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一台长城JTC512型彩电,出现亮度低,图像只有模糊彩色轮廓的故障。由故障现象可知是无亮度信号引起的,应从亮度驱动电路查起,这部分工作原理见附图所示。经检测,亮度信号驱动管Q_(253)的e极电压为8.5V(正常值为6.8V).b极电压亦高于正常值,说明这部分电路工作异常。为了排除相关电路的影响,断开D_(082),使其与数字显示驱动电路分开,这时发现Q_(253)的e极、b极电压恢复正常,光栅渐亮,图像呈品红色。
A Great Wall JTC512-type TV, there is low brightness, the image is only fuzzy color outline of the fault. It is known from the phenomenon of failure is caused by no brightness signal should be detected from the brightness of the drive circuit, this part of the working principle shown in the drawings. After testing, the luminance signal drives the tube e (253) the e pole voltage is 8.5V (the normal value is 6.8V) .B pole voltage is also higher than the normal value, this part of circuit work is abnormal. In order to eliminate the influence of the related circuit, disconnect D_ (082) and make it separate from the digital display driver circuit. At this time, it is found that the e pole of Q_ (253), the voltage of the b pole is restored to normal, the grating is faded and the picture is magenta.