| 摘要 |
PROBLEM TO BE SOLVED: To detect abnormality such as the short-circuit of a speaker line in a broadcasting device. SOLUTION: When a signal for broadcasting signal is outputted from an amplifier 3 in a state that a relay switch 4 is turned on, the broadcast signal is inputted to a speaker line 1. Thus, the output currents I and output voltage V of the amplifier 3 are respectively detected by a current sensor 11 and a voltage sensor 12. A CPU 5 calculates an impedance Zs of the speaker line 1 based on the currents I and the voltage V, and when the calculated impedance Zs is smaller than a prescribed reference value Z0, the CPU 5 recognizes that the speaker line 1 is short-circuited, and turns off the relay switch circuit 4. Thus, each circuit can be protected from excess currents running due to the short-circuit of the speaker line 1.
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