| 摘要 |
PROBLEM TO BE SOLVED: To use a telephone set even when a telephone set changeover relay disconnects the telephone set from a public line due to any cause by providing a relay control section and outputting a pulse control signal to the relay so as to restore the telephone set changeover relay when detecting a trunk line voltage from an exchange station. SOLUTION: In the case that a self-hold relay 11 is switched to a contact B at which a telephone set 6 is disconnected from a public line due to a fall of the line terminal 22 during installation or due to vibration on the way of transportation, the terminal connects to the public line 3 after its installation, then a trunk line voltage detection section 15 detects a trunk line voltage from an exchange station. When the trunk line voltage is detected, a relay control section 18 outputs a pulse control signal to a contact A of the self-hold relay of a telephone set changeover section 10 to connect the telephone set 6 to the public line 3. Thus, even when a state of the relay of the telephone set changeover section 10 is changed, the moment when the trunk line voltage of the public line is detected, the relay is restored. Then it is prevented that the terminal is returned to the manufacturer through mis-judgment of a faulty terminal because the telephone set cannot be used after the installation of the terminal.
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