3M 478DA (D-15) - Manual (Page 8)

Technician Troubleshooting Guide Model 481BA (D-20)
Problem Possible Cause Correction
The VEHICLE Indicator
Light (yellow) is OFF and the
vehicle detection tone does
not sound. Defective call switch. Check and replace call
switch.
Defective analog or logic
board. Check and replace analog or
logic board.
Unit will not return to standby
mode when STANDBY
Switch is pressed. Defective logic board. Check and replace logic
board.
Unit will not come out of
standby mode. Defective logic board. Check and replace logic
board.
Outbound audio distorted. Defective analog board. Check and replace analog
board.
Defective internal
microphone. Replace microphone.
Defective outside speaker. Replace speaker.

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