How to troubleshoot no audio on a telephone channel or serial port data communication failure after installation and wiring?

When there is no audio on a telephone channel or serial port data communication failure, troubleshooting can be carried out section by section: first confirm that the local end and the opposite end devices are in a paired configuration and that the E1 line connectors and the impedance type (75 Ω or 120 Ω) are consistent; then check whether the service card slot corresponding to the faulty service is consistent with the service list; then check the service-side wiring, looking at the FXS/FXO and magneto telephone terminals on the telephone side, the E&M 2-wire or 4-wire connection on the audio side, and the wiring sequence and rate of RS232/RS422/RS485 on the data side; finally check the power supply, whether the 220 V or -48 V input is normal, whether the dual power supply is connected and whether the grounding is reliable. For routine maintenance, it is recommended to switch off the power before plugging or unplugging the service cards and the E1 connectors and to clean the connector end faces. If it still cannot be recovered, it is recommended to contact the manufacturer's technical support together with the alarms.