Table 5-3 Gnc 355 General Troubleshooting Guide - Garmin GPS 175 Maintenance Manual

Table 5-3 GNC 355 General Troubleshooting Guide

Symptom
The GNC 355 does
not power on.
The GNC 355 does
not compute
position.
GPS signal level
drops when avionics
are turned on.
GPS signal levels
are very low.
OBS resolver wont
calibrate
OBS indication on
GNC 355 does not
agree with OBS
setting.
GNC 355 is not
receiving heading
from compass
system (ARINC 429
heading input).
190-02207-A2
Rev. 3
Possible Cause
The unit is not getting power to the
main connector P3551.
Not receiving adequate GPS signals.
Noise interference from other avionics.
Improper antenna installation or
routing.
Antenna shaded from satellites.
RF interference at 1575.42 MHz from
VHF COM.
Incompatible resolver or improper
connection.
OBS resolver input not calibrated or
calibrated incorrectly.
Incorrect ARINC 429 input speed
setting.
Wiring connections are incorrect.
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
P3551, pins 21 and 42, and ground to
P3551, 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 GPS antenna installation,
connections, and cable routing. The
GPS antenna must be mounted on the
top of the aircraft.
Make sure the aircraft is clear of
obstructions (hangars, buildings, trees,
etc.).
Add a 1575.42 MHz notch filter in COM
coaxial.
Fix or replace the COM.
Disconnect the ELT antenna coaxial to
check for possible re-radiation.
Move GPS antenna further from the
COM antenna.
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
GNC 355 can be monitored on the
ARINC Inputs page found on the
Diagnostics page. Refer to Section
3.4.4.1.
Check wiring connections.
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