MFD8 losing GPS signal


Furuno Fan
We recently did a complete electronics refit of our boat and have a N2K network with Maretron GPS and a Furuno MFD8 (among other things). The MFD8 continually loses the GPS data and sounds an alarm. All of the other MFD's onboard show the still active GPS, as does the computer charting program and the Maretron USB100 through N2KAnalyzer. In other words, every time the MFD8 warns me that the GPS is down, every other instrument and software using or able to access that GPS tells me it is working just fine. After a while, the MFD8 will regain the GPS data and be happy again. For a few hours, at least, until it does the same thing.

Any thoughts would be appreciated.

I haven't heard of this problem before. I could be that the GPS is losing fix for such a short period that only the MFD8 is noticing it. When dealing with NMEA 2000 items it could be something is wrong with the backbone commuications. (Bad terminator etc) The network can get echoes or communication problems, if something isn't right. Sometimes this can affect only one item and not the entire network. It might take a dealer with NMEA 2000 tester to get to the bottom of it. You could always send your MFD8 in for testing if you suspect its NMEA 2000 port. This is a very strange case indeed. You don't have any transmitting antennas near your GPS antenna do you?
Jeff from Furuno is helping me troubleshoot this. I think we have a lead - there is a VHF/AIS radio with the AIS output connected on one MFD8 0183 port and the DSC output connected to another MFD8 0183 port. The VHF/AIS radio has a separate GPS hooked to it and I think it is putting GPS info on the 0183 line. I had the position sentence input box checked on the MFD8 0183 DSC line, so perhaps it was getting a second GPS input through there. I have unchecked this sentence and will see if the problem goes away.

This wouldn't have happened at all if Furuno supported AIS on N2K...(just sayin')

Just thought I would follow this up. Turns out the problem was location specific. We were in a marina next to a military base. There was a big radio tower near our boat. Every day, at the same time, we would briefly lose GPS signal. So would all our other GPS sources (HH, iphone, etc), but they seemed to recover the signal faster than the Furuno, so it wasn't obvious at first that they were being effected. The interruptions were brief and only during one hour of most days. The MFD8 was the only instrument that didn't return to operation quickly - the others recaptured signal immediately and were only noticeable if I happened to be staring right at them when the signal was lost. The MFD8 gets its GPS input from a Maretron GPS. The Maretron GPS would only experience a brief interruption, as shown on other instrument displays, but the MFD8 would take several minutes to be happy again.

Anyway, leaving the marina solved the problem and it has not happened since.

Thanks for the follow up. The MFD has auto switching abilities so when you lose GPS, it starts searching for other possible GPS units connected to your MFD to use. When it doesn't find any, it goes back to the original. This would be why the delay is longer. It is trying to look for another GPS to use because your primary selected GPS lost data. Glad you found the cause. We have heard of others having GPS issues from time to time around military bases. I guess it is part of the price of freedom. Thanks again for sharing.