概述(shu)

開關(guan)電(dian)(dian)源(yuan)在工業自(zi)動(dong)化時(shi)代(dai)，已經(jing)被用于到所有(you)行業，其精(jing)密電(dian)(dian)路板(ban)和(he)對電(dian)(dian)流電(dian)(dian)源(yuan)的嚴格要求(qiu)，使得開關(guan)電(dian)(dian)源(yuan)電(dian)(dian)路板(ban)維修成為(wei)PCB維修行業中(zhong)難度比(bi)較大的一中(zhong)常見故障設(she)備(bei)。  

在(zai)開(kai)關(guan)(guan)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)維修之前，我(wo)們必須了解開(kai)關(guan)(guan)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)的(de)(de)(de)(de)工(gong)(gong)作(zuo)原理，電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)先(xian)將高電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)交流(liu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)通過(guo)全橋二極管整流(liu)以后(hou)成為高電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)的(de)(de)(de)(de)波動(dong)直(zhi)流(liu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)，再(zai)經(jing)過(guo)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)容濾(lv)波以后(hou)成為較為平滑的(de)(de)(de)(de)高壓(ya)(ya)直(zhi)流(liu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)。這時，控(kong)(kong)制電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路控(kong)(kong)制大功率(lv)開(kai)關(guan)(guan)管將高壓(ya)(ya)直(zhi)流(liu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)按照一定(ding)的(de)(de)(de)(de)高頻(pin)頻(pin)率(lv)分(fen)批送到高頻(pin)變壓(ya)(ya)器的(de)(de)(de)(de)初級(ji)。接著，把從次級(ji)線圈輸(shu)出的(de)(de)(de)(de)降(jiang)壓(ya)(ya)后(hou)的(de)(de)(de)(de)高頻(pin)低壓(ya)(ya)交流(liu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)通過(guo)整流(liu)濾(lv)波轉(zhuan)換為能使負(fu)載工(gong)(gong)作(zuo)的(de)(de)(de)(de)低電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)強電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)的(de)(de)(de)(de)直(zhi)流(liu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)。其(qi)中，控(kong)(kong)制電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)路是必不可(ke)少(shao)的(de)(de)(de)(de)部(bu)分(fen)。它(ta)能有(you)效的(de)(de)(de)(de)監控(kong)(kong)輸(shu)出端的(de)(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)值，并向功率(lv)開(kai)關(guan)(guan)管發出信號控(kong)(kong)制電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)上下調整的(de)(de)(de)(de)幅(fu)度。在(zai)開(kai)關(guan)(guan)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)中，由于(yu)電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)源(yuan)輸(shu)入部(bu)分(fen)工(gong)(gong)作(zuo)在(zai)高電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(ya)、大電(dian)(dian)(dian)(dian)(dian)(dian)(dian)(dian)流(liu)的(de)(de)(de)(de)狀態下，故障率(lv)最高;其次(ci)輸(shu)出直(zhi)流(liu)部分的整(zheng)流(liu)二極(ji)管(guan)、保護二極(ji)管(guan)、大功率開關三極(ji)管(guan)較易(yi)損壞，再就是脈(mo)寬(kuan)調制器(qi)的反饋(kui)和保護部分。

一(yi)、在斷(duan)電情況下

首(shou)先，在開關(guan)電源沒通電前(qian)，先用萬用表測(ce)一(yi)下(xia)(xia)高壓(ya)電容兩端的電壓(ya)先。如果是開關(guan)電源不起(qi)(qi)振(zhen)或開關(guan)管開路引起(qi)(qi)的故障，則大多數情況下(xia)(xia)，高壓(ya)濾波(bo)電容兩端的電壓(ya)未(wei)泄放掉，此電壓(ya)有300多(duo)伏，如(ru)果不小心被閣下玉(yu)手摸到(dao)，一定(ding)讓你留下難忘的記憶!  

由于檢修電(dian)源(yuan)要(yao)接觸到220V高壓(ya)電，人體(ti)一旦接觸36V以上的(de)電(dian)(dian)壓就有(you)生命危(wei)險。因此，在(zai)有(you)可能的(de)條件(jian)下，盡量先檢(jian)查一下在(zai)斷電(dian)(dian)狀(zhuang)態下有(you)無明顯(xian)的(de)短路、元器(qi)件(jian)損(sun)壞故障。首先，打(da)開電(dian)(dian)源(yuan)的(de)外(wai)殼(ke)，檢(jian)查保(bao)險絲是(shi)否(fou)熔(rong)斷，再觀察電(dian)(dian)源(yuan)的(de)內(nei)部情(qing)況，如(ru)果發現電(dian)(dian)源(yuan)的(de)PCB板(ban)上(shang)元件破裂(lie)，則應重點檢(jian)查此元件，一般(ban)來講這是出現故(gu)障(zhang)的主要原因;聞一下電源內(nei)部是(shi)否(fou)有(you)糊味，檢查(cha)是(shi)否(fou)有(you)燒焦的元器件;問一(yi)下電源損壞(huai)的(de)經過，是否對(dui)電源進行(xing)違規的(de)操作，這一(yi)點對(dui)于(yu)維修任何設(she)備都是必須的(de)。在初步檢查(cha)以后(hou)，還要對(dui)電源進行(xing)更深入地檢測。  

用萬用表測量AC電源(yuan)線兩端的正(zheng)反(fan)向電阻(zu)及(ji)電容器(qi)充電情(qing)況，如果(guo)電阻(zu)值(zhi)過低，說明電源(yuan)內部存在短(duan)路，正(zheng)常(chang)時其阻(zu)值(zhi)應能達到100千歐以上;電容器應(ying)能夠充(chong)放電，如果損壞，則(ze)表現(xian)為(wei)AC電源線兩端(duan)阻(zu)值低，呈短路狀態，否則(ze)可(ke)能是開(kai)(kai)關管擊(ji)(ji)穿。然后檢查直(zhi)流輸出部分脫開(kai)(kai)負載，分別測量各(ge)組(zu)輸出端(duan)的對地電阻(zu)，正(zheng)常時，表針應(ying)(ying)有電容器充放(fang)電擺動，最后指示的應(ying)(ying)為(wei)該路的泄放(fang)電阻(zu)的阻(zu)值。否則(ze)多數是整(zheng)流二極管反向(xiang)擊(ji)(ji)穿所致。

二、加電檢測

在通過以上檢(jian)測后，就可(ke)以進行加電(dian)測試。這時候才是關(guan)鍵所在，需(xu)要有一(yi)(yi)定的(de)經驗(yan)、電(dian)子基(ji)礎及(ji)維修技(ji)巧。一(yi)(yi)般來(lai)講應重點(dian)檢(jian)查一(yi)(yi)下電(dian)源(yuan)的(de)輸(shu)入端，開(kai)關(guan)三極管，電(dian)源(yuan)保護電(dian)路以及(ji)電(dian)源(yuan)的(de)輸(shu)出電(dian)壓電(dian)流等(deng)。如(ru)果電(dian)源(yuan)啟動一(yi)(yi)下就停止，則該電(dian)源(yuan)處于保護狀態下，可(ke)直(zhi)接(jie)測量(liang)PWM芯片保(bao)護輸入腳的(de)電(dian)壓(ya)(ya)，如(ru)果(guo)電(dian)壓(ya)(ya)超出(chu)規定值，則說明電(dian)源的(de)處于保(bao)護狀(zhuang)態(tai)下(xia)，應重(zhong)點檢查產生保(bao)護的(de)原因。由于接觸到高(gao)電(dian)壓(ya)(ya)，建議(yi)沒有電(dian)子基礎(chu)的(de)朋(peng)友需要(yao)小心(xin)操作(zuo)。

三、常(chang)見故障(zhang)

1.保險(xian)絲熔斷

一(yi)(yi)般情況下，保險(xian)絲(si)熔斷說(shuo)明電(dian)(dian)(dian)源(yuan)(yuan)的內部線路(lu)(lu)有(you)(you)問(wen)題。由(you)于(yu)電(dian)(dian)(dian)源(yuan)(yuan)工作在高電(dian)(dian)(dian)壓、大電(dian)(dian)(dian)流的狀態(tai)下，電(dian)(dian)(dian)網電(dian)(dian)(dian)壓的波動、浪涌都會(hui)引起電(dian)(dian)(dian)源(yuan)(yuan)內電(dian)(dian)(dian)流瞬(shun)間(jian)增大而(er)使保險(xian)絲(si)熔斷。重點(dian)應檢(jian)查電(dian)(dian)(dian)源(yuan)(yuan)輸入端的整(zheng)流二極管(guan)，高壓濾波電(dian)(dian)(dian)解電(dian)(dian)(dian)容，逆變功(gong)率開(kai)關管(guan)等(deng)，檢(jian)查一(yi)(yi)下這(zhe)些(xie)元(yuan)(yuan)器件有(you)(you)無擊(ji)穿、開(kai)路(lu)(lu)、損壞(huai)等(deng)。如果確實是保險(xian)絲(si)熔斷，應該首先查看電(dian)(dian)(dian)路(lu)(lu)板上的各個(ge)元(yuan)(yuan)件，看這(zhe)些(xie)元(yuan)(yuan)件的外表有(you)(you)沒(mei)有(you)(you)被燒糊，有(you)(you)沒(mei)有(you)(you)電(dian)(dian)(dian)解液溢出。如果沒(mei)有(you)(you)發(fa)現上述情況，則用萬(wan)用表測量開(kai)關管(guan)有(you)(you)無擊(ji)穿短路(lu)(lu)。  

2.無直流電壓(ya)輸出(chu)或(huo)電壓(ya)輸出(chu)不穩定  

如(ru)果(guo)保(bao)險(xian)絲是(shi)完好的，在有負載(zai)情況下(xia)，各級直流電(dian)壓(ya)無輸出(chu)。這種(zhong)情況主要是(shi)以下(xia)原(yuan)因造成的：電(dian)源中出(chu)現(xian)(xian)開(kai)路(lu)(lu)、短路(lu)(lu)現(xian)(xian)象，過壓(ya)、過流保(bao)護電(dian)路(lu)(lu)出(chu)現(xian)(xian)故障(zhang)，振(zhen)蕩電(dian)路(lu)(lu)沒(mei)有工(gong)作，電(dian)源負載(zai)過重，高(gao)頻(pin)整(zheng)流濾波電(dian)路(lu)(lu)中整(zheng)流二極(ji)管被擊(ji)穿，濾波電(dian)容漏電(dian)等(deng)。在用(yong)萬用(yong)表測量次級元件(jian)，排除了高(gao)頻(pin)整(zheng)流二極(ji)管擊(ji)穿、負載(zai)短路(lu)(lu)的情況后，如(ru)果(guo)這時輸出(chu)為零，則可以肯定是(shi)電(dian)源的控制電(dian)路(lu)(lu)出(chu)了故障(zhang)。  

3.電源(yuan)負載能力差  

電(dian)源(yuan)負載能力差是一個常見的故障(zhang)，一般都是出現在(zai)老(lao)式(shi)或是工作時間長的電(dian)源(yuan)中(zhong)，主要原因是各元器(qi)件(jian)老(lao)化，開(kai)關管(guan)的工作不穩(wen)定，沒有及時進行散(san)熱等。應重點(dian)檢查(cha)穩(wen)壓二極(ji)管(guan)是否(fou)發熱漏電(dian)，整(zheng)流二極(ji)管(guan)損(sun)壞、高壓濾波電(dian)容損(sun)壞等。  

電(dian)源維(wei)修實例1：某設備電源(yuan)，通電后無(wu)電壓輸出(chu)，電源(yuan)內部發出(chu)‘吱(zhi)(zhi)吱(zhi)(zhi)吱(zhi)(zhi)’聲。這是電源過載或無負載的(de)典型特征。先(xian)仔細(xi)檢(jian)(jian)查各個元器件，重點檢(jian)(jian)測整流二極管(guan)(guan)、開(kai)關管(guan)(guan)等(deng)。

經過(guo)仔細(xi)檢查，發現一個整流二極管(guan)(1N4007)的表(biao)面已(yi)燒黑，而且(qie)電(dian)(dian)路(lu)板也給燒黑了。找到(dao)同型號(hao)的二極管換下，在(zai)用(yong)萬(wan)用(yong)表(biao)一測果(guo)然是(shi)擊穿(chuan)的。接上電(dian)(dian)源，可風扇不轉，‘吱吱吱’聲(sheng)依然存在。用萬用表量+12V輸出只(zhi)有+0.2V，+ 5V只有0.1V。這說明元件被擊穿時電源啟動自(zi)保護。測量初級和次(ci)級開(kai)(kai)關(guan)(guan)管(guan)，發現(xian)初級開(kai)(kai)關(guan)(guan)管(guan)中有(you)一(yi)個已(yi)損壞，用相同型號的開(kai)(kai)關(guan)(guan)管(guan)換上，故障排除。以(yi)上檢(jian)查走了彎路，未通電前(qian)，應測量一(yi)下開(kai)(kai)關(guan)(guan)管(guan)是否損壞。  

電源維修實例2：沒(mei)有‘吱(zhi)吱(zhi)吱(zhi)’聲,上(shang)一個保險絲就(jiu)燒一個保險絲。由于保險絲不(bu)斷地被熔(rong)斷，搜索范圍就(jiu)縮小了。可(ke)能發生的(de)情況(kuang)有3種：整流(liu)橋(qiao)擊穿(chuan)(chuan)，大電(dian)(dian)解(jie)電(dian)(dian)容擊穿(chuan)(chuan)，初(chu)級開(kai)關(guan)(guan)(guan)管擊穿(chuan)(chuan)。電(dian)(dian)源的整流(liu)橋(qiao)一(yi)(yi)般是分立的四個(ge)整流(liu)二極管，或(huo)是將四個(ge)二極管固化在一(yi)(yi)起(qi)。將整流(liu)橋(qiao)拆(chai)下一(yi)(yi)量(liang)是正(zheng)常的。大電(dian)(dian)解(jie)電(dian)(dian)容拆(chai)下測試后也正(zheng)常，注(zhu)(zhu)意(yi)(yi)焊(han)回時要注(zhu)(zhu)意(yi)(yi)正(zheng)負極。最后的可能(neng)就(jiu)只剩開(kai)關(guan)(guan)(guan)管了。這(zhe)個(ge)電(dian)(dian)源的初(chu)級只有(you)一(yi)(yi)個(ge)大功率的開(kai)關(guan)(guan)(guan)管。拆(chai)下一(yi)(yi)量(liang)果然擊穿(chuan)(chuan)，找同型號開(kai)關(guan)(guan)(guan)管換上，問題解(jie)決。  

其實，電(dian)(dian)源(yuan)(yuan)維(wei)修(xiu)電(dian)(dian)源(yuan)(yuan)并不難(nan)，一般電(dian)(dian)源(yuan)(yuan)故(gu)障(zhang)都可(ke)以歸納總結為：保險絲熔斷、整流二(er)極管損壞、濾波電(dian)(dian)容開路或擊穿、開關(guan)管擊穿以及電(dian)(dian)源(yuan)(yuan)自保護等，另外開關(guan)電(dian)(dian)源(yuan)(yuan)的(de)電(dian)(dian)路相對較簡單，故(gu)障(zhang)類型也比(bi)較少，很容易(yi)就能判斷出(chu)故(gu)障(zhang)位置。所以電(dian)(dian)源(yuan)(yuan)維(wei)修(xiu)只要有(you)足夠的(de)電(dian)(dian)子(zi)基礎知識，再多看看相關(guan)技(ji)術文章，平時多動動手，注(zhu)意(yi)維(wei)修(xiu)經(jing)驗的(de)積累，電(dian)(dian)源(yuan)(yuan)故(gu)障(zhang)維(wei)修(xiu)還(huan)是挺好解決的(de)。  

任何芯片級維修工作，都(dou)離不開經(jing)驗(yan)的(de)積(ji)累和靈活的(de)維修思(si)路。在遇(yu)到(dao)故(gu)障無法排除(chu)，或者是找不到(dao)故(gu)障根源(yuan)的(de)時候，往往靜下心來(lai)，或者干(gan)脆休息(xi)一(yi)小會兒，多(duo)角度(du)的(de)思(si)考(kao)和排除(chu)故(gu)障，往往會有(you)意想(xiang)不到(dao)的(de)效果。