臺式(shi)機電(dian)源(yuan)的工作(zuo)原理分析 臺式(shi)機電(dian)源(yuan)故障處理辦法

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)里的(de)(de)每(mei)個部件(jian)(jian)的(de)(de)電能(neng)都有(you)同一(yi)個來源(yuan)(yuan)——就是電源(yuan)(yuan)。電源(yuan)(yuan)必須(xu)為(wei)所(suo)(suo)有(you)的(de)(de)設(she)(she)備(bei)不(bu)間斷(duan)地提供穩(wen)定的(de)(de)、連續的(de)(de)電流。如果(guo)電源(yuan)(yuan)過量或(huo)不(bu)足，所(suo)(suo)連接的(de)(de)設(she)(she)備(bei)就有(you)可(ke)能(neng)不(bu)能(neng)正常運作，看(kan)起來象(xiang)壞(huai)了一(yi)樣。比如，內存不(bu)能(neng)刷新(xin)，造成數據(ju)丟(diu)失，會(hui)導致軟件(jian)(jian)錯(cuo)誤；而(er)CPU可(ke)能(neng)死鎖，或(huo)隨(sui)機(ji)地重啟動；硬盤可(ke)能(neng)不(bu)轉(zhuan)，不(bu)能(neng)正常處理控制信號(hao)。既(ji)然這么多的(de)(de)設(she)(she)備(bei)都與(yu)電源(yuan)(yuan)息(xi)息(xi)相(xiang)關，那把電源(yuan)(yuan)看(kan)作PC系統(tong)里最重要的(de)(de)部件(jian)(jian)就毫不(bu)過分(fen)(fen)。從(cong)微機(ji)的(de)(de)故(gu)障(zhang)(zhang)統(tong)計來看(kan)，電源(yuan)(yuan)部分(fen)(fen)的(de)(de)故(gu)障(zhang)(zhang)占(zhan)總故(gu)障(zhang)(zhang)率相(xiang)當高的(de)(de)比例。

（一(yi)）電源出現問題，其表現是多方(fang)面的：

1、導致(zhi)硬盤出現(xian)壞(huai)道或(huo)損壞(huai)。不好(hao)的電源易(yi)導致(zhi)硬盤出現(xian)假(jia)壞(huai)道，這種故障一般(ban)可通過軟(ruan)件修復。如(ru)果(guo)用戶碰到此類(lei)情況，首先要(yao)檢(jian)查電源。在修復硬盤的同(tong)時，還應換一個(ge)好(hao)電源。

2、噪(zao)聲(sheng)(sheng)增(zeng)大。不僅電源本身風扇的(de)噪(zao)音(yin)會增(zeng)大，還可(ke)能導致聲(sheng)(sheng)卡的(de)噪(zao)聲(sheng)(sheng)增(zeng)大。

3、光驅(qu)讀盤性能(neng)不好。如果你新配的計算(suan)機或新買的CD-ROM讀盤不好，很可能(neng)是(shi)電源有問(wen)題(ti)。

4、超(chao)(chao)頻不穩(wen)定(ding)。超(chao)(chao)頻是否(fou)穩(wen)定(ding)與(yu)電源質量的好(hao)壞關系很大(da)。

5、顯示屏上有(you)水波(bo)紋。有(you)可能是電源的(de)電磁輻射外瀉，干擾太大(da)。

6、主機經常莫名奇妙地重新(xin)啟動(dong)。有(you)可(ke)能(neng)是電源的(de)功率不夠等。

7、不好的(de)電(dian)源(yuan)在(zai)+5VSB上提供不了10mA的(de)電(dian)流，造成進(jin)入睡眠狀態(tai)后就長(chang)睡不醒，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(ta)部件相比，電源(yuan)部分(fen)使(shi)用的(de)分(fen)立元(yuan)件比重(zhong)最(zui)大，這也為維修(xiu)人(ren)員提(ti)供了(le)一個比較適合自己動手修(xiu)理(li)(li)的(de)機會。只要熟(shu)悉(xi)脈(mo)寬調制(zhi)型開關直流(liu)穩壓(ya)電源(yuan)的(de)基(ji)本(ben)原理(li)(li)，在沒有工(gong)作(zuo)原理(li)(li)圖的(de)情(qing)況下(xia)，根據實物基(ji)本(ben)上就能(neng)了(le)解該電源(yuan)的(de)工(gong)作(zuo)原理(li)(li)和器件的(de)工(gong)作(zuo)狀態，很容易(yi)下(xia)手進行維修(xiu)。

微機電(dian)源(yuan)一般容易出的故障有(you)以(yi)下(xia)幾種(zhong)：保險絲熔斷、電(dian)源(yuan)無輸出或輸出電(dian)壓不穩定、電(dian)源(yuan)有(you)輸出但開機無顯(xian)示、電(dian)源(yuan)負載能力差(cha)。下(xia)面分別介紹其檢(jian)修方法：

故障一：保險絲熔斷

出(chu)現此(ci)類(lei)故障(zhang)時(shi)，先(xian)打開(kai)電(dian)(dian)(dian)(dian)源外(wai)殼，檢(jian)查電(dian)(dian)(dian)(dian)源上(shang)的(de)(de)保險絲是(shi)否(fou)熔斷，據(ju)此(ci)可以初步確定逆(ni)變(bian)電(dian)(dian)(dian)(dian)路(lu)是(shi)否(fou)發生了故障(zhang)。若是(shi)，則不外(wai)如下三種情(qing)況造成(cheng)(cheng)：輸(shu)入回(hui)路(lu)中(zhong)某個(ge)橋式整流二極管(guan)被(bei)擊穿(chuan)；高壓(ya)濾(lv)波(bo)電(dian)(dian)(dian)(dian)解電(dian)(dian)(dian)(dian)容(rong)被(bei)擊穿(chuan)；逆(ni)變(bian)功率(lv)開(kai)關管(guan)損壞(huai)。其主要原因是(shi)因為直流濾(lv)波(bo)及變(bian)換(huan)振(zhen)蕩電(dian)(dian)(dian)(dian)路(lu)長時(shi)間(jian)工作在(zai)高壓(ya)(＋300V)、大(da)電(dian)(dian)(dian)(dian)流狀態，特別是(shi)由(you)于(yu)交流電(dian)(dian)(dian)(dian)壓(ya)變(bian)化(hua)較大(da)、輸(shu)出(chu)負載較重時(shi)，易出(chu)現保險絲熔斷的(de)(de)故障(zhang)。直流濾(lv)波(bo)電(dian)(dian)(dian)(dian)路(lu)由(you)四(si)只(zhi)整流二極管(guan)、兩只(zhi)100KΩ左(zuo)右限(xian)流電(dian)(dian)(dian)(dian)阻和兩只(zhi)330μF左(zuo)右的(de)(de)電(dian)(dian)(dian)(dian)解電(dian)(dian)(dian)(dian)容(rong)組成(cheng)(cheng)；變(bian)換(huan)振(zhen)蕩電(dian)(dian)(dian)(dian)路(lu)則主要由(you)裝在(zai)同一散熱片(pian)上(shang)的(de)(de)兩只(zhi)型號相同的(de)(de)大(da)功率(lv)開(kai)關管(guan)組成(cheng)(cheng)。

交流(liu)保險(xian)絲熔斷后，關(guan)(guan)機拔掉電(dian)源插頭，首先(xian)仔細觀察電(dian)路板上各高壓(ya)元(yuan)(yuan)(yuan)件的(de)(de)外表是(shi)(shi)否有(you)被擊穿燒糊或電(dian)解液溢出(chu)的(de)(de)痕跡，若(ruo)無異常，用(yong)萬用(yong)表測(ce)量(liang)輸入端的(de)(de)值(zhi)(zhi)，若(ruo)小(xiao)于200KΩ，說明后端有(you)局部(bu)短路現象，再(zai)(zai)分別測(ce)量(liang)兩個(ge)大功(gong)率開(kai)關(guan)(guan)管e、c極(ji)(ji)間的(de)(de)阻(zu)值(zhi)(zhi)，若(ruo)小(xiao)于100KΩ，則說明開(kai)關(guan)(guan)管已損(sun)壞(huai)，測(ce)量(liang)四只整流(liu)二級管正(zheng)、反向電(dian)阻(zu)和兩個(ge)限(xian)流(liu)電(dian)阻(zu)的(de)(de)阻(zu)值(zhi)(zhi)，用(yong)萬用(yong)表測(ce)量(liang)其充放電(dian)情況以(yi)判定是(shi)(shi)否正(zheng)常。另外在更換(huan)(huan)開(kai)關(guan)(guan)管時(shi)，如果無法找到同型(xing)號產品而(er)選擇代用(yong)品時(shi)，應(ying)注意集(ji)電(dian)極(ji)(ji)-發射(she)極(ji)(ji)反向擊穿電(dian)壓(ya)Vceo、集(ji)電(dian)極(ji)(ji)最大允許耗散功(gong)率Pcm、集(ji)電(dian)極(ji)(ji)-基極(ji)(ji)反向擊穿電(dian)壓(ya)Vcbo的(de)(de)參(can)數(shu)(shu)應(ying)大于或等于原晶體管的(de)(de)參(can)數(shu)(shu)。再(zai)(zai)一個(ge)要注意的(de)(de)是(shi)(shi)：切(qie)不可(ke)在查(cha)(cha)出(chu)某元(yuan)(yuan)(yuan)件損(sun)壞(huai)時(shi)，更換(huan)(huan)后便直(zhi)接(jie)開(kai)機，這樣很可(ke)能由(you)于其它高壓(ya)元(yuan)(yuan)(yuan)件仍有(you)故(gu)障又將更換(huan)(huan)的(de)(de)元(yuan)(yuan)(yuan)件損(sun)壞(huai)。一定要對上述電(dian)路的(de)(de)所有(you)高壓(ya)元(yuan)(yuan)(yuan)件進行全面檢查(cha)(cha)測(ce)量(liang)后，才能徹底排除(chu)保險(xian)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)分析與排除：若(ruo)保險絲完好，在有負載(zai)情(qing)況下，各(ge)級直流(liu)(liu)(liu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)無輸出，其可能(neng)原因有：電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)中(zhong)(zhong)(zhong)出現(xian)開路(lu)(lu)(lu)(lu)、短路(lu)(lu)(lu)(lu)現(xian)象，過(guo)壓(ya)、過(guo)流(liu)(liu)(liu)保護電(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)(lu)出現(xian)故障(zhang)，振蕩電(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)(lu)沒有工(gong)作(zuo)，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)負載(zai)過(guo)重(zhong)，高頻(pin)整流(liu)(liu)(liu)濾電(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)(lu)中(zhong)(zhong)(zhong)整流(liu)(liu)(liu)二(er)極管(guan)被(bei)擊(ji)穿，濾波(bo)(bo)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)容漏(lou)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)等。處理(li)方(fang)法為(wei)：用(yong)(yong)萬用(yong)(yong)表測量(liang)(liang)系(xi)統板＋5V電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)的對地電(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻，若(ruo)大于0.8Ω，則(ze)說明系(xi)統板無短路(lu)(lu)(lu)(lu)現(xian)象；將微機配置改為(wei)最小化(hua)，即機器中(zhong)(zhong)(zhong)只留(liu)主(zhu)板、電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)、蜂鳴器，測量(liang)(liang)各(ge)輸出端的直流(liu)(liu)(liu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)，若(ruo)仍無輸出，說明故障(zhang)出在微機電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)的控(kong)制電(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)(lu)中(zhong)(zhong)(zhong)。控(kong)制電(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)(lu)主(zhu)要由(you)集成(cheng)(cheng)開關電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)控(kong)制器(TL-496、GS3424等)和過(guo)壓(ya)保護電(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)(lu)組成(cheng)(cheng)，控(kong)制電(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)(lu)工(gong)作(zuo)是(shi)否(fou)正常直接關系(xi)到直流(liu)(liu)(liu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)有無輸出。過(guo)壓(ya)保護電(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)(lu)主(zhu)要由(you)小功(gong)率(lv)三(san)極管(guan)或可控(kong)硅及相(xiang)關元件(jian)組成(cheng)(cheng)，可用(yong)(yong)萬用(yong)(yong)表測量(liang)(liang)該(gai)三(san)極管(guan)是(shi)否(fou)被(bei)擊(ji)穿(若(ruo)是(shi)可控(kong)硅則(ze)需焊(han)下測量(liang)(liang))、相(xiang)關電(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻及電(dian)(dian)(dian)(dian)(dian)(dian)(dian)容是(shi)否(fou)損壞。最后用(yong)(yong)萬用(yong)(yong)表靜(jing)態測量(liang)(liang)高頻(pin)濾波(bo)(bo)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)(lu)中(zhong)(zhong)(zhong)整流(liu)(liu)(liu)二(er)極管(guan)及低壓(ya)濾波(bo)(bo)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)容是(shi)否(fou)損壞。

故障三：電源有輸出，但開機無顯示

故障分析(xi)與排除：出現此故障的(de)可(ke)能原因是“POWER GOOD”輸入的(de)Reset信(xin)號延遲時(shi)間不(bu)夠(gou)，或(huo)“POWER GOOD”無輸出。

開機(ji)后，用電壓表測量“POWERGOOD”的輸(shu)出(chu)(chu)端(接主機(ji)電源插(cha)頭的1腳)，如果(guo)無＋5V輸(shu)出(chu)(chu)，再檢查延(yan)時(shi)元器件，若有＋5V輸(shu)出(chu)(chu)，則(ze)更(geng)換延(yan)時(shi)電路的延(yan)時(shi)電容即可(ke)。

故障四：電源負載能力差

故障分(fen)析與(yu)排(pai)除：電(dian)(dian)源(yuan)在只(zhi)向主板、軟(ruan)驅供電(dian)(dian)時(shi)能(neng)正(zheng)常(chang)工作(zuo)，當接上硬盤(pan)、光驅后，屏(ping)幕變白而不(bu)能(neng)正(zheng)常(chang)工作(zuo)。其可能(neng)原因有：晶體管工作(zuo)點(dian)未(wei)選擇好，高壓濾波電(dian)(dian)容漏(lou)(lou)電(dian)(dian)或(huo)損(sun)壞，穩壓二極(ji)管發(fa)熱(re)漏(lou)(lou)電(dian)(dian)，整流二級管損(sun)壞等(deng)。

調(diao)換(huan)振蕩回路中各(ge)晶體(ti)管(guan)(guan)，使其(qi)增益提高(gao)，或(huo)調(diao)大(da)晶體(ti)管(guan)(guan)的(de)工作點。用萬用表檢測出(chu)有問題的(de)部件后，更(geng)換(huan)可(ke)控硅、穩(wen)壓二極(ji)管(guan)(guan)、高(gao)壓濾波電容或(huo)整(zheng)流二極(ji)管(guan)(guan)即可(ke)。

故障五：無直流輸出

可能出現(xian)(xian)故(gu)障(zhang)的(de)(de)(de)(de)(de)部(bu)(bu)位(wei)(wei)(wei)有(you)：保(bao)險(xian)管(guan)燒斷(duan)，變(bian)換器不工(gong)作，控(kong)制(zhi)電(dian)(dian)(dian)路(lu)(lu)故(gu)障(zhang)。打開(kai)電(dian)(dian)(dian)源(yuan)盒，發現(xian)(xian)保(bao)險(xian)管(guan)去掉。根(gen)據(ju)用(yong)(yong)(yong)(yong)戶反映保(bao)險(xian)管(guan)屢換屢燒。焊(han)下(xia)整流(liu)(liu)二極管(guan)和變(bian)換器功(gong)率開(kai)關(guan)管(guan)，用(yong)(yong)(yong)(yong)萬用(yong)(yong)(yong)(yong)表(biao)檢(jian)測(ce)(ce)都正(zheng)常(chang)(chang)，用(yong)(yong)(yong)(yong)高阻檔檢(jian)測(ce)(ce)交(jiao)(jiao)流(liu)(liu)輸(shu)入端無(wu)短(duan)(duan)路(lu)(lu)現(xian)(xian)象(xiang)。檢(jian)測(ce)(ce)整流(liu)(liu)濾(lv)波(bo)電(dian)(dian)(dian)容正(zheng)常(chang)(chang)。根(gen)據(ju)保(bao)險(xian)管(guan)燒斷(duan)的(de)(de)(de)(de)(de)現(xian)(xian)象(xiang)判斷(duan)，故(gu)障(zhang)部(bu)(bu)位(wei)(wei)(wei)應在變(bian)換器初級繞組前，但沒有(you)發現(xian)(xian)短(duan)(duan)路(lu)(lu)的(de)(de)(de)(de)(de)地方(fang)。只(zhi)(zhi)好恢(hui)復(fu)原態，換保(bao)險(xian)管(guan)加電(dian)(dian)(dian)實驗(yan)。接(jie)通交(jiao)(jiao)流(liu)(liu)電(dian)(dian)(dian)源(yuan)，保(bao)險(xian)燒斷(duan)，立即(ji)斷(duan)開(kai)交(jiao)(jiao)流(liu)(liu)電(dian)(dian)(dian)源(yuan)檢(jian)查(cha)，保(bao)險(xian)管(guan)燒得漆黑。可見(jian)交(jiao)(jiao)流(liu)(liu)輸(shu)入電(dian)(dian)(dian)路(lu)(lu)有(you)嚴重(zhong)的(de)(de)(de)(de)(de)短(duan)(duan)路(lu)(lu)現(xian)(xian)象(xiang)，斷(duan)開(kai)整流(liu)(liu)橋(qiao)的(de)(de)(de)(de)(de)交(jiao)(jiao)流(liu)(liu)輸(shu)入。在整流(liu)(liu)橋(qiao)交(jiao)(jiao)流(liu)(liu)輸(shu)入兩端加接(jie)保(bao)險(xian)管(guan)，直(zhi)(zhi)接(jie)接(jie)到(dao)交(jiao)(jiao)流(liu)(liu)電(dian)(dian)(dian)源(yuan)上(shang)。接(jie)通電(dian)(dian)(dian)源(yuan)，穩壓(ya)電(dian)(dian)(dian)源(yuan)風(feng)機旋轉正(zheng)常(chang)(chang)，測(ce)(ce)試(shi)(shi)各直(zhi)(zhi)流(liu)(liu)輸(shu)出電(dian)(dian)(dian)壓(ya)正(zheng)常(chang)(chang)。可見(jian)故(gu)障(zhang)部(bu)(bu)位(wei)(wei)(wei)在交(jiao)(jiao)流(liu)(liu)濾(lv)波(bo)電(dian)(dian)(dian)路(lu)(lu)中(zhong)，而用(yong)(yong)(yong)(yong)萬用(yong)(yong)(yong)(yong)表(biao)檢(jian)測(ce)(ce)已無(wu)能為力。這(zhe)時想到(dao)替(ti)(ti)代(dai)法，從(cong)另一(yi)臺電(dian)(dian)(dian)源(yuan)上(shang)拆下(xia)兩個(ge)交(jiao)(jiao)流(liu)(liu)濾(lv)波(bo)電(dian)(dian)(dian)容替(ti)(ti)代(dai)，(因(yin)焊(han)接(jie)簡單，所以先(xian)換電(dian)(dian)(dian)容)加電(dian)(dian)(dian)測(ce)(ce)試(shi)(shi)，直(zhi)(zhi)流(liu)(liu)穩壓(ya)電(dian)(dian)(dian)源(yuan)工(gong)作正(zheng)常(chang)(chang)。可見(jian)故(gu)障(zhang)部(bu)(bu)位(wei)(wei)(wei)在這(zhe)兩個(ge)電(dian)(dian)(dian)容中(zhong)，用(yong)(yong)(yong)(yong)高壓(ya)絕(jue)緣儀測(ce)(ce)試(shi)(shi)，其中(zhong)一(yi)只(zhi)(zhi)電(dian)(dian)(dian)容高壓(ya)擊穿。

故障六：開機后計算機自檢(jian)，引導正常，在屏幕(mu)提示“INSERT SYSTEM DISK IN DRIVE A AND PRESS ANY KEY”時插入DOS盤(pan)，軟驅(qu)不讀(du)盤(pan)。

從故障現象分析，故障部位(wei)在軟(ruan)盤(pan)(pan)驅(qu)動器、軟(ruan)盤(pan)(pan)適(shi)配(pei)器或(huo)系統中。經過(guo)替代法，證(zheng)明這臺機器上(shang)的(de)軟(ruan)盤(pan)(pan)適(shi)配(pei)器、軟(ruan)盤(pan)(pan)驅(qu)動器是(shi)好(hao)(hao)的(de)。最(zui)后把主板拆(chai)下來驗證(zheng)是(shi)好(hao)(hao)的(de)，恢復原態后加電試驗，故障不能消除(chu)。因(yin)此(ci)懷疑(yi)到(dao)電源部分。

在機箱里拔下5寸軟(ruan)(ruan)(ruan)驅(qu)電(dian)源(yuan)插(cha)頭。開(kai)(kai)機，用(yong)萬用(yong)表檢測直流(liu)(liu)輸(shu)出(chu)(chu)(chu)(chu)，＋5V，＋12V都(dou)正(zheng)常(chang)。斷電(dian)插(cha)好軟(ruan)(ruan)(ruan)驅(qu)電(dian)源(yuan)插(cha)頭，再開(kai)(kai)機故障(zhang)(zhang)(zhang)不(bu)變。后(hou)在全負(fu)(fu)載下測直流(liu)(liu)輸(shu)出(chu)(chu)(chu)(chu)＋5V為(wei)＋4.1V，＋2V為(wei)＋10.4V。由于電(dian)源(yuan)輸(shu)出(chu)(chu)(chu)(chu)電(dian)壓降(jiang)(jiang)低(di)影響(xiang)(xiang)軟(ruan)(ruan)(ruan)驅(qu)馬(ma)達(da)的(de)(de)正(zheng)常(chang)運行(xing)，造(zao)成不(bu)能(neng)正(zheng)常(chang)讀盤。原因(yin)找到后(hou)，拆下電(dian)源(yuan)進行(xing)維(wei)(wei)修，當(dang)負(fu)(fu)載較輕時(shi)，電(dian)源(yuan)輸(shu)出(chu)(chu)(chu)(chu)正(zheng)常(chang)；當(dang)負(fu)(fu)載加(jia)重，電(dian)源(yuan)輸(shu)出(chu)(chu)(chu)(chu)降(jiang)(jiang)低(di)。說明穩壓電(dian)源(yuan)負(fu)(fu)載能(neng)力降(jiang)(jiang)低(di)。打開(kai)(kai)電(dian)源(yuan)盒蓋，用(yong)示波(bo)器檢測TL494組(zu)(zu)件8，11端和信號放大管的(de)(de)波(bo)形幅(fu)度不(bu)受負(fu)(fu)載影響(xiang)(xiang)。檢測到變換(huan)(huan)器＋5V繞(rao)組(zu)(zu)波(bo)形時(shi)，負(fu)(fu)載對(dui)其有(you)影響(xiang)(xiang)，但變化(hua)幅(fu)度很小(xiao)，因(yin)此懷(huai)疑(yi)＋5V整流(liu)(liu)二極(ji)管正(zheng)向壓降(jiang)(jiang)變大，造(zao)成輸(shu)出(chu)(chu)(chu)(chu)能(neng)力降(jiang)(jiang)低(di)。更(geng)換(huan)(huan)＋5V整流(liu)(liu)管后(hou)，再次(ci)(ci)加(jia)電(dian)測試，故障(zhang)(zhang)(zhang)不(bu)能(neng)排除(chu)，這(zhe)(zhe)時(shi)維(wei)(wei)修陷入了(le)困境(jing)。后(hou)來冷靜(jing)分(fen)析，影響(xiang)(xiang)直流(liu)(liu)輸(shu)出(chu)(chu)(chu)(chu)的(de)(de)因(yin)素還有(you)功(gong)(gong)率開(kai)(kai)關(guan)管。更(geng)換(huan)(huan)功(gong)(gong)率開(kai)(kai)關(guan)管后(hou)開(kai)(kai)機試驗，在負(fu)(fu)載發生變化(hua)時(shi)，直流(liu)(liu)輸(shu)出(chu)(chu)(chu)(chu)正(zheng)常(chang)，故障(zhang)(zhang)(zhang)排除(chu)。換(huan)(huan)下的(de)(de)功(gong)(gong)率管用(yong)JL-1進行(xing)測試，放大倍數很小(xiao)。后(hou)從用(yong)戶(hu)處了(le)解到這(zhe)(zhe)臺機已連續工作(zuo)4年多了(le)。這(zhe)(zhe)是功(gong)(gong)率管老化(hua)造(zao)成了(le)這(zhe)(zhe)次(ci)(ci)故障(zhang)(zhang)(zhang)。從這(zhe)(zhe)起事例中(zhong)得出(chu)(chu)(chu)(chu)，微(wei)機發生故障(zhang)(zhang)(zhang)時(shi)應首(shou)先檢查直流(liu)(liu)電(dian)源(yuan)的(de)(de)輸(shu)出(chu)(chu)(chu)(chu)電(dian)壓，這(zhe)(zhe)對(dui)維(wei)(wei)修人員縮小(xiao)故障(zhang)(zhang)(zhang)范圍，快速(su)排除(chu)故障(zhang)(zhang)(zhang)極(ji)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。

根據故障現象分析，電(dian)源(yuan)通電(dian)后有直流輸出，說(shuo)明(ming)(ming)電(dian)源(yuan)基本上是能(neng)正(zheng)常工(gong)作的(de)。調整＋5V采(cai)樣電(dian)位器(qi)，電(dian)壓不(bu)能(neng)提升，說(shuo)明(ming)(ming)故障發生在控(kong)制電(dian)路中。在電(dian)源(yuan)通電(dian)后有＋3.5V的(de)輸出分析，可能(neng)是控(kong)制信號單邊工(gong)作造成的(de)。

根(gen)據故(gu)(gu)(gu)(gu)障分析，在(zai)電(dian)源(yuan)通(tong)電(dian)之(zhi)后用萬用表檢測TL494的各腳電(dian)平(ping)，由于直(zhi)流(liu)輸(shu)出(chu)(chu)不(bu)正(zheng)常(chang)(chang)(chang)，所以1端(duan)電(dian)平(ping)比正(zheng)常(chang)(chang)(chang)值偏(pian)低。8，11兩端(duan)電(dian)平(ping)用直(zhi)流(liu)電(dian)壓檔測在(zai)2.0V左(zuo)右 屬于正(zheng)常(chang)(chang)(chang)。用示(shi)波器觀(guan)察8，11兩端(duan)和信(xin)號放大(da)管(guan)的輸(shu)出(chu)(chu)幅度在(zai)12V左(zuo)右都(dou)正(zheng)常(chang)(chang)(chang)，排(pai)除了單邊工作的懷疑。在(zai)故(gu)(gu)(gu)(gu)障部位(wei)不(bu)能(neng)確(que)定的情(qing)況下，用新的TL494電(dian)路(lu)替換(huan)(huan)后＋5V電(dian)壓能(neng)提高(gao)到(dao)(dao)＋4V多(duo)一點(dian)，仍不(bu)能(neng)達(da)到(dao)(dao)正(zheng)常(chang)(chang)(chang)輸(shu)出(chu)(chu)。最后決定換(huan)(huan)功率開關(guan)管(guan)，換(huan)(huan)后直(zhi)流(liu)輸(shu)出(chu)(chu)達(da)到(dao)(dao)正(zheng)常(chang)(chang)(chang)值，故(gu)(gu)(gu)(gu)障排(pai)除。從(cong)維修情(qing)況分析，這起故(gu)(gu)(gu)(gu)障也(ye)是由于開關(guan)管(guan)老(lao)化所造(zao)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)現象分(fen)析(xi)可能是(shi)電(dian)(dian)源開(kai)關(guan)(guan)接觸不良(liang)造成的(de)。換電(dian)(dian)源開(kai)關(guan)(guan)后(hou)，故障(zhang)不能排(pai)除。不過(guo)在打開(kai)電(dian)(dian)源開(kai)關(guan)(guan)，等大約十多分(fen)鐘后(hou)，微機自(zi)動(dong)啟動(dong)，由(you)此分(fen)析(xi)，故障(zhang)出(chu)在電(dian)(dian)源控制部(bu)分(fen)元件溫度性能不良(liang)造成的(de)故障(zhang)。

把電(dian)(dian)(dian)源從機箱中(zhong)取(qu)出(chu)，打開電(dian)(dian)(dian)源蓋(gai)，加(jia)上(shang)負載通電(dian)(dian)(dian)檢測，開機時(shi)＋5V有＋1.2V，＋12V有＋3V輸(shu)出(chu)，交流整流300V輸(shu)出(chu)正常。查功率(lv)開關管是好的，用(yong)烙鐵對(dui)功率(lv)管加(jia)溫后再啟動，故障不能(neng)排(pai)(pai)除(chu)，由(you)此(ci)排(pai)(pai)除(chu)了功率(lv)管溫度性(xing)能(neng)不良(liang)的嫌疑，判斷故障部(bu)位在變換器(qi)次級繞(rao)組(zu)后面的電(dian)(dian)(dian)路部(bu)分(fen)。加(jia)電(dian)(dian)(dian)開機后用(yong)萬用(yong)表(biao)測TL494各腳的電(dian)(dian)(dian)平(ping)時(shi)發(fa)現，輔助電(dian)(dian)(dian)源輸(shu)入端電(dian)(dian)(dian)壓只有5V多一(yi)點，加(jia)電(dian)(dian)(dian)一(yi)段(duan)時(shi)間(jian)后，電(dian)(dian)(dian)壓逐步上(shang)升，在輔助電(dian)(dian)(dian)源電(dian)(dian)(dian)壓逐步上(shang)升過程中(zhong)，電(dian)(dian)(dian)源輸(shu)出(chu)也逐步上(shang)升到(dao)正常值(zhi)。這(zhe)象電(dian)(dian)(dian)容緩慢充電(dian)(dian)(dian)過程。因此(ci)在輔助電(dian)(dian)(dian)源電(dian)(dian)(dian)路中(zhong)查找(zhao)到(dao)電(dian)(dian)(dian)容C15，用(yong)萬用(yong)表(biao)測漏電(dian)(dian)(dian)較大。換后故障排(pai)(pai)除(chu)。