Ais problem

[KREW2]

I have a Comar-multi AIS reciever, linked to a SH cp180i.
Every winter layup I take the AIS unit home and reinstate it before launch. After reconnection this year all seemed to work fine.
Last week when sailing to the RTI race we hit fog, so down I went to switch it on only to find the power led barely glowing, and no signal lights working. On arrival into Cowes I removed the plotter to stow it below, and the AIS unit worked. Further investigation showed the common ground on the NMEA lead to be the problem. Just plugging the cable into the back of the plotter, without switching it on caused it to fail again.
Disconnecting the AIS unit from the common ground allowed it to work, but of course this gave no data on the plotter screen.
I have double checked all wiring, and it seems right, Comar have been very helpful but equally baffled. They have asked me to return the unit to them, which I will do next week, unless someone on hear has any ideas as to what the problem may be

 

[lw395]

Sounds like the plotter is pulling a lot of power through the data interface.
This may be caused by bad earth or supply on the plotter, wiring fault etc.
Does the plotter work OK without the AIS connected?
Is it powered from the same supply?

Is it possible to set the signal levels of the interface at one or other ends?
Have you earthed a 'data minus' line which is not earth?
Have you connected two data outputs together?

 

[KREW2]

Sounds like the plotter is pulling a lot of power through the data interface.
This may be caused by bad earth or supply on the plotter, wiring fault etc.
Does the plotter work OK without the AIS connected?
Is it powered from the same supply?

Is it possible to set the signal levels of the interface at one or other ends?
Have you earthed a 'data minus' line which is not earth?
Have you connected two data outputs together?

Hi, no, the plotter comes from a different switch on the control panel, and yes it works fine.
The AIS power comes from the same switch as the DSC radio, the NMEA ground for all 3 are connected together, it will work with the radio ground connected but power goes when I connect the cable into the back of the plotter, even with it not powered up, this however does not affect the radio in any way, and it displays the position data from the plotter fine.
If this deluge stops I will check the plotter earth tomorrow. I have been through all the other connections several times, and all seems okay, however I may undo everything and start from scratch.
Thanks

 

[ianj99]

I had a strange problem with a Navicom RT650 vhf with AIS.

It kept resetting itself. The screen would go blank and then it would bleep and start up and work for 30secs and then the cycle would repeat indefinitely. I was just about to return it for repair until...

I traced it to some strange feedback loop caused by a Shipmodul multiplexer I use.
I had forgotten to disable sending of the R650's AIS data out of the nmea output used to feed gps data to the RT650.

Its really something the RT650's firmware should be designed to ignore but probably would not arise in normal use.

 

[KREW2]

Sounds like the plotter is pulling a lot of power through the data interface.
This may be caused by bad earth or supply on the plotter, wiring fault etc.
Does the plotter work OK without the AIS connected?
Is it powered from the same supply?

Is it possible to set the signal levels of the interface at one or other ends?
Have you earthed a 'data minus' line which is not earth?
Have you connected two data outputs together?

Many thanks, sorted today.
As you suggested I decided to check the earth side first, the SH cp180i has a 2 amp in-line fuse on the negative, so I started with this, and noticed the bayonet fitting loose, opening it up showed it to be corroded, and the springy bit had rusted away completely leaving a sloppy fit on the fuse. A bodge repair just to test it and all worked fine. I'm surprised the plotter worked at all.
Another problem solved thanks to YBW forums.