Garmin GPS 128 and XMDSC VHF NMEA problem

[LadyStardust]

I am trying to fix a neighbours problem with his Garmin to XMDSC Vhf NMEA connection.
It is wired up with the Garmin out (blue) to his NMEA in on the DSC set (yellow) and the NMEA return on the DSC set (green) going back to the Black (earth/-ve) on the Garmin. I replaced his cables and it was working fine , a few minutes later after I powered down and up again it stopped working. Just turning the Sets on and off can make it work properly, not at all, or the VHF can display LL that has us somewhere in the Indian ocean.
Im convinced the wiring is fine. The VHF DSC works perfectly on my boat connected to my Navman GPS, also a GPS repeater works perfectly when connected to the Garmin!
It's pull your hair out time!
Any suggestions ?

 

[markdj]

Check the output from the Garmin is set to nmea/nmea at 4800 baud rate and nmea 0183 v2.

 

[cpedw]

I have the same combination of GPS and DSC. Approximately once per day, the DSC alarm sounds becaue it doesn't know where it is. After a few minutes it all goes back to normal. It seems to be a glitch of the XM radio. I think there was a thread here some time ago where it was described but I couldn't find it with a quick search. As far as I know, there's no solution to this.
Derek