Garmin 400W Series, Instructions Manual

400W Series 

190-01226-14 Rev. 3 

Instructions for Continued Airworthiness Bell 407 

Page 14 of 26 

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:  

Table 2 Troubleshooting Guide 

Problem Possible 

Cause 

Solution 

The 400W Series unit 
does not power on. 



 The unit is not getting power to the 

main connector P4001. 



  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. 

The 400W Series unit 
does not compute a 
position. 



 Not receiving signals. 



  Check the GPS antenna connections. 

Make sure the aircraft is clear of 
hangars, buildings, trees, etc. 



  Wait 20 minutes for unit to complete 

cycle. 

GPS signal levels 
drop when avionics 
are turned on. 



 Noise interference from other 

avionics. 



  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. 

The GPS signal levels 
are very low. 



 Improper antenna installation or 

coax routing. 



  Check GPS antenna installation, 

connections, and cable routing. The 
GPS antenna must be mounted on the 
top of the aircraft. 



 Antenna shaded from satellites. 



  Make sure the aircraft is clear of 

hangars, buildings, trees, etc. 



 RF interference at 1575.42 MHz 

from VHF COM. 



  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.