| 摘要 |
PURPOSE:To enable execution of checking of speaker circuit, by connecting a direct- current signal source to the line in a way to enable changeover with speaker amplifier. CONSTITUTION:A direct-current signal for detection of fault sent out from a direct- current signal source 7 flows in a second loop of direct-current signal source 7, 8, line 4, thransformer 3', alternating-current blocking circuit 11, signal generator 10, line 4, switching unit 8, and direct-current signal source 7. When there is a fault in the speaker circuit, the loop is not completed, and direct-current signal is not given to the signal generator 10, so that only the detection signal of the frequency alloted to the speaker 2 is not generated. A detector 6 judges to be nomral when the arriving detection signals are all frequencues allotted to each speaker 2, and, otherwise, judges that the circuit in the speaker 2 to which the frequeny is alloted is defective. |
