臺式機電(dian)源的工作原理分析 臺式機電(dian)源故障處理辦(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(xi)統(tong)里的(de)每個部(bu)(bu)件(jian)的(de)電(dian)(dian)能(neng)(neng)都有(you)同一個來(lai)源(yuan)——就(jiu)是電(dian)(dian)源(yuan)。電(dian)(dian)源(yuan)必須為所(suo)有(you)的(de)設(she)備不(bu)間斷地提供(gong)穩定的(de)、連(lian)續的(de)電(dian)(dian)流。如(ru)果電(dian)(dian)源(yuan)過量或不(bu)足，所(suo)連(lian)接的(de)設(she)備就(jiu)有(you)可(ke)能(neng)(neng)不(bu)能(neng)(neng)正(zheng)常運(yun)作，看起來(lai)象壞了一樣。比如(ru)，內存不(bu)能(neng)(neng)刷新(xin)，造成數(shu)據丟失，會導致軟(ruan)件(jian)錯誤；而CPU可(ke)能(neng)(neng)死鎖，或隨機地重(zhong)(zhong)啟動；硬盤可(ke)能(neng)(neng)不(bu)轉(zhuan)，不(bu)能(neng)(neng)正(zheng)常處(chu)理控制信號。既然這么多的(de)設(she)備都與電(dian)(dian)源(yuan)息息相關，那把電(dian)(dian)源(yuan)看作PC系(xi)統(tong)里最(zui)重(zhong)(zhong)要的(de)部(bu)(bu)件(jian)就(jiu)毫不(bu)過分。從微機的(de)故(gu)(gu)障統(tong)計(ji)來(lai)看，電(dian)(dian)源(yuan)部(bu)(bu)分的(de)故(gu)(gu)障占總故(gu)(gu)障率相當高的(de)比例。

（一(yi)）電源出現問(wen)題，其表現是多(duo)方面(mian)的：

1、導致硬(ying)盤出現壞(huai)道或損壞(huai)。不(bu)好的電(dian)源(yuan)易導致硬(ying)盤出現假壞(huai)道，這種故障一(yi)般可通過(guo)軟(ruan)件修復。如果用戶碰到此(ci)類情況(kuang)，首先要(yao)檢(jian)查電(dian)源(yuan)。在修復硬(ying)盤的同時，還應(ying)換一(yi)個好電(dian)源(yuan)。

2、噪(zao)聲(sheng)增大。不(bu)僅電源(yuan)本身(shen)風扇的(de)噪(zao)音會增大，還(huan)可能導致聲(sheng)卡(ka)的(de)噪(zao)聲(sheng)增大。

3、光(guang)驅讀盤性能不好(hao)。如果你新配的計算(suan)機或(huo)新買(mai)的CD-ROM讀盤不好(hao)，很可能是電源有問題。

4、超(chao)頻不穩定。超(chao)頻是(shi)否穩定與電(dian)源質量的好(hao)壞關(guan)系(xi)很(hen)大。

5、顯(xian)示屏上有水波紋。有可(ke)能是電(dian)源的(de)電(dian)磁(ci)輻射外(wai)瀉，干擾太大。

6、主機經常莫名奇(qi)妙地重新(xin)啟(qi)動。有可能是電源的功率不夠等。

7、不好的電(dian)源在+5VSB上提供不了(le)10mA的電(dian)流，造成進入睡眠狀態后就(jiu)長睡不醒，且(qie)+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(wei)機的(de)(de)其他部件(jian)(jian)相(xiang)比，電源部分使用(yong)的(de)(de)分立元件(jian)(jian)比重(zhong)最大(da)，這也為維(wei)修(xiu)人(ren)員提(ti)供(gong)了一個(ge)比較適合自己動手修(xiu)理(li)的(de)(de)機會。只要熟悉(xi)脈寬調(diao)制型開關直(zhi)流(liu)穩(wen)壓電源的(de)(de)基(ji)本原(yuan)理(li)，在沒(mei)有工(gong)作原(yuan)理(li)圖的(de)(de)情(qing)況下，根據實物基(ji)本上(shang)就(jiu)能了解該電源的(de)(de)工(gong)作原(yuan)理(li)和器件(jian)(jian)的(de)(de)工(gong)作狀(zhuang)態，很容易下手進行維(wei)修(xiu)。

微機電源(yuan)一般容(rong)易出(chu)的(de)故障(zhang)有(you)以下(xia)幾種：保險絲(si)熔斷、電源(yuan)無輸(shu)(shu)出(chu)或輸(shu)(shu)出(chu)電壓不穩定、電源(yuan)有(you)輸(shu)(shu)出(chu)但開機無顯示、電源(yuan)負載(zai)能力差。下(xia)面分別(bie)介紹其檢修方法：

故障一：保險絲熔斷

出現此(ci)類故(gu)障時(shi)，先打開電(dian)(dian)源外(wai)殼，檢查電(dian)(dian)源上(shang)的保(bao)險(xian)絲(si)(si)是(shi)(shi)(shi)(shi)否熔斷，據此(ci)可以初步(bu)確定逆變電(dian)(dian)路(lu)(lu)(lu)是(shi)(shi)(shi)(shi)否發(fa)生了故(gu)障。若是(shi)(shi)(shi)(shi)，則不外(wai)如下(xia)三種情況造成(cheng)：輸(shu)入回路(lu)(lu)(lu)中某個橋式整(zheng)流(liu)(liu)二(er)極(ji)管(guan)被(bei)擊(ji)穿；高壓濾波電(dian)(dian)解(jie)電(dian)(dian)容(rong)被(bei)擊(ji)穿；逆變功率開關管(guan)損壞。其(qi)主要(yao)原(yuan)因(yin)是(shi)(shi)(shi)(shi)因(yin)為直(zhi)流(liu)(liu)濾波及變換振蕩(dang)電(dian)(dian)路(lu)(lu)(lu)長時(shi)間工作在高壓(＋300V)、大電(dian)(dian)流(liu)(liu)狀態，特別是(shi)(shi)(shi)(shi)由于交流(liu)(liu)電(dian)(dian)壓變化較大、輸(shu)出負(fu)載較重時(shi)，易(yi)出現保(bao)險(xian)絲(si)(si)熔斷的故(gu)障。直(zhi)流(liu)(liu)濾波電(dian)(dian)路(lu)(lu)(lu)由四(si)只整(zheng)流(liu)(liu)二(er)極(ji)管(guan)、兩(liang)只100KΩ左右限流(liu)(liu)電(dian)(dian)阻和兩(liang)只330μF左右的電(dian)(dian)解(jie)電(dian)(dian)容(rong)組(zu)成(cheng)；變換振蕩(dang)電(dian)(dian)路(lu)(lu)(lu)則主要(yao)由裝在同一散(san)熱片(pian)上(shang)的兩(liang)只型號相(xiang)同的大功率開關管(guan)組(zu)成(cheng)。

交流(liu)保險(xian)(xian)絲熔斷(duan)后(hou)(hou)，關機(ji)拔掉(diao)電(dian)(dian)(dian)(dian)(dian)(dian)源插頭(tou)，首(shou)先仔(zi)細觀察(cha)電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)板上各高(gao)壓元(yuan)(yuan)件(jian)(jian)的(de)(de)外表(biao)是否(fou)(fou)有(you)(you)(you)被擊穿(chuan)燒糊或電(dian)(dian)(dian)(dian)(dian)(dian)解液溢出的(de)(de)痕跡，若無異常，用(yong)萬用(yong)表(biao)測(ce)(ce)量輸入(ru)端的(de)(de)值(zhi)，若小于200KΩ，說明后(hou)(hou)端有(you)(you)(you)局部短路(lu)(lu)現象，再(zai)分別(bie)測(ce)(ce)量兩(liang)個大(da)功(gong)率(lv)開(kai)(kai)關管e、c極(ji)(ji)間的(de)(de)阻值(zhi)，若小于100KΩ，則說明開(kai)(kai)關管已損壞，測(ce)(ce)量四只整流(liu)二級(ji)管正(zheng)、反(fan)向(xiang)電(dian)(dian)(dian)(dian)(dian)(dian)阻和兩(liang)個限(xian)流(liu)電(dian)(dian)(dian)(dian)(dian)(dian)阻的(de)(de)阻值(zhi)，用(yong)萬用(yong)表(biao)測(ce)(ce)量其充放電(dian)(dian)(dian)(dian)(dian)(dian)情況以判定是否(fou)(fou)正(zheng)常。另外在更換(huan)開(kai)(kai)關管時(shi)，如果無法找(zhao)到同型號產品(pin)而(er)選擇代用(yong)品(pin)時(shi)，應注意集(ji)電(dian)(dian)(dian)(dian)(dian)(dian)極(ji)(ji)-發射(she)極(ji)(ji)反(fan)向(xiang)擊穿(chuan)電(dian)(dian)(dian)(dian)(dian)(dian)壓Vceo、集(ji)電(dian)(dian)(dian)(dian)(dian)(dian)極(ji)(ji)最大(da)允許耗(hao)散(san)功(gong)率(lv)Pcm、集(ji)電(dian)(dian)(dian)(dian)(dian)(dian)極(ji)(ji)-基極(ji)(ji)反(fan)向(xiang)擊穿(chuan)電(dian)(dian)(dian)(dian)(dian)(dian)壓Vcbo的(de)(de)參數(shu)應大(da)于或等于原晶體管的(de)(de)參數(shu)。再(zai)一個要注意的(de)(de)是：切不可在查(cha)出某元(yuan)(yuan)件(jian)(jian)損壞時(shi)，更換(huan)后(hou)(hou)便(bian)直接開(kai)(kai)機(ji)，這樣很可能(neng)由于其它高(gao)壓元(yuan)(yuan)件(jian)(jian)仍有(you)(you)(you)故障(zhang)(zhang)又將(jiang)更換(huan)的(de)(de)元(yuan)(yuan)件(jian)(jian)損壞。一定要對上述(shu)電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)的(de)(de)所(suo)有(you)(you)(you)高(gao)壓元(yuan)(yuan)件(jian)(jian)進行全面檢查(cha)測(ce)(ce)量后(hou)(hou)，才能(neng)徹底(di)排除(chu)保險(xian)(xian)絲熔斷(duan)故障(zhang)(zhang)。

故障二：無直流電壓輸出或電壓輸出不穩定

故障(zhang)分析(xi)與排除(chu)：若(ruo)保險絲完(wan)好，在(zai)有負載(zai)情況(kuang)下，各級直流電(dian)(dian)(dian)(dian)壓(ya)(ya)無輸(shu)出(chu)，其(qi)可能(neng)原因有：電(dian)(dian)(dian)(dian)源(yuan)中出(chu)現(xian)開路(lu)(lu)、短(duan)路(lu)(lu)現(xian)象(xiang)(xiang)，過(guo)壓(ya)(ya)、過(guo)流保護電(dian)(dian)(dian)(dian)路(lu)(lu)出(chu)現(xian)故障(zhang)，振(zhen)蕩電(dian)(dian)(dian)(dian)路(lu)(lu)沒有工(gong)作，電(dian)(dian)(dian)(dian)源(yuan)負載(zai)過(guo)重(zhong)，高頻(pin)整流濾(lv)電(dian)(dian)(dian)(dian)路(lu)(lu)中整流二極(ji)管(guan)被擊(ji)穿，濾(lv)波電(dian)(dian)(dian)(dian)容漏電(dian)(dian)(dian)(dian)等。處理方法為：用(yong)萬(wan)用(yong)表(biao)測(ce)量系統板(ban)(ban)＋5V電(dian)(dian)(dian)(dian)源(yuan)的對地(di)電(dian)(dian)(dian)(dian)阻(zu)(zu)，若(ruo)大于0.8Ω，則(ze)說明系統板(ban)(ban)無短(duan)路(lu)(lu)現(xian)象(xiang)(xiang)；將微(wei)機(ji)(ji)配置(zhi)改為最小(xiao)化，即(ji)機(ji)(ji)器中只留主板(ban)(ban)、電(dian)(dian)(dian)(dian)源(yuan)、蜂鳴(ming)器，測(ce)量各輸(shu)出(chu)端的直流電(dian)(dian)(dian)(dian)壓(ya)(ya)，若(ruo)仍無輸(shu)出(chu)，說明故障(zhang)出(chu)在(zai)微(wei)機(ji)(ji)電(dian)(dian)(dian)(dian)源(yuan)的控(kong)制(zhi)(zhi)電(dian)(dian)(dian)(dian)路(lu)(lu)中。控(kong)制(zhi)(zhi)電(dian)(dian)(dian)(dian)路(lu)(lu)主要由集(ji)成開關(guan)電(dian)(dian)(dian)(dian)源(yuan)控(kong)制(zhi)(zhi)器(TL-496、GS3424等)和過(guo)壓(ya)(ya)保護電(dian)(dian)(dian)(dian)路(lu)(lu)組成，控(kong)制(zhi)(zhi)電(dian)(dian)(dian)(dian)路(lu)(lu)工(gong)作是(shi)(shi)否正(zheng)常直接關(guan)系到直流電(dian)(dian)(dian)(dian)壓(ya)(ya)有無輸(shu)出(chu)。過(guo)壓(ya)(ya)保護電(dian)(dian)(dian)(dian)路(lu)(lu)主要由小(xiao)功率(lv)三極(ji)管(guan)或可控(kong)硅(gui)及相關(guan)元件組成，可用(yong)萬(wan)用(yong)表(biao)測(ce)量該三極(ji)管(guan)是(shi)(shi)否被擊(ji)穿(若(ruo)是(shi)(shi)可控(kong)硅(gui)則(ze)需焊(han)下測(ce)量)、相關(guan)電(dian)(dian)(dian)(dian)阻(zu)(zu)及電(dian)(dian)(dian)(dian)容是(shi)(shi)否損壞(huai)(huai)。最后用(yong)萬(wan)用(yong)表(biao)靜態測(ce)量高頻(pin)濾(lv)波電(dian)(dian)(dian)(dian)路(lu)(lu)中整流二極(ji)管(guan)及低(di)壓(ya)(ya)濾(lv)波電(dian)(dian)(dian)(dian)容是(shi)(shi)否損壞(huai)(huai)。

故障三：電源有輸出，但開機無顯示

故障分析與排除：出現(xian)此(ci)故障的可能原因是“POWER GOOD”輸(shu)入的Reset信號延遲(chi)時間不夠，或“POWER GOOD”無輸(shu)出。

開(kai)機(ji)后，用電壓表(biao)測(ce)量“POWERGOOD”的輸(shu)出(chu)端(接主(zhu)機(ji)電源插頭的1腳(jiao))，如果無＋5V輸(shu)出(chu)，再檢(jian)查延(yan)時(shi)元器件，若(ruo)有＋5V輸(shu)出(chu)，則更(geng)換延(yan)時(shi)電路的延(yan)時(shi)電容即(ji)可(ke)。

故障四：電源負載能力差

故障分析與排(pai)除：電(dian)(dian)源在(zai)只向主板、軟驅供電(dian)(dian)時能(neng)(neng)正常工(gong)(gong)作(zuo)，當(dang)接(jie)上硬(ying)盤、光(guang)驅后，屏幕(mu)變白而不能(neng)(neng)正常工(gong)(gong)作(zuo)。其可能(neng)(neng)原因有：晶體管工(gong)(gong)作(zuo)點未選擇好，高壓濾波電(dian)(dian)容漏(lou)電(dian)(dian)或損壞，穩(wen)壓二(er)極管發熱漏(lou)電(dian)(dian)，整流二(er)級(ji)管損壞等。

調(diao)換振蕩(dang)回路(lu)中各晶(jing)體管，使(shi)其(qi)增(zeng)益提高，或調(diao)大晶(jing)體管的(de)工作點。用(yong)萬用(yong)表檢測(ce)出(chu)有問題的(de)部件后(hou)，更換可(ke)控硅、穩(wen)壓二極管、高壓濾波電容(rong)或整流二極管即可(ke)。

故障五：無直流輸出

可(ke)(ke)能(neng)出現(xian)(xian)故(gu)(gu)障(zhang)的(de)(de)(de)部位(wei)有(you)(you)：保險(xian)管(guan)(guan)(guan)(guan)燒斷(duan)(duan)，變(bian)換(huan)(huan)器(qi)(qi)不工作，控制電(dian)(dian)(dian)(dian)路故(gu)(gu)障(zhang)。打開(kai)電(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)盒，發(fa)現(xian)(xian)保險(xian)管(guan)(guan)(guan)(guan)去掉(diao)。根(gen)據用(yong)(yong)戶反(fan)映保險(xian)管(guan)(guan)(guan)(guan)屢換(huan)(huan)屢燒。焊下整流(liu)(liu)(liu)(liu)二極(ji)管(guan)(guan)(guan)(guan)和變(bian)換(huan)(huan)器(qi)(qi)功率開(kai)關(guan)管(guan)(guan)(guan)(guan)，用(yong)(yong)萬(wan)用(yong)(yong)表檢(jian)測(ce)(ce)都(dou)正常(chang)，用(yong)(yong)高(gao)阻(zu)檔檢(jian)測(ce)(ce)交(jiao)(jiao)(jiao)流(liu)(liu)(liu)(liu)輸入(ru)端(duan)無短路現(xian)(xian)象。檢(jian)測(ce)(ce)整流(liu)(liu)(liu)(liu)濾(lv)波(bo)電(dian)(dian)(dian)(dian)容正常(chang)。根(gen)據保險(xian)管(guan)(guan)(guan)(guan)燒斷(duan)(duan)的(de)(de)(de)現(xian)(xian)象判斷(duan)(duan)，故(gu)(gu)障(zhang)部位(wei)應在變(bian)換(huan)(huan)器(qi)(qi)初(chu)級繞組前(qian)，但沒(mei)有(you)(you)發(fa)現(xian)(xian)短路的(de)(de)(de)地方。只(zhi)好恢復原態(tai)，換(huan)(huan)保險(xian)管(guan)(guan)(guan)(guan)加(jia)電(dian)(dian)(dian)(dian)實驗。接(jie)通交(jiao)(jiao)(jiao)流(liu)(liu)(liu)(liu)電(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)，保險(xian)燒斷(duan)(duan)，立即斷(duan)(duan)開(kai)交(jiao)(jiao)(jiao)流(liu)(liu)(liu)(liu)電(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)檢(jian)查(cha)，保險(xian)管(guan)(guan)(guan)(guan)燒得漆黑。可(ke)(ke)見(jian)交(jiao)(jiao)(jiao)流(liu)(liu)(liu)(liu)輸入(ru)電(dian)(dian)(dian)(dian)路有(you)(you)嚴重的(de)(de)(de)短路現(xian)(xian)象，斷(duan)(duan)開(kai)整流(liu)(liu)(liu)(liu)橋的(de)(de)(de)交(jiao)(jiao)(jiao)流(liu)(liu)(liu)(liu)輸入(ru)。在整流(liu)(liu)(liu)(liu)橋交(jiao)(jiao)(jiao)流(liu)(liu)(liu)(liu)輸入(ru)兩端(duan)加(jia)接(jie)保險(xian)管(guan)(guan)(guan)(guan)，直(zhi)接(jie)接(jie)到(dao)交(jiao)(jiao)(jiao)流(liu)(liu)(liu)(liu)電(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)上。接(jie)通電(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)，穩(wen)壓電(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)風機旋轉正常(chang)，測(ce)(ce)試各直(zhi)流(liu)(liu)(liu)(liu)輸出電(dian)(dian)(dian)(dian)壓正常(chang)。可(ke)(ke)見(jian)故(gu)(gu)障(zhang)部位(wei)在交(jiao)(jiao)(jiao)流(liu)(liu)(liu)(liu)濾(lv)波(bo)電(dian)(dian)(dian)(dian)路中，而用(yong)(yong)萬(wan)用(yong)(yong)表檢(jian)測(ce)(ce)已無能(neng)為力。這時想到(dao)替代法，從另(ling)一(yi)臺(tai)電(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)上拆下兩個(ge)交(jiao)(jiao)(jiao)流(liu)(liu)(liu)(liu)濾(lv)波(bo)電(dian)(dian)(dian)(dian)容替代，(因(yin)焊接(jie)簡單，所以先換(huan)(huan)電(dian)(dian)(dian)(dian)容)加(jia)電(dian)(dian)(dian)(dian)測(ce)(ce)試，直(zhi)流(liu)(liu)(liu)(liu)穩(wen)壓電(dian)(dian)(dian)(dian)源(yuan)(yuan)(yuan)工作正常(chang)。可(ke)(ke)見(jian)故(gu)(gu)障(zhang)部位(wei)在這兩個(ge)電(dian)(dian)(dian)(dian)容中，用(yong)(yong)高(gao)壓絕緣儀(yi)測(ce)(ce)試，其中一(yi)只(zhi)電(dian)(dian)(dian)(dian)容高(gao)壓擊穿。

故障六：開機后計算機自檢，引導正(zheng)常(chang)，在(zai)屏幕提示“INSERT SYSTEM DISK IN DRIVE A AND PRESS ANY KEY”時插(cha)入DOS盤，軟驅不(bu)讀盤。

從(cong)故障(zhang)(zhang)(zhang)現象(xiang)分析，故障(zhang)(zhang)(zhang)部位(wei)在軟盤驅(qu)動器(qi)(qi)、軟盤適(shi)(shi)配(pei)器(qi)(qi)或系統中(zhong)。經過替(ti)代法(fa)，證明這臺機器(qi)(qi)上的(de)軟盤適(shi)(shi)配(pei)器(qi)(qi)、軟盤驅(qu)動器(qi)(qi)是好的(de)。最(zui)后把主板拆(chai)下來驗(yan)證是好的(de)，恢復(fu)原態后加電(dian)試驗(yan)，故障(zhang)(zhang)(zhang)不能(neng)消除(chu)。因(yin)此懷疑(yi)到電(dian)源(yuan)部分。

在機箱里(li)拔(ba)下(xia)5寸軟(ruan)驅(qu)電(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)插(cha)(cha)頭(tou)。開機，用(yong)萬用(yong)表檢測(ce)直(zhi)(zhi)流輸(shu)出(chu)(chu)，＋5V，＋12V都正常(chang)。斷電(dian)(dian)(dian)(dian)(dian)插(cha)(cha)好軟(ruan)驅(qu)電(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)插(cha)(cha)頭(tou)，再(zai)開機故(gu)障(zhang)不變(bian)(bian)(bian)。后(hou)在全負(fu)載(zai)下(xia)測(ce)直(zhi)(zhi)流輸(shu)出(chu)(chu)＋5V為＋4.1V，＋2V為＋10.4V。由于電(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)輸(shu)出(chu)(chu)電(dian)(dian)(dian)(dian)(dian)壓降低(di)影響(xiang)軟(ruan)驅(qu)馬達(da)的(de)正常(chang)運行，造成(cheng)不能(neng)正常(chang)讀(du)盤。原因找(zhao)到(dao)后(hou)，拆下(xia)電(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)進行維(wei)修，當(dang)負(fu)載(zai)較輕時(shi)，電(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)輸(shu)出(chu)(chu)正常(chang)；當(dang)負(fu)載(zai)加重，電(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)輸(shu)出(chu)(chu)降低(di)。說明穩壓電(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)負(fu)載(zai)能(neng)力降低(di)。打開電(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)盒(he)蓋(gai)，用(yong)示波(bo)器(qi)檢測(ce)TL494組件8，11端和(he)信號放(fang)大(da)(da)管(guan)(guan)的(de)波(bo)形幅度不受負(fu)載(zai)影響(xiang)。檢測(ce)到(dao)變(bian)(bian)(bian)換器(qi)＋5V繞組波(bo)形時(shi)，負(fu)載(zai)對其有(you)影響(xiang)，但變(bian)(bian)(bian)化(hua)(hua)幅度很(hen)小，因此懷疑(yi)＋5V整(zheng)流二極管(guan)(guan)正向壓降變(bian)(bian)(bian)大(da)(da)，造成(cheng)輸(shu)出(chu)(chu)能(neng)力降低(di)。更(geng)換＋5V整(zheng)流管(guan)(guan)后(hou)，再(zai)次(ci)加電(dian)(dian)(dian)(dian)(dian)測(ce)試(shi)，故(gu)障(zhang)不能(neng)排(pai)除(chu)(chu)，這(zhe)時(shi)維(wei)修陷入了(le)困境(jing)。后(hou)來冷靜分析，影響(xiang)直(zhi)(zhi)流輸(shu)出(chu)(chu)的(de)因素還有(you)功(gong)率(lv)開關(guan)管(guan)(guan)。更(geng)換功(gong)率(lv)開關(guan)管(guan)(guan)后(hou)開機試(shi)驗，在負(fu)載(zai)發(fa)生變(bian)(bian)(bian)化(hua)(hua)時(shi)，直(zhi)(zhi)流輸(shu)出(chu)(chu)正常(chang)，故(gu)障(zhang)排(pai)除(chu)(chu)。換下(xia)的(de)功(gong)率(lv)管(guan)(guan)用(yong)JL-1進行測(ce)試(shi)，放(fang)大(da)(da)倍數(shu)很(hen)小。后(hou)從用(yong)戶(hu)處了(le)解(jie)到(dao)這(zhe)臺(tai)機已連續工(gong)作4年多了(le)。這(zhe)是(shi)功(gong)率(lv)管(guan)(guan)老(lao)化(hua)(hua)造成(cheng)了(le)這(zhe)次(ci)故(gu)障(zhang)。從這(zhe)起事例中得出(chu)(chu)，微機發(fa)生故(gu)障(zhang)時(shi)應首(shou)先檢查直(zhi)(zhi)流電(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)的(de)輸(shu)出(chu)(chu)電(dian)(dian)(dian)(dian)(dian)壓，這(zhe)對維(wei)修人員縮小故(gu)障(zhang)范(fan)圍，快速排(pai)除(chu)(chu)故(gu)障(zhang)極為有(you)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(gen)據故(gu)障(zhang)現(xian)象分(fen)析，電(dian)源通電(dian)后有直流輸出(chu)，說(shuo)(shuo)明電(dian)源基本上(shang)是能(neng)正常工(gong)作的(de)。調整＋5V采樣電(dian)位器，電(dian)壓不能(neng)提升，說(shuo)(shuo)明故(gu)障(zhang)發生(sheng)在控制電(dian)路中。在電(dian)源通電(dian)后有＋3.5V的(de)輸出(chu)分(fen)析，可能(neng)是控制信號單邊工(gong)作造成的(de)。

根(gen)據(ju)故(gu)(gu)障分(fen)析，在(zai)電(dian)源通電(dian)之(zhi)后(hou)用(yong)(yong)萬用(yong)(yong)表檢(jian)測TL494的(de)各腳(jiao)電(dian)平，由于(yu)直(zhi)流輸(shu)(shu)出不正(zheng)(zheng)(zheng)常(chang)(chang)，所以1端電(dian)平比(bi)正(zheng)(zheng)(zheng)常(chang)(chang)值偏(pian)低。8，11兩(liang)端電(dian)平用(yong)(yong)直(zhi)流電(dian)壓檔測在(zai)2.0V左右(you) 屬于(yu)正(zheng)(zheng)(zheng)常(chang)(chang)。用(yong)(yong)示波器觀(guan)察(cha)8，11兩(liang)端和信號放大管(guan)的(de)輸(shu)(shu)出幅(fu)度在(zai)12V左右(you)都正(zheng)(zheng)(zheng)常(chang)(chang)，排(pai)(pai)除(chu)了單邊工(gong)作的(de)懷疑。在(zai)故(gu)(gu)障部(bu)位不能確(que)定的(de)情(qing)(qing)況(kuang)下，用(yong)(yong)新(xin)的(de)TL494電(dian)路替換后(hou)＋5V電(dian)壓能提(ti)高到＋4V多一點，仍不能達到正(zheng)(zheng)(zheng)常(chang)(chang)輸(shu)(shu)出。最后(hou)決定換功率(lv)開(kai)關管(guan)，換后(hou)直(zhi)流輸(shu)(shu)出達到正(zheng)(zheng)(zheng)常(chang)(chang)值，故(gu)(gu)障排(pai)(pai)除(chu)。從(cong)維修情(qing)(qing)況(kuang)分(fen)析，這起故(gu)(gu)障也是(shi)由于(yu)開(kai)關管(guan)老化所造成(cheng)的(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(zhang)(zhang)現象分(fen)析可能是電(dian)(dian)源(yuan)開(kai)關(guan)接(jie)觸(chu)不(bu)(bu)良(liang)造(zao)成(cheng)的。換電(dian)(dian)源(yuan)開(kai)關(guan)后，故(gu)障(zhang)(zhang)不(bu)(bu)能排除。不(bu)(bu)過在打(da)開(kai)電(dian)(dian)源(yuan)開(kai)關(guan)，等(deng)大約(yue)十多分(fen)鐘后，微機自動啟(qi)動，由此分(fen)析，故(gu)障(zhang)(zhang)出在電(dian)(dian)源(yuan)控(kong)制部(bu)分(fen)元(yuan)件溫度(du)性能不(bu)(bu)良(liang)造(zao)成(cheng)的故(gu)障(zhang)(zhang)。

把電(dian)(dian)(dian)(dian)(dian)(dian)源從機(ji)箱中(zhong)取出(chu)(chu)，打開(kai)(kai)電(dian)(dian)(dian)(dian)(dian)(dian)源蓋(gai)，加上(shang)負載通電(dian)(dian)(dian)(dian)(dian)(dian)檢(jian)測(ce)(ce)，開(kai)(kai)機(ji)時＋5V有＋1.2V，＋12V有＋3V輸(shu)出(chu)(chu)，交流整流300V輸(shu)出(chu)(chu)正(zheng)常。查功(gong)(gong)率(lv)(lv)開(kai)(kai)關管是好的，用烙鐵對功(gong)(gong)率(lv)(lv)管加溫后再啟動，故障(zhang)不能排(pai)(pai)除(chu)，由此排(pai)(pai)除(chu)了功(gong)(gong)率(lv)(lv)管溫度性能不良(liang)的嫌(xian)疑，判(pan)斷故障(zhang)部位在變換器次級繞組后面(mian)的電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)部分。加電(dian)(dian)(dian)(dian)(dian)(dian)開(kai)(kai)機(ji)后用萬(wan)用表測(ce)(ce)TL494各腳的電(dian)(dian)(dian)(dian)(dian)(dian)平(ping)時發現，輔助電(dian)(dian)(dian)(dian)(dian)(dian)源輸(shu)入端電(dian)(dian)(dian)(dian)(dian)(dian)壓只有5V多(duo)一(yi)點，加電(dian)(dian)(dian)(dian)(dian)(dian)一(yi)段時間后，電(dian)(dian)(dian)(dian)(dian)(dian)壓逐步(bu)上(shang)升，在輔助電(dian)(dian)(dian)(dian)(dian)(dian)源電(dian)(dian)(dian)(dian)(dian)(dian)壓逐步(bu)上(shang)升過程中(zhong)，電(dian)(dian)(dian)(dian)(dian)(dian)源輸(shu)出(chu)(chu)也逐步(bu)上(shang)升到正(zheng)常值。這(zhe)象(xiang)電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)緩慢充電(dian)(dian)(dian)(dian)(dian)(dian)過程。因此在輔助電(dian)(dian)(dian)(dian)(dian)(dian)源電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)(lu)中(zhong)查找到電(dian)(dian)(dian)(dian)(dian)(dian)容(rong)C15，用萬(wan)用表測(ce)(ce)漏電(dian)(dian)(dian)(dian)(dian)(dian)較大(da)。換后故障(zhang)排(pai)(pai)除(chu)。