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Initially suspected AFC pulse waveform distortion lines , resulting in a horizontal position shift in the image on the screen . With an oscilloscope into the decoder board AFC pulse ( Figure 1 Y2 ¢Ü end ) waveform and amplitude were normal , check the center line adjustment potentiometer R602 and related components C601, R607, D603, R610 and found no abnormalities . A closer observation of the failure phenomenon , found fault horizontal position of the image has not changed, only the right part is "cut " out . Symptoms consistent with the analysis of the line scan period , and in the video signal path , only the CRT electron beam blanking pulse can shut down , if the line blanking pulse waveform distortion of the electron beam during the scanning process is incorrectly being closed , it will this failure phenomenon. Therefore , the goal of turning the line blanking circuit check .BYMservice manual download site
About the aircraft line blanking circuit in Figure 1 , the line output transformer ¢ß pin output flyback pulse positive sexual behavior all the way through R674 for AFC comparison signal from Y2 ¢Ü terminal into decoding circuitry. Another pass C657 coupling , R668, D609, R669, R670, D616 shaping , D615 clamp after D617, W terminal ¢Þ, R608, Y2 terminals ¢Ù into decoding block IC801 (IX0969CENl) line blanking input of 35 feet.BYMservice manual download site
Waveform shown in solid lines in Figure 2 with an oscilloscope measurements W ¢Þ retrace pulses. The role of the line blanking pulse is to reverse the process of electron beam scanning lines closed , so the forward line scan period , blanking pulse should be kept low in order to appear only at high scan retrace period. Therefore, the normal horizontal blanking pulse waveform shown in dashed lines in Fig should . It is because of the blanking pulse is elevated in the late positive bottom -level scanning process , resulting in the latter part of the electron beam line scan process is erroneously being closed , causing the image to be "cut " phenomenon.
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