Garmin GNC 420 Maintenance Manual page 65

5.7.2 Com Testing
Before starting com testing, note the following:
1. Disable the audio compressor unless otherwise specified. The compressor
can be disabled for testing purposes by manually grounding the
SQUELCH/COMPRESSOR TEST input at Pin 3 of J2.
2. The 8.33 kHz channel mode uses a channel ID that does not match the actual operating
frequency. Channel ID is used to specify test frequency. Unless otherwise specified, set
the receive channel to 127.000 MHz. Table 5-1 shows the channel ID and frequency for
the standard receiver test channels.
3. Unless otherwise specified, set the receive channel to 127.000 MHz for 25 kHz channel
mode, and 127.005 MHz for 8.33 kHz channel mode. Where no channel mode is
specified, perform the test at 127.000 MHz, 25 kHz channel mode.
25 kHz Channel
118.025 MHz
127.000 MHz
136.975 MHz
5.7.2.1 Power Input Check
Before starting com testing, verify the following com board power requirements. If excessive
current readings are noted, stop testing and replace the Com Board.
1. Receive Mode (J2-11 and 12):
Voltage _________ (+ 27.5 V)
Tolerance _________ ( 0.4 V)
Max Current _________ (15 mA)
2. Transmit Mode: +28 Volt Radios (J2-11 and 12):
Voltage _________ (+ 27.5 V)
Tolerance _________ ( 0.4 V)
Max Current_________ (3.0 A)
Page 5-14
Rev. C
Table 5-1. Channel ID and Frequency
8.33 kHz Channel
118.030 MHz
127.005 MHz
136.980 MHz
Channel
Frequency
118.025 MHz
127.000 MHz
136.975 MHz
400 SERIES MAINTENANCE MANUAL
P/N 190-00140-05