Gtn General Troubleshooting; Table 4-1 Gtn Troubleshooting Guide - Garmin GTN 6 Series Maintenance Manual

4.1 GTN General Troubleshooting

This section provides information to assist troubleshooting if problems occur after completing the
maintenance. Refer to the GTN System Configuration and Checkout Log retained in the rotorcraft
permanent maintenance records for a list of the interfaced equipment and system configuration data.
If any system fault persists after performing the associated troubleshooting actions, return the unit to
Garmin for service. Refer to
Problem
GTN does not
power on.
GTN does not
compute a position.
GPS signal levels
drop when avionics
are turned on.
GPS signal levels
are very low.
GTN COM does not
transmit.
Sidetone level is too
low or too high.
190-01007-B1
Rev. 4
Section 1.2.

Table 4-1 GTN Troubleshooting Guide

Possible Cause
The unit is not
Ensure power is connected to the main 78-pin connector
getting power to
P1001, pins 19 and 20, and ground to P1001, and pins 77
the main
and 78. Check circuit breakers and main avionics switch.
connector P1001.
Check the GPS antenna connections. Make sure the
Not receiving
rotorcraft is clear of hangars, buildings, trees, etc.
adequate GPS
Wait 20 minutes for GTN to download full GPS almanac
signals.
and acquire position.
Turn all avionics off, then turn on each piece one at a time
Noise interference
to isolate the source of the interference. Route GPS cable
from other
and locate GPS antenna away from sources of
avionics.
interference.
Improper antenna Check GPS antenna installation, connections, and cable
installation or routing. The GPS antenna must be mounted on the top of
coaxial routing. the rotorcraft.
Antenna is
Make sure the rotorcraft is clear of hangars, buildings,
shaded from
trees, etc.
satellites.
Add a 1575.42 MHz notch filter in COM coaxial. Fix or
RF interference at
replace the COM. Disconnect the ELT antenna coaxial to
1575.42 MHz
check for possible re-radiation. Move GPS antenna further
from VHF COM.
from the COM antenna.
Check that the MIC 1 Transmit (P1003-11) input is pulled
The PTT input is
low for transmit. The state of this discrete input can be
not being pulled
monitored on the Discrete Inputs page found on the GTN
low.
Diagnostics page. Refer to Section 3.3.5.
Make sure power input is connected to the COM 44-pin
No transmit power
connector P1003-30, 43, and 44, and ground to P1003-37,
to COM.
-38, and -40.
The input voltage
Increase input supply voltage to >11VDC.
is too low.
Wrong type of
headsets or If necessary, adjust the sidetone level. Sidetone adjustment
sidetone level is found on the COM Setup Config Mode page.
needs adjustment.
GTN 6XX/7XX Part 27 AML STC Maintenance Manual
Corrective Action
Page 4-2