Quindar 45480 TONE RECEIVER is a field‑bus compatible signal conditioning module used in industrial telemetering and PLC systems to detect and decode acoustic or electrical tones transmitted by a Quindar Scanner Transmitter. Common failure modes for this class of units include loss of tone detection due to damaged input traces, degraded relay contacts (if present), or corrupted firmware stored in the internal flash memory. Initial checks should verify that the module receives proper 24 V DC power and that its I/O pins are not shorted; visually inspect the board for burn marks, cracked solder joints, or loose connectors. If the unit is powered but no tone signal is reported, test the input with a known tone generator and review any diagnostic LEDs or status registers for error codes.[oss-gpt-20b]