故障现象:接通电源开关,彩电有时能够启动,有时则启动不了。不能启动时,电源指示灯一亮即灭,整机处于“三无”状态,同时机内发出尖细的“吱吱”声。分析与检修:根据故障现象判断,该机电源部分基本正常,只是由于保护电路动作而迫使电源停振。因此,应重点检查保护电路。分析电原理图可知:日立CPT—2177SF/DU型彩电保护电路是以可控硅Q902 Symptoms: Turn on the power switch, color TV sometimes start, sometimes can not start. Can not start, the power indicator light is off, the whole machine in the “three noes” state, while the machine issued a tactile “creak” sound. Analysis and Maintenance: According to the phenomenon of failure to determine the basic normal part of the machine power, just because of the protection circuit action and forcing the power to stop vibration. Therefore, should focus on checking the protection circuit. Analysis of electrical schematic shows: Hitachi CPT-2177SF / DU type TV protection circuit is based on silicon Q902