System Maintenance Manual

G1000/GFC700 System Maintenance Manual – C90A/C90GT/C90GTi King Air Page 5-55
190-00682-01 Revision F
5.9.6 GMA Common Problems
Symptom/Failure
Message
Recommended Action
Noise in Audio
Most often the cause of the noise is external to the GMA. Try the following to locate the
source of the noise before replacing the GMA:
• Try a different pair of headsets. Noise cancelling headsets may pick up and/or
generate more noise than standard headsets from their own circuitry.
• Check for noise with the engine turned off.
9 If the noise is present only when the engine is running, check the generator
and/or ignition system as possible sources of noise (see applicable airframe
specific maintenance manual).
• Check for noise as all electrical equipment is turned on and off (strobes, other
radios, etc.).
9 If the noise is identified from one electrical system or component refer to the
applicable airframe specific maintenance manual.
• Ensure the NAV/COM squelch is not open.
• Ensure the ADF and DME audio is not active.
• Ensure the marker beacon audio is not active.
• Ensure the ICS squelch is not open.
9 Master squelch level can be adjusted on the GMA CONFIGURATION page for
higher noise environments.
• Replace unit only after all possible external sources of noise are eliminated.
Buttons Do Not Work.
• Some buttons are disabled in the GMA CONFIGURATION page by default. This is
to remove potential sources of audio noise for inputs that are not used. If in doubt
as to which buttons should be disabled, reload GMA config files and other config
files for optional equipment installed in the aircraft (i.e. ADF, HF, etc.) from the
loader card.
COM Bleedover
• Verify on the GMA CONFIGURATION page that “Disable Split COM” has a green
box. Due to the closeness of the COM antennas and high power of the COM
transceivers, Split COM operation is not approved. If the box is black (indicating
COM ½ button is active), highlight “Disable Split COM” with the cursor and press the
ENT key to turn the box green which will deactivate Split COM mode.
Speaker Cuts Out
• Reduce volume level of the item that caused the speaker to cut out when turned up.
A speaker protection circuit disables the speaker output if the volume is too high. If
the volume is not sufficient, replace aircraft cabin speaker, reference the Airframe
Maintenance Manual.
Mic Audio Heard in
Speaker
• Reduce ICS Volume.
GMA XTALK – GMA
crosstalk error has
occurred.
• Ensure both GMA units are receiving power.
• Ensure both units are properly configured by verifying there are no GMA alert
messages.
• Check interconnect wiring between the GMA’s for faults.
• Replace GMA1.
• If problem persists, reinstall GMA1 and replace GMA2.