臺式機電源(yuan)的工作原理(li)分析 臺式機電源(yuan)故(gu)障處理(li)辦法

一、臺式機電源的工作原理分析

PC電源的原理同故障

PC系統(tong)里(li)的(de)(de)(de)每(mei)個(ge)部件的(de)(de)(de)電(dian)(dian)能(neng)(neng)(neng)(neng)都有同一個(ge)來源——就是(shi)電(dian)(dian)源。電(dian)(dian)源必須為所有的(de)(de)(de)設備不(bu)(bu)(bu)間斷地(di)提(ti)供(gong)穩定的(de)(de)(de)、連續的(de)(de)(de)電(dian)(dian)流(liu)。如果電(dian)(dian)源過量或(huo)不(bu)(bu)(bu)足(zu)，所連接的(de)(de)(de)設備就有可(ke)能(neng)(neng)(neng)(neng)不(bu)(bu)(bu)能(neng)(neng)(neng)(neng)正常(chang)運(yun)作，看(kan)(kan)起來象壞了一樣(yang)。比如，內(nei)存不(bu)(bu)(bu)能(neng)(neng)(neng)(neng)刷新，造成(cheng)數據丟失(shi)，會導致軟件錯(cuo)誤；而CPU可(ke)能(neng)(neng)(neng)(neng)死鎖，或(huo)隨機(ji)地(di)重啟動(dong)；硬盤可(ke)能(neng)(neng)(neng)(neng)不(bu)(bu)(bu)轉，不(bu)(bu)(bu)能(neng)(neng)(neng)(neng)正常(chang)處理(li)控制(zhi)信(xin)號。既然這(zhe)么(me)多的(de)(de)(de)設備都與電(dian)(dian)源息息相(xiang)關，那把電(dian)(dian)源看(kan)(kan)作PC系統(tong)里(li)最(zui)重要的(de)(de)(de)部件就毫(hao)不(bu)(bu)(bu)過分。從微機(ji)的(de)(de)(de)故障(zhang)統(tong)計來看(kan)(kan)，電(dian)(dian)源部分的(de)(de)(de)故障(zhang)占總故障(zhang)率相(xiang)當高的(de)(de)(de)比例。

（一(yi)）電源出現問題，其表(biao)現是(shi)多(duo)方面的：

1、導致(zhi)硬盤出(chu)(chu)現壞(huai)道或損壞(huai)。不好的電(dian)源易導致(zhi)硬盤出(chu)(chu)現假壞(huai)道，這種故障一般可(ke)通過軟件(jian)修復。如(ru)果用戶碰到(dao)此類情況，首先要檢查電(dian)源。在修復硬盤的同(tong)時，還應換一個(ge)好電(dian)源。

2、噪(zao)(zao)(zao)聲增(zeng)大。不僅電源本身風扇的(de)噪(zao)(zao)(zao)音會增(zeng)大，還可能(neng)導致(zhi)聲卡的(de)噪(zao)(zao)(zao)聲增(zeng)大。

3、光驅(qu)讀(du)盤(pan)(pan)性能(neng)不好。如(ru)果你(ni)新配的(de)計算機或新買(mai)的(de)CD-ROM讀(du)盤(pan)(pan)不好，很可能(neng)是電源有問題。

4、超頻不穩(wen)定(ding)。超頻是否穩(wen)定(ding)與電源質(zhi)量的好壞(huai)關系很大。

5、顯示屏上有(you)水波紋。有(you)可(ke)能是電(dian)源的電(dian)磁輻射外瀉，干擾(rao)太大(da)。

6、主(zhu)機(ji)經常莫名(ming)奇妙地重新啟動。有(you)可能是電源(yuan)的功率(lv)不夠(gou)等(deng)。

7、不(bu)(bu)好的(de)電(dian)源(yuan)在+5VSB上提供不(bu)(bu)了10mA的(de)電(dian)流，造成進(jin)入睡(shui)眠狀態后就長睡(shui)不(bu)(bu)醒，且+5V不(bu)(bu)穩定，會導致鼠標(biao)經(jing)常失靈。

（二）臺式機電源常見8個故障處理辦法

與微(wei)機(ji)的其他部(bu)件(jian)相比(bi)(bi)，電(dian)源部(bu)分(fen)使用的分(fen)立元(yuan)件(jian)比(bi)(bi)重最大(da)，這也為維修人員提供了一個(ge)比(bi)(bi)較適合自己(ji)動(dong)手(shou)修理(li)(li)(li)的機(ji)會。只(zhi)要(yao)熟悉脈寬調制型開(kai)關直流穩(wen)壓電(dian)源的基本(ben)原理(li)(li)(li)，在(zai)沒有工作(zuo)原理(li)(li)(li)圖的情況下，根(gen)據實物基本(ben)上就能了解該電(dian)源的工作(zuo)原理(li)(li)(li)和(he)器件(jian)的工作(zuo)狀態，很(hen)容易(yi)下手(shou)進行維修。

微機電源(yuan)(yuan)一般容(rong)易出(chu)(chu)(chu)的故障(zhang)有(you)以下幾種：保險(xian)絲熔斷、電源(yuan)(yuan)無輸(shu)出(chu)(chu)(chu)或輸(shu)出(chu)(chu)(chu)電壓不(bu)穩定、電源(yuan)(yuan)有(you)輸(shu)出(chu)(chu)(chu)但開機無顯示、電源(yuan)(yuan)負載能(neng)力差。下面分別介紹其檢修方(fang)法：

故障一：保險絲熔斷

出現此(ci)類故(gu)障(zhang)時(shi)，先打開電(dian)(dian)源(yuan)外殼，檢查(cha)電(dian)(dian)源(yuan)上的(de)保險(xian)絲是否熔斷，據(ju)此(ci)可(ke)以(yi)初步確(que)定逆變(bian)電(dian)(dian)路是否發生了故(gu)障(zhang)。若(ruo)是，則(ze)不外如下三種情況造成(cheng)(cheng)：輸(shu)入(ru)回路中某個橋式整流二(er)極管(guan)被(bei)擊穿；高壓(ya)濾波電(dian)(dian)解電(dian)(dian)容被(bei)擊穿；逆變(bian)功(gong)率開關管(guan)損壞(huai)。其主(zhu)要原因是因為直(zhi)流濾波及變(bian)換(huan)振蕩電(dian)(dian)路長時(shi)間工作在(zai)高壓(ya)(＋300V)、大(da)電(dian)(dian)流狀態，特別是由于交流電(dian)(dian)壓(ya)變(bian)化較(jiao)大(da)、輸(shu)出負載較(jiao)重時(shi)，易出現保險(xian)絲熔斷的(de)故(gu)障(zhang)。直(zhi)流濾波電(dian)(dian)路由四只整流二(er)極管(guan)、兩只100KΩ左(zuo)(zuo)右限(xian)流電(dian)(dian)阻和兩只330μF左(zuo)(zuo)右的(de)電(dian)(dian)解電(dian)(dian)容組成(cheng)(cheng)；變(bian)換(huan)振蕩電(dian)(dian)路則(ze)主(zhu)要由裝在(zai)同一散熱片(pian)上的(de)兩只型號相同的(de)大(da)功(gong)率開關管(guan)組成(cheng)(cheng)。

交流(liu)保(bao)險絲(si)熔(rong)斷(duan)后，關(guan)(guan)機(ji)拔掉電(dian)(dian)(dian)(dian)(dian)源插頭，首(shou)先仔細觀察(cha)電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)板上各高(gao)(gao)壓元件(jian)的(de)(de)外表(biao)是(shi)(shi)否有被擊穿(chuan)燒糊或電(dian)(dian)(dian)(dian)(dian)解液溢出的(de)(de)痕(hen)跡，若無異常，用萬用表(biao)測量輸入端的(de)(de)值(zhi)，若小于(yu)200KΩ，說明后端有局部短路(lu)(lu)現象，再(zai)分別(bie)測量兩個大功(gong)率開(kai)關(guan)(guan)管(guan)(guan)e、c極(ji)(ji)間(jian)的(de)(de)阻值(zhi)，若小于(yu)100KΩ，則說明開(kai)關(guan)(guan)管(guan)(guan)已損(sun)壞(huai)，測量四只整流(liu)二級管(guan)(guan)正、反向電(dian)(dian)(dian)(dian)(dian)阻和(he)兩個限流(liu)電(dian)(dian)(dian)(dian)(dian)阻的(de)(de)阻值(zhi)，用萬用表(biao)測量其(qi)充放電(dian)(dian)(dian)(dian)(dian)情(qing)況以判(pan)定(ding)是(shi)(shi)否正常。另外在更換(huan)開(kai)關(guan)(guan)管(guan)(guan)時，如果無法找到同型(xing)號產品而選(xuan)擇代(dai)用品時，應注意集(ji)電(dian)(dian)(dian)(dian)(dian)極(ji)(ji)-發(fa)射極(ji)(ji)反向擊穿(chuan)電(dian)(dian)(dian)(dian)(dian)壓Vceo、集(ji)電(dian)(dian)(dian)(dian)(dian)極(ji)(ji)最(zui)大允(yun)許(xu)耗散(san)功(gong)率Pcm、集(ji)電(dian)(dian)(dian)(dian)(dian)極(ji)(ji)-基極(ji)(ji)反向擊穿(chuan)電(dian)(dian)(dian)(dian)(dian)壓Vcbo的(de)(de)參數應大于(yu)或等于(yu)原晶體管(guan)(guan)的(de)(de)參數。再(zai)一(yi)個要注意的(de)(de)是(shi)(shi)：切不可(ke)(ke)在查(cha)出某元件(jian)損(sun)壞(huai)時，更換(huan)后便直接開(kai)機(ji)，這樣很可(ke)(ke)能(neng)由于(yu)其(qi)它高(gao)(gao)壓元件(jian)仍(reng)有故(gu)障又將更換(huan)的(de)(de)元件(jian)損(sun)壞(huai)。一(yi)定(ding)要對上述(shu)電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)的(de)(de)所有高(gao)(gao)壓元件(jian)進行全面(mian)檢查(cha)測量后，才能(neng)徹底排除保(bao)險絲(si)熔(rong)斷(duan)故(gu)障。

故障二：無直流電壓輸出或電壓輸出不穩定

故障(zhang)分析與排除：若保(bao)險絲完好(hao)，在有(you)(you)負載情況下，各(ge)級直流(liu)電(dian)(dian)(dian)壓(ya)(ya)無輸出，其(qi)可(ke)(ke)能(neng)原因有(you)(you)：電(dian)(dian)(dian)源中(zhong)(zhong)出現(xian)開路(lu)、短路(lu)現(xian)象，過壓(ya)(ya)、過流(liu)保(bao)護(hu)電(dian)(dian)(dian)路(lu)出現(xian)故障(zhang)，振蕩電(dian)(dian)(dian)路(lu)沒有(you)(you)工(gong)作(zuo)，電(dian)(dian)(dian)源負載過重，高頻(pin)整(zheng)流(liu)濾(lv)電(dian)(dian)(dian)路(lu)中(zhong)(zhong)整(zheng)流(liu)二極(ji)管被擊穿，濾(lv)波(bo)電(dian)(dian)(dian)容漏電(dian)(dian)(dian)等(deng)。處(chu)理方法為：用(yong)(yong)萬(wan)用(yong)(yong)表(biao)(biao)測(ce)量(liang)系(xi)統(tong)板＋5V電(dian)(dian)(dian)源的(de)對地電(dian)(dian)(dian)阻，若大(da)于0.8Ω，則說明系(xi)統(tong)板無短路(lu)現(xian)象；將微機配(pei)置(zhi)改(gai)為最(zui)小(xiao)化，即機器(qi)中(zhong)(zhong)只留(liu)主(zhu)(zhu)板、電(dian)(dian)(dian)源、蜂鳴器(qi)，測(ce)量(liang)各(ge)輸出端的(de)直流(liu)電(dian)(dian)(dian)壓(ya)(ya)，若仍無輸出，說明故障(zhang)出在微機電(dian)(dian)(dian)源的(de)控(kong)(kong)制(zhi)電(dian)(dian)(dian)路(lu)中(zhong)(zhong)。控(kong)(kong)制(zhi)電(dian)(dian)(dian)路(lu)主(zhu)(zhu)要(yao)由集成開關(guan)電(dian)(dian)(dian)源控(kong)(kong)制(zhi)器(qi)(TL-496、GS3424等(deng))和過壓(ya)(ya)保(bao)護(hu)電(dian)(dian)(dian)路(lu)組成，控(kong)(kong)制(zhi)電(dian)(dian)(dian)路(lu)工(gong)作(zuo)是(shi)否(fou)(fou)正常直接關(guan)系(xi)到直流(liu)電(dian)(dian)(dian)壓(ya)(ya)有(you)(you)無輸出。過壓(ya)(ya)保(bao)護(hu)電(dian)(dian)(dian)路(lu)主(zhu)(zhu)要(yao)由小(xiao)功(gong)率三(san)(san)極(ji)管或可(ke)(ke)控(kong)(kong)硅(gui)及相(xiang)關(guan)元件組成，可(ke)(ke)用(yong)(yong)萬(wan)用(yong)(yong)表(biao)(biao)測(ce)量(liang)該三(san)(san)極(ji)管是(shi)否(fou)(fou)被擊穿(若是(shi)可(ke)(ke)控(kong)(kong)硅(gui)則需焊下測(ce)量(liang))、相(xiang)關(guan)電(dian)(dian)(dian)阻及電(dian)(dian)(dian)容是(shi)否(fou)(fou)損壞(huai)。最(zui)后(hou)用(yong)(yong)萬(wan)用(yong)(yong)表(biao)(biao)靜態測(ce)量(liang)高頻(pin)濾(lv)波(bo)電(dian)(dian)(dian)路(lu)中(zhong)(zhong)整(zheng)流(liu)二極(ji)管及低壓(ya)(ya)濾(lv)波(bo)電(dian)(dian)(dian)容是(shi)否(fou)(fou)損壞(huai)。

故障三：電源有輸出，但開機無顯示

故障分(fen)析與排除：出現此故障的(de)可能(neng)原(yuan)因是“POWER GOOD”輸入(ru)的(de)Reset信號延遲時(shi)間不(bu)夠(gou)，或“POWER GOOD”無輸出。

開機(ji)后，用電(dian)壓表測量“POWERGOOD”的輸出(chu)(chu)端(duan)(接主機(ji)電(dian)源插頭的1腳)，如果無＋5V輸出(chu)(chu)，再(zai)檢查延(yan)時(shi)元器件，若有＋5V輸出(chu)(chu)，則更(geng)換延(yan)時(shi)電(dian)路的延(yan)時(shi)電(dian)容(rong)即(ji)可。

故障四：電源負載能力差

故(gu)障分析與排除：電源(yuan)在只向(xiang)主(zhu)板、軟(ruan)驅供電時能(neng)(neng)正(zheng)常工作，當接(jie)上硬盤、光驅后，屏幕變白(bai)而(er)不能(neng)(neng)正(zheng)常工作。其可(ke)能(neng)(neng)原因(yin)有：晶體管工作點未選擇好(hao)，高壓濾波電容(rong)漏電或損壞，穩壓二(er)極(ji)管發熱漏電，整流二(er)級管損壞等。

調(diao)換振蕩回路中各晶體管(guan)(guan)，使(shi)其增益提高(gao)，或(huo)調(diao)大晶體管(guan)(guan)的(de)工作(zuo)點。用萬用表檢(jian)測出有(you)問題(ti)的(de)部件后，更換可(ke)(ke)控硅、穩壓(ya)二(er)極管(guan)(guan)、高(gao)壓(ya)濾(lv)波電(dian)容或(huo)整流二(er)極管(guan)(guan)即可(ke)(ke)。

故障五：無直流輸出

可(ke)(ke)能出現故(gu)(gu)障的(de)(de)部(bu)(bu)(bu)位(wei)有：保(bao)險(xian)管(guan)燒(shao)斷，變(bian)換(huan)器不工作，控制(zhi)電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)故(gu)(gu)障。打(da)開(kai)(kai)(kai)電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)盒(he)，發現保(bao)險(xian)管(guan)去掉。根據用(yong)戶反映(ying)保(bao)險(xian)管(guan)屢換(huan)屢燒(shao)。焊下整(zheng)(zheng)流(liu)(liu)二極(ji)管(guan)和變(bian)換(huan)器功率開(kai)(kai)(kai)關(guan)管(guan)，用(yong)萬用(yong)表檢(jian)測都正(zheng)(zheng)常，用(yong)高阻檔檢(jian)測交(jiao)流(liu)(liu)輸入(ru)端無(wu)短路(lu)(lu)現象。檢(jian)測整(zheng)(zheng)流(liu)(liu)濾波(bo)電(dian)(dian)(dian)(dian)(dian)(dian)容正(zheng)(zheng)常。根據保(bao)險(xian)管(guan)燒(shao)斷的(de)(de)現象判(pan)斷，故(gu)(gu)障部(bu)(bu)(bu)位(wei)應在(zai)變(bian)換(huan)器初級繞組前，但(dan)沒(mei)有發現短路(lu)(lu)的(de)(de)地方。只好恢復原態，換(huan)保(bao)險(xian)管(guan)加電(dian)(dian)(dian)(dian)(dian)(dian)實驗。接通交(jiao)流(liu)(liu)電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)，保(bao)險(xian)燒(shao)斷，立即斷開(kai)(kai)(kai)交(jiao)流(liu)(liu)電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)檢(jian)查，保(bao)險(xian)管(guan)燒(shao)得漆(qi)黑。可(ke)(ke)見交(jiao)流(liu)(liu)輸入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)有嚴重的(de)(de)短路(lu)(lu)現象，斷開(kai)(kai)(kai)整(zheng)(zheng)流(liu)(liu)橋的(de)(de)交(jiao)流(liu)(liu)輸入(ru)。在(zai)整(zheng)(zheng)流(liu)(liu)橋交(jiao)流(liu)(liu)輸入(ru)兩端加接保(bao)險(xian)管(guan)，直接接到交(jiao)流(liu)(liu)電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)上。接通電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)，穩壓電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)風機旋轉正(zheng)(zheng)常，測試(shi)各直流(liu)(liu)輸出電(dian)(dian)(dian)(dian)(dian)(dian)壓正(zheng)(zheng)常。可(ke)(ke)見故(gu)(gu)障部(bu)(bu)(bu)位(wei)在(zai)交(jiao)流(liu)(liu)濾波(bo)電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)中(zhong)，而用(yong)萬用(yong)表檢(jian)測已無(wu)能為力。這時想到替代(dai)法，從另一臺電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)上拆下兩個交(jiao)流(liu)(liu)濾波(bo)電(dian)(dian)(dian)(dian)(dian)(dian)容替代(dai)，(因焊接簡單，所以先換(huan)電(dian)(dian)(dian)(dian)(dian)(dian)容)加電(dian)(dian)(dian)(dian)(dian)(dian)測試(shi)，直流(liu)(liu)穩壓電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)工作正(zheng)(zheng)常。可(ke)(ke)見故(gu)(gu)障部(bu)(bu)(bu)位(wei)在(zai)這兩個電(dian)(dian)(dian)(dian)(dian)(dian)容中(zhong)，用(yong)高壓絕緣儀測試(shi)，其中(zhong)一只電(dian)(dian)(dian)(dian)(dian)(dian)容高壓擊穿(chuan)。

故障(zhang)六：開(kai)機后計(ji)算機自檢(jian)，引導正常，在屏幕(mu)提示“INSERT SYSTEM DISK IN DRIVE A AND PRESS ANY KEY”時(shi)插入DOS盤(pan)，軟驅不讀(du)盤(pan)。

從故障現象分析，故障部位在軟(ruan)(ruan)盤(pan)(pan)驅(qu)動器(qi)(qi)、軟(ruan)(ruan)盤(pan)(pan)適配器(qi)(qi)或系統中(zhong)。經過(guo)替代法，證(zheng)明這臺(tai)機器(qi)(qi)上的(de)軟(ruan)(ruan)盤(pan)(pan)適配器(qi)(qi)、軟(ruan)(ruan)盤(pan)(pan)驅(qu)動器(qi)(qi)是(shi)好的(de)。最后(hou)把主板拆下來驗(yan)證(zheng)是(shi)好的(de)，恢(hui)復(fu)原態(tai)后(hou)加電試(shi)驗(yan)，故障不(bu)能消除。因(yin)此懷疑到電源部分。

在機(ji)(ji)(ji)(ji)箱里拔下(xia)5寸軟驅電(dian)(dian)(dian)(dian)源(yuan)插頭。開(kai)(kai)(kai)機(ji)(ji)(ji)(ji)，用(yong)(yong)萬(wan)用(yong)(yong)表檢(jian)(jian)測(ce)(ce)(ce)直流(liu)(liu)(liu)輸(shu)(shu)出(chu)，＋5V，＋12V都(dou)正(zheng)常(chang)。斷電(dian)(dian)(dian)(dian)插好軟驅電(dian)(dian)(dian)(dian)源(yuan)插頭，再開(kai)(kai)(kai)機(ji)(ji)(ji)(ji)故(gu)(gu)障(zhang)(zhang)不(bu)變(bian)。后在全(quan)負(fu)載下(xia)測(ce)(ce)(ce)直流(liu)(liu)(liu)輸(shu)(shu)出(chu)＋5V為(wei)＋4.1V，＋2V為(wei)＋10.4V。由于電(dian)(dian)(dian)(dian)源(yuan)輸(shu)(shu)出(chu)電(dian)(dian)(dian)(dian)壓降低(di)影(ying)響(xiang)(xiang)軟驅馬(ma)達的(de)正(zheng)常(chang)運行，造(zao)(zao)成不(bu)能正(zheng)常(chang)讀盤。原(yuan)因(yin)(yin)找到(dao)后，拆(chai)下(xia)電(dian)(dian)(dian)(dian)源(yuan)進行維修，當負(fu)載較輕時(shi)，電(dian)(dian)(dian)(dian)源(yuan)輸(shu)(shu)出(chu)正(zheng)常(chang)；當負(fu)載加(jia)重(zhong)，電(dian)(dian)(dian)(dian)源(yuan)輸(shu)(shu)出(chu)降低(di)。說明穩壓電(dian)(dian)(dian)(dian)源(yuan)負(fu)載能力降低(di)。打開(kai)(kai)(kai)電(dian)(dian)(dian)(dian)源(yuan)盒蓋，用(yong)(yong)示波器檢(jian)(jian)測(ce)(ce)(ce)TL494組(zu)件8，11端和(he)信號放大(da)(da)(da)管(guan)(guan)的(de)波形(xing)幅(fu)度(du)不(bu)受負(fu)載影(ying)響(xiang)(xiang)。檢(jian)(jian)測(ce)(ce)(ce)到(dao)變(bian)換(huan)(huan)器＋5V繞(rao)組(zu)波形(xing)時(shi)，負(fu)載對其有(you)影(ying)響(xiang)(xiang)，但變(bian)化幅(fu)度(du)很小，因(yin)(yin)此懷疑＋5V整(zheng)流(liu)(liu)(liu)二極管(guan)(guan)正(zheng)向壓降變(bian)大(da)(da)(da)，造(zao)(zao)成輸(shu)(shu)出(chu)能力降低(di)。更換(huan)(huan)＋5V整(zheng)流(liu)(liu)(liu)管(guan)(guan)后，再次加(jia)電(dian)(dian)(dian)(dian)測(ce)(ce)(ce)試，故(gu)(gu)障(zhang)(zhang)不(bu)能排除，這時(shi)維修陷入了(le)困境。后來冷(leng)靜分(fen)析，影(ying)響(xiang)(xiang)直流(liu)(liu)(liu)輸(shu)(shu)出(chu)的(de)因(yin)(yin)素還有(you)功率(lv)開(kai)(kai)(kai)關(guan)管(guan)(guan)。更換(huan)(huan)功率(lv)開(kai)(kai)(kai)關(guan)管(guan)(guan)后開(kai)(kai)(kai)機(ji)(ji)(ji)(ji)試驗(yan)，在負(fu)載發(fa)生(sheng)(sheng)變(bian)化時(shi)，直流(liu)(liu)(liu)輸(shu)(shu)出(chu)正(zheng)常(chang)，故(gu)(gu)障(zhang)(zhang)排除。換(huan)(huan)下(xia)的(de)功率(lv)管(guan)(guan)用(yong)(yong)JL-1進行測(ce)(ce)(ce)試，放大(da)(da)(da)倍數(shu)很小。后從用(yong)(yong)戶處了(le)解到(dao)這臺機(ji)(ji)(ji)(ji)已連續(xu)工作4年多了(le)。這是(shi)功率(lv)管(guan)(guan)老化造(zao)(zao)成了(le)這次故(gu)(gu)障(zhang)(zhang)。從這起(qi)事例中得出(chu)，微機(ji)(ji)(ji)(ji)發(fa)生(sheng)(sheng)故(gu)(gu)障(zhang)(zhang)時(shi)應首先檢(jian)(jian)查直流(liu)(liu)(liu)電(dian)(dian)(dian)(dian)源(yuan)的(de)輸(shu)(shu)出(chu)電(dian)(dian)(dian)(dian)壓，這對維修人員縮小故(gu)(gu)障(zhang)(zhang)范圍，快(kuai)速排除故(gu)(gu)障(zhang)(zhang)極為(wei)有(you)益。

故障七：PC機電源一臺，加滿負載后＋5V輸出＋3.5V，＋12V輸出＋9V多一點。調整＋5V采樣電位器，電壓不能提升。

根據故障現(xian)象分析，電(dian)(dian)源(yuan)通電(dian)(dian)后有直流輸(shu)出，說明電(dian)(dian)源(yuan)基(ji)本上是能正常工作(zuo)的(de)。調整＋5V采樣電(dian)(dian)位(wei)器，電(dian)(dian)壓(ya)不能提(ti)升，說明故障發(fa)生(sheng)在控制(zhi)電(dian)(dian)路(lu)中。在電(dian)(dian)源(yuan)通電(dian)(dian)后有＋3.5V的(de)輸(shu)出分析，可能是控制(zhi)信號單(dan)邊工作(zuo)造成的(de)。

根據故障(zhang)(zhang)(zhang)分析(xi)，在(zai)電(dian)源通電(dian)之后(hou)用(yong)(yong)萬用(yong)(yong)表(biao)檢測TL494的各腳電(dian)平(ping)，由于直(zhi)流(liu)輸出(chu)不正常(chang)(chang)，所以(yi)1端電(dian)平(ping)比正常(chang)(chang)值偏低。8，11兩端電(dian)平(ping)用(yong)(yong)直(zhi)流(liu)電(dian)壓(ya)檔測在(zai)2.0V左右 屬(shu)于正常(chang)(chang)。用(yong)(yong)示波(bo)器觀察8，11兩端和信(xin)號放(fang)大管的輸出(chu)幅(fu)度在(zai)12V左右都正常(chang)(chang)，排(pai)除了(le)單邊工作的懷(huai)疑。在(zai)故障(zhang)(zhang)(zhang)部(bu)位不能(neng)確定的情況(kuang)下(xia)，用(yong)(yong)新的TL494電(dian)路替換后(hou)＋5V電(dian)壓(ya)能(neng)提高到＋4V多一點(dian)，仍不能(neng)達到正常(chang)(chang)輸出(chu)。最后(hou)決定換功率(lv)開關管，換后(hou)直(zhi)流(liu)輸出(chu)達到正常(chang)(chang)值，故障(zhang)(zhang)(zhang)排(pai)除。從維(wei)修情況(kuang)分析(xi)，這起(qi)故障(zhang)(zhang)(zhang)也是由于開關管老化所造成的。

故障八：PC機一臺，接通電源開關，電源指示燈不亮，微機不能啟動。連續按電源開關多次，有時偶然可啟動一次，啟動后微機運行正常。關機后再啟動，又出現不能啟動的現象。

根據故障(zhang)(zhang)現象分(fen)析可能是電源開關(guan)接(jie)觸不(bu)良造成的。換電源開關(guan)后，故障(zhang)(zhang)不(bu)能排除。不(bu)過在(zai)打(da)開電源開關(guan)，等大約十多分(fen)鐘后，微機自動(dong)啟動(dong)，由此分(fen)析，故障(zhang)(zhang)出在(zai)電源控制部分(fen)元件溫度性能不(bu)良造成的故障(zhang)(zhang)。

把電(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)從機箱(xiang)中取出，打(da)開(kai)電(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)蓋，加(jia)(jia)上(shang)負載通電(dian)(dian)(dian)(dian)(dian)檢(jian)測(ce)，開(kai)機時(shi)＋5V有＋1.2V，＋12V有＋3V輸出，交(jiao)流整流300V輸出正(zheng)常。查功率(lv)開(kai)關管(guan)是好的(de)，用(yong)(yong)烙(luo)鐵(tie)對功率(lv)管(guan)加(jia)(jia)溫后再啟動，故障(zhang)不能排(pai)除，由此排(pai)除了功率(lv)管(guan)溫度性能不良的(de)嫌疑，判斷故障(zhang)部位在變(bian)換(huan)器(qi)次級繞組后面的(de)電(dian)(dian)(dian)(dian)(dian)路部分(fen)。加(jia)(jia)電(dian)(dian)(dian)(dian)(dian)開(kai)機后用(yong)(yong)萬用(yong)(yong)表測(ce)TL494各腳(jiao)的(de)電(dian)(dian)(dian)(dian)(dian)平時(shi)發現，輔(fu)助電(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)輸入端電(dian)(dian)(dian)(dian)(dian)壓(ya)只(zhi)有5V多一(yi)點，加(jia)(jia)電(dian)(dian)(dian)(dian)(dian)一(yi)段時(shi)間(jian)后，電(dian)(dian)(dian)(dian)(dian)壓(ya)逐步上(shang)升，在輔(fu)助電(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)電(dian)(dian)(dian)(dian)(dian)壓(ya)逐步上(shang)升過程中，電(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)輸出也逐步上(shang)升到正(zheng)常值。這象電(dian)(dian)(dian)(dian)(dian)容(rong)緩慢(man)充電(dian)(dian)(dian)(dian)(dian)過程。因此在輔(fu)助電(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)電(dian)(dian)(dian)(dian)(dian)路中查找到電(dian)(dian)(dian)(dian)(dian)容(rong)C15，用(yong)(yong)萬用(yong)(yong)表測(ce)漏電(dian)(dian)(dian)(dian)(dian)較大。換(huan)后故障(zhang)排(pai)除。