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Model 478 (D-15) Technician Troubleshooting Guide
3
Troubleshooting Table
Problem Possible Cause Correction
No inbound audio. Power
Indicator Light (green) is
OFF.
No AC power to the unit. Check power supply
transformer or wall outlet.
Defective analog board. Check and replace analog
board.
No inbound audio:
• Power Indicator Light
(green) is ON.
• LISTEN Indicator Light
(green) is OFF.
Defective logic board or
touch pad.
Check and replace logic
board or touch pad.
No inbound audio:
• Power Indicator Light
(green) is ON.
• LISTEN Indicator Light
(green) is ON.
Defective menu speaker,
menu mic, or wiring.
Check and replace menu
speaker, menu mic, or wiring.
Defective analog board. Check and replace analog
board.
Inbound audio distorted. Defective menu speaker,
menu mic, or wiring.
Check and replace menu
speaker, menu mic, or wiring.
Defective analog board. Check and replace analog
board.
No outbound audio. Power
Indicator Light (green) is
OFF.
No AC power to the unit. Check power supply
transformer or wall outlet.
Defective analog board. Check and replace analog
board.
No outbound audio:
• Power Indicator Light
(green) is ON.
• TALK Indicator Light
(red) is OFF when TALK
SWITCH is pressed.
Defective logic board or
touch pad.
Check and replace logic
board or touch pad.
(continued)