installed a ICom M506 & all seemed to work OK for a couple of months. The M506 began to experience "software lockups" that would freeze the system, no keys would work at all and the fuse had to be removed to reset the M506. The lockups continued with increasing frequency and ICom Support basically told me I was full of it, because this could not happen. After months of trying various things, I purchased a 2nd M506 at my cost and replaced the failing M506, which I returned to SeaWide Marine with a detailed problem report; and then waited almost 4 months for a refund. The 2nd M506 began the same software lockups within a month or so. Again, ICom Support stated this could not happen. When I asked about the serial numbered M506 I returned, they claimed they had no knowledge of it, yet SeaWide shows return documents to ICom. ICom then claimed I must have bad power (Tiara 41 in immaculate electrical condition). With an oscilloscope I verified absolutely clean power at dockside with battery charger running (Charles). I tested with engines running and alternators charging, again, clean power. I then disconnected from shore power, turned off all other electronics, including battery charger, and the M506 lockd-up again within about 10 hours. ICom's response, "It can't be happening, we have thousands of these installed and your're the ONLY customer complaining, it must be a problem with your boat." NO OTHER electronics are experiencing any kind of problem! Today I will replace the M506 with a Garmin VHF210 w/Hailer, AIS, & N2K, again at my cost!!! I have installed a fair number of the Garmin VHF210'ws without a hiccup and their customer support at least seems to listen. I have more than 50 years experience with marine electronics, computer systems and networks, and am well known throughout the Hawaiian Islands for building the best marine electrical & electronics systems. I have been selling and installing ICom products for more than 15 years but this 10 month fiasco, and down-right rude attitude from ICom support has forced me to re-evaluate whether I'll ever sell another one of their products and put my customers through this kind of BS. I respected ICom for many years of quality products, but they have failed miserably with this one.


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