Troubleshooting Information - Garmin 400W Series Instructions Manual

conditions. The user must determine by observation when the display brightness is not adequate.
Contact the Garmin factory repair station when the backlight lamp requires service.
2.5.3 Battery Replacement
The 400W series has an internal keep-alive battery that will last about 10 years. The battery is used for
GPS system information. Regular planned replacement is not necessary. The 400W series will display a
'low battery' message when replacement is required. Once the low battery message is displayed, the
battery should be replaced within 1 to 2 months.
If the battery is not replaced and becomes totally discharged, the 400W Series unit will remain fully
operational, but the GPS signal acquisition time may be increased. This acquisition time can be reduced
by entering a new seed position each time the unit is powered on. There is no loss of function or
accuracy of the 400W Series unit with a dead battery.
The battery must be replaced by the Garmin factory repair station or factory authorized repair station.

2.6 Troubleshooting Information

If error indications are displayed on the 400W series unit, consult the Troubleshooting section contained
below:
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.
400W Series
Instructions for Continued Airworthiness Bell 407
Table 2 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.
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.
190-01226-14 Rev. 3
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