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故障现象:一台虹美C5456型彩电开机三无,有“吱吱”声。分析与检修:开机瞬间测+B端有电压,但很快降为零。分析为开关电源不正常或其负载有短路而引起保护电路动作。该机开关电源共有三路保护系统: (1)为115V过压保护电路,由可控硅8V52及三只串联的稳压管V851、VD853、VD854等组成。115V电压升高到128V以上时,三只稳压管击穿导通,可控硅8V52随之导通,115V输出被短路,使开关电源停振。(2)20V电源过流保护,由8V76、
Symptom: A Hong Mei C5456-type TV boot three no, a “creak” sound. Analysis and overhaul: power instantaneous measurement + B terminal voltage, but quickly dropped to zero. Analysis for the switching power supply is not normal or the load caused by short circuit protection circuit action. The switch power supply a total of three-way protection system: (1) 115V over-voltage protection circuit, the SCR 8V52 and three series regulator V851, VD853, VD854 and other components. 115V voltage rises above 128V, three voltage regulator breakdown conduction, SCR followed by conduction 8V52, 115V output is short-circuited, the switching power supply to stop vibration. (2) 20V power supply overcurrent protection, from 8V76,