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故障现象 开机后有一种“叽叽”叫声,且声音越来越大,逐步产生图像左右扭曲,直至无图、无声、无光栅,亦即“三无”。 分析与检修 第一,检查电源电压。在主电路板上测量Q801的④脚,+112V主电源输出端的电压只有15V左右,而Q801的①脚电压为300V,说明开关电源的直流输入电压正常,故障发生在电源及后部电路中。第二,判断故障大致范围。经分析,该机开关电源使用的是STR5412厚膜电路,属自激式开关电源,故可以断开负载,实际操作时断开主负载即行扫描部分电路,接上60W白炽灯泡作为假负载,Q801④脚电压立即升至正常值+112V,说明开关电源正常,原先输出电压低主要由于负载过重,造成电源保护电路动作,故障应在行扫描电路部分。第三,检查行扫描电路。根据负载过重这一情况,首先测量行输出级电源对地的
Symptom After boot, there is a “Jiji” cry, and the sound is bigger and bigger, gradually distorted the image until no picture, no sound, no grating, that is, “three no.” Analysis and maintenance First, check the power supply voltage. Measure the ④ foot of Q801 on the main circuit board, the voltage of the output terminal of + 112V main power is only 15V or so, and the foot voltage of Q801 is 300V, prove the DC input voltage of the switching power supply is normal, the trouble occurs in the power and rear circuit. Second, determine the approximate scope of the fault. The analysis of the switch power supply is STR5412 thick film circuit, a self-excited switching power supply, it can disconnect the load, the actual operation of the main load that is part of the line scan circuit, connected to the 60W incandescent bulb as a dummy load, Q801 ④ The voltage of the foot immediately rose to the normal value of + 112V, indicating that the switching power supply is normal and the original output voltage was low, mainly due to the heavy load, causing the power protection circuit to operate. The fault should be in the scanning circuit part. Third, check the line scan circuit. According to the load is too heavy this situation, first measure the line output stage power to ground