Garmin GMA 340 AUDIO PANEL INSTALLATION MANUAL
Brand: Garmin, Pages: 43
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GMA 340 Installation ManualPage 2-9
The following adjustments can be made through access holes in the top cover of the GMA 340:
1. Marker beacon audio level (Refer to Garmin Service Bulletin 0208 if connecting to a Sandel SN3308
2. Marker beacon sensitivity
3. Aircraft radio speaker output level
4. Pilot PA microphone speaker output level
5. Copilot PA microphone speaker output level
6. MUSIC 1 mute trip level
Refer to figure 2-3 for the location of the access holes.
Exercise care when inserting adjustment tools through the top cover. Damage to
the unit may occur if an adjustment tool is accidentally forced against unintended
components or circuit board paths. Use a 2 mm (max blade width) flat-blade
non-conductive screw driver or adjustment tool.
CCW adjustment increases the marker audio level. CW adjustment increases the levels for the speaker outputs
and MUSIC 1 mute.
For the marker beacon sensitivity adjustments, CW increases the sensitivity. The LOW sensitivity can be
adjusted without affecting the HIGH sensitivity setting. However, adjusting the HIGH sensitivity setting will
affect the LOW sensitivity setting also. If the HIGH sensitivity setting is adjusted, then the LOW sensitivity
setting should be checked and adjusted afterwards, if needed. If your GMA 340 top cover does not have the
marker beacon sensitivity adjustment access holes as indicated in figure 2-3, and you need to adjust the
sensitivity, contact Garmin for instructions.
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Page 2-10GMA 340 Installation Manual
A/C radio SPKR level
Pilot PA MIC SPKR level
Copilot PA MIC SPKR level
Marker audio level
Music1 mute trip level MKR LO Sense MKR HI Sense
Figure 2-3. Access Hole Location (Top View)
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GMA 340 Installation ManualPage 3-1
Figure 3-1. GMA 340 Front Panel
3.1.1 Front Panel Controls
1. Marker Beacon Lights
2. Marker Beacon Receiver Audio Select/Mute Button
3. Marker Beacon Receiver Sensitivity Indicator LEDs
4. Marker Beacon Receiver Sensitivity Selection Button
5. Unit On/Off, Pilot Intercom System (ICS) Volume
6. Pilot ICS Voice Activated (VOX) Intercom Squelch Level
7. Copilot and Passenger ICS Volume Control (Pull out for Passenger Volume)
8. Copilot and Passenger VOX Intercom Squelch Level
9. Crew Isolation Intercom Mode Button
10. Pilot Isolation Intercom Mode Button
11. Passenger Address (PA) Function Button
12. Speaker Function Button (DME in Dual ADF)
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Page 3-2GMA 340 Installation Manual
13. Transceiver Audio Selector Buttons (COM 1, COM 2, COM 3)
14. Transmitter (Audio/Mic) Selection Buttons
15. Split COM Button (SPKR in Dual ADF)
16. Aircraft Radio Audio Selection Buttons (NAV1, NAV2, DME, ADF)
17. Annunciator Test Button
18. Locking Screw Access
19. Photocell – Automatic Annunciator Dimming
3.1.2 On, Off, and Failsafe Operation
The GMA 340 is powered off when the left small knob (figure 3-1, item 5) is rotated fully CCW into the detent.
To turn the unit on rotate the knob clockwise past the click. The knob then functions as the pilot’s ICS volume
control. A failsafe circuit connects the pilot’s headset and microphone directly to COM 1 in case the power is
interrupted or the unit is turned off. Refer to the note in paragraph 2.6.2.
The intensity of the button annunciators and marker beacon LEDs are controlled automatically by a built-in
photocell (19) on the front panel. Nomenclature backlighting is controlled by the aircraft dimmer bus. See
installation wiring diagrams in Appendix B for guidance on connecting the dimmer bus to the GMA 340.
Audio level is controlled by the selected com radio volume control.
Selection of either COM 1, COM 2, or COM 3 (13) for both MIC and audio source is accomplished by pressing
either COM 1 MIC, COM 2 MIC, or COM 3 MIC (14). The active com audio is always heard on the headphones.
Each audio source can be selected independently by pressing COM 1, COM 2, or COM 3 (13). When selected in
this way, they remain active as audio sources independently of which transceiver has been selected as the active
When a microphone is keyed, the active transceiver’s MIC button LED blinks approximately once per second to
indicate the transmitter is active.
When no aircraft radio activity is detected by the GMA 340, the amount of ambient background noise from the
radios is further reduced by theMASQ
TMcircuit. This processing is also applied to the Nav radios (described in
3.1.7). If this feature is not desired, then J1 pin 16 (MASQ INH*) should be tied to ground.
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GMA 340 Installation ManualPage 3-3
3.1.5 Split Com (Not Applicable to Dual ADF)
Pressing the COM 1/2 button (15) activates the split com function. While this mode is active, COM 2 is
dedicated solely to the copilot as a MIC/audio source while COM 1 is dedicated to the pilot as a MIC/audio
source. The pilot can still listen to COM 3, NAV 1, NAV 2, DME, ADF, and MKR. The pilot and copilot can
simultaneously transmit in this mode, the pilot transmitting over COM 1 and the copilot transmitting over COM 2.
The SPLIT COM mode is cancelled by pressing the COM 1/2 button a second time.
While in the split com mode the copilot may make PA announcements while the pilot continues using COM 1
independently. When the PA button is pressed after the split com mode is activated, the copilot’s mic is output
over the cabin speaker when keyed. A second press of the PA button returns the copilot to normal split com
If the com radios in the installation utilize a “transmit interlock” system, the split
com function may require that this feature is enabled. Refer to the radio’s
installation manual for guidance. Garmin makes no expressed or implied
guarantees regarding the suitability of the split com feature in a given
3.1.6 Com Swap Function
The GMA 340 allows the use of a remote mounted switch (typically on the yoke) to alternately transfer the active
microphone back and forth between COM 1 and COM 2. The remote switch should be a momentary type,
connected between J2 pin 20 (SWAP*) and J2 pin 21 (SWAP return). Pressing the remote switch will have no
affect if COM 3 is the active transceiver or when split com is in use.
3.1.7 Aircraft Radios & Navigation
Audio level is controlled by the selected nav radio volume control.
Pressing NAV 1, NAV 2, DME, ADF (16), or MKR (2) (see MKR beacon operation) selects that audio source. A
second button press deselects the audio source.
In addition, the GMA 340 provides inputs for an unswitched aircraft radio (TEL RINGER) and an unmuted,
unswitched aircraft radio (ALT WRN).
3.1.8 Speaker Output
Pressing the SPKR button (12) selects Aircraft radios over the cabin speaker. The speaker output is muted when a
COM microphone is keyed. Speaker level is adjustable through an access hole in the top of the unit (see figure 2-