Troubleshooting; Troubleshooting Procedure; Table 6-1. Troubleshooting Guide - Garmin GPS 400W Installation Manual

6. TROUBLESHOOTING

This section provides information to assist troubleshooting if problems occur after completing the
installation. Devices connected to the 400W Series unit can be useful for determining whether the 400W
Series unit is functioning properly or if there are problems with the installation.

6.1 Troubleshooting Procedure

Problem
The 400W Series
unit does not power
on.
The 400W Series
unit does not
compute a position.
GPS signal levels
drop when avionics
are turned on.
The GPS signal
levels are very low.
The 400W Series
unit does not
transmit.
The sidetone level is
too low or too high.
400W Series Installation Manual
190-00356-02

Table 6-1. Troubleshooting Guide

Possible Cause
The unit is not getting power to
the main connector P4001.
Not receiving signals.
Noise interference from other
avionics.
Improper antenna installation or
coax 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 the COM.
The input voltage is too low.
Wrong type of headsets, or
level needs adjustment.
Solution
Make sure power is connected to the
main 78-pin connector P4001, pins
19 and 20 and ground to P4001, pins
77 and 78. Check circuit breakers
and main avionics switch.
Check the GPS antenna connections.
Make sure the aircraft is clear of
hangars, buildings, trees, etc.
Wait 20 minutes for unit to complete
cycle.
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 aircraft.
Make sure the aircraft is clear of
hangars, buildings, trees, etc.
Move GPS antenna further from the
COM antenna. Add a 1575.42 MHz
notch filter in COM coax. Fix or
replace the COM. Disconnect the
ELT antenna coax to check for
possible re-radiation.
Check that the PTT (mic key) input is
pulled low for transmit.
Make sure power input is connected
to the COM 25-pin connector P4002
11 and 12 and ground to P4002 21
and 22.
Increase input supply voltage to >12
VDC. (>24VDC for 420 AW and
430AW models)
If necessary, adjust the sidetone
level. Sidetone adjustment is found
on the COM Setup page.
Page 6-1
Rev. G