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例1:一台日立CTP-450D型35厘米彩色电视机,接收6频道节目时,图像有一上下移动的左右扭曲的窄带。分析与检修:图像小范围的左右扭曲,常见于AGC电路出故障,特别是峰值检波电容C_(211)开路后容易发生这类现象。因为C_(211)开路后,将无法形成峰值AGC电压,致使中放AGC失控,造成图像扭曲。但检查结果C_(211)良好,与AGC电压有关的电路也无异常。又认真观察故障现象,发现图像扭曲较严重时,行输出变压器有细小的“吱吱”声。由此怀疑开关电源有问题。因为当电源开关管充放电回路的时间常数改变后,行扫描变压器引来的行逆程正脉冲不能很好地使开
Example 1: A Hitachi CTP-450D 35 cm color TV set, when receiving a 6 channel program, has a narrow left-right twisted band that moves up and down. Analysis and Overhaul: Left and right small distortions of the image are common in the AGC circuit failure, especially after the peak detection capacitor C_ (211) open circuit prone to such phenomena. Because C_ (211) open circuit, will not be able to form a peak AGC voltage, resulting in uncontrolled release AGC, resulting in image distortion. However, the test result C_ (211) is good, and the circuit related to the AGC voltage is normal. Also carefully observe the symptoms and found that the image distortion is more serious, the line output transformer has a small “creak” sound. This suspect switching power supply problems. Because when the power switch charge and discharge circuit time constant changes, line scan transformer induced negative stroke positive pulse can not be well turned on