1
SECTION 1
INTRODUCTION
This manual is intended to provide instructions and guidelines for the maintenance and repair of the
GARMIN GNC 250 and GNC 300.
WARNING:
This unit contains static sensitive devices. Service personnel must insure that proper
precautions are taken to prevent damage to this equipment from Electro-Static Discharge (ESD).
Disassembly and repair should only be accomplished at an approved ESD workstations by properly
trained and grounded personnel.
1.1
GENERAL DESCRIPTION
The GNC 250/300 is a full-featured aviation GPS navigation and communication instrument designed
for a fixed panel mounted installation. The GNC 250/300 utilizes the patented GARMIN MultiTrac™
system for tracking up to eight satellites simultaneously. The unit features a GPS receiver; a 4-line,
20 character, high-brightness vacuum fluorescent display; and a front loading NavData® card. The
unit contains a fully TSO’d 760 channel VHF communications transceiver operating from 118.000 to
136.975 Mhz with 5 watt minimum transmitter output power.
The unit is constructed from high quality materials and uses the latest techniques in manufacturing
technology. In order to achieve the desired reliability, size and power requirements, surface mount
components are used extensively. Specialized equipment and procedures are required to repair
circuit boards having surface-mounted components. GARMIN does not authorize the repair of GNC
250/300 circuit boards. All circuit boards and assemblies for the GNC 250/300 can be economically
replaced through the GARMIN board exchange program, if necessary.
A remote mounted battery pack with built-in charger is available for the GNC 250/300 as well as a
28v to 14v converter assembly. The following modules and printed circuit board assemblies are
available for field replacement:
Display Board Assembly:
Contains the vacuum fluorescent display and display circuit board.
Rotary Switch Assembly:
Contains dual concentric switch and an attached flexible circuit.
Control/Display Unit:
Contains bezel, buttons, lens, keypad board, light pipes, plus the Display Board Assembly and
Rotary Switch Assembly.
CPU Board:
Printed circuit board which contains the microprocessor, LSI and power supply circuitry.
Interface Board:
Printed circuit board which connects the CPU board to the NavData® card.
Communications Transceiver Module:
Contains VHF Receiver printed circuit board, transmitter casing and altitude decoder circuits.
