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例1 机型:TCL3498GH型(86cm)彩电故障现象:“三无”,二只红色指示灯不亮。分析与检修:经查发现C916(0.47μF/63V)电容爆裂,怀疑Q905(SE140N)稳压取样块击穿造成的。拆下检查果然如此。由原理图1分析:由于SE140N块失效,导致通过IC902(TLP621光电耦合器)①、②脚内部发光二极管电流不随+B(145V)电压升高而增大,反映在IC902③、④脚内部的光敏管两端阻抗不降,即IC901(STR6709)⑦脚的电压不升高,使IC901(STR6709)内部开关管输出脉冲宽度不减小,这是+B电压输出升高的主要原因。+B电压升高,瞬间高压将可能使Q903、Q904(C1815)二只三极管击穿或
Example 1 Model: TCL3498GH (86cm) Color TV Fault phenomenon: “three no”, two red light does not shine. Analysis and Maintenance: The investigation found that C916 (0.47μF / 63V) capacitor burst, suspected Q905 (SE140N) caused by the breakdown of the sample block breakdown. Remove the check really so. Analysis by principle diagram 1: Due to the failure of the SE140N block, the internal LED current through the IC902 (TLP621 optocoupler) ① and ② pins does not increase with the increase of the voltage at + B (145V), which is reflected in the IC902 ③, ④ feet inside the photosensitive The impedance at both ends of the tube does not drop, that is, the voltage of IC901 (STR6709) ⑦ pin does not rise, so that the output pulse width of the internal switch of IC901 (STR6709) does not decrease, which is the main reason for the increase of + B voltage output. + B voltage increases, an instant high voltage may make Q903, Q904 (C1815) two transistors breakdown or