400W Series Installation Manual Page 6-1190-00356-02 Rev. E6. TROUBLESHOOTINGThis section provides information to assist troubleshooting if problems occur after completing theinstallation. Devices connected to the 400W Series unit can be useful for determining whether the 400WSeries unit is functioning properly or if there are problems with the installation.6.1 Troubleshooting ProcedureTable 6-1. Troubleshooting GuideProblem Possible Cause SolutionThe 400W Seriesunit does not poweron.• The unit is not getting power tothe main connector P4001.• Make sure power is connected to themain 78-pin connector P4001, pins19 and 20 and ground to P4001, pins77 and 78. Check circuit breakersand main avionics switch.• Check the GPS antenna connections.Make sure the aircraft is clear ofhangars, buildings, trees, etc.The 400W Seriesunit does notcompute a position.• Not receiving signals.• Wait 20 minutes for unit to completecycle.GPS signal levelsdrop when avionicsare turned on.• Noise interference from otheravionics.• Turn all avionics off, then turn oneach piece one at a time to isolate thesource of the interference. Route GPScable and locate GPS antenna awayfrom sources of interference.• Improper antenna installationor coax routing.• Check GPS antenna installation,connections, and cable routing. TheGPS antenna must be mounted on thetop of the aircraft.• Antenna shaded from satellites. • Make sure the aircraft is clear ofhangars, buildings, trees, etc.The GPS signallevels are very low.• RF interference at 1575.42MHz from VHF COM.• Move GPS antenna further from theCOM antenna. Add a 1575.42 MHznotch filter in COM coax. Fix orreplace the COM. Disconnect theELT antenna coax to check forpossible re-radiation.• The PTT input is not beingpulled low.• Check that the PTT (mic key) input ispulled low for transmit.• No transmit power to theCOM.• Make sure power input is connectedto the COM 25-pin connector P400211 and 12 and ground to P4002 21and 22.The 400W Seriesunit does nottransmit.• The input voltage is too low. • Increase input supply voltage to >12VDC. (>24VDC for 420 AW and430AW models)
