This happened to me with GNS 530W. With the 530 turned on, the 250XL panel mount and the 396 both lost GPS lock. 530 turned off and they both locked on again. Interestingly the Ipad did not lose GPS lock. I heard it also use Russian GPS.
Snugged up the TNC at the antenna and no more problem.
http://www.bing.com/videos/search?q=...E32B251755F6D6
So, if you lose all your GPSs it might be a loose antenna on one of your GPSs. The scary thing is which one do you turn off first. And given these all in one boxes you may have to give up your VOR/ILS and a com.
GPS signal loss
Linear Mode
