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例1 故障现象:更换新的代用型号的行输出变压器后图、声基本正常,但有严重的“吱吱”声。检修:此开关电源采用行频脉冲同步型电路,“吱吱”声是由电源的开关变压器发出的。是由于电源工作频率偏低引起的。检查电源部分元件未见异常,是不是行频脉冲幅度偏低引起呢?试剪断反馈线圈增加一匝后,“吱吱”声消失.但试机5 min(分钟)后就把开关管V704烧毁,并连同V703也一起烧毁.说明这种做法可能不对,考虑可能是行频脉冲的相位不对,将反馈线圈剪断改变绕制方向后,“吱吱”声消失。
Example 1 Symptom: Replacement of the new generation of model output line after the output transformer, the sound of the basic normal, but a serious “creak” sound. Overhaul: This switching power supply using frequency pulse synchronous circuit, “creak” sound is issued by the power switch transformer. Is due to low frequency power supply caused. Check the power part of the components were not abnormal, is not caused by low line frequency pulse amplitude? Test cut off the feedback coil to add a turn, the “creak” disappeared.But the test machine 5 min (minutes) after the switch tube V704 burned , Together with the V703 also burned together. That this may not be right, consider the phase pulse may be wrong pulse, the feedback coil cut change the winding direction, the “creak” disappear.