I had a similar issue with the Garmin Radio on my 2016 RT 25. My radio was a Garmin VHF 200
The symptoms were: The radio alarm went off after 10 minutes telling me the Radio was unable to acquire a GPS Signal. The additional symptoms were the radio did not show up on wither the NEMA network or the Garmin Marine Network .
During my trouble shooting i tried to alter the order of turning on the devices. First the GPS then the Stereo System,at that point the GPS and the Fusion 750 both showed on the Garmin Network. When I turned on the radio, the Fusion was no longer visible on the network, neither was the VHF and i still got the alarm after 10 minutes, the radio could not acquire a GPS Signal. Additionally I changed the order again, turning on the GPS First and then the VHF, same result.
I began to suspect it was the radio, however, after talking to Garmin I was persuaded to check the nema connections at the device and at the backbone.
To get to the backbone I had to remove the refrigerator and climb into the opening and check the power and the connections. I even switched some connections to see if there was a problem. I could not find one, and put the connections back as I found them. This was extreme boat yoga for a 71 year old.
Finally, I bit the bullet, purchased a Standard Horizon GX2400, with gps, m2k and DSC,[ AIS receive. The 2400 fit nicely into the same opening without modification.I connected it to power, radio antenna, and n2k. It came on without a hitch, my G7612 is is set to auto gps. I can see ais targets on my 7612 charts, the n2k network and the marine network now show all devices. The standard horizon has much better speakers and can support a loud haler etc. you can read which knows is squelch, volume and channel (visible labels)
I have had %the SH installed for a month so I cannot attest to long term, I have had SH on my prior boats. It costs $400 +- on Amazon.
I hope this offers some help with your issue.
Regards
