190-02207-A2
GPS 175/GNX 375/GNC 355 Part 23 AML STC Maintenance Manual
Rev. 3
Page 5-5
The GNC 355 COM
does not transmit.
The PTT input is not being pulled low.
Check that the MIC 1 Transmit (P3552-
11) input is pulled low for transmit. The
state of this discrete input can be
monitored on the
Discrete Inputs
page
found on the
GNC Diagnostics
page.
No transmit power to COM
Make sure power input is connected to
the COM 44-pin connector P3552—30,
-43, and -44, and ground to P3552-37, -
38, and -40.
The input voltage is too low.
Increase input supply voltage to
>11VDC.
The COM sidetone
level is too low or
too high.
Wrong type of headsets or sidetone
level needs adjustment.
If necessary, adjust the sidetone level.
Sidetone adjustment is found on the
COM Setup Config Mode
page.