臺式機電源的工(gong)作原理分析(xi) 臺式機電源故(gu)障(zhang)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(xi)統里的(de)(de)(de)(de)(de)每個部件的(de)(de)(de)(de)(de)電(dian)(dian)能(neng)都有同一個來(lai)源(yuan)——就是電(dian)(dian)源(yuan)。電(dian)(dian)源(yuan)必須為所有的(de)(de)(de)(de)(de)設(she)(she)備(bei)不間斷地提(ti)供穩定的(de)(de)(de)(de)(de)、連續的(de)(de)(de)(de)(de)電(dian)(dian)流。如果電(dian)(dian)源(yuan)過量(liang)或(huo)不足(zu)，所連接的(de)(de)(de)(de)(de)設(she)(she)備(bei)就有可能(neng)不能(neng)正常運作，看起(qi)來(lai)象壞了一樣。比(bi)如，內存不能(neng)刷新，造成(cheng)數據丟(diu)失(shi)，會導致(zhi)軟(ruan)件錯誤(wu)；而CPU可能(neng)死(si)鎖，或(huo)隨(sui)機(ji)地重啟(qi)動(dong)；硬(ying)盤可能(neng)不轉(zhuan)，不能(neng)正常處理控(kong)制信號。既然這么多的(de)(de)(de)(de)(de)設(she)(she)備(bei)都與電(dian)(dian)源(yuan)息息相關(guan)，那把(ba)電(dian)(dian)源(yuan)看作PC系(xi)統里最重要(yao)的(de)(de)(de)(de)(de)部件就毫不過分。從微機(ji)的(de)(de)(de)(de)(de)故(gu)(gu)障(zhang)(zhang)統計來(lai)看，電(dian)(dian)源(yuan)部分的(de)(de)(de)(de)(de)故(gu)(gu)障(zhang)(zhang)占總故(gu)(gu)障(zhang)(zhang)率相當高的(de)(de)(de)(de)(de)比(bi)例(li)。

（一）電源出現(xian)(xian)問題，其表現(xian)(xian)是多方面的(de)：

1、導致(zhi)硬(ying)盤出現(xian)壞道或損壞。不好的(de)電源易(yi)導致(zhi)硬(ying)盤出現(xian)假壞道，這種故(gu)障(zhang)一般可通過軟件(jian)修(xiu)復。如(ru)果用戶碰(peng)到此類(lei)情況，首先要檢查電源。在修(xiu)復硬(ying)盤的(de)同時，還應換一個(ge)好電源。

2、噪聲(sheng)(sheng)增大。不僅電源本身風扇的噪音(yin)會增大，還(huan)可能導致聲(sheng)(sheng)卡的噪聲(sheng)(sheng)增大。

3、光驅(qu)讀盤性(xing)能不好。如果你(ni)新配的計算機或(huo)新買的CD-ROM讀盤不好，很(hen)可(ke)能是電(dian)源有問題。

4、超(chao)頻不穩定(ding)。超(chao)頻是否(fou)穩定(ding)與電源質量的好壞關系很大。

5、顯示(shi)屏(ping)上有水波紋。有可能是電(dian)(dian)源(yuan)的電(dian)(dian)磁輻射外瀉，干擾(rao)太大。

6、主機經常莫名奇妙地重新啟動。有可能是電源(yuan)的功(gong)率不夠等。

7、不(bu)好的(de)電源在(zai)+5VSB上(shang)提供(gong)不(bu)了(le)10mA的(de)電流，造成進入睡(shui)眠(mian)狀態后就長睡(shui)不(bu)醒(xing)，且+5V不(bu)穩定，會導致鼠標經常失(shi)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)相比，電(dian)源部分(fen)使用的(de)分(fen)立元(yuan)件(jian)比重最大，這也為(wei)維修人員提供了一個(ge)比較(jiao)適合(he)自己(ji)動手修理的(de)機會。只要熟悉(xi)脈寬調制型開關直流穩壓電(dian)源的(de)基本原(yuan)(yuan)理，在(zai)沒有工作(zuo)原(yuan)(yuan)理圖的(de)情(qing)況下，根據(ju)實物基本上就能(neng)了解該電(dian)源的(de)工作(zuo)原(yuan)(yuan)理和器件(jian)的(de)工作(zuo)狀(zhuang)態，很容易下手進行維修。

微機(ji)電(dian)源一般(ban)容易出(chu)(chu)的故障有以下(xia)幾種：保險絲熔斷(duan)、電(dian)源無輸出(chu)(chu)或輸出(chu)(chu)電(dian)壓不穩定、電(dian)源有輸出(chu)(chu)但開(kai)機(ji)無顯(xian)示、電(dian)源負載(zai)能力(li)差。下(xia)面(mian)分別介紹其(qi)檢(jian)修方法：

故障一：保險絲熔斷

出(chu)現此(ci)類故(gu)障時(shi)，先(xian)打(da)開電(dian)(dian)(dian)(dian)(dian)(dian)源外殼，檢查電(dian)(dian)(dian)(dian)(dian)(dian)源上的(de)(de)保險(xian)絲是(shi)否(fou)熔斷(duan)，據此(ci)可(ke)以(yi)初(chu)步(bu)確(que)定逆變電(dian)(dian)(dian)(dian)(dian)(dian)路是(shi)否(fou)發生(sheng)了故(gu)障。若是(shi)，則不外如下三種情況造成：輸入回路中某個橋式整(zheng)流二極管被擊(ji)穿；高壓濾(lv)波電(dian)(dian)(dian)(dian)(dian)(dian)解電(dian)(dian)(dian)(dian)(dian)(dian)容被擊(ji)穿；逆變功(gong)率開關管損(sun)壞。其(qi)主要(yao)原因是(shi)因為直流濾(lv)波及變換振(zhen)蕩電(dian)(dian)(dian)(dian)(dian)(dian)路長(chang)時(shi)間工(gong)作在高壓(＋300V)、大(da)電(dian)(dian)(dian)(dian)(dian)(dian)流狀態，特別是(shi)由(you)于交流電(dian)(dian)(dian)(dian)(dian)(dian)壓變化較大(da)、輸出(chu)負(fu)載較重時(shi)，易出(chu)現保險(xian)絲熔斷(duan)的(de)(de)故(gu)障。直流濾(lv)波電(dian)(dian)(dian)(dian)(dian)(dian)路由(you)四只整(zheng)流二極管、兩只100KΩ左右限(xian)流電(dian)(dian)(dian)(dian)(dian)(dian)阻和兩只330μF左右的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)解電(dian)(dian)(dian)(dian)(dian)(dian)容組成；變換振(zhen)蕩電(dian)(dian)(dian)(dian)(dian)(dian)路則主要(yao)由(you)裝在同一散熱片上的(de)(de)兩只型(xing)號相(xiang)同的(de)(de)大(da)功(gong)率開關管組成。

交流(liu)(liu)保險絲熔斷(duan)后(hou)(hou)，關機拔掉電源(yuan)插頭，首先仔(zi)細觀(guan)察電路(lu)板上各(ge)高壓(ya)(ya)元(yuan)件(jian)的(de)外表是否(fou)有(you)被擊(ji)(ji)穿燒糊或電解液溢出(chu)的(de)痕跡(ji)，若無(wu)異(yi)常，用(yong)萬用(yong)表測(ce)量(liang)(liang)(liang)輸入端(duan)的(de)值，若小于(yu)(yu)200KΩ，說明(ming)(ming)后(hou)(hou)端(duan)有(you)局(ju)部短路(lu)現象，再(zai)分(fen)別測(ce)量(liang)(liang)(liang)兩個大功(gong)率開(kai)關管(guan)e、c極(ji)間(jian)的(de)阻(zu)(zu)值，若小于(yu)(yu)100KΩ，則說明(ming)(ming)開(kai)關管(guan)已(yi)損(sun)壞，測(ce)量(liang)(liang)(liang)四只(zhi)整(zheng)流(liu)(liu)二級(ji)管(guan)正(zheng)、反向(xiang)電阻(zu)(zu)和兩個限流(liu)(liu)電阻(zu)(zu)的(de)阻(zu)(zu)值，用(yong)萬用(yong)表測(ce)量(liang)(liang)(liang)其充放(fang)電情況以(yi)判定(ding)是否(fou)正(zheng)常。另(ling)外在(zai)(zai)更換開(kai)關管(guan)時，如(ru)果無(wu)法找(zhao)到同型(xing)號產品而選擇代用(yong)品時，應(ying)注意集(ji)電極(ji)-發(fa)射(she)極(ji)反向(xiang)擊(ji)(ji)穿電壓(ya)(ya)Vceo、集(ji)電極(ji)最大允許耗散(san)功(gong)率Pcm、集(ji)電極(ji)-基極(ji)反向(xiang)擊(ji)(ji)穿電壓(ya)(ya)Vcbo的(de)參(can)數應(ying)大于(yu)(yu)或等于(yu)(yu)原晶體管(guan)的(de)參(can)數。再(zai)一(yi)個要(yao)注意的(de)是：切不可(ke)在(zai)(zai)查出(chu)某元(yuan)件(jian)損(sun)壞時，更換后(hou)(hou)便直接開(kai)機，這樣(yang)很可(ke)能(neng)由(you)于(yu)(yu)其它高壓(ya)(ya)元(yuan)件(jian)仍(reng)有(you)故障(zhang)又將(jiang)更換的(de)元(yuan)件(jian)損(sun)壞。一(yi)定(ding)要(yao)對(dui)上述電路(lu)的(de)所有(you)高壓(ya)(ya)元(yuan)件(jian)進行全(quan)面檢(jian)查測(ce)量(liang)(liang)(liang)后(hou)(hou)，才能(neng)徹底排除保險絲熔斷(duan)故障(zhang)。

故障二：無直流電壓輸出或電壓輸出不穩定

故障(zhang)(zhang)分析與排(pai)除：若保險絲完好(hao)，在有(you)(you)負(fu)載(zai)情況下(xia)，各(ge)級直(zhi)流(liu)電(dian)(dian)壓(ya)無(wu)輸(shu)出(chu)，其可能原因有(you)(you)：電(dian)(dian)源中出(chu)現開路(lu)(lu)(lu)、短路(lu)(lu)(lu)現象，過(guo)壓(ya)、過(guo)流(liu)保護(hu)電(dian)(dian)路(lu)(lu)(lu)出(chu)現故障(zhang)(zhang)，振蕩(dang)電(dian)(dian)路(lu)(lu)(lu)沒有(you)(you)工作，電(dian)(dian)源負(fu)載(zai)過(guo)重，高頻整(zheng)流(liu)濾(lv)電(dian)(dian)路(lu)(lu)(lu)中整(zheng)流(liu)二極(ji)管(guan)被擊(ji)穿(chuan)，濾(lv)波電(dian)(dian)容(rong)漏電(dian)(dian)等。處理方法(fa)為(wei)：用(yong)(yong)(yong)萬用(yong)(yong)(yong)表測(ce)(ce)(ce)量(liang)系(xi)(xi)統板(ban)＋5V電(dian)(dian)源的(de)(de)對地(di)電(dian)(dian)阻，若大(da)于0.8Ω，則說明(ming)系(xi)(xi)統板(ban)無(wu)短路(lu)(lu)(lu)現象；將微機配置改為(wei)最(zui)小(xiao)化，即(ji)機器中只(zhi)留主(zhu)板(ban)、電(dian)(dian)源、蜂(feng)鳴(ming)器，測(ce)(ce)(ce)量(liang)各(ge)輸(shu)出(chu)端的(de)(de)直(zhi)流(liu)電(dian)(dian)壓(ya)，若仍無(wu)輸(shu)出(chu)，說明(ming)故障(zhang)(zhang)出(chu)在微機電(dian)(dian)源的(de)(de)控(kong)(kong)制電(dian)(dian)路(lu)(lu)(lu)中。控(kong)(kong)制電(dian)(dian)路(lu)(lu)(lu)主(zhu)要由集成(cheng)開關電(dian)(dian)源控(kong)(kong)制器(TL-496、GS3424等)和(he)過(guo)壓(ya)保護(hu)電(dian)(dian)路(lu)(lu)(lu)組成(cheng)，控(kong)(kong)制電(dian)(dian)路(lu)(lu)(lu)工作是(shi)(shi)否正常直(zhi)接關系(xi)(xi)到直(zhi)流(liu)電(dian)(dian)壓(ya)有(you)(you)無(wu)輸(shu)出(chu)。過(guo)壓(ya)保護(hu)電(dian)(dian)路(lu)(lu)(lu)主(zhu)要由小(xiao)功率三(san)極(ji)管(guan)或可控(kong)(kong)硅(gui)及相關元件(jian)組成(cheng)，可用(yong)(yong)(yong)萬用(yong)(yong)(yong)表測(ce)(ce)(ce)量(liang)該三(san)極(ji)管(guan)是(shi)(shi)否被擊(ji)穿(chuan)(若是(shi)(shi)可控(kong)(kong)硅(gui)則需焊下(xia)測(ce)(ce)(ce)量(liang))、相關電(dian)(dian)阻及電(dian)(dian)容(rong)是(shi)(shi)否損壞。最(zui)后用(yong)(yong)(yong)萬用(yong)(yong)(yong)表靜態測(ce)(ce)(ce)量(liang)高頻濾(lv)波電(dian)(dian)路(lu)(lu)(lu)中整(zheng)流(liu)二極(ji)管(guan)及低壓(ya)濾(lv)波電(dian)(dian)容(rong)是(shi)(shi)否損壞。

故障三：電源有輸出，但開機無顯示

故(gu)障分析與排除：出現此故(gu)障的(de)可能(neng)原因是“POWER GOOD”輸(shu)入的(de)Reset信(xin)號延遲時(shi)間(jian)不夠(gou)，或(huo)“POWER GOOD”無輸(shu)出。

開機后，用電壓表(biao)測量(liang)“POWERGOOD”的(de)(de)輸(shu)(shu)出端(接主(zhu)機電源插頭的(de)(de)1腳)，如果無＋5V輸(shu)(shu)出，再檢查延時元器(qi)件，若有＋5V輸(shu)(shu)出，則更換延時電路的(de)(de)延時電容即(ji)可。

故障四：電源負載能力差

故障分析(xi)與排除：電源在(zai)只向主(zhu)板、軟(ruan)驅供電時能正常工作(zuo)，當接上(shang)硬盤(pan)、光驅后，屏幕變白而不能正常工作(zuo)。其可能原因有：晶(jing)體管工作(zuo)點(dian)未選擇好，高(gao)壓濾(lv)波電容漏電或損壞，穩(wen)壓二極管發(fa)熱漏電，整流二級管損壞等。

調換(huan)振蕩回(hui)路(lu)中各晶體管(guan)(guan)，使(shi)其增(zeng)益提高，或(huo)調大晶體管(guan)(guan)的工(gong)作點。用萬用表檢(jian)測出有(you)問題的部(bu)件后，更(geng)換(huan)可控硅、穩壓二極管(guan)(guan)、高壓濾波電容或(huo)整流二極管(guan)(guan)即可。

故障五：無直流輸出

可能出(chu)現故(gu)障(zhang)的(de)(de)(de)部位有(you)：保(bao)險(xian)(xian)管(guan)燒(shao)(shao)斷，變換(huan)(huan)器(qi)不工作，控制(zhi)電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)故(gu)障(zhang)。打開(kai)(kai)電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)盒，發現保(bao)險(xian)(xian)管(guan)去掉。根(gen)據(ju)用(yong)(yong)戶(hu)反(fan)映保(bao)險(xian)(xian)管(guan)屢換(huan)(huan)屢燒(shao)(shao)。焊(han)下整(zheng)流(liu)二極管(guan)和變換(huan)(huan)器(qi)功率開(kai)(kai)關管(guan)，用(yong)(yong)萬用(yong)(yong)表(biao)檢(jian)(jian)(jian)測都正(zheng)(zheng)常(chang)，用(yong)(yong)高阻檔檢(jian)(jian)(jian)測交(jiao)(jiao)流(liu)輸入(ru)端無短(duan)路(lu)(lu)現象。檢(jian)(jian)(jian)測整(zheng)流(liu)濾(lv)波電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)正(zheng)(zheng)常(chang)。根(gen)據(ju)保(bao)險(xian)(xian)管(guan)燒(shao)(shao)斷的(de)(de)(de)現象判斷，故(gu)障(zhang)部位應在變換(huan)(huan)器(qi)初級(ji)繞組前，但沒有(you)發現短(duan)路(lu)(lu)的(de)(de)(de)地方。只(zhi)好恢復原態，換(huan)(huan)保(bao)險(xian)(xian)管(guan)加電(dian)(dian)(dian)(dian)(dian)(dian)實驗。接(jie)(jie)通交(jiao)(jiao)流(liu)電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)，保(bao)險(xian)(xian)燒(shao)(shao)斷，立(li)即斷開(kai)(kai)交(jiao)(jiao)流(liu)電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)檢(jian)(jian)(jian)查(cha)，保(bao)險(xian)(xian)管(guan)燒(shao)(shao)得漆黑(hei)。可見交(jiao)(jiao)流(liu)輸入(ru)電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)有(you)嚴重的(de)(de)(de)短(duan)路(lu)(lu)現象，斷開(kai)(kai)整(zheng)流(liu)橋的(de)(de)(de)交(jiao)(jiao)流(liu)輸入(ru)。在整(zheng)流(liu)橋交(jiao)(jiao)流(liu)輸入(ru)兩(liang)端加接(jie)(jie)保(bao)險(xian)(xian)管(guan)，直(zhi)接(jie)(jie)接(jie)(jie)到(dao)交(jiao)(jiao)流(liu)電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)上(shang)。接(jie)(jie)通電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)，穩(wen)(wen)壓(ya)電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)風(feng)機旋(xuan)轉正(zheng)(zheng)常(chang)，測試各直(zhi)流(liu)輸出(chu)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)正(zheng)(zheng)常(chang)。可見故(gu)障(zhang)部位在交(jiao)(jiao)流(liu)濾(lv)波電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)中(zhong)，而(er)用(yong)(yong)萬用(yong)(yong)表(biao)檢(jian)(jian)(jian)測已無能為力(li)。這時(shi)想(xiang)到(dao)替(ti)代(dai)法，從(cong)另一臺電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)上(shang)拆(chai)下兩(liang)個(ge)交(jiao)(jiao)流(liu)濾(lv)波電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)替(ti)代(dai)，(因(yin)焊(han)接(jie)(jie)簡單，所以先換(huan)(huan)電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong))加電(dian)(dian)(dian)(dian)(dian)(dian)測試，直(zhi)流(liu)穩(wen)(wen)壓(ya)電(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)(yuan)工作正(zheng)(zheng)常(chang)。可見故(gu)障(zhang)部位在這兩(liang)個(ge)電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)中(zhong)，用(yong)(yong)高壓(ya)絕緣儀(yi)測試，其(qi)中(zhong)一只(zhi)電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)(rong)高壓(ya)擊穿(chuan)。

故障(zhang)六(liu)：開機后(hou)計(ji)算機自檢，引(yin)導(dao)正常，在屏(ping)幕提示(shi)“INSERT SYSTEM DISK IN DRIVE A AND PRESS ANY KEY”時插入DOS盤(pan)，軟驅(qu)不讀盤(pan)。

從故(gu)障現象(xiang)分析，故(gu)障部位在(zai)軟(ruan)盤驅(qu)動器(qi)(qi)、軟(ruan)盤適配(pei)器(qi)(qi)或系統中。經過替代(dai)法，證明這臺機器(qi)(qi)上的(de)軟(ruan)盤適配(pei)器(qi)(qi)、軟(ruan)盤驅(qu)動器(qi)(qi)是(shi)好的(de)。最后把主板拆下來驗(yan)證是(shi)好的(de)，恢復原態后加電(dian)試驗(yan)，故(gu)障不能消除。因此懷疑到電(dian)源部分。

在(zai)機箱里拔下(xia)5寸軟驅(qu)電(dian)(dian)(dian)(dian)源(yuan)插(cha)(cha)頭(tou)。開(kai)機，用(yong)(yong)萬用(yong)(yong)表檢測(ce)(ce)直(zhi)流(liu)(liu)(liu)(liu)輸(shu)(shu)(shu)出(chu)(chu)(chu)，＋5V，＋12V都正(zheng)(zheng)(zheng)常(chang)(chang)。斷電(dian)(dian)(dian)(dian)插(cha)(cha)好軟驅(qu)電(dian)(dian)(dian)(dian)源(yuan)插(cha)(cha)頭(tou)，再(zai)開(kai)機故(gu)(gu)(gu)障(zhang)不變。后(hou)在(zai)全負(fu)載(zai)下(xia)測(ce)(ce)直(zhi)流(liu)(liu)(liu)(liu)輸(shu)(shu)(shu)出(chu)(chu)(chu)＋5V為＋4.1V，＋2V為＋10.4V。由于電(dian)(dian)(dian)(dian)源(yuan)輸(shu)(shu)(shu)出(chu)(chu)(chu)電(dian)(dian)(dian)(dian)壓(ya)降低(di)(di)(di)(di)影(ying)響(xiang)軟驅(qu)馬達的正(zheng)(zheng)(zheng)常(chang)(chang)運行(xing)，造(zao)成(cheng)不能正(zheng)(zheng)(zheng)常(chang)(chang)讀盤。原因(yin)找到(dao)后(hou)，拆下(xia)電(dian)(dian)(dian)(dian)源(yuan)進(jin)行(xing)維(wei)(wei)修(xiu)，當負(fu)載(zai)較(jiao)輕(qing)時(shi)，電(dian)(dian)(dian)(dian)源(yuan)輸(shu)(shu)(shu)出(chu)(chu)(chu)正(zheng)(zheng)(zheng)常(chang)(chang)；當負(fu)載(zai)加(jia)重，電(dian)(dian)(dian)(dian)源(yuan)輸(shu)(shu)(shu)出(chu)(chu)(chu)降低(di)(di)(di)(di)。說明(ming)穩壓(ya)電(dian)(dian)(dian)(dian)源(yuan)負(fu)載(zai)能力降低(di)(di)(di)(di)。打開(kai)電(dian)(dian)(dian)(dian)源(yuan)盒蓋，用(yong)(yong)示波(bo)器檢測(ce)(ce)TL494組(zu)件8，11端和信號(hao)放大管(guan)(guan)的波(bo)形幅(fu)度(du)不受負(fu)載(zai)影(ying)響(xiang)。檢測(ce)(ce)到(dao)變換(huan)器＋5V繞組(zu)波(bo)形時(shi)，負(fu)載(zai)對(dui)其有影(ying)響(xiang)，但變化幅(fu)度(du)很小，因(yin)此懷疑＋5V整流(liu)(liu)(liu)(liu)二極(ji)管(guan)(guan)正(zheng)(zheng)(zheng)向(xiang)壓(ya)降變大，造(zao)成(cheng)輸(shu)(shu)(shu)出(chu)(chu)(chu)能力降低(di)(di)(di)(di)。更換(huan)＋5V整流(liu)(liu)(liu)(liu)管(guan)(guan)后(hou)，再(zai)次(ci)加(jia)電(dian)(dian)(dian)(dian)測(ce)(ce)試(shi)，故(gu)(gu)(gu)障(zhang)不能排(pai)(pai)除(chu)，這(zhe)時(shi)維(wei)(wei)修(xiu)陷入(ru)了(le)(le)困境。后(hou)來冷靜分(fen)析，影(ying)響(xiang)直(zhi)流(liu)(liu)(liu)(liu)輸(shu)(shu)(shu)出(chu)(chu)(chu)的因(yin)素還有功率開(kai)關(guan)(guan)管(guan)(guan)。更換(huan)功率開(kai)關(guan)(guan)管(guan)(guan)后(hou)開(kai)機試(shi)驗，在(zai)負(fu)載(zai)發生變化時(shi)，直(zhi)流(liu)(liu)(liu)(liu)輸(shu)(shu)(shu)出(chu)(chu)(chu)正(zheng)(zheng)(zheng)常(chang)(chang)，故(gu)(gu)(gu)障(zhang)排(pai)(pai)除(chu)。換(huan)下(xia)的功率管(guan)(guan)用(yong)(yong)JL-1進(jin)行(xing)測(ce)(ce)試(shi)，放大倍數很小。后(hou)從(cong)用(yong)(yong)戶(hu)處了(le)(le)解(jie)到(dao)這(zhe)臺機已(yi)連續工作4年多了(le)(le)。這(zhe)是功率管(guan)(guan)老化造(zao)成(cheng)了(le)(le)這(zhe)次(ci)故(gu)(gu)(gu)障(zhang)。從(cong)這(zhe)起(qi)事例(li)中得出(chu)(chu)(chu)，微(wei)機發生故(gu)(gu)(gu)障(zhang)時(shi)應首(shou)先檢查直(zhi)流(liu)(liu)(liu)(liu)電(dian)(dian)(dian)(dian)源(yuan)的輸(shu)(shu)(shu)出(chu)(chu)(chu)電(dian)(dian)(dian)(dian)壓(ya)，這(zhe)對(dui)維(wei)(wei)修(xiu)人員(yuan)縮小故(gu)(gu)(gu)障(zhang)范圍，快速排(pai)(pai)除(chu)故(gu)(gu)(gu)障(zhang)極(ji)為有益。

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(zhang)現象分析，電(dian)(dian)源(yuan)(yuan)通電(dian)(dian)后有直流輸出(chu)，說(shuo)明電(dian)(dian)源(yuan)(yuan)基(ji)本上是能正常工作(zuo)的。調整＋5V采(cai)樣電(dian)(dian)位器，電(dian)(dian)壓(ya)不(bu)能提(ti)升(sheng)，說(shuo)明故障(zhang)發生在控制電(dian)(dian)路(lu)中。在電(dian)(dian)源(yuan)(yuan)通電(dian)(dian)后有＋3.5V的輸出(chu)分析，可能是控制信號單邊(bian)工作(zuo)造成的。

根據(ju)故障(zhang)(zhang)(zhang)分(fen)析(xi)，在電(dian)(dian)(dian)源通(tong)電(dian)(dian)(dian)之后用萬(wan)用表(biao)檢測(ce)TL494的(de)(de)各腳電(dian)(dian)(dian)平，由于直流輸(shu)出不(bu)正(zheng)(zheng)(zheng)常(chang)(chang)，所以1端(duan)電(dian)(dian)(dian)平比(bi)正(zheng)(zheng)(zheng)常(chang)(chang)值偏低。8，11兩(liang)端(duan)電(dian)(dian)(dian)平用直流電(dian)(dian)(dian)壓(ya)檔測(ce)在2.0V左(zuo)右 屬(shu)于正(zheng)(zheng)(zheng)常(chang)(chang)。用示波(bo)器觀察8，11兩(liang)端(duan)和(he)信號放(fang)大管(guan)的(de)(de)輸(shu)出幅(fu)度(du)在12V左(zuo)右都正(zheng)(zheng)(zheng)常(chang)(chang)，排除了單邊工作的(de)(de)懷疑(yi)。在故障(zhang)(zhang)(zhang)部位不(bu)能確(que)定(ding)的(de)(de)情況(kuang)下(xia)，用新的(de)(de)TL494電(dian)(dian)(dian)路替(ti)換后＋5V電(dian)(dian)(dian)壓(ya)能提高(gao)到(dao)＋4V多一點，仍不(bu)能達到(dao)正(zheng)(zheng)(zheng)常(chang)(chang)輸(shu)出。最后決定(ding)換功率開關管(guan)，換后直流輸(shu)出達到(dao)正(zheng)(zheng)(zheng)常(chang)(chang)值，故障(zhang)(zhang)(zhang)排除。從維修情況(kuang)分(fen)析(xi)，這起故障(zhang)(zhang)(zhang)也(ye)是由于開關管(guan)老化所造成的(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。

根據(ju)故(gu)障現象分析可能(neng)(neng)是(shi)電(dian)(dian)源開(kai)(kai)關接觸不良(liang)造成(cheng)的。換電(dian)(dian)源開(kai)(kai)關后，故(gu)障不能(neng)(neng)排除(chu)。不過(guo)在打(da)開(kai)(kai)電(dian)(dian)源開(kai)(kai)關，等大(da)約十多分鐘后，微機自(zi)動啟動，由此(ci)分析，故(gu)障出在電(dian)(dian)源控(kong)制部分元件溫度性能(neng)(neng)不良(liang)造成(cheng)的故(gu)障。

把電(dian)(dian)(dian)(dian)源從機(ji)(ji)箱(xiang)中(zhong)(zhong)取出(chu)，打開(kai)電(dian)(dian)(dian)(dian)源蓋(gai)，加(jia)上(shang)負(fu)載(zai)通電(dian)(dian)(dian)(dian)檢測，開(kai)機(ji)(ji)時(shi)＋5V有＋1.2V，＋12V有＋3V輸出(chu)，交流(liu)整流(liu)300V輸出(chu)正常(chang)。查(cha)(cha)功(gong)率(lv)開(kai)關管是好(hao)的(de)，用(yong)烙鐵對功(gong)率(lv)管加(jia)溫后再啟動，故(gu)(gu)障(zhang)不能(neng)排除，由此排除了(le)功(gong)率(lv)管溫度性能(neng)不良(liang)的(de)嫌疑，判斷故(gu)(gu)障(zhang)部(bu)位在變換器次級(ji)繞組后面的(de)電(dian)(dian)(dian)(dian)路部(bu)分。加(jia)電(dian)(dian)(dian)(dian)開(kai)機(ji)(ji)后用(yong)萬(wan)用(yong)表測TL494各(ge)腳的(de)電(dian)(dian)(dian)(dian)平(ping)時(shi)發現，輔(fu)助電(dian)(dian)(dian)(dian)源輸入端電(dian)(dian)(dian)(dian)壓(ya)只有5V多一點，加(jia)電(dian)(dian)(dian)(dian)一段時(shi)間后，電(dian)(dian)(dian)(dian)壓(ya)逐(zhu)(zhu)(zhu)步上(shang)升，在輔(fu)助電(dian)(dian)(dian)(dian)源電(dian)(dian)(dian)(dian)壓(ya)逐(zhu)(zhu)(zhu)步上(shang)升過程(cheng)中(zhong)(zhong)，電(dian)(dian)(dian)(dian)源輸出(chu)也逐(zhu)(zhu)(zhu)步上(shang)升到正常(chang)值。這象電(dian)(dian)(dian)(dian)容緩慢充電(dian)(dian)(dian)(dian)過程(cheng)。因此在輔(fu)助電(dian)(dian)(dian)(dian)源電(dian)(dian)(dian)(dian)路中(zhong)(zhong)查(cha)(cha)找到電(dian)(dian)(dian)(dian)容C15，用(yong)萬(wan)用(yong)表測漏電(dian)(dian)(dian)(dian)較大。換后故(gu)(gu)障(zhang)排除。