GeoQuip is a "One Stop Trimble Repair Facility" that provides fast, high quality repair and service for a wide variety of GPS systems. This includes maintenance and repair of Trimble GPS Systems that are under manufacturer's warranty and in the post-warranty period. GeoQuip is an Authorized Trimble service center...   Our Certified Technicians will keep your GPS System working long after the warranty has expired.

GPS is a complex technology but understanding it can be quite easy if you take it one step at a time. Trimble has a tutorial that is designed to give you a good basic understanding of the principles behind GPS Systems without loading you down with too much technical detail.
GPS System Tutorial