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

4 TROUBLESHOOTING

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 GTS Processor 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.
Side tone level is too low or
too high.
190-01007-B1
Rev. 1

Table 4-1. GTN Troubleshooting Guide

Possible Cause
The unit is not getting power
to the main connector P1001.
Not receiving adequate GPS
signals.
Noise interference from other
avionics.
Improper antenna installation
or coaxial routing.
Antenna shaded from
satellites.
RF interference at 1575.42
MHz from VHF COM.
The PTT input is not being
pulled low.
No transmit power to COM.
The input voltage is too low.
Wrong type of headsets, or
side tone level needs
adjustment.
Corrective Action
Ensure power is connected to the main 78-pin connector P1001, pins 19 and 20 and ground to
P1001, pins 77 and 78. Check circuit breakers and main avionics switch.
Check the GPS antenna connections. Make sure the rotorcraft is clear of hangars, buildings,
trees, etc.
Wait 20 minutes for GTN to download full GPS almanac and acquire position.
Turn all avionics off, then turn on each piece one at a time to isolate the source of the
interference. Route GPS cable and locate GPS antenna away from sources of interference.
Check GPS antenna installation, connections, and cable routing. The GPS antenna must be
mounted on the top of the rotorcraft.
Make sure the rotorcraft is clear of 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 that the MIC 1 Transmit (P1003-11) input is pulled low for transmit. The state of this
discrete input can be monitored on the Discrete Inputs page found on the GTN Diagnostics
page. See Section 3.3.5.
Make sure power input is connected to the COM 44-pin connector P1003-30, 43 and 44 and
ground to P1003-37, -38, and -40.
Increase input supply voltage to >11VDC.
If necessary, adjust the side tone level. Side tone adjustment is found on the COM Setup Config
Mode page.
GTN 6XX/7XX Part 27 AML STC Maintenance Manual
Section 1.2
Page 4-1