| 摘要 |
PURPOSE:To view clearly onscreen characters without fail by fixing the vertical synchronizing frequency of the free run of a no-signal, etc., to a normal frequency. CONSTITUTION:When the output of a synchronous detector circuit 6 is received by a television signal, it is 'L', and a changeover switch circuit 5 connects a variable resistance 2 to a vertical oscillator circuit 1. When the operation is made in a no-signal state, the output of the synchronous detector circuit 6 comes to 'H', because a synchronizing signal is not inputted, and the changeover switch circuit 5 connects a variable resistance 4 to the vertical oscillator circuit 1. Since the value of the variable resistance 4 is preset so that the vertical synchronizing frequency at free run can be a normal frequency, 50Hz, for instance, it stays always at a vertical synchronizing frequency of 50Hz in both normal action and no-signal states, whereby the position of onscreen display will not fluctuate.
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