開關電源簡介

開關電源是利用現代電(dian)(dian)力電(dian)(dian)子技(ji)術(shu)，控制(zhi)開(kai)(kai)關(guan)晶體管開(kai)(kai)通(tong)和(he)關(guan)斷(duan)的時間(jian)比率，維(wei)持穩定輸(shu)出電(dian)(dian)壓的一種(zhong)電(dian)(dian)源。廣泛運用在(zai)工業(ye)、軍事、科研、通(tong)訊、醫療(liao)及(ji)多種(zhong)家用電(dian)(dian)器中。開(kai)(kai)關(guan)電(dian)(dian)源的發展與應用在(zai)節約(yue)能(neng)源、節約(yue)資源及(ji)保(bao)護環境方(fang)面都具有重(zhong)要的意義(yi)。下面我們就來看看開(kai)(kai)關(guan)電(dian)(dian)源電(dian)(dian)路圖與維(wei)修(xiu)技(ji)巧(qiao)。

開(kai)關電(dian)(dian)源的主要電(dian)(dian)路(lu)是由輸(shu)(shu)(shu)入電(dian)(dian)磁干擾濾波(bo)器（EMI）、整流(liu)濾波(bo)電(dian)(dian)路(lu)、功率變換電(dian)(dian)路(lu)、PWM控制器電(dian)(dian)路(lu)、輸(shu)(shu)(shu)出(chu)整流(liu)濾波(bo)電(dian)(dian)路(lu)組成。輔(fu)助電(dian)(dian)路(lu)有輸(shu)(shu)(shu)入過欠壓保護(hu)(hu)電(dian)(dian)路(lu)、輸(shu)(shu)(shu)出(chu)過欠壓保護(hu)(hu)電(dian)(dian)路(lu)、輸(shu)(shu)(shu)出(chu)過流(liu)保護(hu)(hu)電(dian)(dian)路(lu)、輸(shu)(shu)(shu)出(chu)短路(lu)保護(hu)(hu)電(dian)(dian)路(lu)等。

開關電源的維修步驟

加電檢測

該圖片由注冊用戶"沉靜時光"提供，版權聲明反饋

通電(dian)后觀察電(dian)源是(shi)否有燒保(bao)險及個別(bie)元件冒(mao)煙等現象(xiang)，若有要及時切斷供電(dian)進行檢修。

測量高壓濾(lv)波(bo)電(dian)容(rong)兩端有(you)無(wu)300伏(fu)輸(shu)出(chu)，若無(wu)應(ying)重點查整流(liu)二極管(guan)、濾(lv)波(bo)電(dian)容(rong)等。

測量(liang)高頻變壓器次級線圈(quan)有無輸(shu)出(chu)，若無應重(zhong)點(dian)查(cha)開關管(guan)是否(fou)損壞，是否(fou)起振，保(bao)護電路(lu)是否(fou)動作等(deng)(deng)，若有則應重(zhong)點(dian)檢查(cha)各輸(shu)出(chu)側的(de)整流二(er)極管(guan)、濾波電容、三通穩壓管(guan)等(deng)(deng)。

如(ru)果(guo)電(dian)源啟(qi)動一下(xia)(xia)就(jiu)停止，則(ze)(ze)該電(dian)源處于保護(hu)狀(zhuang)態(tai)(tai)下(xia)(xia)，可直接測(ce)量PWM芯片保護(hu)輸入(ru)腳的(de)電(dian)壓(ya)，如(ru)果(guo)電(dian)壓(ya)超出(chu)規(gui)定(ding)值，則(ze)(ze)說明電(dian)源處于保護(hu)狀(zhuang)態(tai)(tai)下(xia)(xia)，應(ying)重點檢查產生保護(hu)的(de)原因。

總之(zhi)，開關電(dian)源(yuan)電(dian)路有(you)易有(you)難，功率有(you)大有(you)小，輸出電(dian)壓多種多樣。只要按照(zhao)上述(shu)維修(xiu)(xiu)技(ji)巧，多動手進行(xing)開關電(dian)源(yuan)的維修(xiu)(xiu)，就(jiu)能迅速地(di)排除開關電(dian)源(yuan)故障，達到事半功倍(bei)的效(xiao)果。

斷電后看聞問量

看(kan)：打開電源(yuan)的(de)外殼，檢查保(bao)險(xian)絲是(shi)否熔(rong)斷(duan)，再(zai)觀察電源(yuan)的(de)內部(bu)情況，如果發(fa)現電源(yuan)的(de)PCB板上(shang)有燒焦處或元(yuan)件破裂，則(ze)應重點(dian)檢查此(ci)處元(yuan)件及相關電路(lu)元(yuan)件。

聞：聞一(yi)下(xia)電(dian)源內部是(shi)否有(you)糊味(wei)，檢查是(shi)否有(you)燒(shao)焦的元(yuan)器件。

問：問一下電(dian)源損壞的經過，是否對電(dian)源進行違規操作(zuo)。

量：沒通電(dian)(dian)(dian)(dian)前(qian)，用(yong)萬用(yong)表量一下高壓電(dian)(dian)(dian)(dian)容兩(liang)端(duan)的(de)(de)電(dian)(dian)(dian)(dian)壓先(xian)。如(ru)果是開(kai)(kai)關(guan)(guan)電(dian)(dian)(dian)(dian)源不起(qi)振或開(kai)(kai)關(guan)(guan)管開(kai)(kai)路引(yin)起(qi)的(de)(de)故障(zhang)，則(ze)(ze)大多數情況下，高壓濾波電(dian)(dian)(dian)(dian)容兩(liang)端(duan)的(de)(de)電(dian)(dian)(dian)(dian)壓未泄放(fang)悼，用(yong)萬用(yong)表測(ce)量AC電(dian)(dian)(dian)(dian)源線(xian)兩(liang)端(duan)的(de)(de)正反向電(dian)(dian)(dian)(dian)阻(zu)及電(dian)(dian)(dian)(dian)容器充電(dian)(dian)(dian)(dian)情況，電(dian)(dian)(dian)(dian)阻(zu)值不應(ying)過低，否則(ze)(ze)電(dian)(dian)(dian)(dian)源內部可能存在(zai)短路。電(dian)(dian)(dian)(dian)容器應(ying)能充放(fang)電(dian)(dian)(dian)(dian)。脫(tuo)開(kai)(kai)負載(zai)，分別測(ce)量各組輸出(chu)端(duan)的(de)(de)對地電(dian)(dian)(dian)(dian)阻(zu)，正常時，表針應(ying)有電(dian)(dian)(dian)(dian)容器充放(fang)電(dian)(dian)(dian)(dian)擺動，最(zui)后指(zhi)示的(de)(de)應(ying)為該路的(de)(de)泄放(fang)電(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，保險(xian)絲熔斷說明開(kai)關電(dian)(dian)(dian)源(yuan)(yuan)的內部電(dian)(dian)(dian)路存在短路或過流的故障。由于開(kai)關電(dian)(dian)(dian)源(yuan)(yuan)工(gong)作在高電(dian)(dian)(dian)壓，大(da)(da)電(dian)(dian)(dian)流的狀(zhuang)(zhuang)態(tai)下，直流濾波(bo)(bo)和變(bian)換振蕩電(dian)(dian)(dian)路在高壓狀(zhuang)(zhuang)態(tai)工(gong)作時(shi)間太長，電(dian)(dian)(dian)壓變(bian)化(hua)相對大(da)(da)。電(dian)(dian)(dian)網電(dian)(dian)(dian)壓的波(bo)(bo)動，浪(lang)涌都會(hui)引(yin)起電(dian)(dian)(dian)源(yuan)(yuan)內電(dian)(dian)(dian)流瞬(shun)間增大(da)(da)而(er)使(shi)保險(xian)絲熔斷。重點應檢查電(dian)(dian)(dian)源(yuan)(yuan)輸入端的整流二極管(guan)(guan)，高壓濾波(bo)(bo)電(dian)(dian)(dian)解電(dian)(dian)(dian)容，開(kai)關功率管(guan)(guan)，UC3842本(ben)身及外圍元器(qi)件等(deng)。檢查一下這些元器(qi)件有無擊穿，開(kai)路，損壞(huai)，燒(shao)焦(jiao)，炸裂等(deng)現象。

維修方(fang)法：首先仔細查看(kan)電(dian)(dian)(dian)路(lu)板上(shang)面的(de)(de)(de)各個元(yuan)件，看(kan)是(shi)(shi)(shi)否(fou)在(zai)這(zhe)些元(yuan)件的(de)(de)(de)外表(biao)有(you)(you)(you)沒有(you)(you)(you)被燒(shao)糊,有(you)(you)(you)沒有(you)(you)(you)電(dian)(dian)(dian)解液(ye)溢(yi)出，聞(wen)(wen)一(yi)聞(wen)(wen)有(you)(you)(you)沒有(you)(you)(you)異味(wei)。經看(kan)，聞(wen)(wen)之后(hou)，再用萬用表(biao)進(jin)行(xing)檢(jian)查。首先測(ce)(ce)量(liang)(liang)一(yi)下(xia)(xia)電(dian)(dian)(dian)源(yuan)輸入(ru)(ru)端(duan)的(de)(de)(de)電(dian)(dian)(dian)阻值，若(ruo)小于200K，則說明后(hou)端(duan)有(you)(you)(you)局部(bu)短(duan)(duan)路(lu)現象(xiang)，然后(hou)分別測(ce)(ce)量(liang)(liang)四只(zhi)整流(liu)二(er)極(ji)管正(zheng)，反(fan)向電(dian)(dian)(dian)阻和兩(liang)個限流(liu)電(dian)(dian)(dian)阻的(de)(de)(de)阻值，看(kan)其有(you)(you)(you)無(wu)短(duan)(duan)路(lu)或燒(shao)壞(huai)；然后(hou)再測(ce)(ce)量(liang)(liang)一(yi)下(xia)(xia)電(dian)(dian)(dian)源(yuan)濾波(bo)電(dian)(dian)(dian)容是(shi)(shi)(shi)否(fou)能(neng)進(jin)行(xing)正(zheng)常充放電(dian)(dian)(dian)，再就測(ce)(ce)量(liang)(liang)一(yi)下(xia)(xia)開關(guan)(guan)功率(lv)(lv)管是(shi)(shi)(shi)否(fou)擊穿損壞(huai)，以(yi)及UC3842本身，及周圍元(yuan)件是(shi)(shi)(shi)否(fou)擊穿，燒(shao)壞(huai)等。需要說明的(de)(de)(de)一(yi)點是(shi)(shi)(shi)：因是(shi)(shi)(shi)在(zai)路(lu)測(ce)(ce)量(liang)(liang)，有(you)(you)(you)可(ke)能(neng)會使(shi)測(ce)(ce)量(liang)(liang)結果有(you)(you)(you)誤(wu)，造成誤(wu)判(pan)。因此必(bi)要時可(ke)把元(yuan)器(qi)件焊(han)下(xia)(xia)來再進(jin)行(xing)測(ce)(ce)量(liang)(liang)。如果仍(reng)然沒有(you)(you)(you)上(shang)述(shu)情況則測(ce)(ce)量(liang)(liang)一(yi)下(xia)(xia)輸入(ru)(ru)電(dian)(dian)(dian)源(yuan)線及輸出電(dian)(dian)(dian)源(yuan)線是(shi)(shi)(shi)否(fou)內部(bu)短(duan)(duan)路(lu)。一(yi)般情況下(xia)(xia)，熔斷(duan)(duan)器(qi)熔斷(duan)(duan)故(gu)障，整流(liu)二(er)極(ji)管，電(dian)(dian)(dian)源(yuan)濾波(bo)電(dian)(dian)(dian)容，開關(guan)(guan)功率(lv)(lv)管，UC3842是(shi)(shi)(shi)易(yi)損件，損壞(huai)的(de)(de)(de)概(gai)率(lv)(lv)可(ke)達95%以(yi)上(shang)，一(yi)般著重檢(jian)查一(yi)下(xia)(xia)這(zhe)些元(yuan)器(qi)件，就可(ke)很容易(yi)排除(chu)此類(lei)故(gu)障。

2、無直流電壓輸出或電壓輸出不穩定

如果保險絲(si)是(shi)完好的(de)，在(zai)有(you)負(fu)載的(de)情況(kuang)下(xia)，各(ge)級(ji)直(zhi)流(liu)電(dian)(dian)壓(ya)無輸出(chu)。這種情況(kuang)主要是(shi)以下(xia)原因造(zao)成的(de)：電(dian)(dian)源中出(chu)現(xian)開路(lu)(lu)(lu)，短路(lu)(lu)(lu)現(xian)象，過壓(ya)，過流(liu)保護電(dian)(dian)路(lu)(lu)(lu)出(chu)現(xian)故障，振(zhen)蕩(dang)電(dian)(dian)路(lu)(lu)(lu)沒有(you)工作，電(dian)(dian)源負(fu)載過重，高(gao)頻整(zheng)流(liu)濾波電(dian)(dian)路(lu)(lu)(lu)中整(zheng)流(liu)二極管(guan)被擊(ji)穿，濾波電(dian)(dian)容漏電(dian)(dian)等。

維修方法：首先，用(yong)萬(wan)用(yong)表測(ce)量一(yi)(yi)下高頻(pin)(pin)變壓(ya)器(qi)次(ci)級的(de)各個元器(qi)件(jian)(jian)是否有損壞(huai)。在(zai)排(pai)除(chu)了(le)高頻(pin)(pin)整流二極管(guan)擊(ji)穿(chuan)、負載短路的(de)情況后，然后在(zai)測(ce)量各輸出(chu)端的(de)直流電(dian)(dian)(dian)壓(ya)，如果這時輸出(chu)仍(reng)為(wei)零，則可(ke)以肯定(ding)是電(dian)(dian)(dian)源(yuan)的(de)控(kong)制電(dian)(dian)(dian)路出(chu)了(le)故障。控(kong)制電(dian)(dian)(dian)路的(de)兩部分(fen)是集成開關(guan)電(dian)(dian)(dian)源(yuan)控(kong)制器(qi)和過(guo)壓(ya)保護電(dian)(dian)(dian)路。最后用(yong)萬(wan)用(yong)表靜態測(ce)量高頻(pin)(pin)濾波電(dian)(dian)(dian)路中整流二極管(guan)及低壓(ya)濾波電(dian)(dian)(dian)容是否損壞(huai)。如果確(que)實相(xiang)關(guan)的(de)元件(jian)(jian)損壞(huai)，在(zai)更(geng)換好新的(de)完(wan)好的(de)元件(jian)(jian)后，開機(ji)測(ce)試，一(yi)(yi)般故障即可(ke)排(pai)除(chu)。需要說(shuo)明(ming)的(de)是：電(dian)(dian)(dian)源(yuan)輸出(chu)線斷線或開焊，虛焊也會造成這種故障。在(zai)維修時應注(zhu)意這一(yi)(yi)點。

3、電源負載能力差

電(dian)源(yuan)(yuan)負載能力差是一(yi)個常見(jian)的故障，一(yi)般都是出現在老(lao)式或是工作時間長的電(dian)源(yuan)(yuan)中，主要原(yuan)因是各元(yuan)器件老(lao)化，開關管(guan)的工作不穩(wen)定，沒有及時進行(xing)散熱(re)等。此外還有穩(wen)壓二極管(guan)發熱(re)漏電(dian)，整(zheng)流二極管(guan)損壞等。

維修(xiu)方(fang)法：用(yong)萬用(yong)表著(zhu)重(zhong)檢查一(yi)(yi)下穩壓二(er)極管(guan)，高壓濾波電(dian)容(rong)，限流電(dian)阻有(you)無變(bian)質等再(zai)仔細檢查一(yi)(yi)下電(dian)路板上的所有(you)焊(han)點(dian)是否開焊(han)，虛接(jie)等。把(ba)開焊(han)的焊(han)點(dian)重(zhong)新焊(han)牢，更換(huan)變(bian)質的元器(qi)件(jian)，一(yi)(yi)般(ban)故(gu)障即可排除。

4、無直流電壓輸出，但保險絲完好

這種現象說明開(kai)關電源未(wei)工作，或者工作后進入了保護狀態。

維修方(fang)法(fa)：首先應判斷(duan)(duan)一(yi)下(xia)開(kai)(kai)關電(dian)源的(de)(de)(de)主(zhu)控(kong)芯片(pian)UC3842是(shi)否處在(zai)工作(zuo)狀態或(huo)已(yi)經損(sun)(sun)壞(huai)。判斷(duan)(duan)方(fang)法(fa)是(shi)這(zhe)樣的(de)(de)(de)：加電(dian)測(ce)UC3842的(de)(de)(de)第7腳(jiao)(jiao)對(dui)地(di)電(dian)壓，若測(ce)第8腳(jiao)(jiao)有+5V電(dian)壓，1，2，4，6腳(jiao)(jiao)也有不(bu)同(tong)的(de)(de)(de)電(dian)壓，則(ze)說明電(dian)路已(yi)起(qi)振，UC3842基本正常；若7腳(jiao)(jiao)電(dian)壓低(di)，其余管腳(jiao)(jiao)無電(dian)壓或(huo)不(bu)波動，則(ze)UC3842已(yi)損(sun)(sun)壞(huai)。UC3842芯片(pian)損(sun)(sun)壞(huai)最常見的(de)(de)(de)是(shi)6，7腳(jiao)(jiao)對(dui)地(di)擊(ji)穿，5，7腳(jiao)(jiao)對(dui)地(di)擊(ji)穿和1，7腳(jiao)(jiao)對(dui)地(di)擊(ji)穿。如果這(zhe)幾只腳(jiao)(jiao)都為擊(ji)穿，而開(kai)(kai)關電(dian)源還是(shi)不(bu)能(neng)正常啟動，則(ze)UC3842必壞(huai)，應直接更(geng)換。若判斷(duan)(duan)芯片(pian)未(wei)壞(huai)，則(ze)就著重檢查開(kai)(kai)關功率(lv)管的(de)(de)(de)柵極（G極）的(de)(de)(de)限流電(dian)阻是(shi)否開(kai)(kai)焊，虛接，變值，變質(zhi)以及(ji)開(kai)(kai)關功率(lv)管本身(shen)是(shi)否性能(neng)不(bu)良(liang)。除此之外，電(dian)源輸(shu)出線(xian)也有可能(neng)斷(duan)(duan)線(xian)或(huo)接觸不(bu)良(liang)也會(hui)造成(cheng)這(zhe)種(zhong)故障(zhang)。因此在(zai)維修時也應注意檢查一(yi)下(xia)。

5、有直流電壓輸出，但輸出電壓過高

這(zhe)種故障往往來(lai)自(zi)于(yu)穩壓(ya)取(qu)樣和穩壓(ya)控制電(dian)(dian)(dian)路(lu)出現故障所(suo)致(zhi)。在(zai)開關電(dian)(dian)(dian)源中，直流輸出、取(qu)樣電(dian)(dian)(dian)阻、誤差取(qu)樣放大器（如LM324，LM358等）、光耦合(he)器（PC817）、電(dian)(dian)(dian)源控制芯(xin)片（UC3842）等電(dian)(dian)(dian)路(lu)共同構成了一個閉合(he)的控制環(huan)路(lu)，任何一處出問題(ti)都會導致(zhi)輸出電(dian)(dian)(dian)壓(ya)升高(gao)。

維修方法：由(you)于(yu)開關(guan)電(dian)(dian)(dian)(dian)源中有過(guo)壓(ya)保(bao)(bao)護(hu)電(dian)(dian)(dian)(dian)路(lu)，輸出(chu)(chu)電(dian)(dian)(dian)(dian)壓(ya)過(guo)高首先會使(shi)過(guo)壓(ya)保(bao)(bao)護(hu)電(dian)(dian)(dian)(dian)路(lu)動作(zuo)。因此對(dui)于(yu)這種故障的(de)維修，我們可以通過(guo)斷開過(guo)壓(ya)保(bao)(bao)護(hu)電(dian)(dian)(dian)(dian)路(lu)，使(shi)過(guo)壓(ya)保(bao)(bao)護(hu)電(dian)(dian)(dian)(dian)路(lu)不(bu)(bu)起作(zuo)用，在這時，測量開機(ji)瞬間的(de)電(dian)(dian)(dian)(dian)源主電(dian)(dian)(dian)(dian)壓(ya)。如(ru)果(guo)測量值(zhi)比正常值(zhi)高出(chu)(chu)IV以上，說(shuo)明輸出(chu)(chu)電(dian)(dian)(dian)(dian)壓(ya)過(guo)高。我們應著(zhu)重檢查取樣電(dian)(dian)(dian)(dian)阻(zu)是否(fou)變(bian)值(zhi)或(huo)損壞，精(jing)密穩壓(ya)放(fang)大器（TL431）或(huo)光耦合器（PC817）性能(neng)不(bu)(bu)良，變(bian)質或(huo)損壞；其中精(jing)密穩壓(ya)放(fang)大器（TL431）極(ji)(ji)易(yi)損壞，我們可用下述方法對(dui)精(jing)密穩壓(ya)放(fang)大器（TL431）作(zuo)出(chu)(chu)好壞的(de)判別(bie)：將(jiang)TL431的(de)參(can)考端（Ref）與(yu)它(ta)的(de)陰極(ji)(ji)（Cathode）相連，串10k的(de)電(dian)(dian)(dian)(dian)阻(zu)，接入(ru)5V電(dian)(dian)(dian)(dian)壓(ya)，若(ruo)陽極(ji)(ji)（Anode）與(yu)陰極(ji)(ji)之間為(wei)2、5V，并且等待片刻還(huan)仍然為(wei)2、5V，則為(wei)好管(guan)，否(fou)則為(wei)壞管(guan)。

6、有直流電壓輸出，但輸出直流電壓過低

對于這(zhe)種故障現象，根據維修(xiu)經驗可知(zhi)，除穩壓(ya)控制電路會引起(qi)輸(shu)出電壓(ya)過低(di)外，還有一些原因會引起(qi)輸(shu)出電壓(ya)過低(di)，主要(yao)有以(yi)下(xia)幾點:

①　開關電源負(fu)載(zai)有短路(lu)故障。此時(shi)，應(ying)斷(duan)開開關電源電路(lu)的所有負(fu)載(zai)，以區分(fen)是開關電源電路(lu)還是負(fu)載(zai)電路(lu)有故障。若斷(duan)開負(fu)載(zai)電路(lu)電壓(ya)輸出正(zheng)常(chang)(chang)，說明是負(fu)載(zai)過重；若仍不正(zheng)常(chang)(chang)，說明開關電源電路(lu)有故障。

②　輸(shu)出(chu)電(dian)壓端(duan)整(zheng)流二極管、濾波電(dian)容失效等，可(ke)以(yi)通(tong)過代換法進(jin)行(xing)判(pan)斷。

③　開(kai)關(guan)功率管(guan)的(de)性能(neng)(neng)下降，必然導致開(kai)關(guan)管(guan)不能(neng)(neng)正常導通，使電源的(de)內阻增加，帶負(fu)載能(neng)(neng)力下降。

④　開關功(gong)(gong)率管的源(yuan)極（S極），通常接一(yi)個阻(zu)值(zhi)(zhi)很小，但功(gong)(gong)率很大的電阻(zu)，作為過(guo)流保(bao)護檢測電阻(zu)，此電阻(zu)的阻(zu)值(zhi)(zhi)一(yi)般在(zai)0.2到(dao)0.8之間。此電阻(zu)如變(bian)值(zhi)(zhi)或(huo)開焊，接觸不良也(ye)會造成輸出電壓過(guo)低的故障。

高頻變壓(ya)器不良，不但(dan)造(zao)成輸出(chu)電(dian)壓(ya)下降，還會造(zao)成開(kai)關功率管激勵不足從而屢(lv)損(sun)開(kai)關管。

⑤　高壓直(zhi)流濾波(bo)電(dian)容不良，造成電(dian)源帶負載(zai)能力差，一(yi)接負載(zai)輸出電(dian)壓便下降。

⑥　電(dian)(dian)(dian)源輸(shu)出線接觸不良，有一定的接觸電(dian)(dian)(dian)阻，造成輸(shu)出電(dian)(dian)(dian)壓(ya)過低。

⑦　電(dian)(dian)網電(dian)(dian)壓(ya)(ya)(ya)是否(fou)過(guo)(guo)低(di)(di)(di)。雖然開關電(dian)(dian)源在(zai)低(di)(di)(di)壓(ya)(ya)(ya)下仍然可以輸(shu)(shu)出額定(ding)的(de)電(dian)(dian)壓(ya)(ya)(ya)值(zhi)，但當電(dian)(dian)網電(dian)(dian)壓(ya)(ya)(ya)低(di)(di)(di)于開關電(dian)(dian)源的(de)最(zui)低(di)(di)(di)電(dian)(dian)壓(ya)(ya)(ya)限定(ding)值(zhi)時，也會(hui)使輸(shu)(shu)出電(dian)(dian)壓(ya)(ya)(ya)過(guo)(guo)低(di)(di)(di)。

維(wei)(wei)修(xiu)方法(fa)：對于這種故(gu)障(zhang)我們可以(yi)(yi)根據以(yi)(yi)上故(gu)障(zhang)原因(yin)，來逐一(yi)(yi)進行(xing)排查(cha)。但(dan)在實(shi)際維(wei)(wei)修(xiu)時，可根據實(shi)際情況(kuang)來進行(xing)排查(cha)，不(bu)一(yi)(yi)定要(yao)逐一(yi)(yi)排查(cha)。首(shou)先用萬(wan)用表(biao)檢(jian)查(cha)一(yi)(yi)下(xia)高(gao)(gao)(gao)壓(ya)直流(liu)濾(lv)波電(dian)容(rong)(rong)(rong)是否變(bian)(bian)質(zhi)，容(rong)(rong)(rong)量是否下(xia)降，能否正常充放電(dian)。如無以(yi)(yi)上現象，則測量一(yi)(yi)下(xia)開關功率(lv)管(guan)的柵極(ji)(ji)（G極(ji)(ji)）的限流(liu)電(dian)阻(zu)(zu)以(yi)(yi)及源極(ji)(ji)（S極(ji)(ji)）的過流(liu)保護檢(jian)測電(dian)阻(zu)(zu)是否變(bian)(bian)值(zhi)，變(bian)(bian)質(zhi)或(huo)開焊(han)，接(jie)觸不(bu)良。經判別(bie)后，若無問(wen)題，我們就檢(jian)查(cha)一(yi)(yi)下(xia)高(gao)(gao)(gao)頻(pin)變(bian)(bian)壓(ya)器(qi)的鐵(tie)芯(xin)是否完好無損。因(yin)在日常生活使(shi)用中，不(bu)可避免(mian)的重摔或(huo)重幢，使(shi)高(gao)(gao)(gao)頻(pin)變(bian)(bian)壓(ya)器(qi)的鐵(tie)芯(xin)損壞。使(shi)高(gao)(gao)(gao)頻(pin)變(bian)(bian)壓(ya)器(qi)的磁(ci)(ci)通(tong)量，磁(ci)(ci)感應(ying)強度，以(yi)(yi)及磁(ci)(ci)路等都會受到很大的影響，造成(cheng)傳輸的效率(lv)，能量將會大打(da)折扣。由于高(gao)(gao)(gao)頻(pin)變(bian)(bian)壓(ya)器(qi)為了減小渦(wo)流(liu)，增大高(gao)(gao)(gao)頻(pin)交流(liu)電(dian)的傳輸效率(lv)，它的鐵(tie)芯(xin)是用軟(ruan)磁(ci)(ci)鐵(tie)氧(yang)體制作而成(cheng)的。這種磁(ci)(ci)性材料具有(you)高(gao)(gao)(gao)的導磁(ci)(ci)率(lv)，但(dan)質(zhi)脆，易碎。因(yin)此它的損壞率(lv)也是很高(gao)(gao)(gao)的。因(yin)此在維(wei)(wei)修(xiu)時千萬(wan)不(bu)要(yao)忘了檢(jian)查(cha)此處，以(yi)(yi)免(mian)走(zou)彎(wan)路。除此之外還有(you)可能就是輸出濾(lv)波電(dian)容(rong)(rong)(rong)容(rong)(rong)(rong)量降低，甚至失容(rong)(rong)(rong)或(huo)開焊(han)，虛(xu)接(jie)；電(dian)源輸出限流(liu)電(dian)阻(zu)(zu)變(bian)(bian)值(zhi)或(huo)虛(xu)接(jie)，電(dian)源輸出線虛(xu)接(jie)等。在實(shi)際維(wei)(wei)修(xiu)時，這些因(yin)素都不(bu)要(yao)放過，都應(ying)檢(jian)查(cha)一(yi)(yi)下(xia)，以(yi)(yi)保證萬(wan)無一(yi)(yi)失。

7、散熱風扇不轉

這種(zhong)故(gu)障原因主(zhu)要(yao)是由于(yu)控(kong)制風(feng)扇(shan)的(de)三極管（8550或8050）損壞(huai)(huai)，或者風(feng)扇(shan)本身損壞(huai)(huai)或風(feng)葉(xie)被(bei)雜物卡住。但(dan)有(you)些開關(guan)電源中采用的(de)是智能散(san)(san)熱，對(dui)于(yu)采用這種(zhong)方(fang)式散(san)(san)熱的(de)開關(guan)電源，熱敏(min)電阻損壞(huai)(huai)的(de)概率是很大的(de)。

維修方(fang)法：首先(xian)用萬用表(biao)測(ce)(ce)量一下控制風扇的三極管是否損壞(huai)，若(ruo)測(ce)(ce)得(de)此管未損壞(huai)那就有可能(neng)是風扇本身(shen)損壞(huai)。可以把風扇從(cong)電(dian)(dian)(dian)(dian)路板上(shang)拔(ba)下來，另外(wai)接上(shang)一個12V的直流電(dian)(dian)(dian)(dian)（注意(yi)正負(fu)極），看(kan)是否轉(zhuan)動，并(bing)看(kan)有無異物卡住。若(ruo)擺動幾下風扇的電(dian)(dian)(dian)(dian)線，風扇就轉(zhuan)動，則(ze)說明電(dian)(dian)(dian)(dian)線內(nei)部有斷線或接頭接觸不良(liang)。若(ruo)仍不轉(zhuan)動，則(ze)風扇必壞(huai)。對于采用智能(neng)散(san)熱的開關電(dian)(dian)(dian)(dian)源來說，除按(an)上(shang)述檢(jian)查外(wai)，還(huan)應(ying)檢(jian)查一下熱敏電(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)是否不良(liang)或損壞(huai)，開焊等。但要注意(yi)此熱敏電(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)為負(fu)溫度(du)系數的熱敏電(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)，更換時應(ying)注意(yi)。