Tell us the result, willya? That's really interesting. If just some of the avionics turn off, it may be load / voltage related. If all of them go, it may be just one relay that's actually either designed to do this or is somehow malfunctioning. I'd almost say it's the avionics master relay itself, but those are supposed to be fail-safe (fail to "on"). I always just turned the avionics master off, but you may be in an area that's somewhat "transponder critical". A previous poster says there was no loss of avionics for him, so we have a mystery.