開關電源簡介

開關電源是利用(yong)現代電(dian)力(li)電(dian)子技(ji)術，控制開關(guan)晶體管開通和關(guan)斷(duan)的(de)(de)時間(jian)比率，維持(chi)穩定輸出電(dian)壓(ya)的(de)(de)一種(zhong)電(dian)源(yuan)。廣泛(fan)運用(yong)在工業、軍事、科研、通訊、醫療及多種(zhong)家(jia)用(yong)電(dian)器中。開關(guan)電(dian)源(yuan)的(de)(de)發(fa)展與(yu)應用(yong)在節(jie)約能源(yuan)、節(jie)約資源(yuan)及保護環境方面都具有重要的(de)(de)意義。下(xia)面我們就來看(kan)看(kan)開關(guan)電(dian)源(yuan)電(dian)路圖與(yu)維修(xiu)技(ji)巧。

開關(guan)電(dian)(dian)(dian)(dian)(dian)源的主要電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)(lu)(lu)是(shi)由(you)輸入電(dian)(dian)(dian)(dian)(dian)磁干擾濾(lv)波器(qi)(qi)（EMI）、整流濾(lv)波電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)(lu)(lu)、功率變換電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)(lu)(lu)、PWM控制(zhi)器(qi)(qi)電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)(lu)(lu)、輸出(chu)整流濾(lv)波電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)(lu)(lu)組(zu)成。輔助電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)(lu)(lu)有輸入過欠(qian)壓保護(hu)電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)(lu)(lu)、輸出(chu)過欠(qian)壓保護(hu)電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)(lu)(lu)、輸出(chu)過流保護(hu)電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)(lu)(lu)、輸出(chu)短路(lu)(lu)(lu)(lu)(lu)保護(hu)電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)(lu)(lu)(lu)等。

開關電源的維修步驟

加電檢測

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通(tong)電后觀(guan)察(cha)電源是否有(you)燒保(bao)險及個別元(yuan)件冒(mao)煙(yan)等現象，若(ruo)有(you)要(yao)及時(shi)切斷(duan)供電進(jin)行檢(jian)修(xiu)。

測(ce)量(liang)高(gao)壓濾波電(dian)容兩端有無(wu)(wu)300伏(fu)輸出，若(ruo)無(wu)(wu)應重點查整流二極管(guan)、濾波電(dian)容等(deng)。

測(ce)量高頻變壓器次級線圈有(you)無輸出(chu)，若(ruo)無應重(zhong)點查(cha)開關管(guan)是否損(sun)壞，是否起振，保護電路是否動作等，若(ruo)有(you)則應重(zhong)點檢查(cha)各輸出(chu)側的整流(liu)二極管(guan)、濾(lv)波電容、三通穩壓管(guan)等。

如果電源啟動一下(xia)就停止，則該電源處于保(bao)護(hu)狀(zhuang)態(tai)下(xia)，可直接測量(liang)PWM芯(xin)片保(bao)護(hu)輸入腳(jiao)的(de)電壓(ya)(ya)，如果電壓(ya)(ya)超(chao)出規定(ding)值，則說(shuo)明電源處于保(bao)護(hu)狀(zhuang)態(tai)下(xia)，應(ying)重點(dian)檢查(cha)產(chan)生保(bao)護(hu)的(de)原因(yin)。

總之，開(kai)關(guan)電(dian)源電(dian)路(lu)有易有難，功(gong)率有大(da)有小，輸出電(dian)壓多種多樣。只要按(an)照上述維修技巧，多動手進行(xing)開(kai)關(guan)電(dian)源的維修，就能(neng)迅速地排除開(kai)關(guan)電(dian)源故障，達到(dao)事半功(gong)倍的效(xiao)果(guo)。

斷電后看聞問量

看：打開電(dian)源的外(wai)殼，檢查保險(xian)絲是否熔斷，再觀察電(dian)源的內部情況，如果發現電(dian)源的PCB板上有燒焦處或元件(jian)破裂(lie)，則應重(zhong)點檢查此處元件(jian)及相關電(dian)路(lu)元件(jian)。

聞(wen)：聞(wen)一下(xia)電源內(nei)部是否有糊味，檢查是否有燒焦的元器(qi)件(jian)。

問：問一下(xia)電源(yuan)損(sun)壞的經(jing)過，是(shi)否對電源(yuan)進行(xing)違規(gui)操作。

量(liang)：沒通電(dian)(dian)(dian)(dian)(dian)(dian)(dian)前，用(yong)萬用(yong)表量(liang)一下高壓(ya)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)兩(liang)端的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)先。如果是開關(guan)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源不起(qi)(qi)振(zhen)或開關(guan)管開路(lu)引起(qi)(qi)的(de)(de)故(gu)障，則(ze)大多數情況(kuang)下，高壓(ya)濾波電(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)兩(liang)端的(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)未泄(xie)放悼，用(yong)萬用(yong)表測量(liang)AC電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源線兩(liang)端的(de)(de)正反向電(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)及(ji)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)器充電(dian)(dian)(dian)(dian)(dian)(dian)(dian)情況(kuang)，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)值不應(ying)(ying)過低(di)，否則(ze)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)源內部(bu)可(ke)能存(cun)在短路(lu)。電(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)器應(ying)(ying)能充放電(dian)(dian)(dian)(dian)(dian)(dian)(dian)。脫開負載，分別測量(liang)各組輸出端的(de)(de)對(dui)地電(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)，正常時(shi)，表針應(ying)(ying)有電(dian)(dian)(dian)(dian)(dian)(dian)(dian)容(rong)(rong)器充放電(dian)(dian)(dian)(dian)(dian)(dian)(dian)擺動，最后(hou)指示的(de)(de)應(ying)(ying)為該(gai)路(lu)的(de)(de)泄(xie)放電(dian)(dian)(dian)(dian)(dian)(dian)(dian)阻(zu)的(de)(de)阻(zu)值。

開關電源常見故障檢修

1、保險絲熔斷

一般情況下(xia)(xia)，保險(xian)絲熔斷說明開(kai)關電(dian)(dian)源的內部(bu)電(dian)(dian)路(lu)存在(zai)短路(lu)或(huo)過流的故障。由于開(kai)關電(dian)(dian)源工作在(zai)高(gao)電(dian)(dian)壓，大電(dian)(dian)流的狀(zhuang)態(tai)下(xia)(xia)，直流濾波和變(bian)換振(zhen)蕩電(dian)(dian)路(lu)在(zai)高(gao)壓狀(zhuang)態(tai)工作時間太(tai)長，電(dian)(dian)壓變(bian)化(hua)相對大。電(dian)(dian)網電(dian)(dian)壓的波動，浪(lang)涌都(dou)會引起(qi)電(dian)(dian)源內電(dian)(dian)流瞬間增大而使保險(xian)絲熔斷。重點應檢查電(dian)(dian)源輸入端的整(zheng)流二極(ji)管，高(gao)壓濾波電(dian)(dian)解電(dian)(dian)容，開(kai)關功(gong)率管，UC3842本(ben)身及外圍元器件等。檢查一下(xia)(xia)這(zhe)些元器件有(you)無擊穿，開(kai)路(lu)，損壞，燒焦(jiao)，炸裂等現象。

維修(xiu)方法(fa)：首先(xian)仔細查看(kan)(kan)電(dian)(dian)(dian)(dian)(dian)路板上面的(de)(de)(de)各個元(yuan)件，看(kan)(kan)是(shi)否(fou)在這些(xie)元(yuan)件的(de)(de)(de)外表有(you)沒(mei)(mei)有(you)被燒(shao)糊,有(you)沒(mei)(mei)有(you)電(dian)(dian)(dian)(dian)(dian)解液溢出，聞(wen)一(yi)(yi)聞(wen)有(you)沒(mei)(mei)有(you)異味(wei)。經看(kan)(kan)，聞(wen)之后(hou)，再(zai)用萬(wan)用表進(jin)行(xing)(xing)檢(jian)查。首先(xian)測量(liang)一(yi)(yi)下(xia)(xia)(xia)電(dian)(dian)(dian)(dian)(dian)源輸入端的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)值(zhi)，若小(xiao)于(yu)200K，則說明后(hou)端有(you)局部短路現(xian)象(xiang)，然后(hou)分別測量(liang)四只整(zheng)流(liu)二(er)極管正，反(fan)向電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)和兩個限流(liu)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)的(de)(de)(de)阻(zu)(zu)值(zhi)，看(kan)(kan)其有(you)無(wu)短路或燒(shao)壞(huai)；然后(hou)再(zai)測量(liang)一(yi)(yi)下(xia)(xia)(xia)電(dian)(dian)(dian)(dian)(dian)源濾波電(dian)(dian)(dian)(dian)(dian)容是(shi)否(fou)能進(jin)行(xing)(xing)正常充(chong)放電(dian)(dian)(dian)(dian)(dian)，再(zai)就(jiu)測量(liang)一(yi)(yi)下(xia)(xia)(xia)開(kai)關(guan)功率(lv)(lv)管是(shi)否(fou)擊(ji)穿(chuan)(chuan)損(sun)(sun)壞(huai)，以(yi)及UC3842本身，及周圍(wei)元(yuan)件是(shi)否(fou)擊(ji)穿(chuan)(chuan)，燒(shao)壞(huai)等。需要(yao)說明的(de)(de)(de)一(yi)(yi)點是(shi)：因是(shi)在路測量(liang)，有(you)可(ke)(ke)(ke)能會(hui)使測量(liang)結果有(you)誤(wu)，造成誤(wu)判。因此(ci)必要(yao)時可(ke)(ke)(ke)把元(yuan)器(qi)件焊下(xia)(xia)(xia)來再(zai)進(jin)行(xing)(xing)測量(liang)。如果仍然沒(mei)(mei)有(you)上述(shu)情況則測量(liang)一(yi)(yi)下(xia)(xia)(xia)輸入電(dian)(dian)(dian)(dian)(dian)源線及輸出電(dian)(dian)(dian)(dian)(dian)源線是(shi)否(fou)內(nei)部短路。一(yi)(yi)般(ban)情況下(xia)(xia)(xia)，熔斷(duan)器(qi)熔斷(duan)故障，整(zheng)流(liu)二(er)極管，電(dian)(dian)(dian)(dian)(dian)源濾波電(dian)(dian)(dian)(dian)(dian)容，開(kai)關(guan)功率(lv)(lv)管，UC3842是(shi)易損(sun)(sun)件，損(sun)(sun)壞(huai)的(de)(de)(de)概率(lv)(lv)可(ke)(ke)(ke)達95%以(yi)上，一(yi)(yi)般(ban)著重檢(jian)查一(yi)(yi)下(xia)(xia)(xia)這些(xie)元(yuan)器(qi)件，就(jiu)可(ke)(ke)(ke)很容易排除此(ci)類故障。

2、無直流電壓輸出或電壓輸出不穩定

如(ru)果保險絲是完好的(de)，在有(you)負載(zai)(zai)的(de)情(qing)況(kuang)下，各級(ji)直流電(dian)壓(ya)無輸出(chu)。這種情(qing)況(kuang)主要(yao)是以(yi)下原因造成(cheng)的(de)：電(dian)源中出(chu)現開路，短路現象，過(guo)壓(ya)，過(guo)流保護電(dian)路出(chu)現故(gu)障，振蕩電(dian)路沒有(you)工(gong)作，電(dian)源負載(zai)(zai)過(guo)重(zhong)，高頻整(zheng)流濾波(bo)電(dian)路中整(zheng)流二極(ji)管被擊穿，濾波(bo)電(dian)容漏電(dian)等。

維(wei)修方法：首先，用(yong)萬(wan)用(yong)表(biao)測量一下高頻(pin)變壓器(qi)次級的(de)(de)(de)各(ge)個元(yuan)器(qi)件(jian)是(shi)否有損壞(huai)。在(zai)排除了高頻(pin)整流二極(ji)管擊穿、負載短(duan)路的(de)(de)(de)情況(kuang)后(hou)，然后(hou)在(zai)測量各(ge)輸出端(duan)的(de)(de)(de)直流電(dian)壓，如果(guo)這時輸出仍為零，則可以肯定是(shi)電(dian)源(yuan)的(de)(de)(de)控(kong)制電(dian)路出了故障。控(kong)制電(dian)路的(de)(de)(de)兩部分是(shi)集成開關(guan)(guan)電(dian)源(yuan)控(kong)制器(qi)和(he)過壓保護電(dian)路。最后(hou)用(yong)萬(wan)用(yong)表(biao)靜態測量高頻(pin)濾波(bo)電(dian)路中整流二極(ji)管及低壓濾波(bo)電(dian)容是(shi)否損壞(huai)。如果(guo)確實相關(guan)(guan)的(de)(de)(de)元(yuan)件(jian)損壞(huai)，在(zai)更換好新的(de)(de)(de)完好的(de)(de)(de)元(yuan)件(jian)后(hou)，開機測試，一般故障即可排除。需要(yao)說(shuo)明的(de)(de)(de)是(shi)：電(dian)源(yuan)輸出線斷(duan)線或開焊，虛焊也會造(zao)成這種故障。在(zai)維(wei)修時應(ying)注意這一點。

3、電源負載能力差

電源負載能力差(cha)是一個常見的故障，一般都是出現在老式或(huo)是工(gong)作時間長的電源中，主要原因(yin)是各元器件(jian)老化(hua)，開關管的工(gong)作不(bu)穩(wen)定，沒(mei)有及時進行(xing)散熱等(deng)。此(ci)外還有穩(wen)壓二(er)(er)極管發熱漏電，整流二(er)(er)極管損壞等(deng)。

維(wei)修方法(fa)：用(yong)萬用(yong)表著重檢查一(yi)下(xia)(xia)穩(wen)壓二極管，高壓濾波電容(rong)，限流(liu)電阻有無(wu)變(bian)質等再仔(zi)細檢查一(yi)下(xia)(xia)電路板上的(de)(de)所有焊點(dian)是否開(kai)焊，虛(xu)接等。把開(kai)焊的(de)(de)焊點(dian)重新焊牢(lao)，更(geng)換(huan)變(bian)質的(de)(de)元器件，一(yi)般(ban)故障即(ji)可排除。

4、無直流電壓輸出，但保險絲完好

這(zhe)種(zhong)現象說明(ming)開關電(dian)源未工(gong)作，或者工(gong)作后進入了保護狀(zhuang)態。

維修方(fang)法：首先(xian)應(ying)判(pan)斷(duan)一(yi)下開(kai)關電(dian)(dian)源(yuan)(yuan)的(de)主控芯(xin)片(pian)UC3842是否處在工作狀(zhuang)態(tai)或(huo)(huo)已經損壞。判(pan)斷(duan)方(fang)法是這(zhe)樣的(de)：加電(dian)(dian)測(ce)UC3842的(de)第7腳(jiao)對地(di)電(dian)(dian)壓(ya)，若測(ce)第8腳(jiao)有(you)+5V電(dian)(dian)壓(ya)，1，2，4，6腳(jiao)也有(you)不(bu)(bu)同的(de)電(dian)(dian)壓(ya)，則(ze)說明(ming)電(dian)(dian)路已起振，UC3842基本正常；若7腳(jiao)電(dian)(dian)壓(ya)低，其余管(guan)腳(jiao)無電(dian)(dian)壓(ya)或(huo)(huo)不(bu)(bu)波動，則(ze)UC3842已損壞。UC3842芯(xin)片(pian)損壞最常見的(de)是6，7腳(jiao)對地(di)擊(ji)穿(chuan)，5，7腳(jiao)對地(di)擊(ji)穿(chuan)和1，7腳(jiao)對地(di)擊(ji)穿(chuan)。如果這(zhe)幾只(zhi)腳(jiao)都(dou)為擊(ji)穿(chuan)，而開(kai)關電(dian)(dian)源(yuan)(yuan)還(huan)是不(bu)(bu)能(neng)正常啟動，則(ze)UC3842必壞，應(ying)直(zhi)接更換。若判(pan)斷(duan)芯(xin)片(pian)未壞，則(ze)就著重檢查(cha)開(kai)關功率(lv)管(guan)的(de)柵(zha)極（G極）的(de)限流電(dian)(dian)阻(zu)是否開(kai)焊，虛接，變值(zhi)，變質(zhi)以及(ji)開(kai)關功率(lv)管(guan)本身(shen)是否性能(neng)不(bu)(bu)良(liang)。除(chu)此之外(wai)，電(dian)(dian)源(yuan)(yuan)輸出線(xian)(xian)也有(you)可能(neng)斷(duan)線(xian)(xian)或(huo)(huo)接觸不(bu)(bu)良(liang)也會造成(cheng)這(zhe)種(zhong)故(gu)障。因此在維修時也應(ying)注(zhu)意檢查(cha)一(yi)下。

5、有直流電壓輸出，但輸出電壓過高

這種(zhong)故障往往來自于穩(wen)壓(ya)取(qu)(qu)樣(yang)(yang)和穩(wen)壓(ya)控制(zhi)電路出(chu)(chu)現故障所(suo)致。在開關電源(yuan)(yuan)中，直流輸(shu)出(chu)(chu)、取(qu)(qu)樣(yang)(yang)電阻、誤差取(qu)(qu)樣(yang)(yang)放大(da)器(qi)（如LM324，LM358等(deng)(deng)）、光(guang)耦合器(qi)（PC817）、電源(yuan)(yuan)控制(zhi)芯片（UC3842）等(deng)(deng)電路共同構(gou)成(cheng)了一個(ge)閉合的控制(zhi)環路，任何一處(chu)出(chu)(chu)問題都會導致輸(shu)出(chu)(chu)電壓(ya)升高。

維修方(fang)法：由于(yu)開(kai)關(guan)電(dian)(dian)源(yuan)中(zhong)有(you)過(guo)壓(ya)(ya)保(bao)(bao)護(hu)電(dian)(dian)路，輸出電(dian)(dian)壓(ya)(ya)過(guo)高(gao)首先(xian)會使過(guo)壓(ya)(ya)保(bao)(bao)護(hu)電(dian)(dian)路動作(zuo)。因此對于(yu)這(zhe)種故(gu)障的(de)(de)維修，我(wo)們(men)(men)可(ke)以(yi)通過(guo)斷開(kai)過(guo)壓(ya)(ya)保(bao)(bao)護(hu)電(dian)(dian)路，使過(guo)壓(ya)(ya)保(bao)(bao)護(hu)電(dian)(dian)路不起作(zuo)用，在(zai)這(zhe)時，測量開(kai)機瞬間(jian)(jian)的(de)(de)電(dian)(dian)源(yuan)主電(dian)(dian)壓(ya)(ya)。如果(guo)測量值(zhi)比正常值(zhi)高(gao)出IV以(yi)上，說明輸出電(dian)(dian)壓(ya)(ya)過(guo)高(gao)。我(wo)們(men)(men)應著重檢查取樣(yang)電(dian)(dian)阻(zu)是否(fou)變值(zhi)或(huo)損(sun)(sun)壞(huai)，精(jing)密(mi)穩壓(ya)(ya)放大器(qi)（TL431）或(huo)光耦合器(qi)（PC817）性(xing)能不良，變質或(huo)損(sun)(sun)壞(huai)；其中(zhong)精(jing)密(mi)穩壓(ya)(ya)放大器(qi)（TL431）極(ji)易損(sun)(sun)壞(huai)，我(wo)們(men)(men)可(ke)用下述方(fang)法對精(jing)密(mi)穩壓(ya)(ya)放大器(qi)（TL431）作(zuo)出好壞(huai)的(de)(de)判(pan)別：將(jiang)TL431的(de)(de)參考端（Ref）與它的(de)(de)陰極(ji)（Cathode）相(xiang)連，串10k的(de)(de)電(dian)(dian)阻(zu)，接入5V電(dian)(dian)壓(ya)(ya)，若陽極(ji)（Anode）與陰極(ji)之間(jian)(jian)為(wei)2、5V，并且等待片刻還仍然為(wei)2、5V，則為(wei)好管(guan)，否(fou)則為(wei)壞(huai)管(guan)。

6、有直流電壓輸出，但輸出直流電壓過低

對于這種(zhong)故(gu)障現象，根據(ju)維(wei)修經(jing)驗可知，除穩壓(ya)控制電路會(hui)引(yin)起(qi)輸(shu)出(chu)電壓(ya)過低外，還(huan)有一些原因會(hui)引(yin)起(qi)輸(shu)出(chu)電壓(ya)過低，主(zhu)要有以下幾(ji)點:

①　開關(guan)電(dian)(dian)源(yuan)負(fu)(fu)載有(you)短路故障。此時，應斷開開關(guan)電(dian)(dian)源(yuan)電(dian)(dian)路的所有(you)負(fu)(fu)載，以區分是(shi)開關(guan)電(dian)(dian)源(yuan)電(dian)(dian)路還是(shi)負(fu)(fu)載電(dian)(dian)路有(you)故障。若斷開負(fu)(fu)載電(dian)(dian)路電(dian)(dian)壓輸出正(zheng)常(chang)，說(shuo)明(ming)是(shi)負(fu)(fu)載過重；若仍不正(zheng)常(chang)，說(shuo)明(ming)開關(guan)電(dian)(dian)源(yuan)電(dian)(dian)路有(you)故障。

②　輸出電壓端(duan)整流二極管、濾波(bo)電容失效等，可以通過代換(huan)法進行判(pan)斷。

③　開關功率管的性能下(xia)降，必然(ran)導致(zhi)開關管不能正(zheng)常導通，使電源的內(nei)阻增加(jia)，帶負載能力(li)下(xia)降。

④　開關功率(lv)管的源極（S極），通常接(jie)(jie)一個阻值很小(xiao)，但功率(lv)很大的電(dian)阻，作為過流保護(hu)檢測電(dian)阻，此電(dian)阻的阻值一般在0.2到0.8之間。此電(dian)阻如變值或開焊，接(jie)(jie)觸不(bu)良也會(hui)造成(cheng)輸(shu)出電(dian)壓過低的故(gu)障(zhang)。

高(gao)頻變壓器不(bu)良(liang)，不(bu)但造成輸出電壓下(xia)降，還(huan)會造成開關功率管(guan)激勵不(bu)足從(cong)而(er)屢損(sun)開關管(guan)。

⑤　高壓直(zhi)流(liu)濾波電容(rong)不良，造成電源帶負(fu)載能力差，一接負(fu)載輸出電壓便下降。

⑥　電源輸出線接觸(chu)不(bu)良，有(you)一定的接觸(chu)電阻(zu)，造成(cheng)輸出電壓(ya)過(guo)低。

⑦　電(dian)(dian)網電(dian)(dian)壓(ya)是否過低(di)。雖然(ran)開關電(dian)(dian)源在低(di)壓(ya)下仍然(ran)可以輸出(chu)額(e)定的(de)電(dian)(dian)壓(ya)值(zhi)，但(dan)當電(dian)(dian)網電(dian)(dian)壓(ya)低(di)于開關電(dian)(dian)源的(de)最(zui)低(di)電(dian)(dian)壓(ya)限定值(zhi)時，也會使(shi)輸出(chu)電(dian)(dian)壓(ya)過低(di)。

維修(xiu)方法：對于這種故(gu)障我(wo)們可(ke)以(yi)根據(ju)以(yi)上故(gu)障原(yuan)因(yin)，來(lai)逐(zhu)一(yi)(yi)進(jin)行(xing)排查(cha)(cha)。但在實(shi)(shi)際維修(xiu)時，可(ke)根據(ju)實(shi)(shi)際情況來(lai)進(jin)行(xing)排查(cha)(cha)，不(bu)一(yi)(yi)定要(yao)逐(zhu)一(yi)(yi)排查(cha)(cha)。首先用萬(wan)用表檢查(cha)(cha)一(yi)(yi)下高壓(ya)直流(liu)(liu)濾(lv)波電(dian)容(rong)(rong)是否變(bian)(bian)質，容(rong)(rong)量(liang)是否下降，能否正常充放(fang)電(dian)。如無(wu)以(yi)上現象，則測量(liang)一(yi)(yi)下開關功率管的(de)(de)柵極（G極）的(de)(de)限流(liu)(liu)電(dian)阻(zu)以(yi)及源(yuan)極（S極）的(de)(de)過流(liu)(liu)保護檢測電(dian)阻(zu)是否變(bian)(bian)值，變(bian)(bian)質或開焊，接觸不(bu)良。經判別后(hou)，若無(wu)問題，我(wo)們就(jiu)檢查(cha)(cha)一(yi)(yi)下高頻(pin)變(bian)(bian)壓(ya)器(qi)(qi)的(de)(de)鐵芯(xin)是否完(wan)好(hao)無(wu)損(sun)。因(yin)在日常生(sheng)活使(shi)用中，不(bu)可(ke)避(bi)免的(de)(de)重(zhong)摔或重(zhong)幢(chuang)，使(shi)高頻(pin)變(bian)(bian)壓(ya)器(qi)(qi)的(de)(de)鐵芯(xin)損(sun)壞。使(shi)高頻(pin)變(bian)(bian)壓(ya)器(qi)(qi)的(de)(de)磁(ci)(ci)通量(liang)，磁(ci)(ci)感應強度，以(yi)及磁(ci)(ci)路等都會(hui)受(shou)到(dao)很大的(de)(de)影(ying)響，造(zao)成傳輸(shu)(shu)的(de)(de)效率，能量(liang)將會(hui)大打折扣。由于高頻(pin)變(bian)(bian)壓(ya)器(qi)(qi)為了(le)減小(xiao)渦流(liu)(liu)，增大高頻(pin)交流(liu)(liu)電(dian)的(de)(de)傳輸(shu)(shu)效率，它的(de)(de)鐵芯(xin)是用軟磁(ci)(ci)鐵氧體制作而成的(de)(de)。這種磁(ci)(ci)性材料具有高的(de)(de)導(dao)磁(ci)(ci)率，但質脆，易碎。因(yin)此(ci)它的(de)(de)損(sun)壞率也是很高的(de)(de)。因(yin)此(ci)在維修(xiu)時千萬(wan)不(bu)要(yao)忘(wang)了(le)檢查(cha)(cha)此(ci)處，以(yi)免走彎路。除(chu)此(ci)之外還有可(ke)能就(jiu)是輸(shu)(shu)出濾(lv)波電(dian)容(rong)(rong)容(rong)(rong)量(liang)降低，甚至失(shi)容(rong)(rong)或開焊，虛(xu)接；電(dian)源(yuan)輸(shu)(shu)出限流(liu)(liu)電(dian)阻(zu)變(bian)(bian)值或虛(xu)接，電(dian)源(yuan)輸(shu)(shu)出線虛(xu)接等。在實(shi)(shi)際維修(xiu)時，這些因(yin)素都不(bu)要(yao)放(fang)過，都應檢查(cha)(cha)一(yi)(yi)下，以(yi)保證萬(wan)無(wu)一(yi)(yi)失(shi)。

7、散熱風扇不轉

這(zhe)種(zhong)故障原(yuan)因主要是由于(yu)控制風(feng)扇的三極管（8550或(huo)8050）損(sun)壞，或(huo)者風(feng)扇本身(shen)損(sun)壞或(huo)風(feng)葉被雜物卡住(zhu)。但有些開關電(dian)源(yuan)中(zhong)采(cai)用的是智能散(san)熱，對于(yu)采(cai)用這(zhe)種(zhong)方式散(san)熱的開關電(dian)源(yuan)，熱敏電(dian)阻損(sun)壞的概率是很大的。

維修方法：首先(xian)用萬用表測(ce)(ce)量(liang)一下(xia)控制風扇(shan)的(de)三極管(guan)是否損壞，若測(ce)(ce)得(de)此管(guan)未損壞那就(jiu)有(you)可能是風扇(shan)本身(shen)損壞。可以把(ba)風扇(shan)從(cong)電(dian)路板上拔下(xia)來，另(ling)外接(jie)上一個12V的(de)直流(liu)電(dian)（注意(yi)正(zheng)負極），看(kan)是否轉(zhuan)動，并(bing)看(kan)有(you)無(wu)異物卡(ka)住。若擺動幾下(xia)風扇(shan)的(de)電(dian)線，風扇(shan)就(jiu)轉(zhuan)動，則(ze)說明(ming)電(dian)線內部有(you)斷線或接(jie)頭(tou)接(jie)觸不良(liang)。若仍不轉(zhuan)動，則(ze)風扇(shan)必壞。對(dui)于采(cai)用智能散熱(re)(re)的(de)開關電(dian)源來說，除(chu)按上述檢(jian)查外，還應檢(jian)查一下(xia)熱(re)(re)敏電(dian)阻是否不良(liang)或損壞，開焊等。但要(yao)注意(yi)此熱(re)(re)敏電(dian)阻為負溫度系數的(de)熱(re)(re)敏電(dian)阻，更換時(shi)應注意(yi)。