開關電源是利(li)用(yong)現代電(dian)力電(dian)子技(ji)術，控制(zhi)開關晶體管開通(tong)(tong)和(he)關斷的時間比率，維持(chi)穩定輸出電(dian)壓的一種(zhong)電(dian)源(yuan)。廣泛運用(yong)在(zai)工業、軍事、科(ke)研、通(tong)(tong)訊(xun)、醫療及多種(zhong)家用(yong)電(dian)器中。開關電(dian)源(yuan)的發展與應用(yong)在(zai)節約(yue)能源(yuan)、節約(yue)資源(yuan)及保(bao)護環境方(fang)面都具(ju)有重要的意義(yi)。下面我們就來看看開關電(dian)源(yuan)電(dian)路圖與維修技(ji)巧。
開關電(dian)(dian)源的主(zhu)要(yao)電(dian)(dian)路(lu)(lu)是由輸(shu)(shu)入電(dian)(dian)磁干擾濾波器（EMI）、整(zheng)流濾波電(dian)(dian)路(lu)(lu)、功率(lv)變換電(dian)(dian)路(lu)(lu)、PWM控制器電(dian)(dian)路(lu)(lu)、輸(shu)(shu)出(chu)整(zheng)流濾波電(dian)(dian)路(lu)(lu)組成。輔(fu)助電(dian)(dian)路(lu)(lu)有輸(shu)(shu)入過(guo)欠壓保(bao)護(hu)電(dian)(dian)路(lu)(lu)、輸(shu)(shu)出(chu)過(guo)欠壓保(bao)護(hu)電(dian)(dian)路(lu)(lu)、輸(shu)(shu)出(chu)過(guo)流保(bao)護(hu)電(dian)(dian)路(lu)(lu)、輸(shu)(shu)出(chu)短路(lu)(lu)保(bao)護(hu)電(dian)(dian)路(lu)(lu)等。
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通電后觀察電源(yuan)是否有燒保(bao)險及個別(bie)元件冒煙等(deng)現(xian)象，若有要及時切斷供電進行檢(jian)修。
測量高壓濾波電(dian)(dian)容兩端有(you)無300伏(fu)輸出，若無應重點查整流(liu)二極管、濾波電(dian)(dian)容等。
測量高頻變壓(ya)器次級(ji)線圈有(you)無輸出(chu)(chu)，若無應重點查開關管(guan)是否損(sun)壞，是否起振(zhen)，保(bao)護電路是否動(dong)作(zuo)等(deng)，若有(you)則應重點檢查各輸出(chu)(chu)側的整(zheng)流二極管(guan)、濾(lv)波電容、三(san)通(tong)穩壓(ya)管(guan)等(deng)。
如果電(dian)(dian)源啟動一下就停止，則該電(dian)(dian)源處于保護狀(zhuang)態(tai)下，可直接(jie)測量PWM芯片保護輸入腳(jiao)的電(dian)(dian)壓，如果電(dian)(dian)壓超出規定值，則說(shuo)明電(dian)(dian)源處于保護狀(zhuang)態(tai)下，應(ying)重點檢查產生(sheng)保護的原因。
總(zong)之，開關(guan)電(dian)源電(dian)路有(you)(you)易有(you)(you)難，功率有(you)(you)大(da)有(you)(you)小(xiao)，輸出電(dian)壓多(duo)種多(duo)樣(yang)。只要按(an)照上述(shu)維修技巧，多(duo)動手進行開關(guan)電(dian)源的(de)維修，就能(neng)迅速地排除開關(guan)電(dian)源故障，達到(dao)事半功倍的(de)效果。
看：打開電(dian)源(yuan)的外(wai)殼，檢查保險絲是(shi)否熔斷，再觀察(cha)電(dian)源(yuan)的內部(bu)情(qing)況，如果發(fa)現電(dian)源(yuan)的PCB板(ban)上有燒焦處或(huo)元(yuan)件破裂，則應重(zhong)點檢查此(ci)處元(yuan)件及相關電(dian)路元(yuan)件。
聞(wen)：聞(wen)一下電源內部是否有(you)(you)糊味(wei)，檢查是否有(you)(you)燒焦的(de)元器件。
問：問一(yi)下電源損壞的經過，是(shi)否對電源進(jin)行違(wei)規操作(zuo)。
量(liang)(liang)(liang)：沒通(tong)電(dian)(dian)(dian)(dian)(dian)前，用(yong)萬用(yong)表量(liang)(liang)(liang)一下高壓(ya)電(dian)(dian)(dian)(dian)(dian)容(rong)兩端(duan)的電(dian)(dian)(dian)(dian)(dian)壓(ya)先。如(ru)果是開(kai)關電(dian)(dian)(dian)(dian)(dian)源不(bu)起(qi)振或開(kai)關管開(kai)路引起(qi)的故障，則大(da)多數情況下，高壓(ya)濾波電(dian)(dian)(dian)(dian)(dian)容(rong)兩端(duan)的電(dian)(dian)(dian)(dian)(dian)壓(ya)未泄放悼，用(yong)萬用(yong)表測量(liang)(liang)(liang)AC電(dian)(dian)(dian)(dian)(dian)源線兩端(duan)的正反向電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)及(ji)電(dian)(dian)(dian)(dian)(dian)容(rong)器(qi)充(chong)電(dian)(dian)(dian)(dian)(dian)情況，電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)值不(bu)應(ying)(ying)(ying)過低，否則電(dian)(dian)(dian)(dian)(dian)源內部可能存在短路。電(dian)(dian)(dian)(dian)(dian)容(rong)器(qi)應(ying)(ying)(ying)能充(chong)放電(dian)(dian)(dian)(dian)(dian)。脫開(kai)負載，分別測量(liang)(liang)(liang)各組輸出端(duan)的對(dui)地電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)，正常時，表針應(ying)(ying)(ying)有電(dian)(dian)(dian)(dian)(dian)容(rong)器(qi)充(chong)放電(dian)(dian)(dian)(dian)(dian)擺動，最后(hou)指示的應(ying)(ying)(ying)為(wei)該路的泄放電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)的阻(zu)(zu)(zu)值。
一般情(qing)況下，保(bao)(bao)險絲熔斷說明開(kai)關(guan)電源(yuan)的(de)(de)內(nei)部電路(lu)存在(zai)短路(lu)或過流(liu)的(de)(de)故障。由于開(kai)關(guan)電源(yuan)工作(zuo)在(zai)高(gao)電壓(ya)(ya)，大(da)電流(liu)的(de)(de)狀(zhuang)(zhuang)態(tai)下，直流(liu)濾波(bo)(bo)和變換振蕩電路(lu)在(zai)高(gao)壓(ya)(ya)狀(zhuang)(zhuang)態(tai)工作(zuo)時間太長(chang)，電壓(ya)(ya)變化相(xiang)對(dui)大(da)。電網電壓(ya)(ya)的(de)(de)波(bo)(bo)動，浪涌(yong)都(dou)會(hui)引起電源(yuan)內(nei)電流(liu)瞬間增大(da)而使保(bao)(bao)險絲熔斷。重點應檢(jian)(jian)查電源(yuan)輸入端的(de)(de)整流(liu)二極管(guan)，高(gao)壓(ya)(ya)濾波(bo)(bo)電解電容，開(kai)關(guan)功率管(guan)，UC3842本身及外圍(wei)元(yuan)器(qi)件(jian)等(deng)。檢(jian)(jian)查一下這些(xie)元(yuan)器(qi)件(jian)有無擊穿，開(kai)路(lu)，損壞，燒焦，炸(zha)裂等(deng)現象(xiang)。
維修(xiu)方法：首先(xian)仔細(xi)查(cha)(cha)看電(dian)(dian)(dian)(dian)路(lu)(lu)板上面的各個(ge)元(yuan)(yuan)件(jian)(jian)(jian)，看是(shi)否(fou)(fou)(fou)在這(zhe)些(xie)元(yuan)(yuan)件(jian)(jian)(jian)的外(wai)表(biao)有(you)(you)沒有(you)(you)被燒(shao)糊,有(you)(you)沒有(you)(you)電(dian)(dian)(dian)(dian)解液(ye)溢出，聞(wen)一(yi)聞(wen)有(you)(you)沒有(you)(you)異味。經看，聞(wen)之后，再(zai)用萬用表(biao)進(jin)(jin)行(xing)檢(jian)查(cha)(cha)。首先(xian)測(ce)(ce)量(liang)(liang)(liang)(liang)一(yi)下(xia)(xia)電(dian)(dian)(dian)(dian)源輸入端(duan)的電(dian)(dian)(dian)(dian)阻(zu)值，若小于200K，則說(shuo)(shuo)明(ming)后端(duan)有(you)(you)局部(bu)短(duan)路(lu)(lu)現象(xiang)，然后分別測(ce)(ce)量(liang)(liang)(liang)(liang)四只整流(liu)二極管正，反向電(dian)(dian)(dian)(dian)阻(zu)和兩(liang)個(ge)限流(liu)電(dian)(dian)(dian)(dian)阻(zu)的阻(zu)值，看其有(you)(you)無短(duan)路(lu)(lu)或燒(shao)壞(huai)(huai)；然后再(zai)測(ce)(ce)量(liang)(liang)(liang)(liang)一(yi)下(xia)(xia)電(dian)(dian)(dian)(dian)源濾(lv)波電(dian)(dian)(dian)(dian)容是(shi)否(fou)(fou)(fou)能(neng)進(jin)(jin)行(xing)正常充放電(dian)(dian)(dian)(dian)，再(zai)就測(ce)(ce)量(liang)(liang)(liang)(liang)一(yi)下(xia)(xia)開關功率管是(shi)否(fou)(fou)(fou)擊(ji)穿(chuan)損壞(huai)(huai)，以(yi)及UC3842本身，及周(zhou)圍(wei)元(yuan)(yuan)件(jian)(jian)(jian)是(shi)否(fou)(fou)(fou)擊(ji)穿(chuan)，燒(shao)壞(huai)(huai)等。需要說(shuo)(shuo)明(ming)的一(yi)點是(shi)：因(yin)是(shi)在路(lu)(lu)測(ce)(ce)量(liang)(liang)(liang)(liang)，有(you)(you)可(ke)能(neng)會使(shi)測(ce)(ce)量(liang)(liang)(liang)(liang)結(jie)果有(you)(you)誤，造成誤判。因(yin)此必(bi)要時可(ke)把(ba)元(yuan)(yuan)器件(jian)(jian)(jian)焊下(xia)(xia)來再(zai)進(jin)(jin)行(xing)測(ce)(ce)量(liang)(liang)(liang)(liang)。如果仍(reng)然沒有(you)(you)上述情(qing)況則測(ce)(ce)量(liang)(liang)(liang)(liang)一(yi)下(xia)(xia)輸入電(dian)(dian)(dian)(dian)源線及輸出電(dian)(dian)(dian)(dian)源線是(shi)否(fou)(fou)(fou)內部(bu)短(duan)路(lu)(lu)。一(yi)般(ban)情(qing)況下(xia)(xia)，熔斷器熔斷故(gu)障(zhang)，整流(liu)二極管，電(dian)(dian)(dian)(dian)源濾(lv)波電(dian)(dian)(dian)(dian)容，開關功率管，UC3842是(shi)易(yi)損件(jian)(jian)(jian)，損壞(huai)(huai)的概(gai)率可(ke)達95%以(yi)上，一(yi)般(ban)著重(zhong)檢(jian)查(cha)(cha)一(yi)下(xia)(xia)這(zhe)些(xie)元(yuan)(yuan)器件(jian)(jian)(jian)，就可(ke)很容易(yi)排除此類故(gu)障(zhang)。
如果保險絲是(shi)完(wan)好的(de)，在有負載(zai)的(de)情(qing)況下(xia)，各級直流(liu)電壓無(wu)輸出。這種(zhong)情(qing)況主要是(shi)以下(xia)原因造成的(de)：電源中出現(xian)開路(lu)，短路(lu)現(xian)象，過壓，過流(liu)保護電路(lu)出現(xian)故障，振蕩電路(lu)沒有工作，電源負載(zai)過重(zhong)，高頻整流(liu)濾(lv)波電路(lu)中整流(liu)二極管(guan)被擊穿(chuan)，濾(lv)波電容漏電等。
維(wei)修(xiu)方法：首先，用萬(wan)用表(biao)測(ce)(ce)(ce)量一下(xia)高頻變壓器次級的(de)各(ge)個元器件是否有損壞。在排(pai)(pai)除了高頻整流(liu)二極管(guan)擊穿、負載短路(lu)的(de)情(qing)況后(hou)，然后(hou)在測(ce)(ce)(ce)量各(ge)輸(shu)出端(duan)的(de)直(zhi)流(liu)電(dian)(dian)壓，如果這時輸(shu)出仍為零，則(ze)可以(yi)肯定(ding)是電(dian)(dian)源的(de)控(kong)制電(dian)(dian)路(lu)出了故(gu)障。控(kong)制電(dian)(dian)路(lu)的(de)兩(liang)部分是集成開(kai)關(guan)電(dian)(dian)源控(kong)制器和(he)過壓保護電(dian)(dian)路(lu)。最后(hou)用萬(wan)用表(biao)靜態測(ce)(ce)(ce)量高頻濾波(bo)電(dian)(dian)路(lu)中整流(liu)二極管(guan)及低壓濾波(bo)電(dian)(dian)容是否損壞。如果確實相關(guan)的(de)元件損壞，在更換好新的(de)完好的(de)元件后(hou)，開(kai)機測(ce)(ce)(ce)試(shi)，一般故(gu)障即(ji)可排(pai)(pai)除。需要說(shuo)明的(de)是：電(dian)(dian)源輸(shu)出線(xian)斷線(xian)或(huo)開(kai)焊，虛焊也會造成這種故(gu)障。在維(wei)修(xiu)時應注(zhu)意這一點(dian)。
電源負載(zai)能力(li)差是一個常見的故障，一般都是出現在老(lao)式或(huo)是工作時(shi)間長的電源中，主要原因是各(ge)元器(qi)件老(lao)化，開關管的工作不穩定，沒有及時(shi)進行(xing)散熱等。此外還(huan)有穩壓二(er)(er)極(ji)管發熱漏電，整流二(er)(er)極(ji)管損壞等。
維修方法：用(yong)萬用(yong)表著(zhu)重檢查一下穩壓(ya)二極(ji)管，高壓(ya)濾(lv)波電(dian)容，限流(liu)電(dian)阻有無變(bian)質(zhi)等再仔(zi)細檢查一下電(dian)路板(ban)上(shang)的所有焊(han)點是(shi)否開焊(han)，虛接等。把開焊(han)的焊(han)點重新焊(han)牢，更換變(bian)質(zhi)的元(yuan)器件，一般故障(zhang)即可排除(chu)。
這種現象(xiang)說(shuo)明開關電(dian)源(yuan)未工(gong)作，或者(zhe)工(gong)作后(hou)進入了保(bao)護狀(zhuang)態。
維(wei)修(xiu)(xiu)方法：首先(xian)應判斷(duan)一(yi)下(xia)開關(guan)電(dian)(dian)(dian)源(yuan)(yuan)的(de)主控(kong)芯片UC3842是否(fou)處在(zai)工作(zuo)狀態(tai)或(huo)已經損壞(huai)(huai)(huai)。判斷(duan)方法是這樣(yang)的(de)：加電(dian)(dian)(dian)測UC3842的(de)第7腳(jiao)(jiao)(jiao)對地電(dian)(dian)(dian)壓(ya)(ya)，若(ruo)(ruo)測第8腳(jiao)(jiao)(jiao)有+5V電(dian)(dian)(dian)壓(ya)(ya)，1，2，4，6腳(jiao)(jiao)(jiao)也有不(bu)(bu)同的(de)電(dian)(dian)(dian)壓(ya)(ya)，則說明電(dian)(dian)(dian)路已起振，UC3842基本正常(chang)；若(ruo)(ruo)7腳(jiao)(jiao)(jiao)電(dian)(dian)(dian)壓(ya)(ya)低，其余管(guan)腳(jiao)(jiao)(jiao)無(wu)電(dian)(dian)(dian)壓(ya)(ya)或(huo)不(bu)(bu)波(bo)動(dong)，則UC3842已損壞(huai)(huai)(huai)。UC3842芯片損壞(huai)(huai)(huai)最常(chang)見的(de)是6，7腳(jiao)(jiao)(jiao)對地擊(ji)穿(chuan)，5，7腳(jiao)(jiao)(jiao)對地擊(ji)穿(chuan)和(he)1，7腳(jiao)(jiao)(jiao)對地擊(ji)穿(chuan)。如果(guo)這幾只腳(jiao)(jiao)(jiao)都為(wei)擊(ji)穿(chuan)，而開關(guan)電(dian)(dian)(dian)源(yuan)(yuan)還是不(bu)(bu)能(neng)(neng)(neng)正常(chang)啟(qi)動(dong)，則UC3842必(bi)壞(huai)(huai)(huai)，應直接更換。若(ruo)(ruo)判斷(duan)芯片未(wei)壞(huai)(huai)(huai)，則就著重檢查開關(guan)功率管(guan)的(de)柵極（G極）的(de)限流電(dian)(dian)(dian)阻是否(fou)開焊，虛接，變值，變質以及開關(guan)功率管(guan)本身是否(fou)性能(neng)(neng)(neng)不(bu)(bu)良。除此(ci)之(zhi)外，電(dian)(dian)(dian)源(yuan)(yuan)輸出線也有可(ke)能(neng)(neng)(neng)斷(duan)線或(huo)接觸不(bu)(bu)良也會造成這種故(gu)障(zhang)。因此(ci)在(zai)維(wei)修(xiu)(xiu)時也應注意檢查一(yi)下(xia)。
這種故(gu)障往(wang)往(wang)來(lai)自(zi)于穩(wen)壓取(qu)樣和穩(wen)壓控制(zhi)電(dian)(dian)路出現故(gu)障所致。在(zai)開關電(dian)(dian)源中，直流輸出、取(qu)樣電(dian)(dian)阻、誤差取(qu)樣放大器（如LM324，LM358等）、光耦合(he)器（PC817）、電(dian)(dian)源控制(zhi)芯片（UC3842）等電(dian)(dian)路共同構(gou)成(cheng)了一(yi)個閉合(he)的控制(zhi)環路，任(ren)何(he)一(yi)處出問題都會(hui)導(dao)致輸出電(dian)(dian)壓升高(gao)。
維(wei)修方(fang)法：由(you)于開(kai)關(guan)電(dian)(dian)(dian)(dian)源中有過(guo)壓(ya)保護(hu)電(dian)(dian)(dian)(dian)路，輸(shu)出(chu)(chu)(chu)電(dian)(dian)(dian)(dian)壓(ya)過(guo)高首先會使過(guo)壓(ya)保護(hu)電(dian)(dian)(dian)(dian)路動作。因此(ci)對于這(zhe)種故障的(de)維(wei)修，我(wo)們可以通過(guo)斷開(kai)過(guo)壓(ya)保護(hu)電(dian)(dian)(dian)(dian)路，使過(guo)壓(ya)保護(hu)電(dian)(dian)(dian)(dian)路不起(qi)作用，在這(zhe)時(shi)，測(ce)量開(kai)機瞬間的(de)電(dian)(dian)(dian)(dian)源主電(dian)(dian)(dian)(dian)壓(ya)。如果測(ce)量值比(bi)正常值高出(chu)(chu)(chu)IV以上，說(shuo)明(ming)輸(shu)出(chu)(chu)(chu)電(dian)(dian)(dian)(dian)壓(ya)過(guo)高。我(wo)們應(ying)著重檢查取樣電(dian)(dian)(dian)(dian)阻(zu)是(shi)否(fou)變(bian)值或(huo)損壞，精密穩(wen)壓(ya)放(fang)大器(qi)（TL431）或(huo)光耦合器(qi)（PC817）性能不良，變(bian)質(zhi)或(huo)損壞；其中精密穩(wen)壓(ya)放(fang)大器(qi)（TL431）極(ji)易損壞，我(wo)們可用下述方(fang)法對精密穩(wen)壓(ya)放(fang)大器(qi)（TL431）作出(chu)(chu)(chu)好壞的(de)判(pan)別：將TL431的(de)參考端（Ref）與(yu)它的(de)陰極(ji)（Cathode）相連，串10k的(de)電(dian)(dian)(dian)(dian)阻(zu)，接入5V電(dian)(dian)(dian)(dian)壓(ya)，若(ruo)陽極(ji)（Anode）與(yu)陰極(ji)之間為2、5V，并且等待片刻(ke)還仍然為2、5V，則為好管，否(fou)則為壞管。
對于這種故障(zhang)現象，根據維修經驗可(ke)知，除穩壓控制(zhi)電路(lu)會引起輸出(chu)電壓過低外(wai)，還(huan)有一(yi)些(xie)原(yuan)因會引起輸出(chu)電壓過低，主要有以下(xia)幾點(dian):
① 開關電(dian)(dian)源負(fu)載(zai)有短路(lu)(lu)(lu)故(gu)障(zhang)(zhang)。此時，應(ying)斷開開關電(dian)(dian)源電(dian)(dian)路(lu)(lu)(lu)的所有負(fu)載(zai)，以區(qu)分是(shi)開關電(dian)(dian)源電(dian)(dian)路(lu)(lu)(lu)還是(shi)負(fu)載(zai)電(dian)(dian)路(lu)(lu)(lu)有故(gu)障(zhang)(zhang)。若斷開負(fu)載(zai)電(dian)(dian)路(lu)(lu)(lu)電(dian)(dian)壓輸出正(zheng)(zheng)常(chang)，說明(ming)是(shi)負(fu)載(zai)過重；若仍不正(zheng)(zheng)常(chang)，說明(ming)開關電(dian)(dian)源電(dian)(dian)路(lu)(lu)(lu)有故(gu)障(zhang)(zhang)。
② 輸(shu)出電(dian)(dian)壓(ya)端整流二極管、濾(lv)波(bo)電(dian)(dian)容(rong)失(shi)效等，可以通(tong)過代換法(fa)進行判斷。
③ 開關功(gong)率管的性能(neng)下降，必然導(dao)致開關管不(bu)能(neng)正(zheng)常導(dao)通，使電(dian)源的內阻增(zeng)加，帶負載能(neng)力下降。
④ 開(kai)關功率管的(de)源極(ji)（S極(ji)），通常接(jie)一個阻值(zhi)(zhi)很小，但(dan)功率很大的(de)電阻，作為(wei)過流保護檢測電阻，此電阻的(de)阻值(zhi)(zhi)一般在0.2到0.8之間。此電阻如變值(zhi)(zhi)或(huo)開(kai)焊，接(jie)觸不良也會造(zao)成輸出電壓過低的(de)故障(zhang)。
高頻變壓器(qi)不良，不但造(zao)成(cheng)輸(shu)出(chu)電壓下降，還會(hui)造(zao)成(cheng)開(kai)關功率(lv)管激勵不足(zu)從而(er)屢(lv)損開(kai)關管。
⑤ 高壓直流(liu)濾波電(dian)(dian)容不良，造成電(dian)(dian)源帶負載(zai)能力差，一接負載(zai)輸(shu)出(chu)電(dian)(dian)壓便下降。
⑥ 電(dian)(dian)源輸出線接觸(chu)不良，有一定的接觸(chu)電(dian)(dian)阻，造(zao)成輸出電(dian)(dian)壓過低。
⑦ 電(dian)(dian)(dian)(dian)網(wang)電(dian)(dian)(dian)(dian)壓(ya)是否過低。雖然開關(guan)(guan)電(dian)(dian)(dian)(dian)源(yuan)在低壓(ya)下仍然可以輸出額定的電(dian)(dian)(dian)(dian)壓(ya)值，但當電(dian)(dian)(dian)(dian)網(wang)電(dian)(dian)(dian)(dian)壓(ya)低于開關(guan)(guan)電(dian)(dian)(dian)(dian)源(yuan)的最(zui)低電(dian)(dian)(dian)(dian)壓(ya)限定值時，也會使(shi)輸出電(dian)(dian)(dian)(dian)壓(ya)過低。
維(wei)修(xiu)方法(fa)：對于這(zhe)種(zhong)故障我(wo)們(men)可(ke)以根據以上故障原因(yin)(yin)，來逐一進行(xing)排查(cha)(cha)(cha)。但在實(shi)(shi)際維(wei)修(xiu)時，可(ke)根據實(shi)(shi)際情況來進行(xing)排查(cha)(cha)(cha)，不(bu)(bu)一定要(yao)逐一排查(cha)(cha)(cha)。首先(xian)用(yong)(yong)萬用(yong)(yong)表(biao)檢(jian)(jian)查(cha)(cha)(cha)一下(xia)(xia)高(gao)(gao)壓直流(liu)濾(lv)波電(dian)(dian)容(rong)是(shi)(shi)否(fou)變質，容(rong)量是(shi)(shi)否(fou)下(xia)(xia)降，能否(fou)正常充放(fang)電(dian)(dian)。如(ru)無(wu)以上現象，則(ze)測量一下(xia)(xia)開關功率(lv)管的(de)柵(zha)極(ji)(ji)（G極(ji)(ji)）的(de)限流(liu)電(dian)(dian)阻以及源極(ji)(ji)（S極(ji)(ji)）的(de)過流(liu)保(bao)護(hu)檢(jian)(jian)測電(dian)(dian)阻是(shi)(shi)否(fou)變值，變質或開焊，接觸不(bu)(bu)良。經判別后，若無(wu)問(wen)題，我(wo)們(men)就(jiu)檢(jian)(jian)查(cha)(cha)(cha)一下(xia)(xia)高(gao)(gao)頻變壓器(qi)的(de)鐵芯是(shi)(shi)否(fou)完(wan)好無(wu)損(sun)。因(yin)(yin)在日常生(sheng)活使用(yong)(yong)中，不(bu)(bu)可(ke)避免(mian)的(de)重摔或重幢，使高(gao)(gao)頻變壓器(qi)的(de)鐵芯損(sun)壞。使高(gao)(gao)頻變壓器(qi)的(de)磁(ci)通量，磁(ci)感應(ying)強(qiang)度，以及磁(ci)路(lu)等都(dou)(dou)會受到很大的(de)影響，造成(cheng)傳(chuan)輸(shu)(shu)(shu)的(de)效率(lv)，能量將(jiang)會大打折扣。由(you)于高(gao)(gao)頻變壓器(qi)為(wei)了減小(xiao)渦流(liu)，增大高(gao)(gao)頻交(jiao)流(liu)電(dian)(dian)的(de)傳(chuan)輸(shu)(shu)(shu)效率(lv)，它的(de)鐵芯是(shi)(shi)用(yong)(yong)軟磁(ci)鐵氧體制作而(er)成(cheng)的(de)。這(zhe)種(zhong)磁(ci)性材(cai)料具有(you)高(gao)(gao)的(de)導磁(ci)率(lv)，但質脆，易碎。因(yin)(yin)此(ci)它的(de)損(sun)壞率(lv)也是(shi)(shi)很高(gao)(gao)的(de)。因(yin)(yin)此(ci)在維(wei)修(xiu)時千(qian)萬不(bu)(bu)要(yao)忘了檢(jian)(jian)查(cha)(cha)(cha)此(ci)處，以免(mian)走彎路(lu)。除此(ci)之外還有(you)可(ke)能就(jiu)是(shi)(shi)輸(shu)(shu)(shu)出濾(lv)波電(dian)(dian)容(rong)容(rong)量降低，甚至(zhi)失(shi)容(rong)或開焊，虛接；電(dian)(dian)源輸(shu)(shu)(shu)出限流(liu)電(dian)(dian)阻變值或虛接，電(dian)(dian)源輸(shu)(shu)(shu)出線虛接等。在實(shi)(shi)際維(wei)修(xiu)時，這(zhe)些(xie)因(yin)(yin)素(su)都(dou)(dou)不(bu)(bu)要(yao)放(fang)過，都(dou)(dou)應(ying)檢(jian)(jian)查(cha)(cha)(cha)一下(xia)(xia)，以保(bao)證萬無(wu)一失(shi)。
這(zhe)種(zhong)故障原因主要是由(you)于(yu)控制(zhi)風(feng)(feng)扇的(de)三極管（8550或(huo)8050）損壞，或(huo)者風(feng)(feng)扇本(ben)身損壞或(huo)風(feng)(feng)葉被(bei)雜(za)物卡住。但有些開關電源(yuan)(yuan)中采用(yong)的(de)是智能散(san)熱(re)(re)，對于(yu)采用(yong)這(zhe)種(zhong)方式散(san)熱(re)(re)的(de)開關電源(yuan)(yuan)，熱(re)(re)敏(min)電阻(zu)損壞的(de)概率是很大的(de)。
維(wei)修方法：首先用萬用表測(ce)(ce)量一(yi)下(xia)(xia)控制風(feng)(feng)扇的(de)三極(ji)管是否(fou)損壞(huai)，若(ruo)測(ce)(ce)得此管未(wei)損壞(huai)那就有可能是風(feng)(feng)扇本身損壞(huai)。可以把風(feng)(feng)扇從電(dian)(dian)路板上拔下(xia)(xia)來(lai)，另(ling)外(wai)接(jie)上一(yi)個12V的(de)直(zhi)流電(dian)(dian)（注意正(zheng)負(fu)極(ji)），看是否(fou)轉(zhuan)動，并看有無異物卡住。若(ruo)擺動幾下(xia)(xia)風(feng)(feng)扇的(de)電(dian)(dian)線，風(feng)(feng)扇就轉(zhuan)動，則說明電(dian)(dian)線內部有斷線或接(jie)頭接(jie)觸不(bu)良。若(ruo)仍不(bu)轉(zhuan)動，則風(feng)(feng)扇必壞(huai)。對于采用智能散熱(re)(re)的(de)開(kai)關(guan)電(dian)(dian)源(yuan)來(lai)說，除按上述檢(jian)(jian)查外(wai)，還應檢(jian)(jian)查一(yi)下(xia)(xia)熱(re)(re)敏(min)電(dian)(dian)阻(zu)是否(fou)不(bu)良或損壞(huai)，開(kai)焊等。但要注意此熱(re)(re)敏(min)電(dian)(dian)阻(zu)為負(fu)溫度系數的(de)熱(re)(re)敏(min)電(dian)(dian)阻(zu)，更換時應注意。
