Garmin APOLLO GX SERIES, Service Manual

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Garmin AT Rev --
© 2004 Garmin AT GX Service Manual 7-29
Intercom/Monitor
1. Connect a 100 ohm resistor and AC power meter (or voltmeter) across the headphone
output.
2. Connect a 4 ohm resistor and AC power meter (or voltmeter) across the speaker output.
3. Move TEST/MIC1 switch to TEST on the TST-10 test station.
4. Inject a 1000 µV RF signal with a 500 Hz 85% AM modulated tone into the Comm antenna
port.
5. Inject a 50 mV 2000 Hz audio tone into the MIC1 port.
6. Adjust the volume control on the Comm radio so that there are at least 12 watts (1.73 volts
across 4 ohms) on the speaker output.
7. Set the INT/OFF switch on the TST-10 to INT; the speaker should be disabled.
Speaker disabled with INT switch ON __________ OK
Headset operational with INT switch ON __________ OK
8. Move TEST/MIC1 switch to MIC1 on the TST-10.
9. Connect a test box to the headphone output line, adjust volume to a reasonable level, and
listen for the two tones. The low tone is from the radio receiver and the high tone is from the
intercom.
Intercom and receiver tones present __________ OK
Speaker Output Response
1. Inject a 1000 µV RF signal with 85% AM modulation at 1 kHz into the Comm antenna port.
2. Channel the Comm to the same frequency as the signal generator.
3. Connect a 4 ohm resistor and AC power meter (or voltmeter) across the speaker output.
4. Turn up the volume control on the Comm radio to make sure the output power can be greater
than 12 watts (6.93 Vrms volts across 4 ohms). Record this level.
5. Change the modulation frequency to 350 Hz and record the output power at the speaker.
6. Change the modulation frequency to 2.5 kHz and record the output power at the speaker.
7. The audio power at 350 Hz or 2.5 kHz should not be down greater than 6 dB with respect to
the power at 1 kHz.
Audio response: 350 Hz = ___ NMT 6 dB 1KHz = ___ 0 dB 2.5 KHz = ___ NMT 6 dB