190-02207-A2
GPS 175/GNX 375/GNC 355 Part 23 AML STC Maintenance Manual
Rev. 3
Page 5-2
5.1 General Troubleshooting
This section provides information to assist troubleshooting if problems occur after completing the
maintenance. Refer to the GPS 175/GNX 375/GNC 355 System Configuration Log retained in the aircraft
permanent records for system configuration data. When troubleshooting the GPS 175, GNX 375, or
GNC 355 system, refer to the wire routing drawings and interconnect wiring diagrams that are retained in
the aircraft permanent records.
Table 5-1 GPS 175 General Troubleshooting Guide
Symptom
Possible Cause
Corrective Action
The GPS 175 does
not power on.
The unit is not getting power to the
main connector P1751.
Check circuit breakers and main
avionics switch. Ensure power is
connected to the main 62-pin connector
P1751, pins 21 and 42, and ground to
P1751, pins 20 and 41.
The GPS 175 does
not compute
position.
Not receiving adequate GPS signals.
Check the GPS antenna connections.
Make sure the aircraft is clear of
obstructions (hangars, buildings, trees,
etc.).
GPS signal level
drops when avionics
are turned on.
Noise interference from other avionics.
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.
GPS signal levels
are very low.
Improper antenna installation or
routing.
Check GPS antenna installation,
connections, and cable routing. The
GPS antenna must be mounted on the
top of the aircraft.
Antenna shaded from satellites.
Make sure the aircraft is clear of
obstructions (hangars, buildings, trees,
etc.).
OBS resolver wont
calibrate
Incompatible resolver or improper
connection.
Check the resolver specifications and
wiring.
OBS indication on
GPS 175 does not
agree with OBS
setting.
OBS resolver input not calibrated or
calibrated incorrectly.
Check wiring and calibration.
GPS 175 is not
receiving heading
from compass
system (ARINC 429
heading input).
Incorrect ARINC 429 input speed
setting.
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.
Wiring connections are incorrect.
The raw data being received by the
GPS 175 can be monitored on the
ARINC Inputs
page found on the
Diagnostics
page. Refer to Section
3.4.4.1.
Check wiring connections.
