開關電源是利用現(xian)代電(dian)力電(dian)子(zi)技術，控制開關晶體管開通(tong)和關斷(duan)的時間比率，維(wei)持穩定輸出電(dian)壓的一種電(dian)源(yuan)。廣(guang)泛運用在(zai)工業、軍事(shi)、科研、通(tong)訊、醫療及(ji)(ji)多種家用電(dian)器(qi)中。開關電(dian)源(yuan)的發展(zhan)與應用在(zai)節約(yue)(yue)能源(yuan)、節約(yue)(yue)資源(yuan)及(ji)(ji)保護環境方面都具有重要的意義。下(xia)面我們就(jiu)來看(kan)看(kan)開關電(dian)源(yuan)電(dian)路圖與維(wei)修技巧(qiao)。
開關電(dian)(dian)(dian)源的主要電(dian)(dian)(dian)路(lu)(lu)是由輸入電(dian)(dian)(dian)磁(ci)干擾濾波器（EMI）、整流濾波電(dian)(dian)(dian)路(lu)(lu)、功率(lv)變(bian)換電(dian)(dian)(dian)路(lu)(lu)、PWM控制器電(dian)(dian)(dian)路(lu)(lu)、輸出(chu)整流濾波電(dian)(dian)(dian)路(lu)(lu)組成。輔(fu)助電(dian)(dian)(dian)路(lu)(lu)有輸入過(guo)(guo)欠(qian)壓保護電(dian)(dian)(dian)路(lu)(lu)、輸出(chu)過(guo)(guo)欠(qian)壓保護電(dian)(dian)(dian)路(lu)(lu)、輸出(chu)過(guo)(guo)流保護電(dian)(dian)(dian)路(lu)(lu)、輸出(chu)短路(lu)(lu)保護電(dian)(dian)(dian)路(lu)(lu)等(deng)。
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通電后觀察(cha)電源(yuan)是(shi)否有燒保險(xian)及個別元件(jian)冒煙等現象，若有要及時(shi)切斷供電進行檢修。
測量高壓濾波電容兩端(duan)有無(wu)300伏輸出，若無(wu)應重點查整流二極(ji)管(guan)、濾波電容等(deng)。
測量(liang)高頻變壓器(qi)次級線(xian)圈有無輸出，若(ruo)無應(ying)重(zhong)點(dian)查開關(guan)管(guan)是(shi)否(fou)損壞(huai)，是(shi)否(fou)起(qi)振，保護(hu)電路是(shi)否(fou)動作(zuo)等，若(ruo)有則應(ying)重(zhong)點(dian)檢查各輸出側的整流(liu)二極管(guan)、濾波電容(rong)、三通(tong)穩壓管(guan)等。
如果(guo)電(dian)源(yuan)啟(qi)動一下就停止，則該(gai)電(dian)源(yuan)處于保(bao)護(hu)狀態下，可直接(jie)測量PWM芯片(pian)保(bao)護(hu)輸入腳的(de)電(dian)壓(ya)，如果(guo)電(dian)壓(ya)超出規定值(zhi)，則說明電(dian)源(yuan)處于保(bao)護(hu)狀態下，應(ying)重點檢查(cha)產(chan)生保(bao)護(hu)的(de)原因。
總之，開關(guan)電(dian)(dian)源電(dian)(dian)路有(you)(you)(you)易有(you)(you)(you)難，功率有(you)(you)(you)大(da)有(you)(you)(you)小，輸出電(dian)(dian)壓多(duo)種多(duo)樣(yang)。只要(yao)按照上述維(wei)修技巧，多(duo)動手進(jin)行開關(guan)電(dian)(dian)源的(de)維(wei)修，就(jiu)能迅速地排(pai)除開關(guan)電(dian)(dian)源故障，達到事半(ban)功倍(bei)的(de)效果。
看：打開(kai)電(dian)源的外殼(ke)，檢查(cha)保(bao)險絲(si)是否熔(rong)斷，再(zai)觀察電(dian)源的內部情況，如果(guo)發現電(dian)源的PCB板上有燒焦處(chu)或(huo)元(yuan)(yuan)件破裂，則應重點檢查(cha)此處(chu)元(yuan)(yuan)件及相關(guan)電(dian)路元(yuan)(yuan)件。
聞(wen)：聞(wen)一下(xia)電(dian)源內部是否有糊味，檢(jian)查是否有燒焦的元(yuan)器件。
問：問一下電源(yuan)損(sun)壞的經過，是(shi)否對電源(yuan)進(jin)行違規操作。
量：沒通(tong)電(dian)(dian)(dian)(dian)前，用萬(wan)用表(biao)量一下高(gao)壓電(dian)(dian)(dian)(dian)容(rong)兩端的電(dian)(dian)(dian)(dian)壓先(xian)。如果是(shi)開(kai)(kai)關電(dian)(dian)(dian)(dian)源(yuan)不(bu)起振或開(kai)(kai)關管(guan)開(kai)(kai)路引起的故障(zhang)，則(ze)大多數情況下，高(gao)壓濾(lv)波電(dian)(dian)(dian)(dian)容(rong)兩端的電(dian)(dian)(dian)(dian)壓未泄放(fang)悼，用萬(wan)用表(biao)測量AC電(dian)(dian)(dian)(dian)源(yuan)線兩端的正反(fan)向(xiang)電(dian)(dian)(dian)(dian)阻(zu)(zu)及電(dian)(dian)(dian)(dian)容(rong)器充電(dian)(dian)(dian)(dian)情況，電(dian)(dian)(dian)(dian)阻(zu)(zu)值(zhi)不(bu)應(ying)過低，否則(ze)電(dian)(dian)(dian)(dian)源(yuan)內部(bu)可能存在短路。電(dian)(dian)(dian)(dian)容(rong)器應(ying)能充放(fang)電(dian)(dian)(dian)(dian)。脫開(kai)(kai)負載，分別測量各(ge)組(zu)輸出端的對地電(dian)(dian)(dian)(dian)阻(zu)(zu)，正常時，表(biao)針應(ying)有電(dian)(dian)(dian)(dian)容(rong)器充放(fang)電(dian)(dian)(dian)(dian)擺動，最后指示的應(ying)為該路的泄放(fang)電(dian)(dian)(dian)(dian)阻(zu)(zu)的阻(zu)(zu)值(zhi)。
一(yi)般情況下(xia)(xia)，保(bao)險(xian)絲熔斷說明開關(guan)(guan)電(dian)(dian)源(yuan)的(de)內部電(dian)(dian)路(lu)存在(zai)(zai)短路(lu)或過流的(de)故障(zhang)。由于開關(guan)(guan)電(dian)(dian)源(yuan)工作在(zai)(zai)高電(dian)(dian)壓(ya)，大(da)電(dian)(dian)流的(de)狀態(tai)(tai)下(xia)(xia)，直流濾波和變(bian)換(huan)振蕩電(dian)(dian)路(lu)在(zai)(zai)高壓(ya)狀態(tai)(tai)工作時(shi)間太長(chang)，電(dian)(dian)壓(ya)變(bian)化相(xiang)對大(da)。電(dian)(dian)網電(dian)(dian)壓(ya)的(de)波動，浪涌都會引起(qi)電(dian)(dian)源(yuan)內電(dian)(dian)流瞬間增大(da)而使保(bao)險(xian)絲熔斷。重點應(ying)檢(jian)(jian)查(cha)電(dian)(dian)源(yuan)輸入端的(de)整(zheng)流二極管(guan)，高壓(ya)濾波電(dian)(dian)解電(dian)(dian)容，開關(guan)(guan)功率管(guan)，UC3842本身及外圍元(yuan)器(qi)件(jian)等。檢(jian)(jian)查(cha)一(yi)下(xia)(xia)這些元(yuan)器(qi)件(jian)有無(wu)擊穿，開路(lu)，損壞，燒焦，炸裂等現象。
維(wei)修(xiu)方法(fa)：首先仔細查看(kan)(kan)電(dian)(dian)(dian)(dian)(dian)路板上(shang)面(mian)的各個(ge)元(yuan)件，看(kan)(kan)是(shi)否(fou)在(zai)這(zhe)些(xie)元(yuan)件的外(wai)表有沒有被燒糊,有沒有電(dian)(dian)(dian)(dian)(dian)解液(ye)溢出(chu)，聞(wen)一聞(wen)有沒有異味。經(jing)看(kan)(kan)，聞(wen)之后，再(zai)用(yong)萬(wan)用(yong)表進(jin)行(xing)檢查。首先測量一下(xia)(xia)(xia)電(dian)(dian)(dian)(dian)(dian)源(yuan)輸(shu)入端(duan)的電(dian)(dian)(dian)(dian)(dian)阻值，若小于200K，則說(shuo)(shuo)明(ming)后端(duan)有局部短路現象，然(ran)后分別測量四(si)只整流(liu)二極(ji)管正，反向(xiang)電(dian)(dian)(dian)(dian)(dian)阻和兩(liang)個(ge)限流(liu)電(dian)(dian)(dian)(dian)(dian)阻的阻值，看(kan)(kan)其有無短路或(huo)燒壞；然(ran)后再(zai)測量一下(xia)(xia)(xia)電(dian)(dian)(dian)(dian)(dian)源(yuan)濾波電(dian)(dian)(dian)(dian)(dian)容是(shi)否(fou)能進(jin)行(xing)正常充(chong)放(fang)電(dian)(dian)(dian)(dian)(dian)，再(zai)就(jiu)測量一下(xia)(xia)(xia)開關功(gong)率管是(shi)否(fou)擊穿(chuan)損壞，以(yi)及UC3842本身，及周(zhou)圍元(yuan)件是(shi)否(fou)擊穿(chuan)，燒壞等。需要說(shuo)(shuo)明(ming)的一點是(shi)：因(yin)是(shi)在(zai)路測量，有可(ke)能會使測量結果(guo)有誤，造成(cheng)誤判。因(yin)此必(bi)要時可(ke)把(ba)元(yuan)器件焊(han)下(xia)(xia)(xia)來(lai)再(zai)進(jin)行(xing)測量。如果(guo)仍然(ran)沒有上(shang)述情況則測量一下(xia)(xia)(xia)輸(shu)入電(dian)(dian)(dian)(dian)(dian)源(yuan)線及輸(shu)出(chu)電(dian)(dian)(dian)(dian)(dian)源(yuan)線是(shi)否(fou)內部短路。一般情況下(xia)(xia)(xia)，熔斷(duan)(duan)器熔斷(duan)(duan)故障(zhang)，整流(liu)二極(ji)管，電(dian)(dian)(dian)(dian)(dian)源(yuan)濾波電(dian)(dian)(dian)(dian)(dian)容，開關功(gong)率管，UC3842是(shi)易損件，損壞的概率可(ke)達95%以(yi)上(shang)，一般著重檢查一下(xia)(xia)(xia)這(zhe)些(xie)元(yuan)器件，就(jiu)可(ke)很容易排除此類故障(zhang)。
如果保(bao)險絲(si)是(shi)完好的，在有負載(zai)的情況(kuang)下，各級直(zhi)流電(dian)(dian)(dian)壓(ya)無輸出(chu)。這種情況(kuang)主要是(shi)以下原因(yin)造成(cheng)的：電(dian)(dian)(dian)源(yuan)(yuan)中出(chu)現開路(lu)，短路(lu)現象，過(guo)壓(ya)，過(guo)流保(bao)護電(dian)(dian)(dian)路(lu)出(chu)現故障(zhang)，振(zhen)蕩電(dian)(dian)(dian)路(lu)沒有工作，電(dian)(dian)(dian)源(yuan)(yuan)負載(zai)過(guo)重，高頻整流濾(lv)波電(dian)(dian)(dian)路(lu)中整流二極管被(bei)擊穿(chuan)，濾(lv)波電(dian)(dian)(dian)容漏電(dian)(dian)(dian)等(deng)。
維修(xiu)方法：首先，用萬用表測量(liang)(liang)一下高頻變壓(ya)器(qi)次級的(de)各個元(yuan)器(qi)件(jian)(jian)(jian)是(shi)否有損(sun)(sun)壞(huai)。在(zai)(zai)排(pai)除了(le)高頻整(zheng)流二(er)極(ji)管(guan)擊穿、負(fu)載短路(lu)的(de)情(qing)況(kuang)后(hou)(hou)，然后(hou)(hou)在(zai)(zai)測量(liang)(liang)各輸(shu)出端的(de)直流電(dian)(dian)(dian)壓(ya)，如果這時輸(shu)出仍為(wei)零，則可以肯定(ding)是(shi)電(dian)(dian)(dian)源的(de)控(kong)制(zhi)電(dian)(dian)(dian)路(lu)出了(le)故(gu)障。控(kong)制(zhi)電(dian)(dian)(dian)路(lu)的(de)兩部分是(shi)集成開(kai)(kai)關電(dian)(dian)(dian)源控(kong)制(zhi)器(qi)和過(guo)壓(ya)保護電(dian)(dian)(dian)路(lu)。最后(hou)(hou)用萬用表靜態測量(liang)(liang)高頻濾波電(dian)(dian)(dian)路(lu)中整(zheng)流二(er)極(ji)管(guan)及低壓(ya)濾波電(dian)(dian)(dian)容是(shi)否損(sun)(sun)壞(huai)。如果確(que)實相關的(de)元(yuan)件(jian)(jian)(jian)損(sun)(sun)壞(huai)，在(zai)(zai)更(geng)換(huan)好新的(de)完好的(de)元(yuan)件(jian)(jian)(jian)后(hou)(hou)，開(kai)(kai)機(ji)測試，一般故(gu)障即可排(pai)除。需(xu)要說明(ming)的(de)是(shi)：電(dian)(dian)(dian)源輸(shu)出線斷線或開(kai)(kai)焊，虛焊也會(hui)造成這種故(gu)障。在(zai)(zai)維修(xiu)時應注意這一點。
電(dian)源負(fu)載(zai)能力差是(shi)一個常(chang)見(jian)的故障，一般都是(shi)出現(xian)在老式或是(shi)工作(zuo)時間(jian)長的電(dian)源中，主要原因是(shi)各(ge)元器件老化，開關(guan)管的工作(zuo)不穩定(ding)，沒有(you)及時進行散(san)熱等。此外還(huan)有(you)穩壓二極(ji)(ji)管發熱漏電(dian)，整(zheng)流二極(ji)(ji)管損壞等。
維修方法：用(yong)萬用(yong)表著重檢查一下穩壓二極管，高壓濾波電(dian)容，限流電(dian)阻有無變質(zhi)等再仔細檢查一下電(dian)路板(ban)上的(de)(de)(de)所(suo)有焊(han)點(dian)是否開(kai)焊(han)，虛接等。把開(kai)焊(han)的(de)(de)(de)焊(han)點(dian)重新焊(han)牢，更換(huan)變質(zhi)的(de)(de)(de)元(yuan)器件(jian)，一般故障即可排(pai)除。
這種現象(xiang)說(shuo)明開關電源未工(gong)作(zuo)，或者工(gong)作(zuo)后進入了保護狀態。
維修方法(fa)：首先應(ying)(ying)判(pan)斷一(yi)下(xia)開(kai)(kai)關(guan)電(dian)(dian)源的(de)(de)主(zhu)控芯片UC3842是否處在工作狀(zhuang)態或已(yi)經損(sun)壞(huai)(huai)。判(pan)斷方法(fa)是這樣的(de)(de)：加電(dian)(dian)測UC3842的(de)(de)第(di)7腳(jiao)(jiao)(jiao)對(dui)(dui)地電(dian)(dian)壓(ya)(ya)，若(ruo)測第(di)8腳(jiao)(jiao)(jiao)有+5V電(dian)(dian)壓(ya)(ya)，1，2，4，6腳(jiao)(jiao)(jiao)也有不同的(de)(de)電(dian)(dian)壓(ya)(ya)，則(ze)(ze)說明(ming)電(dian)(dian)路已(yi)起振(zhen)，UC3842基本正(zheng)常；若(ruo)7腳(jiao)(jiao)(jiao)電(dian)(dian)壓(ya)(ya)低，其余管腳(jiao)(jiao)(jiao)無(wu)電(dian)(dian)壓(ya)(ya)或不波(bo)動，則(ze)(ze)UC3842已(yi)損(sun)壞(huai)(huai)。UC3842芯片損(sun)壞(huai)(huai)最常見的(de)(de)是6，7腳(jiao)(jiao)(jiao)對(dui)(dui)地擊(ji)穿(chuan)，5，7腳(jiao)(jiao)(jiao)對(dui)(dui)地擊(ji)穿(chuan)和1，7腳(jiao)(jiao)(jiao)對(dui)(dui)地擊(ji)穿(chuan)。如(ru)果這幾只(zhi)腳(jiao)(jiao)(jiao)都為(wei)擊(ji)穿(chuan)，而開(kai)(kai)關(guan)電(dian)(dian)源還是不能(neng)正(zheng)常啟動，則(ze)(ze)UC3842必壞(huai)(huai)，應(ying)(ying)直(zhi)接更(geng)換。若(ruo)判(pan)斷芯片未壞(huai)(huai)，則(ze)(ze)就著重(zhong)檢(jian)查(cha)(cha)開(kai)(kai)關(guan)功率(lv)管的(de)(de)柵極（G極）的(de)(de)限(xian)流電(dian)(dian)阻(zu)是否開(kai)(kai)焊，虛接，變值，變質以及(ji)開(kai)(kai)關(guan)功率(lv)管本身是否性能(neng)不良。除此之(zhi)外，電(dian)(dian)源輸出(chu)線(xian)也有可能(neng)斷線(xian)或接觸(chu)不良也會造成(cheng)這種故障(zhang)。因(yin)此在維修時也應(ying)(ying)注意檢(jian)查(cha)(cha)一(yi)下(xia)。
這種(zhong)故(gu)障(zhang)往往來自于穩壓取(qu)樣(yang)和(he)穩壓控(kong)制電(dian)(dian)路出(chu)現故(gu)障(zhang)所致。在開關電(dian)(dian)源(yuan)(yuan)中，直流輸出(chu)、取(qu)樣(yang)電(dian)(dian)阻、誤(wu)差取(qu)樣(yang)放大器(qi)（如LM324，LM358等）、光耦合器(qi)（PC817）、電(dian)(dian)源(yuan)(yuan)控(kong)制芯片（UC3842）等電(dian)(dian)路共同構成了一個閉合的控(kong)制環路，任(ren)何(he)一處出(chu)問題都(dou)會(hui)導致輸出(chu)電(dian)(dian)壓升高。
維(wei)修方法(fa)：由(you)于開關(guan)電源中(zhong)有過(guo)(guo)(guo)(guo)(guo)壓(ya)(ya)保護電路(lu)(lu)，輸出電壓(ya)(ya)過(guo)(guo)(guo)(guo)(guo)高(gao)首(shou)先(xian)會使過(guo)(guo)(guo)(guo)(guo)壓(ya)(ya)保護電路(lu)(lu)動(dong)作。因(yin)此對于這(zhe)種故障的維(wei)修，我們(men)可以通(tong)過(guo)(guo)(guo)(guo)(guo)斷(duan)開過(guo)(guo)(guo)(guo)(guo)壓(ya)(ya)保護電路(lu)(lu)，使過(guo)(guo)(guo)(guo)(guo)壓(ya)(ya)保護電路(lu)(lu)不起作用，在(zai)這(zhe)時，測(ce)量(liang)開機瞬(shun)間的電源主電壓(ya)(ya)。如果測(ce)量(liang)值(zhi)比正(zheng)常值(zhi)高(gao)出IV以上(shang)，說明輸出電壓(ya)(ya)過(guo)(guo)(guo)(guo)(guo)高(gao)。我們(men)應(ying)著重(zhong)檢查取樣電阻(zu)(zu)是(shi)否變值(zhi)或損(sun)壞(huai)，精密(mi)穩(wen)壓(ya)(ya)放大(da)器（TL431）或光耦合器（PC817）性能不良，變質或損(sun)壞(huai)；其中(zhong)精密(mi)穩(wen)壓(ya)(ya)放大(da)器（TL431）極(ji)(ji)易損(sun)壞(huai)，我們(men)可用下述方法(fa)對精密(mi)穩(wen)壓(ya)(ya)放大(da)器（TL431）作出好(hao)壞(huai)的判別：將TL431的參考端（Ref）與它的陰極(ji)(ji)（Cathode）相(xiang)連，串10k的電阻(zu)(zu)，接入5V電壓(ya)(ya)，若陽極(ji)(ji)（Anode）與陰極(ji)(ji)之間為(wei)(wei)2、5V，并且等待片刻還仍然(ran)為(wei)(wei)2、5V，則為(wei)(wei)好(hao)管(guan)(guan)，否則為(wei)(wei)壞(huai)管(guan)(guan)。
對于(yu)這種故(gu)障(zhang)現象，根(gen)據維(wei)修經驗可知，除穩壓控制電(dian)路會(hui)引起輸(shu)出電(dian)壓過低外(wai)，還有(you)一些原因會(hui)引起輸(shu)出電(dian)壓過低，主要有(you)以下幾(ji)點:
① 開(kai)關(guan)電(dian)源負載(zai)(zai)有(you)(you)短(duan)路(lu)故障。此時，應斷(duan)開(kai)開(kai)關(guan)電(dian)源電(dian)路(lu)的所(suo)有(you)(you)負載(zai)(zai)，以(yi)區分是開(kai)關(guan)電(dian)源電(dian)路(lu)還是負載(zai)(zai)電(dian)路(lu)有(you)(you)故障。若斷(duan)開(kai)負載(zai)(zai)電(dian)路(lu)電(dian)壓輸出正常(chang)，說(shuo)明是負載(zai)(zai)過(guo)重(zhong)；若仍不正常(chang)，說(shuo)明開(kai)關(guan)電(dian)源電(dian)路(lu)有(you)(you)故障。
② 輸出電(dian)壓端整流二極管、濾波電(dian)容(rong)失效等(deng)，可以通過(guo)代換法(fa)進行判斷(duan)。
③ 開關功(gong)率管的(de)性能(neng)下(xia)(xia)降(jiang)，必然導(dao)致(zhi)開關管不能(neng)正常(chang)導(dao)通，使(shi)電(dian)源的(de)內(nei)阻增加，帶負(fu)載能(neng)力下(xia)(xia)降(jiang)。
④ 開關功(gong)率管的源極（S極），通(tong)常接(jie)一個(ge)阻值(zhi)很(hen)(hen)小，但功(gong)率很(hen)(hen)大的電(dian)阻，作為過流保護檢測電(dian)阻，此電(dian)阻的阻值(zhi)一般在0.2到0.8之間。此電(dian)阻如變值(zhi)或開焊，接(jie)觸不良也會造(zao)成輸出電(dian)壓過低的故障。
高頻變壓器(qi)不(bu)良，不(bu)但造成輸出電壓下降(jiang)，還會造成開關功率(lv)管激勵(li)不(bu)足從而屢損開關管。
⑤ 高(gao)壓直流濾(lv)波電容(rong)不良，造成電源帶負(fu)載能力(li)差，一接(jie)負(fu)載輸出電壓便(bian)下(xia)降。
⑥ 電源輸(shu)出(chu)線接(jie)觸不良(liang)，有一定(ding)的(de)接(jie)觸電阻，造成輸(shu)出(chu)電壓(ya)過低。
⑦ 電(dian)(dian)(dian)網電(dian)(dian)(dian)壓是否(fou)過(guo)低。雖(sui)然(ran)開(kai)關電(dian)(dian)(dian)源(yuan)(yuan)在低壓下(xia)仍然(ran)可(ke)以輸出額(e)定(ding)的(de)電(dian)(dian)(dian)壓值(zhi)，但當電(dian)(dian)(dian)網電(dian)(dian)(dian)壓低于開(kai)關電(dian)(dian)(dian)源(yuan)(yuan)的(de)最(zui)低電(dian)(dian)(dian)壓限定(ding)值(zhi)時，也會使輸出電(dian)(dian)(dian)壓過(guo)低。
維(wei)(wei)修(xiu)方法：對于這(zhe)種(zhong)故障我們可以(yi)根據以(yi)上(shang)故障原因(yin)(yin)，來(lai)逐一(yi)(yi)(yi)(yi)進行(xing)排查(cha)(cha)。但(dan)(dan)在實(shi)際維(wei)(wei)修(xiu)時，可根據實(shi)際情況來(lai)進行(xing)排查(cha)(cha)，不(bu)一(yi)(yi)(yi)(yi)定要(yao)逐一(yi)(yi)(yi)(yi)排查(cha)(cha)。首(shou)先用(yong)萬(wan)用(yong)表檢查(cha)(cha)一(yi)(yi)(yi)(yi)下高(gao)壓直流(liu)濾波電容(rong)是(shi)(shi)否(fou)(fou)(fou)變(bian)(bian)(bian)(bian)質，容(rong)量是(shi)(shi)否(fou)(fou)(fou)下降，能否(fou)(fou)(fou)正常充(chong)放電。如(ru)無(wu)以(yi)上(shang)現象，則測量一(yi)(yi)(yi)(yi)下開(kai)關(guan)功(gong)率管的(de)(de)(de)柵極（G極）的(de)(de)(de)限流(liu)電阻以(yi)及(ji)源(yuan)極（S極）的(de)(de)(de)過流(liu)保護檢測電阻是(shi)(shi)否(fou)(fou)(fou)變(bian)(bian)(bian)(bian)值(zhi)，變(bian)(bian)(bian)(bian)質或開(kai)焊，接觸不(bu)良。經判(pan)別后，若(ruo)無(wu)問(wen)題，我們就(jiu)檢查(cha)(cha)一(yi)(yi)(yi)(yi)下高(gao)頻(pin)變(bian)(bian)(bian)(bian)壓器的(de)(de)(de)鐵(tie)芯是(shi)(shi)否(fou)(fou)(fou)完好無(wu)損。因(yin)(yin)在日常生活使用(yong)中，不(bu)可避免的(de)(de)(de)重摔或重幢，使高(gao)頻(pin)變(bian)(bian)(bian)(bian)壓器的(de)(de)(de)鐵(tie)芯損壞(huai)。使高(gao)頻(pin)變(bian)(bian)(bian)(bian)壓器的(de)(de)(de)磁(ci)(ci)(ci)通量，磁(ci)(ci)(ci)感(gan)應(ying)強度(du)，以(yi)及(ji)磁(ci)(ci)(ci)路等(deng)都會受到很大(da)的(de)(de)(de)影響，造成傳輸(shu)的(de)(de)(de)效率，能量將會大(da)打折(zhe)扣。由于高(gao)頻(pin)變(bian)(bian)(bian)(bian)壓器為了減小(xiao)渦流(liu)，增大(da)高(gao)頻(pin)交流(liu)電的(de)(de)(de)傳輸(shu)效率，它的(de)(de)(de)鐵(tie)芯是(shi)(shi)用(yong)軟磁(ci)(ci)(ci)鐵(tie)氧體制作而成的(de)(de)(de)。這(zhe)種(zhong)磁(ci)(ci)(ci)性(xing)材料具(ju)有高(gao)的(de)(de)(de)導磁(ci)(ci)(ci)率，但(dan)(dan)質脆，易碎。因(yin)(yin)此(ci)(ci)(ci)它的(de)(de)(de)損壞(huai)率也是(shi)(shi)很高(gao)的(de)(de)(de)。因(yin)(yin)此(ci)(ci)(ci)在維(wei)(wei)修(xiu)時千萬(wan)不(bu)要(yao)忘了檢查(cha)(cha)此(ci)(ci)(ci)處，以(yi)免走彎路。除(chu)此(ci)(ci)(ci)之外(wai)還有可能就(jiu)是(shi)(shi)輸(shu)出濾波電容(rong)容(rong)量降低，甚至失(shi)容(rong)或開(kai)焊，虛接；電源(yuan)輸(shu)出限流(liu)電阻變(bian)(bian)(bian)(bian)值(zhi)或虛接，電源(yuan)輸(shu)出線(xian)虛接等(deng)。在實(shi)際維(wei)(wei)修(xiu)時，這(zhe)些因(yin)(yin)素(su)都不(bu)要(yao)放過，都應(ying)檢查(cha)(cha)一(yi)(yi)(yi)(yi)下，以(yi)保證萬(wan)無(wu)一(yi)(yi)(yi)(yi)失(shi)。
這種(zhong)故障原因主要是由于控制(zhi)風(feng)扇的(de)三極管(guan)（8550或(huo)(huo)8050）損(sun)壞，或(huo)(huo)者風(feng)扇本身損(sun)壞或(huo)(huo)風(feng)葉被雜物(wu)卡住。但有些開(kai)關(guan)電源(yuan)中采用的(de)是智能(neng)散熱(re)，對(dui)于采用這種(zhong)方式(shi)散熱(re)的(de)開(kai)關(guan)電源(yuan)，熱(re)敏電阻損(sun)壞的(de)概率是很大的(de)。
維(wei)修方法(fa)：首先用萬用表測量一下(xia)(xia)控(kong)制風扇的(de)三極管(guan)是(shi)否損壞(huai)，若測得此(ci)管(guan)未損壞(huai)那就有(you)可能(neng)是(shi)風扇本身(shen)損壞(huai)。可以把風扇從電(dian)(dian)路板上(shang)(shang)拔下(xia)(xia)來，另外接(jie)上(shang)(shang)一個(ge)12V的(de)直(zhi)流電(dian)(dian)（注(zhu)意(yi)(yi)正負極），看是(shi)否轉動(dong)，并看有(you)無(wu)異物(wu)卡住(zhu)。若擺動(dong)幾下(xia)(xia)風扇的(de)電(dian)(dian)線，風扇就轉動(dong)，則(ze)說(shuo)明電(dian)(dian)線內(nei)部(bu)有(you)斷線或(huo)(huo)接(jie)頭接(jie)觸不(bu)(bu)良。若仍(reng)不(bu)(bu)轉動(dong)，則(ze)風扇必壞(huai)。對(dui)于(yu)采用智能(neng)散熱的(de)開關電(dian)(dian)源來說(shuo)，除按上(shang)(shang)述(shu)檢查(cha)外，還應(ying)檢查(cha)一下(xia)(xia)熱敏電(dian)(dian)阻是(shi)否不(bu)(bu)良或(huo)(huo)損壞(huai)，開焊等。但要注(zhu)意(yi)(yi)此(ci)熱敏電(dian)(dian)阻為負溫度系數的(de)熱敏電(dian)(dian)阻，更換時應(ying)注(zhu)意(yi)(yi)。
