The sound of an external device or microphone is not output.

Is the [MIC, OFF, AUX 1, AUX 2, AUX 3] input selector switch on the front panel set to [OFF]? When using an external device, set the [MIC, OFF, AUX 1, AUX 2, AUX 3] input selector switch to the [AUX 1], [AUX 2] or [AUX 3] position (the position corresponding to the terminals to which the device is connected). When using a microphone, set it to the [MIC] position.