Summary
During a call the user receives no audio at the door station, however, video works at the master station receiving the call.
Cause
A mismatch of door stations, incompatible door station with the master station.
Solution
Verify the model number of the master station. If the master station is JF-2MED and the door station is JK, the video works but there is no audio. Change door or master so that both are within the same series; JF with JF, JK with JK/JM, JP with JP, etc.