190-00917-01
GMA 240 Installation Manual
Rev. D
Page 3-3
3.5 Post Installation Checkout
CAUTION
Check wiring connections for errors before inserting the GMA 240 into the rack.
Incorrect wiring could cause internal component damage.
An in-aircraft checkout may be performed in the aircraft on the ramp with known good microphone,
headset, and avionics receivers.
3.5.1 Lamp Test
1. Apply power to the unit by rotating the pilot intercom knob clockwise.
2. Verify that all annunciators on the front panel are illuminated during initial power up.
3.5.2 Failsafe Operation Check
1. Turn the unit off by rotating the pilot intercom knob fully counter clockwise.
2. Check the failsafe operation by exercising the COM 1 microphone, microphone key, and
monitoring received COM 1 audio over the pilot headphone's left earpiece.
3. If installed, check that the failsafe warning is heard in the pilot headphone's left earpiece.
4. Turn the unit back on to continue testing.
3.5.3 Transceiver Operational Check
1. Perform a ramp test radio check by exercising the installed transceivers, microphone, microphone
key, and audio over the headphone.
2. Verify that communications are loud and clear and PTT operation is correct.
3.5.4 Intercom System (ICS) Check
NOTE
Stereo headsets are recommended if stereo jacks are installed. Alternatively, the
installation should employ stereo jacks with a mono/stereo switch that disconnects the
audio panel's right channel output from the jack's ring contact when in mono mode. If a
monaural headset is used in a stereo jack, the audio panel's right channel output is
shorted to ground by the mono headset's plug. This causes excess power supply current to
be drawn. While this does not damage the unit's output circuitry, prolonged periods
(especially at high volume) may cause the internal power input fuse to open. This is
because the unit is optimized for low-power operation in systems with limited power
budgets. In the case of copilot/passenger positions wired in parallel, any stereo listener
will lose right channel audio when another passenger plugs in a mono headset.
1. Set the intercom to the ALL mode [Pilot ISO LED off.]
2. Plug in headsets at each ICS position.
NOTE
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. Check Pilot and Copilot ICS positions for isolation and proper operation of volume and squelch
controls.
