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1 因保护电路误动作而引起的“自动关机”故障在下面列举五个维修实例,分析与检修因保护电路本身故障而引起的“自动关机”故障。例1 机型:松下TC—817型彩电故障现象:开机后图、声正常,一分钟后“自动关机”,出现“三无”。手动关机十分钟后再开机,电视机恢复正常,但一分钟后又重复上述故障。分析与检修:因开机一分钟后才出现自动关机故障,所以怀疑开关电源及行负载电路有软故障。监测开关电源+B1电压,刚开机时为110 V左右(图纸标示111V),一分钟后降至零。切断+B1负载(行输出电路)后,接假负载试机,故障依旧,说明行扫描电路正常。再将+B1输出端滤波电容C814换新,仍无改善。再断开可控硅D808上串联的电感线圈L804的一端后开机,+B1电压稳定在+110V左右,彩电收看正常。拆下D808(TVSKIV158)用万用表测量未见异常,
1 “Automatic Shutdown” Fault Caused by Malfunction of Protection Circuit In the following, five maintenance cases are listed to analyze and troubleshoot “Automatic Shutdown” caused by the failure of the protection circuit itself. Example 1 Model: Panasonic TC-817-type TV Fault phenomenon: boot picture, the sound is normal, after a minute “automatic shutdown”, there “three no.” Turn off the camera manually after ten minutes, and the TV set back to normal, but repeat the above one minute later. Analysis and Overhaul: A minute after the boot appeared automatic shutdown failure, it is suspected that the switching power supply and the line load circuit has a soft fault. Monitor the switching power supply + B1 voltage, about 110 V at boot time (drawing marked 111V), one minute later dropped to zero. Cut off the + B1 load (line output circuit), then leave the load test machine, the fault still shows that the line scan circuit is normal. Then + B1 output capacitor C814 renewal, still no improvement. Then disconnect the thyristor D808 series inductor L804 after the end of the boot, + B1 voltage stabilized at + 110V or so, color TV to watch normal. Remove the D808 (TVSKIV158) with a multimeter to measure no abnormalities,