Figure 5-7 Gnc 355 Com Alert Troubleshooting - Garmin GPS 175 Maintenance Manual

Radio may be
Radio needs service.
inoperative.
Cause Cause
A failure has been
The GNC 355 is not
detected in the COM
able to communicate
transceiver. The
with its COM
transceiver may still
transceiver.
be usable.
Corrective Corrective
Action Action
Verify that COM
This message may
connector pins P3552-
appear after
43 and P3552-44 are
operations in
receiving aircraft
Configuration mode.
power.
Cycle power to the
entire GNC 355 (both
GPS/NAV and COM
Verify that COM
circuit breakers) and
connector pins P3552-
see if the message
37 and P3552-38 are
has cleared.
connected to aircraft
ground.
190-02207-A2
Rev. 3
GNC 355 COM Alerts
Push-to-talk key is Remote transfer key is
stuck. stuck.
Cause Cause
The COM push-to- The COM remote
talk switch is stuck in
transfer key is stuck
the enabled or in the enabled or
pressed state. pressed state.
Corrective
Corrective
Action
Action
Go to the GNC
Press the PTT switch
DIAGNOSTICS –
to cycle its operation.
DISCRETE INPUTS
page in Configuration
mode and check that
the state of the input
changes when the
Go to the GNC COM remote transfer
switch is pressed and
DIAGNOSTICS –
released.
DISCRETE INPUTS
page in Configuration
mode and check that
the state of the input
Verify the COM
changes when the
remote transfer
PTT switch is pressed
switch wiring is
and released.
correct.
Press the COM
Verify the PTT switch
wiring is correct. remote transfer
switch to cycle its
operation.

Figure 5-7 GNC 355 COM Alert Troubleshooting

Remote frequency
Remote frequency
increment key is stuck.
decrement key is
stuck.
Cause Cause
The COM remote The COM remote
frequency increment frequency decrement
key is stuck in the key is stuck in the
enabled or pressed enabled or pressed
state. state.
Corrective
Corrective
Action
Action
Go to the GNC
Go to the GNC
DIAGNOSTICS –
DIAGNOSTICS –
DISCRETE INPUTS DISCRETE INPUTS
page in Configuration
page in Configuration
mode and check that mode and check that
the state of the input the state of the input
changes when the
changes when the
COM remote
COM remote
frequency increment frequency decrement
switch is pressed and
switch is pressed and
released.
released.
Verify the COM Verify the COM
remote frequency remote frequency
increment switch
decrement switch
wiring is correct. wiring is correct.
Press the COM
Press the COM
remote frequency
remote frequency
increment switch to decrement switch to
cycle its operation. cycle its operation.
GPS 175/GNX 375/GNC 355 Part 23 AML STC Maintenance Manual
Overtemp or Locked to 121.5 MHz.
undervoltage.
Hold remote COM
Reducing transmitter transfer key to exit
power.
Cause
Cause
The COM remote
The COM is reporting
transfer switch has
a high temperature.
been pressed for at
least 2 seconds.
Corrective Corrective
Action Action
Ensure the fan is
In Lockout mode, the
functioning properly
COM will tune the
and check for
active frequency to be
adequate airflow
changed. COM
around the unit.
Lockout mode can be
exited by pressing the
COM remote transfer
Ensure the fan is
switch for at least 2
functioning properly
seconds.
and check for
adequate airflow
around the unit.
Ensure that the COM
radio is receiving
adequate input voltage
(11-33 VDC).
If faults still exist,
contact Garmin.
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