I'm afraid even my 2 cents won't be of much help here. The best I can do is the install manuals, no repair manuals or board schematics, etc..
Garmin (like many of the mfgrs) has moved away from repairs in the field and at shops and towards "send it to the mfgr" for repair. With the newer generation goodies out there, it ends up being almost as economical for the mfgr to quickly change a complete board over having a technician or repair shop trying to replace individual components on a board. Not sayings its right, just saying it's the way it is. Gone are the days when you could open up a radio and quickly identify a burnt fuse, voltage regulator, capacitor or whatever. Things are much more integrated now, so I'm afraid that's the way it is.
Sorry I'm not much more help.
My "2 cents" as usual!
Cheers,
Stein