Table 5-2 Gnx 375 General Troubleshooting Guide - Garmin GPS 175 Maintenance Manual

Table 5-2 GNX 375 General Troubleshooting Guide

Symptom
The GNX 375 does
not power on.
The GNX 375 does
not compute
position.
GPS signal level
drops when avionics
are turned on.
OBS resolver wont
calibrate
OBS indication on
GNX 375 does not
agree with OBS
setting.
GNX 375 is not
receiving heading
from compass
system (ARINC 429
heading input).
Poor transponder
performance. Weak
or intermittent radar
contact reported by
ATC.
Loss of, or incorrect
altitude reporting by
the transponder.
Incorrect Mode S
aircraft data
transmitted.
190-02207-A2
Rev. 3
Possible Cause
The unit is not getting power to the
main connector P3751.
Not receiving adequate GPS signals.
Noise interference from other avionics.
Incompatible resolver or improper
connection.
OBS resolver input not calibrated or
calibrated incorrectly.
Incorrect ARINC 429 input speed
setting.
Wiring connections are incorrect.
Improper transponder antenna
installation or routing.
Improper altitude source installation or
configuration.
Incorrect Flight ID configuration.
GPS 175/GNX 375/GNC 355 Part 23 AML STC Maintenance Manual
Corrective Action
Check circuit breakers and main
avionics switch. Ensure power is
connected to the main 62-pin connector
P3751, pins 21 and 42, and ground to
P3751, pins 20 and 41.
Check the GPS antenna connections.
Make sure the aircraft is clear of
obstructions (hangars, buildings, trees,
etc.).
Turn off all other avionics, then turn on
each piece of avionics one at a time to
locate the source of the interference.
Route the GPS cable and locate the
GPS antenna away from the unit that is
causing the interference.
Check the resolver specifications and
wiring.
Check wiring and calibration.
Check ARINC 429 input port speed
setting for the port that the device is
connected to and verify that the speed
is correct for that device.
The raw data being received by the
GNX 375 can be monitored on the
ARINC Inputs page found on the
Diagnostics page. Refer to Section
3.4.4.1.
Check wiring connections.
Check transponder antenna installation,
connections, cable routing, ground
planes, and coaxial cable.
Check the altitude source configuration
and verify that the primary and
secondary sources are properly
configured.
Check the Flight ID Configuration
page and verify the settings are
configured correctly.
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