臺式(shi)機電(dian)(dian)源的工作(zuo)原理(li)(li)分析 臺式(shi)機電(dian)(dian)源故障處理(li)(li)辦(ban)法

一、臺式機電源的工作原理分析

PC電源的原理同故障

PC系統里的(de)(de)每個部(bu)件的(de)(de)電(dian)(dian)能(neng)都有同一個來源(yuan)(yuan)(yuan)(yuan)——就(jiu)(jiu)是電(dian)(dian)源(yuan)(yuan)(yuan)(yuan)。電(dian)(dian)源(yuan)(yuan)(yuan)(yuan)必須為所有的(de)(de)設備(bei)不間斷地提供穩定的(de)(de)、連續的(de)(de)電(dian)(dian)流。如果電(dian)(dian)源(yuan)(yuan)(yuan)(yuan)過(guo)量或不足(zu)，所連接的(de)(de)設備(bei)就(jiu)(jiu)有可能(neng)不能(neng)正常(chang)運(yun)作，看(kan)起來象壞了一樣。比如，內存不能(neng)刷新，造成數據(ju)丟失，會導(dao)致軟件錯誤；而CPU可能(neng)死鎖(suo)，或隨機地重(zhong)啟(qi)動；硬盤(pan)可能(neng)不轉，不能(neng)正常(chang)處理控制信號。既然這么多的(de)(de)設備(bei)都與電(dian)(dian)源(yuan)(yuan)(yuan)(yuan)息(xi)(xi)息(xi)(xi)相(xiang)(xiang)關，那把電(dian)(dian)源(yuan)(yuan)(yuan)(yuan)看(kan)作PC系統里最重(zhong)要(yao)的(de)(de)部(bu)件就(jiu)(jiu)毫不過(guo)分(fen)。從微機的(de)(de)故障(zhang)統計來看(kan)，電(dian)(dian)源(yuan)(yuan)(yuan)(yuan)部(bu)分(fen)的(de)(de)故障(zhang)占總故障(zhang)率(lv)相(xiang)(xiang)當高的(de)(de)比例(li)。

（一(yi)）電源出現(xian)問題，其(qi)表現(xian)是多方(fang)面(mian)的：

1、導(dao)致(zhi)(zhi)硬盤(pan)出(chu)現壞(huai)(huai)道或損(sun)壞(huai)(huai)。不好的(de)電(dian)(dian)源(yuan)易導(dao)致(zhi)(zhi)硬盤(pan)出(chu)現假壞(huai)(huai)道，這種故障一(yi)般可通過軟件修(xiu)復(fu)。如果用(yong)戶碰(peng)到(dao)此類情況，首先要檢查電(dian)(dian)源(yuan)。在修(xiu)復(fu)硬盤(pan)的(de)同時，還應(ying)換(huan)一(yi)個好電(dian)(dian)源(yuan)。

2、噪(zao)聲(sheng)(sheng)增大。不僅電源本身風(feng)扇的(de)噪(zao)音會增大，還可能(neng)導致聲(sheng)(sheng)卡的(de)噪(zao)聲(sheng)(sheng)增大。

3、光驅讀(du)盤(pan)性能不好(hao)。如(ru)果你(ni)新(xin)配的計算機(ji)或新(xin)買(mai)的CD-ROM讀(du)盤(pan)不好(hao)，很可能是電源有問題。

4、超(chao)頻(pin)不(bu)穩定。超(chao)頻(pin)是否穩定與電源質量的好壞關(guan)系(xi)很大。

5、顯示(shi)屏上有水(shui)波紋(wen)。有可能是電(dian)源的電(dian)磁輻射外瀉(xie)，干擾太大(da)。

6、主機(ji)經常莫名奇妙地(di)重(zhong)新啟動。有可能是電源的功率不夠(gou)等。

7、不(bu)好的電源在+5VSB上提(ti)供不(bu)了10mA的電流，造成進入睡眠狀(zhuang)態后就(jiu)長(chang)睡不(bu)醒，且(qie)+5V不(bu)穩定，會導致鼠標經常失靈(ling)。

（二）臺式機電源常見8個故障處理辦法

與微(wei)機的(de)(de)其(qi)他部件(jian)(jian)相比(bi)，電(dian)源(yuan)(yuan)部分使用(yong)的(de)(de)分立元件(jian)(jian)比(bi)重(zhong)最大(da)，這也為維修人員提供了一(yi)個比(bi)較適合自己動手修理(li)(li)的(de)(de)機會。只(zhi)要(yao)熟(shu)悉脈(mo)寬調(diao)制(zhi)型開關直流穩壓電(dian)源(yuan)(yuan)的(de)(de)基本原理(li)(li)，在沒有工作(zuo)原理(li)(li)圖的(de)(de)情(qing)況(kuang)下，根據實物基本上就能了解(jie)該電(dian)源(yuan)(yuan)的(de)(de)工作(zuo)原理(li)(li)和器件(jian)(jian)的(de)(de)工作(zuo)狀態，很容易下手進行維修。

微機電源一般容易出的故障有以下幾種：保險絲熔斷(duan)、電源無輸(shu)(shu)出或輸(shu)(shu)出電壓不穩定(ding)、電源有輸(shu)(shu)出但開機無顯示、電源負載能力差。下面分別介紹其檢修方(fang)法：

故障一：保險絲熔斷

出現(xian)此(ci)類故(gu)障時(shi)，先打開(kai)電(dian)(dian)(dian)源外(wai)(wai)殼(ke)，檢查電(dian)(dian)(dian)源上的(de)保險絲是(shi)(shi)否(fou)(fou)熔(rong)斷，據此(ci)可以初(chu)步確(que)定逆(ni)變(bian)電(dian)(dian)(dian)路(lu)是(shi)(shi)否(fou)(fou)發生了故(gu)障。若是(shi)(shi)，則(ze)不(bu)外(wai)(wai)如下三(san)種情況造成(cheng)：輸入回路(lu)中某個(ge)橋式整流二極管(guan)被(bei)擊穿(chuan)；高(gao)壓濾波(bo)電(dian)(dian)(dian)解(jie)(jie)電(dian)(dian)(dian)容被(bei)擊穿(chuan)；逆(ni)變(bian)功(gong)率(lv)開(kai)關(guan)管(guan)損壞。其(qi)主(zhu)要(yao)原因是(shi)(shi)因為直(zhi)流濾波(bo)及(ji)變(bian)換(huan)振蕩(dang)電(dian)(dian)(dian)路(lu)長時(shi)間工作在高(gao)壓(＋300V)、大電(dian)(dian)(dian)流狀態，特別是(shi)(shi)由于交(jiao)流電(dian)(dian)(dian)壓變(bian)化較大、輸出負載較重時(shi)，易出現(xian)保險絲熔(rong)斷的(de)故(gu)障。直(zhi)流濾波(bo)電(dian)(dian)(dian)路(lu)由四只整流二極管(guan)、兩(liang)只100KΩ左右限流電(dian)(dian)(dian)阻和兩(liang)只330μF左右的(de)電(dian)(dian)(dian)解(jie)(jie)電(dian)(dian)(dian)容組(zu)成(cheng)；變(bian)換(huan)振蕩(dang)電(dian)(dian)(dian)路(lu)則(ze)主(zhu)要(yao)由裝在同(tong)一散熱片上的(de)兩(liang)只型(xing)號(hao)相同(tong)的(de)大功(gong)率(lv)開(kai)關(guan)管(guan)組(zu)成(cheng)。

交流保險絲熔斷后，關(guan)機拔掉(diao)電(dian)源插頭，首先仔細觀察電(dian)路(lu)板上(shang)各(ge)高壓(ya)(ya)元件(jian)(jian)的(de)(de)外表(biao)是否(fou)有(you)被(bei)擊穿燒(shao)糊或(huo)電(dian)解液(ye)溢出的(de)(de)痕跡，若(ruo)無異(yi)常，用(yong)(yong)萬用(yong)(yong)表(biao)測(ce)量輸(shu)入端的(de)(de)值(zhi)，若(ruo)小(xiao)于200KΩ，說(shuo)明后端有(you)局部短路(lu)現象，再分(fen)別測(ce)量兩個(ge)大功率開關(guan)管e、c極(ji)(ji)間(jian)的(de)(de)阻(zu)值(zhi)，若(ruo)小(xiao)于100KΩ，則說(shuo)明開關(guan)管已損壞(huai)，測(ce)量四(si)只整流二級(ji)管正(zheng)、反向(xiang)電(dian)阻(zu)和兩個(ge)限(xian)流電(dian)阻(zu)的(de)(de)阻(zu)值(zhi)，用(yong)(yong)萬用(yong)(yong)表(biao)測(ce)量其充放(fang)電(dian)情況以判定(ding)是否(fou)正(zheng)常。另外在更(geng)換開關(guan)管時，如果無法找到(dao)同型(xing)號產(chan)品(pin)(pin)而選擇代用(yong)(yong)品(pin)(pin)時，應(ying)注意集(ji)(ji)電(dian)極(ji)(ji)-發射極(ji)(ji)反向(xiang)擊穿電(dian)壓(ya)(ya)Vceo、集(ji)(ji)電(dian)極(ji)(ji)最大允許耗散(san)功率Pcm、集(ji)(ji)電(dian)極(ji)(ji)-基極(ji)(ji)反向(xiang)擊穿電(dian)壓(ya)(ya)Vcbo的(de)(de)參(can)數應(ying)大于或(huo)等(deng)于原晶(jing)體管的(de)(de)參(can)數。再一(yi)個(ge)要(yao)注意的(de)(de)是：切不(bu)可在查出某元件(jian)(jian)損壞(huai)時，更(geng)換后便直接(jie)開機，這(zhe)樣很(hen)可能由于其它高壓(ya)(ya)元件(jian)(jian)仍(reng)有(you)故(gu)障又(you)將更(geng)換的(de)(de)元件(jian)(jian)損壞(huai)。一(yi)定(ding)要(yao)對上(shang)述電(dian)路(lu)的(de)(de)所有(you)高壓(ya)(ya)元件(jian)(jian)進行全面檢查測(ce)量后，才能徹底排除保險絲熔斷故(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(yu)排除：若(ruo)保(bao)險絲完(wan)好(hao)，在有(you)負載情況(kuang)下(xia)(xia)，各級直流電(dian)(dian)(dian)壓(ya)(ya)(ya)無(wu)輸(shu)(shu)出，其(qi)可(ke)能原因有(you)：電(dian)(dian)(dian)源(yuan)(yuan)中出現(xian)開路(lu)、短路(lu)現(xian)象，過(guo)壓(ya)(ya)(ya)、過(guo)流保(bao)護電(dian)(dian)(dian)路(lu)出現(xian)故障(zhang)，振蕩電(dian)(dian)(dian)路(lu)沒有(you)工作，電(dian)(dian)(dian)源(yuan)(yuan)負載過(guo)重，高(gao)頻整流濾電(dian)(dian)(dian)路(lu)中整流二(er)極管被擊(ji)穿，濾波(bo)電(dian)(dian)(dian)容漏電(dian)(dian)(dian)等(deng)。處理方法為：用萬(wan)用表(biao)測量(liang)(liang)系統板＋5V電(dian)(dian)(dian)源(yuan)(yuan)的對地(di)電(dian)(dian)(dian)阻，若(ruo)大于0.8Ω，則說明系統板無(wu)短路(lu)現(xian)象；將微(wei)機配置改為最小(xiao)化，即機器中只留主板、電(dian)(dian)(dian)源(yuan)(yuan)、蜂鳴器，測量(liang)(liang)各輸(shu)(shu)出端的直流電(dian)(dian)(dian)壓(ya)(ya)(ya)，若(ruo)仍無(wu)輸(shu)(shu)出，說明故障(zhang)出在微(wei)機電(dian)(dian)(dian)源(yuan)(yuan)的控(kong)制(zhi)(zhi)電(dian)(dian)(dian)路(lu)中。控(kong)制(zhi)(zhi)電(dian)(dian)(dian)路(lu)主要由集成(cheng)(cheng)(cheng)開關電(dian)(dian)(dian)源(yuan)(yuan)控(kong)制(zhi)(zhi)器(TL-496、GS3424等(deng))和過(guo)壓(ya)(ya)(ya)保(bao)護電(dian)(dian)(dian)路(lu)組成(cheng)(cheng)(cheng)，控(kong)制(zhi)(zhi)電(dian)(dian)(dian)路(lu)工作是(shi)否(fou)(fou)正常直接(jie)關系到直流電(dian)(dian)(dian)壓(ya)(ya)(ya)有(you)無(wu)輸(shu)(shu)出。過(guo)壓(ya)(ya)(ya)保(bao)護電(dian)(dian)(dian)路(lu)主要由小(xiao)功(gong)率三(san)極管或可(ke)控(kong)硅及相關元件組成(cheng)(cheng)(cheng)，可(ke)用萬(wan)用表(biao)測量(liang)(liang)該(gai)三(san)極管是(shi)否(fou)(fou)被擊(ji)穿(若(ruo)是(shi)可(ke)控(kong)硅則需(xu)焊下(xia)(xia)測量(liang)(liang))、相關電(dian)(dian)(dian)阻及電(dian)(dian)(dian)容是(shi)否(fou)(fou)損(sun)壞。最后用萬(wan)用表(biao)靜態(tai)測量(liang)(liang)高(gao)頻濾波(bo)電(dian)(dian)(dian)路(lu)中整流二(er)極管及低壓(ya)(ya)(ya)濾波(bo)電(dian)(dian)(dian)容是(shi)否(fou)(fou)損(sun)壞。

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(ci)故障的可能原因是“POWER GOOD”輸入(ru)的Reset信號(hao)延(yan)遲時間(jian)不夠，或“POWER GOOD”無輸出。

開機(ji)后，用電(dian)(dian)壓表測(ce)量“POWERGOOD”的(de)輸出端(接主機(ji)電(dian)(dian)源(yuan)插頭(tou)的(de)1腳)，如果無(wu)＋5V輸出，再檢查延時元器件，若(ruo)有＋5V輸出，則更換(huan)延時電(dian)(dian)路的(de)延時電(dian)(dian)容即可。

故障四：電源負載能力差

故障分析與排除：電(dian)(dian)源(yuan)在只向主板、軟(ruan)驅供電(dian)(dian)時能正(zheng)常(chang)工(gong)作，當接上硬盤、光驅后，屏(ping)幕(mu)變白而不能正(zheng)常(chang)工(gong)作。其可能原(yuan)因有：晶體管工(gong)作點未選擇好，高壓濾波電(dian)(dian)容漏電(dian)(dian)或損壞(huai)，穩壓二(er)極管發熱漏電(dian)(dian)，整流二(er)級管損壞(huai)等。

調換振蕩回路中(zhong)各(ge)晶體管(guan)，使其增益提高，或調大晶體管(guan)的工作點。用萬用表檢測出有問題的部件后，更換可控硅、穩(wen)壓(ya)二極(ji)管(guan)、高壓(ya)濾波電容或整(zheng)流(liu)二極(ji)管(guan)即(ji)可。

故障五：無直流輸出

可能(neng)出現故障(zhang)的(de)部位(wei)有(you)：保(bao)(bao)險(xian)(xian)管(guan)(guan)(guan)(guan)燒斷(duan)，變(bian)換器(qi)不工作，控制電(dian)(dian)(dian)路(lu)(lu)故障(zhang)。打(da)開電(dian)(dian)(dian)源(yuan)盒，發(fa)現保(bao)(bao)險(xian)(xian)管(guan)(guan)(guan)(guan)去掉。根據用(yong)戶反映保(bao)(bao)險(xian)(xian)管(guan)(guan)(guan)(guan)屢換屢燒。焊下(xia)整流(liu)(liu)二極管(guan)(guan)(guan)(guan)和(he)變(bian)換器(qi)功率開關管(guan)(guan)(guan)(guan)，用(yong)萬(wan)用(yong)表檢(jian)(jian)(jian)測(ce)都正(zheng)(zheng)常，用(yong)高(gao)阻檔檢(jian)(jian)(jian)測(ce)交(jiao)(jiao)(jiao)流(liu)(liu)輸(shu)(shu)入(ru)端(duan)無短(duan)路(lu)(lu)現象(xiang)。檢(jian)(jian)(jian)測(ce)整流(liu)(liu)濾波電(dian)(dian)(dian)容正(zheng)(zheng)常。根據保(bao)(bao)險(xian)(xian)管(guan)(guan)(guan)(guan)燒斷(duan)的(de)現象(xiang)判斷(duan)，故障(zhang)部位(wei)應在(zai)變(bian)換器(qi)初級繞組前，但沒有(you)發(fa)現短(duan)路(lu)(lu)的(de)地(di)方。只好恢復原態，換保(bao)(bao)險(xian)(xian)管(guan)(guan)(guan)(guan)加(jia)電(dian)(dian)(dian)實驗。接(jie)(jie)通交(jiao)(jiao)(jiao)流(liu)(liu)電(dian)(dian)(dian)源(yuan)，保(bao)(bao)險(xian)(xian)燒斷(duan)，立(li)即斷(duan)開交(jiao)(jiao)(jiao)流(liu)(liu)電(dian)(dian)(dian)源(yuan)檢(jian)(jian)(jian)查(cha)，保(bao)(bao)險(xian)(xian)管(guan)(guan)(guan)(guan)燒得漆黑(hei)。可見(jian)(jian)交(jiao)(jiao)(jiao)流(liu)(liu)輸(shu)(shu)入(ru)電(dian)(dian)(dian)路(lu)(lu)有(you)嚴重的(de)短(duan)路(lu)(lu)現象(xiang)，斷(duan)開整流(liu)(liu)橋的(de)交(jiao)(jiao)(jiao)流(liu)(liu)輸(shu)(shu)入(ru)。在(zai)整流(liu)(liu)橋交(jiao)(jiao)(jiao)流(liu)(liu)輸(shu)(shu)入(ru)兩(liang)(liang)端(duan)加(jia)接(jie)(jie)保(bao)(bao)險(xian)(xian)管(guan)(guan)(guan)(guan)，直(zhi)(zhi)(zhi)接(jie)(jie)接(jie)(jie)到交(jiao)(jiao)(jiao)流(liu)(liu)電(dian)(dian)(dian)源(yuan)上(shang)。接(jie)(jie)通電(dian)(dian)(dian)源(yuan)，穩壓(ya)電(dian)(dian)(dian)源(yuan)風(feng)機旋轉正(zheng)(zheng)常，測(ce)試(shi)各直(zhi)(zhi)(zhi)流(liu)(liu)輸(shu)(shu)出電(dian)(dian)(dian)壓(ya)正(zheng)(zheng)常。可見(jian)(jian)故障(zhang)部位(wei)在(zai)交(jiao)(jiao)(jiao)流(liu)(liu)濾波電(dian)(dian)(dian)路(lu)(lu)中，而用(yong)萬(wan)用(yong)表檢(jian)(jian)(jian)測(ce)已(yi)無能(neng)為力。這(zhe)時想到替代法，從另一臺電(dian)(dian)(dian)源(yuan)上(shang)拆下(xia)兩(liang)(liang)個交(jiao)(jiao)(jiao)流(liu)(liu)濾波電(dian)(dian)(dian)容替代，(因(yin)焊接(jie)(jie)簡單，所以先換電(dian)(dian)(dian)容)加(jia)電(dian)(dian)(dian)測(ce)試(shi)，直(zhi)(zhi)(zhi)流(liu)(liu)穩壓(ya)電(dian)(dian)(dian)源(yuan)工作正(zheng)(zheng)常。可見(jian)(jian)故障(zhang)部位(wei)在(zai)這(zhe)兩(liang)(liang)個電(dian)(dian)(dian)容中，用(yong)高(gao)壓(ya)絕緣儀(yi)測(ce)試(shi)，其中一只電(dian)(dian)(dian)容高(gao)壓(ya)擊穿。

故障六：開機后計算機自檢(jian)，引導(dao)正常，在屏(ping)幕提示(shi)“INSERT SYSTEM DISK IN DRIVE A AND PRESS ANY KEY”時(shi)插入DOS盤(pan)，軟驅(qu)不讀盤(pan)。

從故(gu)障現象分析，故(gu)障部位(wei)在軟(ruan)盤驅動器(qi)、軟(ruan)盤適配器(qi)或系統中。經過替代(dai)法，證明(ming)這(zhe)臺機器(qi)上的軟(ruan)盤適配器(qi)、軟(ruan)盤驅動器(qi)是(shi)好的。最后把主板拆下(xia)來驗證是(shi)好的，恢復原態后加(jia)電(dian)試驗，故(gu)障不(bu)能消除(chu)。因(yin)此懷疑(yi)到電(dian)源部分。

在(zai)機(ji)箱里拔(ba)下(xia)5寸軟(ruan)驅電(dian)(dian)(dian)(dian)源(yuan)插(cha)頭。開(kai)機(ji)，用(yong)萬用(yong)表(biao)檢(jian)測(ce)直(zhi)流(liu)輸(shu)出(chu)(chu)(chu)(chu)，＋5V，＋12V都正(zheng)常。斷電(dian)(dian)(dian)(dian)插(cha)好軟(ruan)驅電(dian)(dian)(dian)(dian)源(yuan)插(cha)頭，再開(kai)機(ji)故(gu)障(zhang)不(bu)(bu)變。后(hou)(hou)在(zai)全負(fu)(fu)(fu)載(zai)(zai)(zai)下(xia)測(ce)直(zhi)流(liu)輸(shu)出(chu)(chu)(chu)(chu)＋5V為(wei)＋4.1V，＋2V為(wei)＋10.4V。由于電(dian)(dian)(dian)(dian)源(yuan)輸(shu)出(chu)(chu)(chu)(chu)電(dian)(dian)(dian)(dian)壓(ya)(ya)降(jiang)低(di)影響軟(ruan)驅馬達的(de)(de)(de)正(zheng)常運行(xing)，造成(cheng)不(bu)(bu)能(neng)正(zheng)常讀盤。原因找到后(hou)(hou)，拆下(xia)電(dian)(dian)(dian)(dian)源(yuan)進行(xing)維修(xiu)，當(dang)負(fu)(fu)(fu)載(zai)(zai)(zai)較輕(qing)時(shi)，電(dian)(dian)(dian)(dian)源(yuan)輸(shu)出(chu)(chu)(chu)(chu)正(zheng)常；當(dang)負(fu)(fu)(fu)載(zai)(zai)(zai)加(jia)重，電(dian)(dian)(dian)(dian)源(yuan)輸(shu)出(chu)(chu)(chu)(chu)降(jiang)低(di)。說明穩壓(ya)(ya)電(dian)(dian)(dian)(dian)源(yuan)負(fu)(fu)(fu)載(zai)(zai)(zai)能(neng)力降(jiang)低(di)。打開(kai)電(dian)(dian)(dian)(dian)源(yuan)盒蓋，用(yong)示波器檢(jian)測(ce)TL494組件8，11端和信號放(fang)大(da)管(guan)的(de)(de)(de)波形幅度不(bu)(bu)受負(fu)(fu)(fu)載(zai)(zai)(zai)影響。檢(jian)測(ce)到變換(huan)器＋5V繞(rao)組波形時(shi)，負(fu)(fu)(fu)載(zai)(zai)(zai)對其有(you)影響，但變化幅度很小，因此懷(huai)疑＋5V整(zheng)流(liu)二極管(guan)正(zheng)向(xiang)壓(ya)(ya)降(jiang)變大(da)，造成(cheng)輸(shu)出(chu)(chu)(chu)(chu)能(neng)力降(jiang)低(di)。更換(huan)＋5V整(zheng)流(liu)管(guan)后(hou)(hou)，再次(ci)加(jia)電(dian)(dian)(dian)(dian)測(ce)試，故(gu)障(zhang)不(bu)(bu)能(neng)排(pai)除(chu)，這(zhe)時(shi)維修(xiu)陷入了困(kun)境。后(hou)(hou)來冷(leng)靜分析，影響直(zhi)流(liu)輸(shu)出(chu)(chu)(chu)(chu)的(de)(de)(de)因素還(huan)有(you)功(gong)(gong)率開(kai)關管(guan)。更換(huan)功(gong)(gong)率開(kai)關管(guan)后(hou)(hou)開(kai)機(ji)試驗，在(zai)負(fu)(fu)(fu)載(zai)(zai)(zai)發生變化時(shi)，直(zhi)流(liu)輸(shu)出(chu)(chu)(chu)(chu)正(zheng)常，故(gu)障(zhang)排(pai)除(chu)。換(huan)下(xia)的(de)(de)(de)功(gong)(gong)率管(guan)用(yong)JL-1進行(xing)測(ce)試，放(fang)大(da)倍數(shu)很小。后(hou)(hou)從用(yong)戶(hu)處了解到這(zhe)臺機(ji)已連續工作(zuo)4年多了。這(zhe)是(shi)功(gong)(gong)率管(guan)老化造成(cheng)了這(zhe)次(ci)故(gu)障(zhang)。從這(zhe)起事例(li)中得(de)出(chu)(chu)(chu)(chu)，微機(ji)發生故(gu)障(zhang)時(shi)應首先(xian)檢(jian)查(cha)直(zhi)流(liu)電(dian)(dian)(dian)(dian)源(yuan)的(de)(de)(de)輸(shu)出(chu)(chu)(chu)(chu)電(dian)(dian)(dian)(dian)壓(ya)(ya)，這(zhe)對維修(xiu)人員縮小故(gu)障(zhang)范圍，快速排(pai)除(chu)故(gu)障(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(xiang)分析(xi)，電源通電后有(you)(you)直流輸出，說(shuo)明(ming)電源基本上是能(neng)正常(chang)工(gong)作的(de)。調(diao)整(zheng)＋5V采(cai)樣電位器，電壓不能(neng)提(ti)升，說(shuo)明(ming)故障發生(sheng)在控制電路中。在電源通電后有(you)(you)＋3.5V的(de)輸出分析(xi)，可(ke)能(neng)是控制信號(hao)單(dan)邊(bian)工(gong)作造成的(de)。

根據(ju)故障(zhang)分(fen)(fen)析，在(zai)電(dian)源通(tong)電(dian)之(zhi)后(hou)用萬用表檢測TL494的(de)(de)各腳(jiao)電(dian)平，由于直流輸出(chu)不正(zheng)(zheng)常(chang)，所以1端(duan)電(dian)平比正(zheng)(zheng)常(chang)值偏低。8，11兩(liang)端(duan)電(dian)平用直流電(dian)壓檔(dang)測在(zai)2.0V左(zuo)右(you)(you) 屬(shu)于正(zheng)(zheng)常(chang)。用示波器觀察8，11兩(liang)端(duan)和信號放大管(guan)的(de)(de)輸出(chu)幅度(du)在(zai)12V左(zuo)右(you)(you)都正(zheng)(zheng)常(chang)，排除(chu)了(le)單(dan)邊工(gong)作(zuo)的(de)(de)懷(huai)疑(yi)。在(zai)故障(zhang)部位不能(neng)確定(ding)的(de)(de)情(qing)況下(xia)，用新的(de)(de)TL494電(dian)路替換(huan)后(hou)＋5V電(dian)壓能(neng)提高到＋4V多一(yi)點(dian)，仍不能(neng)達到正(zheng)(zheng)常(chang)輸出(chu)。最后(hou)決定(ding)換(huan)功率開關管(guan)，換(huan)后(hou)直流輸出(chu)達到正(zheng)(zheng)常(chang)值，故障(zhang)排除(chu)。從維修情(qing)況分(fen)(fen)析，這起(qi)故障(zhang)也是(shi)由于開關管(guan)老(lao)化所造成的(de)(de)。

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(gen)據故(gu)(gu)障(zhang)(zhang)現(xian)象分(fen)析可(ke)能是電(dian)源(yuan)開(kai)關接觸不(bu)良造(zao)成的。換(huan)電(dian)源(yuan)開(kai)關后(hou)，故(gu)(gu)障(zhang)(zhang)不(bu)能排除。不(bu)過在打(da)開(kai)電(dian)源(yuan)開(kai)關，等大約十多分(fen)鐘后(hou)，微(wei)機自動啟動，由此分(fen)析，故(gu)(gu)障(zhang)(zhang)出在電(dian)源(yuan)控制部(bu)分(fen)元件溫度(du)性能不(bu)良造(zao)成的故(gu)(gu)障(zhang)(zhang)。

把電(dian)(dian)(dian)(dian)(dian)源從機(ji)箱中(zhong)(zhong)取(qu)出(chu)，打開(kai)電(dian)(dian)(dian)(dian)(dian)源蓋(gai)，加(jia)上(shang)負載(zai)通電(dian)(dian)(dian)(dian)(dian)檢測(ce)，開(kai)機(ji)時(shi)＋5V有(you)(you)＋1.2V，＋12V有(you)(you)＋3V輸(shu)出(chu)，交流(liu)整流(liu)300V輸(shu)出(chu)正常。查功率開(kai)關(guan)管(guan)是好的，用(yong)烙鐵對功率管(guan)加(jia)溫后(hou)(hou)再(zai)啟動，故障(zhang)不(bu)能排除，由此排除了功率管(guan)溫度性能不(bu)良的嫌疑，判斷故障(zhang)部位在變(bian)換(huan)器次級繞組后(hou)(hou)面(mian)的電(dian)(dian)(dian)(dian)(dian)路部分。加(jia)電(dian)(dian)(dian)(dian)(dian)開(kai)機(ji)后(hou)(hou)用(yong)萬用(yong)表(biao)測(ce)TL494各腳(jiao)的電(dian)(dian)(dian)(dian)(dian)平時(shi)發現(xian)，輔助電(dian)(dian)(dian)(dian)(dian)源輸(shu)入(ru)端電(dian)(dian)(dian)(dian)(dian)壓(ya)只(zhi)有(you)(you)5V多一點，加(jia)電(dian)(dian)(dian)(dian)(dian)一段時(shi)間后(hou)(hou)，電(dian)(dian)(dian)(dian)(dian)壓(ya)逐步(bu)上(shang)升，在輔助電(dian)(dian)(dian)(dian)(dian)源電(dian)(dian)(dian)(dian)(dian)壓(ya)逐步(bu)上(shang)升過程(cheng)中(zhong)(zhong)，電(dian)(dian)(dian)(dian)(dian)源輸(shu)出(chu)也逐步(bu)上(shang)升到正常值(zhi)。這象電(dian)(dian)(dian)(dian)(dian)容(rong)緩(huan)慢充電(dian)(dian)(dian)(dian)(dian)過程(cheng)。因此在輔助電(dian)(dian)(dian)(dian)(dian)源電(dian)(dian)(dian)(dian)(dian)路中(zhong)(zhong)查找到電(dian)(dian)(dian)(dian)(dian)容(rong)C15，用(yong)萬用(yong)表(biao)測(ce)漏電(dian)(dian)(dian)(dian)(dian)較大。換(huan)后(hou)(hou)故障(zhang)排除。