ICOM MXA 5000 outputting random data

[MattS]

Bit of a niche question...

I have an old ICOM MXA 5000 AIS receiver on the boat, and it’s doing some weird stuff.

When I take the NMEA output from it to my laptop, it works for a few seconds (with AIS sentences appearing) and then appears to dump a large amount of data out. This sometimes lasts 20-30 seconds. It does this repeatedly, working for only a few seconds in between.

If I disconnect the antenna from the receiver, it seems to stop doing this - and will happily run for 5 mins or more, just outputting the odd signal it can pick without an antenna.

Does anyone recognise this symptom at all with either this unit, or other older units?

Could it be that there are just too many signals in marinas nowadays and it can’t cope?

Could it be something about the VHF signal that’s upsetting it?

Ideas and theories very welcome!

From about 18 seconds in you can see it happen

 

[prv]

I saw something quite similar to this on my Standard Horizon GX2100 a couple of years ago. I wonder if the same third-party AIS module is inside both units?

I‘d been thinking about upgrading to an AIS transmitter anyway, so my “fix“ was to disconnect the radio’s AIS output and ignore it.

Pete

 

[pbu]

My ICOM MXA 5000 does exactly the same. Outputting random data on all ports. When it is powered on it gives a few minutes proper AIS data and even multiplexed GPS data from the NMEA Input. And after the few minutes it start outputting random data, with sometimes (3 to 5 minutes) 2 or 3 lines of NMEA data in between.
Powered from a laboratory powersupply.
NMEA Out and PC Out is exactly the same.

So it seems to be a Icom MXA 5000 habit

 

[VE7MJC]

I have (3) MXA-5000 units and all three have failed - producing the same data output on both RS-422 and RS-232 like you are observing. This ICOM AIS receiver design is time-bombed.

The problem appears to be that of failed ceramic IF filters in the RF receiver frontends (1 each for AIS channel A & B). This is a problem that plagued certain amateur radio models - and is a result of a design mistake (lack of DC blocking capacitor) which leads to a constant DC current through the ceramic causing salt crystal growth.

This is a photograph of the first MXA-5000 I opened. No photo trickery. These were operated in a laboratory environment under controlled conditions.

It is a ~ $2 part if you can source it (M50EW) but without adding blocking capacitors in the repair - the problem will return.



Good analysis in the ham radio community:
The Mysterious Case of the Withering Filters

Consider replacing the receiver with a Software Defined Receiver (SDR) and AIS decoding softare such as AIS-Catcher unless you have a particular reason to remain with a hardware hardware.