Is there one? I thought the thing was nitrogen-filled and needed to go back to the ark if fiddled with. Having said that I've seen pictures of its innards on the net somewhere years ago. What's yours doing wrong? I bought mine in the late 90's and it still works OK.
Dunno if it's the same as mine (a Garmin 28) but leaving it plugged into a live 12v feed for 24 hours or so recharges the memory battery. Garmin support is v. friendly - give them a call.