| 摘要 |
PURPOSE:To attain protection of a CRT with improved accuracy by providing a means to detect abnormality of a deflection signal and a means not to output a video signal to the CRT when the deflection signal disappears. CONSTITUTION:The deflection signals for X-axis and Y-axis from input terminals 4 and 5 are supplied to deflection coils 2 and 3 respectively, and deflect the beams in the CRT 1. Said signals also are outputted respectively to a buffer 8 for deflection signal detection of X-axis-side 8 and that of Y-axis- side 9, and are current-amplified. Then, an analogue arithmetic circuit 20 executes the vector synthesis of said deflection signal of X, Y-axes in order to calculate their absolute values. The result of calculation is A/D-converted by an A/D converter 21 utilizing a sample timing supplied by a timing generat ing circuit 22, and the resulting digital data is outputted to a comparison circuit 23. The circuit 23 temporarily stores the data, then compares it with the A/D- converted digital data using the next sample timing. If no differential results in the comparison, abnormality of the deflection signal is decided, and a video- signal-input prohibiting signal is outputted to a video simplifying circuit 7.
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