看看这个3842的充电器到底哪儿有问题?

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变压器同名端如图:500) {this.resized=true; this.width=500; this.alt='这是一张缩略图，点击可放大。\n按住CTRL，滚动鼠标滚轮可自由缩放';this.style.cursor='hand'}" onclick="if(!this.resized) {return true;} else {window.open('http://u.dianyuan.com/bbs/u/43/1152787564.jpg?x-oss-process=image/watermark,g_center,image_YXJ0aWNsZS9wdWJsaWMvd2F0ZXJtYXJrLnBuZz94LW9zcy1wcm9jZXNzPWltYWdlL3Jlc2l6ZSxQXzQwCg,t_20');}" onmousewheel="return imgzoom(this);">
故障现象是有轻微嗒嗒声,7脚电压在13V左右波动,8脚只有2V左右波动,检查了启动电阻、二极管等也没发现问题,原边绕组对调了一下后没有嗒嗒声了,但是7脚电压仍然波动...