例1 伴音正常,屏幕光栅为一片白色,且有回扫线。分析检修:伴音正常,说明共用通道工作正常。只有白光栅而无图像,说明视频处理电路工作不良,而出现回扫线的原因有:一是加速极电压过高;二是阴极电压过低;三是场消隐脉冲未加入。由电路原理分析,如果加速极电压过高或扬消隐脉冲未加入,不会影响图像和噪点的出现。由此判断回扫线可能是阴极电压过低引起的,而阴极电压的高低主要取决于亮度电路输出电压的高低(见图1)。 Example 1 normal sound, the screen raster is a white, and the flyback line. Analysis and maintenance: normal sound, indicating that the common channel is working properly. Only the white raster without the image, indicating that the video processing circuit is not working, and the emergence of the retrace line for the following reasons: First, accelerating pole voltage is too high; Second, the cathode voltage is too low; Third, the field pedestal pulse is not added. By the circuit principle analysis, if the acceleration voltage is too high or Yang blanking pulse is not added, will not affect the appearance of images and noise. Judging from the flyback line may be caused by the cathode voltage is too low, and the cathode voltage level depends on the brightness of the circuit output voltage level (see Figure 1).