Garmin GMA 340 AUDIO PANEL INSTALLATION MANUAL
Brand: Garmin, Pages: 43
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Page 2-4GMA 340 Installation Manual
Pin # Connector J1 Connector J2
1 Mkr Ant Pilot Headset Return
2 Mkr Ant Return Co-Pilot Headset Return
3 Com 3 In Co-Pilot Headset L
4 Com 3 Return Co-Pilot Headset R
5 Com 3 Mic 14V Lgt Lo/28V Lgt Lo
6 Com 3 Key* 14V Lgt/28V Lgt Lo
7 ADF In (ADF 2 In) 14V Lgt/28V Lgt
8 ADF Return (ADF 2 Return) Aircraft Power
9 Com 1 In Aircraft Power
10 Com 1 Return Aircraft Ground
11 Com 1 Mic Aircraft Ground
12 Com 1 Key* PA Mute*
13 Com 2 In ICS Mute Inhibit*
14 Com 2 Return ICS Mute Inhibit Return
15 Com 2 Mic High Music Gain Select*
16 MASQ Inh* Pilot Headset L
17 Nav 1 In 8 Ohm Select*
18 Nav 1 Return Reserved
19 Nav 2 In Tone Enable*
20 Nav 2 Return Swap*
21 DME In (ADF 1 In) Swap Return
22 DME Return (ADF 1 Return) NC
23 Com 3 Spkr Load Music 1 L In
24 Com 3 Spkr Load Return Music 1 R In
25 Com 1 Spkr Load Music 1 Return
26 Com 1 Spkr Load Return Music 2 L In (NC)
27 Com 2 Spkr Load Music 2 R In (DME In)
28 Com 2 Spkr Load Return Music 2 Return (DME Return)
29 NC FAILSAFE_WARN
30 Com 2 Key* Com TX Mute*
31** Alt Wrn In Pilot Headset R
32** Alt Wrn Return Co-Pilot Mic In
33 Pilot Mic In Co-Pilot Mic Key*
34 Pilot Mic Key* Co-Pilot Mic Return
35 Pilot Mic Return Pass 1 Mic
36 Ext White Lamp; A Pass 1 Mic Return
37 Ext Blue Lamp; O Pass 2 Mic
38 Ext Amber Lamp; M Pass 2 Mic Return
39 Middle Mkr Sens Pass 3 Mic
40 Pass Headset L Pass 3 Mic Return
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GMA 340 Installation ManualPage 2-5
41 Pass Headset R Pass 4 Mic
42 Pass Headset Return Pass 4 Mic Return
43** Tel Ringer Return Spkr Return
44** Tel Ringer In Spkr Out
Table 2-1. J1 and J2 Pin Assignments (Dual ADF in Parentheses)
Wire Gauge22-28 AWG
Hand Crimping Tool Positioner Insertion/
Military P/N M22520/2-01 M22520/2-09 M81969/1-04
Positronic 9507 9502-3 M81969/1-04
ITT Cannon 995-0001-584 995-0001-739 N/A
AMP 601966-1 601966-6 91067-1
Daniels AFM8 K42 M24308/18-1
Astro 615717 615725 M81969/1-04
Table 2-2. Recommended Crimp Tools
Non-Garmin part numbers shown are not maintained by Garmin and consequently
are subject to change without notice.
2.5.2 Audio Shield Termination
The audio shield wires should be terminated at the rear of the unit to the screws between J1 and J2 as shown in
Audio shields daisy chained and
terminated using a lug attached to
either of these screws.
Rear View of backplate and rack
340 P1 340 P2
Figure 2-2. Audio Shield Termination
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Page 2-6GMA 340 Installation Manual
Because the audio panel is a point in the aircraft where signals from many pieces of equipment are brought
together, care must be taken to minimize effects from coupled interference and ground loops.
Coupled interference can sneak into audio system interconnecting cables when they are routed near large AC
electric fields, AC voltage sources, and pulse equipment (strobes, spark plugs, magnetos, EL displays, CRTs, etc).
Interference can also couple into audio system interconnecting cables by magnetic induction when they are routed
near large AC current-carrying conductors or switched DC equipment (heaters, solenoids, fans, autopilot servos,
Ground loops are created when there is more than one path in which return currents can flow, or when signal
returns share the same path as large currents from other equipment. These large currents create differences in
ground potential between the various equipment operating in the aircraft. These differences in potential can
produce an additive effect at an audio panel signal input.
The audio panel may “see” the desired input signal plus an unwanted component injected by ground differentials,
a common cause of alternator-related noise. This is the main reason why all audio jacks should be isolated from
ground. Terminating audio shields just at one end eliminates another potential ground loop injection point.
Single-point grounding cannot be overstressed for the various avionics producing and processing audio signals.
Single-point, in this context, means that the various pieces of equipment share a single common ground
connection back to the airframe. Good aircraft electrical/charging system ground bonding is also important.
The wiring diagrams and accompanying notes in this manual should be followed closely to minimize noise
2.6 POST INSTALLATION CHECKOUT
Check wiring connections for errors before inserting the GMA 340 into the tray.
Incorrect wiring could cause internal component damage.
Except for marker beacon operation, an in-aircraft checkout may be performed in the aircraft on the ramp with
known good microphone, headset, speaker and avionics receivers. Item numbers in parentheses refer to front
panel controls shown in figure 3-1, page 3-1.
2.6.1 Lamp Test
Apply power to the unit by rotating the pilot intercom knob (5) clockwise.
The GMA 340 test button (17) checks the internal LED annunciators and marker beacon LEDs (1). Press TEST
to confirm operation of the LEDs. Cover the photocell (19) with a finger and observe that the LED annunciators
dim automatically. Check the front panel backlighting and dimming function. Each annunciation is illuminated.
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GMA 340 Installation ManualPage 2-7
2.6.2 Failsafe Operation Check
1. Turn the unit off by rotating the pilot intercom knob (5) counter clockwise.
2. Check the failsafe operation by exercising the COM 1 microphone, microphone key and audio over the
For units without Mod 4 incorporated, if a monaural headset is plugged into a stereo
jack the ring conductor will be shorted to the barrel conductor when the headset is
plugged in preventing proper failsafe operation. No audio will be heard. In this type of
installation, either a stereo/mono switch must be installed for proper operation or Mod
4 must be incorporated. If Mod 4 is incorporated, the audio will be heard only in the
left channel of a stereo installation. See note 13 in figures B5 and B7 and refer to
Garmin Service Bulletin 0209.
3. Turn the unit back on to continue testing.
2.6.3 Transceiver Operational Check
1. Perform a ramp test radio check by exercising the installed transceivers, microphone, microphone key and
audio over the headphones and speaker.
2. Verify that communications are loud and clear and PTT operation is correct.
2.6.4 Intercom System (ICS) Check
If a monaural headset is used in one position, no damage will occur if plugging
into a stereo jack. In the case of passenger positions, any stereo listener will lose
one channel when another passenger plugs in a mono headset.
1. Set the intercom to the ALL mode [Crew (9) and Pilot (10) LEDs off.]
2. Plug in headsets at each ICS position.
For helicopter operation using a two-stage Intercom/PTT switch, prior to using
the keyed-intercom mode, the VOX level should be set by adjusting the VOX
knob while the first detent is actuated and held.
3. Adjust squelch (8) and volume (7) for each position and verify that the ICS is working properly.
4. Check Pilot and Copilot ICS positions for isolation and proper operation of volume and squelch controls
(5, 6, 7 and 8).
5. Press the PA button (11). Verify that microphone audio is heard over the speaker.
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Page 2-8GMA 340 Installation Manual
2.6.5 Aircraft Receivers Check
1. Select the audio source corresponding to each installed avionics unit and check for audio over the
2. Check for Pilot/Copilot audio isolation when pressing the COM 1/2 button (15). (Not applicable to Dual
3. Press the SPKR button (12) and verify that any selected audio is heard over the speaker.
2.6.6 Music System Check
Unit Mods 2 and 5 provide times ten gain for volume control of the entertainment
music system. Unit Mod 5 provides either switching this function between unity gain
(0 dB) and times ten gain (20 dB) or hard wiring J2 pin 15 to ground for times ten gain.
When audio levels applied to Music 1 and Music 2 inputs are increased by 20 dB, the
amplification may also increase unwanted audio noise. See note 17 in figures B5 and
B7 and refer to Garmin Service Bulletins 0113 and 0210.
1. Set the intercom to the ALL mode [Crew (9) and Pilot (10) LEDs off.]
2. Connect a stereo audio source to MUSIC 1. Verify that stereo audio is heard over all headset positions.
3. Select an audio source to COM 1 (13) and verify that the sound is muted by active Com 1 audio (break
squelch if necessary).
4. Connect a stereo music source to MUSIC 2. (NA to Dual ADF). Press the CREW button (9) to set the
ICS to the crew mode. Verify that stereo audio is heard in the passenger headsets only.
Be sure to check all aircraft control movements before flight is attempted to
insure that the wiring harness does not touch any moving part. Verify proper
operation of the marker beacon during a flight test under VFR conditions.
This completes the in-aircraft post installation checkout. Perform a flight test after installing the unit to ensure
satisfactory performance of the audio and marker beacon receiver functions. Verify proper operation of the
marker lamps and marker audio, including the marker audio mute function. Check proper operation of the
sensitivity selection [using the SENS button (4)] by flying towards the outer marker position initially using HI
sensitivity. When the COM audio is just barely audible in the headset, switching to LO sensitivity should reduce
or eliminate the audio.