故障现象:刚开机正常,过一段时间后,亮度过亮,调节亮度电位器不起作用。检修:检查时发现显象管工作一段时间后,栅、阴极之间随着灯丝温度的升高,阻抗变小(约1kΩ左右)。阴极电压为15V左右,调亮度电位器电压没有多大的变化。关机后再检查,发现随着显象管灯丝的冷却,栅阴极之间的阻抗逐渐恢复到无穷大。根据故障现象分析,产生故障原因是显象管栅、阴极之间 Symptoms: just boot normally, over a period of time, the brightness is too bright, adjust the brightness potentiometer does not work. Overhaul: inspection found kinescope work for a period of time, the gate, between the cathode as the filament temperature increases, the impedance becomes smaller (about 1kΩ or so). Cathode voltage of about 15V, brightness brightness potentiometer voltage is not much change. After the shutdown and then check and found that with the CRT tube cooling, the impedance between the gate and cathode gradually restored to infinity. According to the fault phenomenon analysis, the cause of the malfunction is between the CRT and the cathode