臺式機電(dian)源的(de)工作原(yuan)理(li)分(fen)析(xi) 臺式機電(dian)源故(gu)障處理(li)辦(ban)法(fa)

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(li)的(de)(de)每個部件的(de)(de)電(dian)(dian)能(neng)(neng)都(dou)有同一(yi)個來源(yuan)(yuan)(yuan)——就是電(dian)(dian)源(yuan)(yuan)(yuan)。電(dian)(dian)源(yuan)(yuan)(yuan)必(bi)須為(wei)所(suo)有的(de)(de)設(she)備不(bu)間斷地提(ti)供穩定(ding)的(de)(de)、連(lian)續的(de)(de)電(dian)(dian)流。如(ru)果(guo)電(dian)(dian)源(yuan)(yuan)(yuan)過量(liang)或不(bu)足，所(suo)連(lian)接的(de)(de)設(she)備就有可(ke)能(neng)(neng)不(bu)能(neng)(neng)正(zheng)常運(yun)作，看起(qi)來象(xiang)壞了一(yi)樣。比如(ru)，內存不(bu)能(neng)(neng)刷新，造成數據(ju)丟失，會導致軟(ruan)件錯誤；而CPU可(ke)能(neng)(neng)死鎖(suo)，或隨機地重(zhong)啟(qi)動(dong)；硬盤可(ke)能(neng)(neng)不(bu)轉，不(bu)能(neng)(neng)正(zheng)常處(chu)理控制信號。既然這么多的(de)(de)設(she)備都(dou)與電(dian)(dian)源(yuan)(yuan)(yuan)息息相關，那把(ba)電(dian)(dian)源(yuan)(yuan)(yuan)看作PC系統里(li)最重(zhong)要的(de)(de)部件就毫不(bu)過分。從微機的(de)(de)故障統計(ji)來看，電(dian)(dian)源(yuan)(yuan)(yuan)部分的(de)(de)故障占總故障率相當高的(de)(de)比例。

（一(yi)）電源出現問(wen)題(ti)，其表現是多方面的：

1、導致硬盤(pan)出現壞道(dao)或損壞。不好的(de)電(dian)源(yuan)易(yi)導致硬盤(pan)出現假壞道(dao)，這種故障一般(ban)可通過軟件修復。如果用(yong)戶碰到(dao)此類情況，首(shou)先要(yao)檢(jian)查電(dian)源(yuan)。在修復硬盤(pan)的(de)同時(shi)，還應換一個好電(dian)源(yuan)。

2、噪聲增大。不僅電(dian)源(yuan)本身風扇的噪音(yin)會(hui)增大，還可能導致(zhi)聲卡的噪聲增大。

3、光驅讀盤性能不(bu)好。如(ru)果你新配的計算機或(huo)新買的CD-ROM讀盤不(bu)好，很可能是電源(yuan)有問題。

4、超頻(pin)(pin)不穩(wen)(wen)定。超頻(pin)(pin)是否穩(wen)(wen)定與電(dian)源質量的(de)好壞關系很大。

5、顯示(shi)屏上有水(shui)波紋。有可(ke)能(neng)是電源(yuan)的電磁輻射外瀉，干擾太大。

6、主機(ji)經(jing)常莫名奇妙地(di)重(zhong)新啟動(dong)。有可能是電源的功(gong)率不夠等。

7、不好的電源(yuan)在+5VSB上提(ti)供不了(le)10mA的電流，造成進入睡(shui)眠狀態后就長(chang)睡(shui)不醒，且+5V不穩定，會導致鼠標經常失靈。

（二）臺式機電源常見8個故障處理辦法

與微機的(de)其他部件(jian)(jian)相比(bi)，電源部分使用的(de)分立元(yuan)件(jian)(jian)比(bi)重最大，這也為維修(xiu)(xiu)人員提供(gong)了(le)一個比(bi)較適合自己動(dong)手修(xiu)(xiu)理(li)的(de)機會。只要熟悉脈寬(kuan)調制型開關(guan)直流穩壓電源的(de)基本(ben)原(yuan)理(li)，在(zai)沒有工(gong)作原(yuan)理(li)圖的(de)情況下(xia)，根據實物基本(ben)上就(jiu)能(neng)了(le)解該電源的(de)工(gong)作原(yuan)理(li)和器(qi)件(jian)(jian)的(de)工(gong)作狀態(tai)，很容易下(xia)手進(jin)行維修(xiu)(xiu)。

微機(ji)電源一(yi)般容易(yi)出的故(gu)障(zhang)有以下幾(ji)種：保(bao)險絲熔斷、電源無(wu)輸出或輸出電壓不穩定、電源有輸出但開機(ji)無(wu)顯示(shi)、電源負(fu)載能(neng)力差(cha)。下面分別介紹其檢(jian)修(xiu)方(fang)法(fa)：

故障一：保險絲熔斷

出(chu)現此(ci)類故障時(shi)，先打開電(dian)(dian)(dian)源外殼，檢(jian)查電(dian)(dian)(dian)源上的(de)保(bao)險絲是(shi)否熔斷，據此(ci)可以初步確(que)定逆變(bian)電(dian)(dian)(dian)路(lu)(lu)是(shi)否發生(sheng)了故障。若(ruo)是(shi)，則不外如下三種情況造成：輸(shu)入回路(lu)(lu)中某個橋式整流(liu)(liu)二極管(guan)(guan)被(bei)擊穿；高壓(ya)濾波(bo)電(dian)(dian)(dian)解電(dian)(dian)(dian)容被(bei)擊穿；逆變(bian)功(gong)率開關管(guan)(guan)損壞。其主(zhu)要原因(yin)是(shi)因(yin)為直流(liu)(liu)濾波(bo)及(ji)變(bian)換振蕩(dang)電(dian)(dian)(dian)路(lu)(lu)長時(shi)間工(gong)作在高壓(ya)(＋300V)、大(da)電(dian)(dian)(dian)流(liu)(liu)狀(zhuang)態，特別是(shi)由(you)于交(jiao)流(liu)(liu)電(dian)(dian)(dian)壓(ya)變(bian)化(hua)較(jiao)大(da)、輸(shu)出(chu)負載較(jiao)重時(shi)，易出(chu)現保(bao)險絲熔斷的(de)故障。直流(liu)(liu)濾波(bo)電(dian)(dian)(dian)路(lu)(lu)由(you)四只(zhi)(zhi)(zhi)整流(liu)(liu)二極管(guan)(guan)、兩(liang)只(zhi)(zhi)(zhi)100KΩ左右限流(liu)(liu)電(dian)(dian)(dian)阻和兩(liang)只(zhi)(zhi)(zhi)330μF左右的(de)電(dian)(dian)(dian)解電(dian)(dian)(dian)容組成；變(bian)換振蕩(dang)電(dian)(dian)(dian)路(lu)(lu)則主(zhu)要由(you)裝在同(tong)一散(san)熱片上的(de)兩(liang)只(zhi)(zhi)(zhi)型號相同(tong)的(de)大(da)功(gong)率開關管(guan)(guan)組成。

交流(liu)保險(xian)絲熔斷后，關(guan)機(ji)拔掉電(dian)(dian)源插頭，首(shou)先仔細(xi)觀察電(dian)(dian)路板上各高壓元(yuan)(yuan)(yuan)件(jian)的(de)(de)(de)外(wai)表是否(fou)有(you)被擊(ji)穿(chuan)燒糊或(huo)電(dian)(dian)解液溢出的(de)(de)(de)痕跡(ji)，若(ruo)無(wu)異常(chang)，用(yong)萬用(yong)表測量(liang)(liang)(liang)輸入(ru)端(duan)的(de)(de)(de)值(zhi)，若(ruo)小于(yu)200KΩ，說明后端(duan)有(you)局部短路現象，再分別(bie)測量(liang)(liang)(liang)兩個(ge)大功率開(kai)(kai)關(guan)管(guan)(guan)e、c極(ji)間的(de)(de)(de)阻(zu)值(zhi)，若(ruo)小于(yu)100KΩ，則說明開(kai)(kai)關(guan)管(guan)(guan)已損壞，測量(liang)(liang)(liang)四只(zhi)整流(liu)二(er)級管(guan)(guan)正、反向電(dian)(dian)阻(zu)和兩個(ge)限流(liu)電(dian)(dian)阻(zu)的(de)(de)(de)阻(zu)值(zhi)，用(yong)萬用(yong)表測量(liang)(liang)(liang)其(qi)充放電(dian)(dian)情況以判定是否(fou)正常(chang)。另外(wai)在更(geng)換(huan)開(kai)(kai)關(guan)管(guan)(guan)時(shi)，如果無(wu)法找到(dao)同型號產品而選擇代用(yong)品時(shi)，應注意(yi)集(ji)(ji)(ji)電(dian)(dian)極(ji)-發射極(ji)反向擊(ji)穿(chuan)電(dian)(dian)壓Vceo、集(ji)(ji)(ji)電(dian)(dian)極(ji)最大允許耗散(san)功率Pcm、集(ji)(ji)(ji)電(dian)(dian)極(ji)-基(ji)極(ji)反向擊(ji)穿(chuan)電(dian)(dian)壓Vcbo的(de)(de)(de)參(can)數應大于(yu)或(huo)等于(yu)原晶體管(guan)(guan)的(de)(de)(de)參(can)數。再一(yi)個(ge)要注意(yi)的(de)(de)(de)是：切(qie)不可在查出某(mou)元(yuan)(yuan)(yuan)件(jian)損壞時(shi)，更(geng)換(huan)后便直接開(kai)(kai)機(ji)，這樣很可能由于(yu)其(qi)它(ta)高壓元(yuan)(yuan)(yuan)件(jian)仍有(you)故障(zhang)又將更(geng)換(huan)的(de)(de)(de)元(yuan)(yuan)(yuan)件(jian)損壞。一(yi)定要對上述電(dian)(dian)路的(de)(de)(de)所有(you)高壓元(yuan)(yuan)(yuan)件(jian)進(jin)行全面檢查測量(liang)(liang)(liang)后，才(cai)能徹底排除保險(xian)絲熔斷故障(zhang)。

故障二：無直流電壓輸出或電壓輸出不穩定

故障分析與排除：若(ruo)保險絲完好(hao)，在(zai)有(you)(you)(you)負(fu)(fu)載(zai)情況(kuang)下，各級直流(liu)(liu)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)無(wu)輸(shu)出(chu)，其可(ke)能原因有(you)(you)(you)：電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)中(zhong)(zhong)出(chu)現(xian)開路(lu)、短路(lu)現(xian)象，過(guo)壓(ya)(ya)、過(guo)流(liu)(liu)保護(hu)(hu)電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)出(chu)現(xian)故障，振蕩電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)沒有(you)(you)(you)工作(zuo)，電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)負(fu)(fu)載(zai)過(guo)重，高頻整流(liu)(liu)濾(lv)(lv)電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)中(zhong)(zhong)整流(liu)(liu)二(er)極(ji)(ji)管(guan)(guan)被(bei)擊穿，濾(lv)(lv)波(bo)(bo)電(dian)(dian)(dian)(dian)(dian)(dian)容漏電(dian)(dian)(dian)(dian)(dian)(dian)等。處(chu)理(li)方(fang)法為：用(yong)萬(wan)用(yong)表(biao)測(ce)量系(xi)統板(ban)(ban)＋5V電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)的(de)對地電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)，若(ruo)大于0.8Ω，則說明(ming)系(xi)統板(ban)(ban)無(wu)短路(lu)現(xian)象；將微機(ji)配置改為最小化，即機(ji)器(qi)中(zhong)(zhong)只留主(zhu)板(ban)(ban)、電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)、蜂(feng)鳴器(qi)，測(ce)量各輸(shu)出(chu)端(duan)的(de)直流(liu)(liu)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)，若(ruo)仍無(wu)輸(shu)出(chu)，說明(ming)故障出(chu)在(zai)微機(ji)電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)的(de)控制電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)中(zhong)(zhong)。控制電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)主(zhu)要由(you)集成(cheng)開關電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)控制器(qi)(TL-496、GS3424等)和過(guo)壓(ya)(ya)保護(hu)(hu)電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)組成(cheng)，控制電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)工作(zuo)是(shi)否正常直接關系(xi)到(dao)直流(liu)(liu)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)有(you)(you)(you)無(wu)輸(shu)出(chu)。過(guo)壓(ya)(ya)保護(hu)(hu)電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)主(zhu)要由(you)小功率三極(ji)(ji)管(guan)(guan)或(huo)可(ke)控硅(gui)及(ji)相(xiang)關元件組成(cheng)，可(ke)用(yong)萬(wan)用(yong)表(biao)測(ce)量該三極(ji)(ji)管(guan)(guan)是(shi)否被(bei)擊穿(若(ruo)是(shi)可(ke)控硅(gui)則需(xu)焊下測(ce)量)、相(xiang)關電(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)及(ji)電(dian)(dian)(dian)(dian)(dian)(dian)容是(shi)否損壞(huai)。最后(hou)用(yong)萬(wan)用(yong)表(biao)靜(jing)態(tai)測(ce)量高頻濾(lv)(lv)波(bo)(bo)電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)中(zhong)(zhong)整流(liu)(liu)二(er)極(ji)(ji)管(guan)(guan)及(ji)低壓(ya)(ya)濾(lv)(lv)波(bo)(bo)電(dian)(dian)(dian)(dian)(dian)(dian)容是(shi)否損壞(huai)。

故障三：電源有輸出，但開機無顯示

故障分析與排除：出現此故障的可能(neng)原因是“POWER GOOD”輸(shu)(shu)入的Reset信號延遲時間不夠，或“POWER GOOD”無輸(shu)(shu)出。

開機后(hou)，用(yong)電(dian)壓表測量“POWERGOOD”的輸(shu)出(chu)(chu)端(接主機電(dian)源插頭(tou)的1腳)，如果(guo)無＋5V輸(shu)出(chu)(chu)，再檢查延(yan)(yan)時(shi)(shi)元器件，若(ruo)有＋5V輸(shu)出(chu)(chu)，則更換延(yan)(yan)時(shi)(shi)電(dian)路的延(yan)(yan)時(shi)(shi)電(dian)容即可。

故障四：電源負載能力差

故(gu)障分(fen)析與排(pai)除：電(dian)(dian)源在只向主板、軟驅供電(dian)(dian)時能正常工(gong)作，當接(jie)上硬盤、光驅后，屏幕變白而(er)不能正常工(gong)作。其(qi)可能原因有：晶體管(guan)工(gong)作點未選(xuan)擇好，高壓濾波電(dian)(dian)容漏電(dian)(dian)或損壞，穩壓二(er)極管(guan)發熱漏電(dian)(dian)，整流二(er)級(ji)管(guan)損壞等。

調(diao)(diao)換(huan)振蕩回路中(zhong)各晶(jing)體(ti)管(guan)，使其增益提高，或(huo)調(diao)(diao)大(da)晶(jing)體(ti)管(guan)的(de)工作(zuo)點(dian)。用萬用表檢測(ce)出有問(wen)題(ti)的(de)部件后(hou)，更換(huan)可(ke)控硅、穩壓二極(ji)管(guan)、高壓濾(lv)波電(dian)容或(huo)整流(liu)二極(ji)管(guan)即可(ke)。

故障五：無直流輸出

可(ke)能(neng)出(chu)現故障(zhang)(zhang)的(de)(de)部(bu)(bu)位(wei)(wei)有(you)：保(bao)險(xian)管(guan)(guan)(guan)燒(shao)斷(duan)，變(bian)換(huan)器(qi)不工作，控(kong)制(zhi)電(dian)路(lu)故障(zhang)(zhang)。打開(kai)(kai)電(dian)源盒(he)，發現保(bao)險(xian)管(guan)(guan)(guan)去掉。根據用(yong)(yong)(yong)戶反(fan)映(ying)保(bao)險(xian)管(guan)(guan)(guan)屢(lv)換(huan)屢(lv)燒(shao)。焊下整(zheng)流(liu)(liu)(liu)(liu)(liu)二極管(guan)(guan)(guan)和(he)變(bian)換(huan)器(qi)功(gong)率開(kai)(kai)關管(guan)(guan)(guan)，用(yong)(yong)(yong)萬(wan)用(yong)(yong)(yong)表檢(jian)測都正常(chang)，用(yong)(yong)(yong)高阻檔檢(jian)測交(jiao)(jiao)(jiao)(jiao)(jiao)流(liu)(liu)(liu)(liu)(liu)輸(shu)(shu)(shu)入(ru)端無短(duan)路(lu)現象。檢(jian)測整(zheng)流(liu)(liu)(liu)(liu)(liu)濾波電(dian)容(rong)(rong)正常(chang)。根據保(bao)險(xian)管(guan)(guan)(guan)燒(shao)斷(duan)的(de)(de)現象判斷(duan)，故障(zhang)(zhang)部(bu)(bu)位(wei)(wei)應在(zai)變(bian)換(huan)器(qi)初級(ji)繞組前，但沒有(you)發現短(duan)路(lu)的(de)(de)地方。只(zhi)好恢復原(yuan)態，換(huan)保(bao)險(xian)管(guan)(guan)(guan)加電(dian)實驗(yan)。接(jie)(jie)通交(jiao)(jiao)(jiao)(jiao)(jiao)流(liu)(liu)(liu)(liu)(liu)電(dian)源，保(bao)險(xian)燒(shao)斷(duan)，立即斷(duan)開(kai)(kai)交(jiao)(jiao)(jiao)(jiao)(jiao)流(liu)(liu)(liu)(liu)(liu)電(dian)源檢(jian)查(cha)，保(bao)險(xian)管(guan)(guan)(guan)燒(shao)得(de)漆(qi)黑。可(ke)見交(jiao)(jiao)(jiao)(jiao)(jiao)流(liu)(liu)(liu)(liu)(liu)輸(shu)(shu)(shu)入(ru)電(dian)路(lu)有(you)嚴(yan)重的(de)(de)短(duan)路(lu)現象，斷(duan)開(kai)(kai)整(zheng)流(liu)(liu)(liu)(liu)(liu)橋的(de)(de)交(jiao)(jiao)(jiao)(jiao)(jiao)流(liu)(liu)(liu)(liu)(liu)輸(shu)(shu)(shu)入(ru)。在(zai)整(zheng)流(liu)(liu)(liu)(liu)(liu)橋交(jiao)(jiao)(jiao)(jiao)(jiao)流(liu)(liu)(liu)(liu)(liu)輸(shu)(shu)(shu)入(ru)兩端加接(jie)(jie)保(bao)險(xian)管(guan)(guan)(guan)，直接(jie)(jie)接(jie)(jie)到(dao)交(jiao)(jiao)(jiao)(jiao)(jiao)流(liu)(liu)(liu)(liu)(liu)電(dian)源上(shang)。接(jie)(jie)通電(dian)源，穩(wen)壓電(dian)源風機旋(xuan)轉正常(chang)，測試各直流(liu)(liu)(liu)(liu)(liu)輸(shu)(shu)(shu)出(chu)電(dian)壓正常(chang)。可(ke)見故障(zhang)(zhang)部(bu)(bu)位(wei)(wei)在(zai)交(jiao)(jiao)(jiao)(jiao)(jiao)流(liu)(liu)(liu)(liu)(liu)濾波電(dian)路(lu)中，而(er)用(yong)(yong)(yong)萬(wan)用(yong)(yong)(yong)表檢(jian)測已無能(neng)為力(li)。這(zhe)時想(xiang)到(dao)替(ti)代(dai)法，從另一臺電(dian)源上(shang)拆下兩個交(jiao)(jiao)(jiao)(jiao)(jiao)流(liu)(liu)(liu)(liu)(liu)濾波電(dian)容(rong)(rong)替(ti)代(dai)，(因焊接(jie)(jie)簡單，所以先換(huan)電(dian)容(rong)(rong))加電(dian)測試，直流(liu)(liu)(liu)(liu)(liu)穩(wen)壓電(dian)源工作正常(chang)。可(ke)見故障(zhang)(zhang)部(bu)(bu)位(wei)(wei)在(zai)這(zhe)兩個電(dian)容(rong)(rong)中，用(yong)(yong)(yong)高壓絕緣儀(yi)測試，其中一只(zhi)電(dian)容(rong)(rong)高壓擊穿。

故障(zhang)六：開機后(hou)計算機自檢，引導正常(chang)，在屏幕提(ti)示“INSERT SYSTEM DISK IN DRIVE A AND PRESS ANY KEY”時插入(ru)DOS盤，軟驅不讀盤。

從(cong)故障現象(xiang)分析，故障部(bu)(bu)位在軟(ruan)盤驅動(dong)器、軟(ruan)盤適配(pei)器或系統中。經過(guo)替(ti)代(dai)法，證明這(zhe)臺機器上的(de)軟(ruan)盤適配(pei)器、軟(ruan)盤驅動(dong)器是好的(de)。最后把(ba)主板拆下(xia)來驗證是好的(de)，恢(hui)復原態后加電試(shi)驗，故障不能消除。因此懷疑到電源部(bu)(bu)分。

在(zai)機(ji)箱里拔下5寸軟(ruan)驅電(dian)(dian)(dian)源(yuan)插(cha)頭(tou)。開機(ji)，用(yong)(yong)萬用(yong)(yong)表檢測(ce)(ce)直(zhi)流輸出(chu)(chu)(chu)，＋5V，＋12V都正(zheng)常(chang)。斷電(dian)(dian)(dian)插(cha)好軟(ruan)驅電(dian)(dian)(dian)源(yuan)插(cha)頭(tou)，再開機(ji)故(gu)障(zhang)(zhang)(zhang)不變(bian)。后在(zai)全(quan)負(fu)(fu)載(zai)(zai)(zai)下測(ce)(ce)直(zhi)流輸出(chu)(chu)(chu)＋5V為(wei)＋4.1V，＋2V為(wei)＋10.4V。由于(yu)電(dian)(dian)(dian)源(yuan)輸出(chu)(chu)(chu)電(dian)(dian)(dian)壓降低(di)影響軟(ruan)驅馬達的正(zheng)常(chang)運行(xing)，造成(cheng)(cheng)不能(neng)正(zheng)常(chang)讀盤。原因(yin)(yin)找(zhao)到(dao)后，拆下電(dian)(dian)(dian)源(yuan)進行(xing)維修(xiu)，當負(fu)(fu)載(zai)(zai)(zai)較輕時(shi)，電(dian)(dian)(dian)源(yuan)輸出(chu)(chu)(chu)正(zheng)常(chang)；當負(fu)(fu)載(zai)(zai)(zai)加重，電(dian)(dian)(dian)源(yuan)輸出(chu)(chu)(chu)降低(di)。說明穩壓電(dian)(dian)(dian)源(yuan)負(fu)(fu)載(zai)(zai)(zai)能(neng)力降低(di)。打開電(dian)(dian)(dian)源(yuan)盒(he)蓋，用(yong)(yong)示波器檢測(ce)(ce)TL494組件8，11端和信號(hao)放大管(guan)(guan)的波形幅度不受負(fu)(fu)載(zai)(zai)(zai)影響。檢測(ce)(ce)到(dao)變(bian)換(huan)器＋5V繞組波形時(shi)，負(fu)(fu)載(zai)(zai)(zai)對其有影響，但變(bian)化(hua)幅度很(hen)小(xiao)，因(yin)(yin)此懷疑(yi)＋5V整流二極管(guan)(guan)正(zheng)向壓降變(bian)大，造成(cheng)(cheng)輸出(chu)(chu)(chu)能(neng)力降低(di)。更換(huan)＋5V整流管(guan)(guan)后，再次加電(dian)(dian)(dian)測(ce)(ce)試，故(gu)障(zhang)(zhang)(zhang)不能(neng)排除(chu)，這(zhe)時(shi)維修(xiu)陷入了困境。后來冷(leng)靜分析，影響直(zhi)流輸出(chu)(chu)(chu)的因(yin)(yin)素(su)還(huan)有功率(lv)開關管(guan)(guan)。更換(huan)功率(lv)開關管(guan)(guan)后開機(ji)試驗，在(zai)負(fu)(fu)載(zai)(zai)(zai)發(fa)生變(bian)化(hua)時(shi)，直(zhi)流輸出(chu)(chu)(chu)正(zheng)常(chang)，故(gu)障(zhang)(zhang)(zhang)排除(chu)。換(huan)下的功率(lv)管(guan)(guan)用(yong)(yong)JL-1進行(xing)測(ce)(ce)試，放大倍數很(hen)小(xiao)。后從(cong)用(yong)(yong)戶處了解到(dao)這(zhe)臺機(ji)已連續工作4年多了。這(zhe)是功率(lv)管(guan)(guan)老(lao)化(hua)造成(cheng)(cheng)了這(zhe)次故(gu)障(zhang)(zhang)(zhang)。從(cong)這(zhe)起(qi)事例中(zhong)得(de)出(chu)(chu)(chu)，微(wei)機(ji)發(fa)生故(gu)障(zhang)(zhang)(zhang)時(shi)應首先(xian)檢查直(zhi)流電(dian)(dian)(dian)源(yuan)的輸出(chu)(chu)(chu)電(dian)(dian)(dian)壓，這(zhe)對維修(xiu)人員縮小(xiao)故(gu)障(zhang)(zhang)(zhang)范圍，快速(su)排除(chu)故(gu)障(zhang)(zhang)(zhang)極為(wei)有益(yi)。

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(gu)障現象分析(xi)，電(dian)(dian)源(yuan)(yuan)通電(dian)(dian)后(hou)有直流輸(shu)出，說(shuo)明電(dian)(dian)源(yuan)(yuan)基(ji)本上是能(neng)正常工作的。調整＋5V采樣電(dian)(dian)位器，電(dian)(dian)壓不能(neng)提升，說(shuo)明故(gu)障發生(sheng)在控制電(dian)(dian)路中(zhong)。在電(dian)(dian)源(yuan)(yuan)通電(dian)(dian)后(hou)有＋3.5V的輸(shu)出分析(xi)，可能(neng)是控制信號單邊工作造成的。

根據故(gu)障(zhang)分(fen)析(xi)，在(zai)電源通電之后(hou)用萬用表檢測TL494的(de)(de)各腳電平，由于直(zhi)(zhi)流(liu)輸出不(bu)正(zheng)(zheng)常(chang)(chang)，所以1端(duan)電平比正(zheng)(zheng)常(chang)(chang)值(zhi)偏低(di)。8，11兩端(duan)電平用直(zhi)(zhi)流(liu)電壓檔測在(zai)2.0V左(zuo)(zuo)右 屬于正(zheng)(zheng)常(chang)(chang)。用示波器觀察8，11兩端(duan)和信號(hao)放大管(guan)的(de)(de)輸出幅度在(zai)12V左(zuo)(zuo)右都正(zheng)(zheng)常(chang)(chang)，排除了(le)單邊工作的(de)(de)懷疑。在(zai)故(gu)障(zhang)部(bu)位(wei)不(bu)能(neng)確定的(de)(de)情況下，用新的(de)(de)TL494電路替換(huan)后(hou)＋5V電壓能(neng)提(ti)高到(dao)(dao)＋4V多一點，仍不(bu)能(neng)達(da)到(dao)(dao)正(zheng)(zheng)常(chang)(chang)輸出。最(zui)后(hou)決定換(huan)功(gong)率開(kai)關管(guan)，換(huan)后(hou)直(zhi)(zhi)流(liu)輸出達(da)到(dao)(dao)正(zheng)(zheng)常(chang)(chang)值(zhi)，故(gu)障(zhang)排除。從維修情況分(fen)析(xi)，這(zhe)起故(gu)障(zhang)也是由于開(kai)關管(guan)老(lao)化所造(zao)成(cheng)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(ju)故(gu)障(zhang)(zhang)(zhang)現象分(fen)析可能是(shi)電源開(kai)關(guan)(guan)接觸不良造成的。換電源開(kai)關(guan)(guan)后，故(gu)障(zhang)(zhang)(zhang)不能排除。不過在打開(kai)電源開(kai)關(guan)(guan)，等大(da)約十多分(fen)鐘后，微機自動啟動，由(you)此分(fen)析，故(gu)障(zhang)(zhang)(zhang)出在電源控(kong)制部分(fen)元(yuan)件溫度性能不良造成的故(gu)障(zhang)(zhang)(zhang)。

把電(dian)(dian)源(yuan)(yuan)從機(ji)箱(xiang)中取出，打開(kai)(kai)(kai)電(dian)(dian)源(yuan)(yuan)蓋，加(jia)上負載通電(dian)(dian)檢測，開(kai)(kai)(kai)機(ji)時(shi)＋5V有＋1.2V，＋12V有＋3V輸出，交流整流300V輸出正常。查(cha)功(gong)率開(kai)(kai)(kai)關(guan)管(guan)是好的(de)，用(yong)烙鐵對功(gong)率管(guan)加(jia)溫(wen)(wen)后(hou)(hou)再啟動，故(gu)障(zhang)不能排除，由(you)此(ci)排除了功(gong)率管(guan)溫(wen)(wen)度性(xing)能不良的(de)嫌疑，判斷故(gu)障(zhang)部位在(zai)變換器次級繞組后(hou)(hou)面的(de)電(dian)(dian)路部分(fen)。加(jia)電(dian)(dian)開(kai)(kai)(kai)機(ji)后(hou)(hou)用(yong)萬用(yong)表(biao)測TL494各腳的(de)電(dian)(dian)平(ping)時(shi)發(fa)現，輔(fu)助(zhu)(zhu)電(dian)(dian)源(yuan)(yuan)輸入端電(dian)(dian)壓只有5V多一點，加(jia)電(dian)(dian)一段時(shi)間(jian)后(hou)(hou)，電(dian)(dian)壓逐步上升，在(zai)輔(fu)助(zhu)(zhu)電(dian)(dian)源(yuan)(yuan)電(dian)(dian)壓逐步上升過(guo)程中，電(dian)(dian)源(yuan)(yuan)輸出也逐步上升到正常值(zhi)。這(zhe)象電(dian)(dian)容緩慢充電(dian)(dian)過(guo)程。因此(ci)在(zai)輔(fu)助(zhu)(zhu)電(dian)(dian)源(yuan)(yuan)電(dian)(dian)路中查(cha)找到電(dian)(dian)容C15，用(yong)萬用(yong)表(biao)測漏電(dian)(dian)較(jiao)大。換后(hou)(hou)故(gu)障(zhang)排除。