| 摘要 |
PURPOSE:To prevent noise generated at the time of abruptly stopping a power by detecting the presence and the absence of the prescribed number of commercial AC power supplies and muting a sound when this power supply is not supplied in a sound signal receiver. CONSTITUTION:The power supply of 50 Hz or 60 Hz from the commercial power 31 is shaped to a square wave in a waveform shaping circuit 32, supplied to a microcomputer 10 and a timer circuit 30 is operated. At a certain time, when the output of the power supply 31 is abruptly stopped, and square wave signal from the circuit 32 does not appear immediately. The computer 10 decides whether there is an interruption processing by the square wave signal of 50 Hz or 60 Hz or not for every elapse of a constant time. According to such interruption processing, the operation of the timer 30 is executed. Accordingly, when the interruption by the square wave signal is not executed within a constant time, a control signal is supplied to a sound signal processing circuit 14 and a video signal processing circuit 9 and the sound and a screen are muted.
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