概(gai)述(shu)

開關(guan)電(dian)源(yuan)在工業自動化時代，已經被用(yong)于(yu)到所有行業，其精密電(dian)路板和對(dui)電(dian)流(liu)電(dian)源(yuan)的嚴格(ge)要(yao)求，使(shi)得開關(guan)電(dian)源(yuan)電(dian)路板維修成為(wei)PCB維修(xiu)行業(ye)中(zhong)(zhong)難度比(bi)較大的一中(zhong)(zhong)常見故障設備。  

在(zai)(zai)開關(guan)(guan)(guan)電(dian)(dian)(dian)源(yuan)維(wei)修之前，我們必(bi)須了解開關(guan)(guan)(guan)電(dian)(dian)(dian)源(yuan)的(de)工(gong)作原理(li)，電(dian)(dian)(dian)源(yuan)先將高(gao)(gao)電(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)(ya)交流(liu)(liu)(liu)(liu)(liu)電(dian)(dian)(dian)通過(guo)(guo)全橋二極管整流(liu)(liu)(liu)(liu)(liu)以后(hou)(hou)成為(wei)(wei)高(gao)(gao)電(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)(ya)的(de)波(bo)(bo)動直(zhi)流(liu)(liu)(liu)(liu)(liu)電(dian)(dian)(dian)，再經過(guo)(guo)電(dian)(dian)(dian)容濾波(bo)(bo)以后(hou)(hou)成為(wei)(wei)較為(wei)(wei)平滑的(de)高(gao)(gao)壓(ya)(ya)(ya)(ya)(ya)直(zhi)流(liu)(liu)(liu)(liu)(liu)電(dian)(dian)(dian)。這時，控制電(dian)(dian)(dian)路(lu)控制大(da)功(gong)率開關(guan)(guan)(guan)管將高(gao)(gao)壓(ya)(ya)(ya)(ya)(ya)直(zhi)流(liu)(liu)(liu)(liu)(liu)電(dian)(dian)(dian)按照一(yi)定的(de)高(gao)(gao)頻(pin)頻(pin)率分批(pi)送到(dao)高(gao)(gao)頻(pin)變壓(ya)(ya)(ya)(ya)(ya)器的(de)初級(ji)。接(jie)著，把(ba)從(cong)次級(ji)線圈輸出(chu)的(de)降壓(ya)(ya)(ya)(ya)(ya)后(hou)(hou)的(de)高(gao)(gao)頻(pin)低壓(ya)(ya)(ya)(ya)(ya)交流(liu)(liu)(liu)(liu)(liu)電(dian)(dian)(dian)通過(guo)(guo)整流(liu)(liu)(liu)(liu)(liu)濾波(bo)(bo)轉(zhuan)換為(wei)(wei)能使負(fu)載工(gong)作的(de)低電(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)(ya)強(qiang)電(dian)(dian)(dian)流(liu)(liu)(liu)(liu)(liu)的(de)直(zhi)流(liu)(liu)(liu)(liu)(liu)電(dian)(dian)(dian)。其(qi)中，控制電(dian)(dian)(dian)路(lu)是必(bi)不可少的(de)部分。它(ta)能有效的(de)監控輸出(chu)端的(de)電(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)(ya)值，并向功(gong)率開關(guan)(guan)(guan)管發(fa)出(chu)信號控制電(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)(ya)上下調整的(de)幅度。在(zai)(zai)開關(guan)(guan)(guan)電(dian)(dian)(dian)源(yuan)中，由于電(dian)(dian)(dian)源(yuan)輸入部分工(gong)作在(zai)(zai)高(gao)(gao)電(dian)(dian)(dian)壓(ya)(ya)(ya)(ya)(ya)、大(da)電(dian)(dian)(dian)流(liu)(liu)(liu)(liu)(liu)的(de)狀態下，故(gu)障率最(zui)高(gao)(gao);其次輸出直(zhi)流(liu)部分(fen)的(de)整流(liu)二極管、保護(hu)二極管、大功率開關(guan)三極管較易(yi)損壞，再(zai)就是脈(mo)寬調制器的(de)反饋和(he)保護(hu)部分(fen)。

一、在斷電情況下

首先，在開(kai)(kai)關(guan)電(dian)(dian)(dian)(dian)源(yuan)沒(mei)通(tong)電(dian)(dian)(dian)(dian)前，先用萬用表測(ce)一下高壓電(dian)(dian)(dian)(dian)容兩(liang)端的電(dian)(dian)(dian)(dian)壓先。如(ru)果是(shi)開(kai)(kai)關(guan)電(dian)(dian)(dian)(dian)源(yuan)不起振或開(kai)(kai)關(guan)管開(kai)(kai)路引起的故障，則大(da)多(duo)數情況下，高壓濾波(bo)電(dian)(dian)(dian)(dian)容兩(liang)端的電(dian)(dian)(dian)(dian)壓未泄(xie)放掉，此電(dian)(dian)(dian)(dian)壓有(you)300多伏，如(ru)果不小心被閣下玉手摸到，一定讓你留(liu)下難忘的記憶!  

由(you)于檢(jian)修電源(yuan)要接(jie)觸到220V高壓電，人體一旦接觸36V以(yi)上的(de)(de)電(dian)(dian)壓就(jiu)有生命(ming)危險(xian)。因此，在(zai)有可能的(de)(de)條件(jian)下，盡量先檢查一下在(zai)斷電(dian)(dian)狀態下有無明(ming)顯的(de)(de)短路、元器件(jian)損壞故障。首先，打開電(dian)(dian)源(yuan)的(de)(de)外殼，檢查保險(xian)絲是(shi)否(fou)熔斷，再觀察電(dian)(dian)源(yuan)的(de)(de)內(nei)部情況，如(ru)果發現電(dian)(dian)源(yuan)的(de)(de)PCB板上(shang)元件破裂，則應(ying)重點檢查(cha)此元件，一般來(lai)講(jiang)這是出現故障(zhang)的主要原(yuan)因;聞(wen)一下電源內部是否有(you)糊味，檢查(cha)是否有(you)燒(shao)焦(jiao)的(de)元器件;問一下(xia)電(dian)源(yuan)(yuan)損壞(huai)的(de)經(jing)過，是(shi)否對(dui)(dui)(dui)電(dian)源(yuan)(yuan)進(jin)行違(wei)規的(de)操作，這一點對(dui)(dui)(dui)于(yu)維(wei)修任(ren)何設備都是(shi)必(bi)須的(de)。在初步檢查(cha)以后(hou)，還要(yao)對(dui)(dui)(dui)電(dian)源(yuan)(yuan)進(jin)行更深入地(di)檢測。  

用萬用表(biao)測量(liang)AC電(dian)(dian)源線兩端(duan)的正反向電(dian)(dian)阻(zu)及(ji)電(dian)(dian)容器充(chong)電(dian)(dian)情況(kuang)，如果電(dian)(dian)阻(zu)值過低，說明電(dian)(dian)源內部存在短(duan)路，正常時其(qi)阻(zu)值應能達到(dao)100千歐以上(shang);電(dian)容器應能(neng)夠充放電(dian)，如果(guo)損壞，則表現(xian)為(wei)AC電(dian)(dian)(dian)源線兩(liang)端(duan)阻(zu)值(zhi)低(di)，呈短路(lu)狀態，否則(ze)可能是開關(guan)管(guan)擊(ji)穿。然后(hou)檢查直(zhi)流輸出部分(fen)脫開負載，分(fen)別(bie)測量各組輸出端(duan)的(de)(de)(de)對(dui)地電(dian)(dian)(dian)阻(zu)，正常時，表針應有電(dian)(dian)(dian)容(rong)器充放電(dian)(dian)(dian)擺動，最后(hou)指(zhi)示的(de)(de)(de)應為該路(lu)的(de)(de)(de)泄放電(dian)(dian)(dian)阻(zu)的(de)(de)(de)阻(zu)值(zhi)。否則(ze)多數是整(zheng)流二極管(guan)反向擊(ji)穿所(suo)致。

二、加電檢測

在(zai)通過以(yi)上(shang)檢測后，就(jiu)可以(yi)進行加電(dian)(dian)測試。這時候才是關(guan)鍵所(suo)在(zai)，需要有(you)一(yi)定(ding)的(de)經驗、電(dian)(dian)子基礎及維(wei)修(xiu)技(ji)巧。一(yi)般來講(jiang)應重點檢查一(yi)下(xia)電(dian)(dian)源(yuan)的(de)輸(shu)入端，開關(guan)三極管，電(dian)(dian)源(yuan)保護電(dian)(dian)路以(yi)及電(dian)(dian)源(yuan)的(de)輸(shu)出電(dian)(dian)壓(ya)電(dian)(dian)流等。如果電(dian)(dian)源(yuan)啟動一(yi)下(xia)就(jiu)停止，則該電(dian)(dian)源(yuan)處于保護狀態下(xia)，可直接測量PWM芯片保護(hu)(hu)(hu)輸入腳(jiao)的(de)(de)(de)電壓，如果(guo)電壓超出(chu)規定值，則說明電源(yuan)的(de)(de)(de)處于保護(hu)(hu)(hu)狀態下，應重點(dian)檢查(cha)產生保護(hu)(hu)(hu)的(de)(de)(de)原因。由于接觸到高電壓，建議沒(mei)有電子基礎的(de)(de)(de)朋友需要小心(xin)操(cao)作。

三、常見(jian)故(gu)障

1.保險(xian)絲熔斷

一(yi)般情況(kuang)下(xia)，保(bao)險絲熔斷說明電(dian)(dian)(dian)(dian)源(yuan)的內部線(xian)路(lu)有(you)問題。由(you)于電(dian)(dian)(dian)(dian)源(yuan)工(gong)作在高電(dian)(dian)(dian)(dian)壓、大電(dian)(dian)(dian)(dian)流(liu)的狀(zhuang)態下(xia)，電(dian)(dian)(dian)(dian)網(wang)電(dian)(dian)(dian)(dian)壓的波動、浪涌都會引起電(dian)(dian)(dian)(dian)源(yuan)內電(dian)(dian)(dian)(dian)流(liu)瞬間增大而使保(bao)險絲熔斷。重點應檢查電(dian)(dian)(dian)(dian)源(yuan)輸入(ru)端的整流(liu)二極(ji)管(guan)，高壓濾波電(dian)(dian)(dian)(dian)解電(dian)(dian)(dian)(dian)容(rong)，逆變(bian)功率開關(guan)管(guan)等，檢查一(yi)下(xia)這(zhe)些元(yuan)(yuan)器件(jian)有(you)無擊穿(chuan)、開路(lu)、損壞等。如(ru)果(guo)(guo)確實(shi)是保(bao)險絲熔斷，應該首先查看電(dian)(dian)(dian)(dian)路(lu)板(ban)上的各個元(yuan)(yuan)件(jian)，看這(zhe)些元(yuan)(yuan)件(jian)的外表有(you)沒有(you)被燒糊，有(you)沒有(you)電(dian)(dian)(dian)(dian)解液溢出。如(ru)果(guo)(guo)沒有(you)發現上述情況(kuang)，則用萬用表測量(liang)開關(guan)管(guan)有(you)無擊穿(chuan)短路(lu)。  

2.無直流(liu)電壓(ya)(ya)輸出或電壓(ya)(ya)輸出不(bu)穩(wen)定  

如果(guo)保險絲是完好(hao)的(de)，在有負(fu)載(zai)(zai)情(qing)(qing)況(kuang)下(xia)，各級(ji)直流(liu)電(dian)壓無輸出。這(zhe)種情(qing)(qing)況(kuang)主要(yao)是以下(xia)原因造成的(de)：電(dian)源(yuan)(yuan)中(zhong)出現開路(lu)(lu)、短路(lu)(lu)現象，過壓、過流(liu)保護電(dian)路(lu)(lu)出現故障(zhang)，振蕩電(dian)路(lu)(lu)沒有工作，電(dian)源(yuan)(yuan)負(fu)載(zai)(zai)過重，高頻整(zheng)流(liu)濾(lv)波(bo)電(dian)路(lu)(lu)中(zhong)整(zheng)流(liu)二極(ji)管被(bei)擊穿，濾(lv)波(bo)電(dian)容漏電(dian)等。在用萬用表測量次(ci)級(ji)元件(jian)，排除了高頻整(zheng)流(liu)二極(ji)管擊穿、負(fu)載(zai)(zai)短路(lu)(lu)的(de)情(qing)(qing)況(kuang)后，如果(guo)這(zhe)時輸出為(wei)零，則可(ke)以肯定是電(dian)源(yuan)(yuan)的(de)控制電(dian)路(lu)(lu)出了故障(zhang)。  

3.電(dian)源負(fu)載能力(li)差  

電(dian)源負載能力差(cha)是(shi)(shi)一個常見(jian)的(de)故障，一般都是(shi)(shi)出現在老(lao)式或是(shi)(shi)工作時(shi)間(jian)長的(de)電(dian)源中(zhong)，主要(yao)原因是(shi)(shi)各元器件(jian)老(lao)化(hua)，開關(guan)管(guan)的(de)工作不穩定，沒有(you)及時(shi)進行散熱等(deng)。應重點檢查穩壓二(er)(er)極(ji)管(guan)是(shi)(shi)否發熱漏(lou)電(dian)，整流二(er)(er)極(ji)管(guan)損壞(huai)、高壓濾波電(dian)容損壞(huai)等(deng)。  

電源維修實例1：某設備(bei)電(dian)源，通電(dian)后無電(dian)壓(ya)輸出(chu)，電(dian)源內(nei)部(bu)發(fa)出(chu)‘吱(zhi)吱(zhi)吱(zhi)’聲。這是電源過載(zai)或無負載(zai)的(de)典型特征。先仔細(xi)檢查各(ge)個元器件，重點檢測整流二極(ji)管、開(kai)關(guan)管等(deng)。

經過仔細檢查，發現一(yi)個整流二(er)極管(1N4007)的表(biao)面(mian)已(yi)燒(shao)黑(hei)，而且電(dian)路板(ban)也給燒(shao)黑(hei)了。找(zhao)到同型號的二極管換(huan)下，在用萬(wan)用表(biao)一(yi)測果然是擊穿的。接上電(dian)源(yuan)，可(ke)風扇不轉，‘吱(zhi)(zhi)吱(zhi)(zhi)吱(zhi)(zhi)’聲(sheng)依然存(cun)在。用(yong)(yong)萬用(yong)(yong)表量+12V輸出只有+0.2V，+ 5V只(zhi)有0.1V。這說明元(yuan)件被擊穿(chuan)時(shi)電源啟(qi)動(dong)自保(bao)護。測量(liang)初級和次級開關管，發現初級開關管中有一個已損(sun)(sun)壞，用相同型號的開關管換上，故障(zhang)排(pai)除。以(yi)上檢查走(zou)了彎路，未通電前，應測量(liang)一下開關管是否(fou)損(sun)(sun)壞。  

電(dian)源維(wei)修(xiu)實(shi)例2：沒(mei)有‘吱吱吱’聲,上一個保險(xian)絲就(jiu)燒一個保險(xian)絲。由于保險(xian)絲不斷地(di)被(bei)熔斷，搜索范圍(wei)就(jiu)縮小了。可能發(fa)生的情況有3種：整(zheng)流(liu)橋(qiao)擊穿，大(da)電(dian)解電(dian)容擊穿，初級開關管擊穿。電(dian)源的(de)整(zheng)流(liu)橋(qiao)一(yi)般是分立的(de)四(si)個(ge)整(zheng)流(liu)二(er)極(ji)(ji)管，或是將四(si)個(ge)二(er)極(ji)(ji)管固(gu)化在一(yi)起。將整(zheng)流(liu)橋(qiao)拆(chai)下一(yi)量是正常的(de)。大(da)電(dian)解電(dian)容拆(chai)下測試(shi)后也正常，注(zhu)意焊回(hui)時要注(zhu)意正負極(ji)(ji)。最后的(de)可能就只剩開關管了。這個(ge)電(dian)源的(de)初級只有(you)一(yi)個(ge)大(da)功率的(de)開關管。拆(chai)下一(yi)量果(guo)然擊穿，找同型號(hao)開關管換上(shang)，問題(ti)解決。  

其實，電(dian)源(yuan)維(wei)修電(dian)源(yuan)并不(bu)難(nan)，一般電(dian)源(yuan)故(gu)障(zhang)都可以歸納總結(jie)為：保險(xian)絲熔斷、整流二極管(guan)損壞、濾(lv)波電(dian)容開路或(huo)擊穿、開關(guan)管(guan)擊穿以及(ji)電(dian)源(yuan)自保護(hu)等，另外開關(guan)電(dian)源(yuan)的電(dian)路相對(dui)較簡單(dan)，故(gu)障(zhang)類型也比較少，很容易就能判斷出(chu)故(gu)障(zhang)位(wei)置。所以電(dian)源(yuan)維(wei)修只要有足夠的電(dian)子基礎知識，再多看(kan)看(kan)相關(guan)技(ji)術(shu)文(wen)章，平(ping)時多動動手(shou)，注(zhu)意維(wei)修經驗(yan)的積累，電(dian)源(yuan)故(gu)障(zhang)維(wei)修還是挺好解決(jue)的。  

任何芯片級維修(xiu)(xiu)工(gong)作，都離不(bu)開經驗的積累(lei)和(he)(he)靈活的維修(xiu)(xiu)思(si)路。在遇到(dao)故(gu)(gu)障無(wu)法(fa)排除，或者(zhe)是找不(bu)到(dao)故(gu)(gu)障根源(yuan)的時候(hou)，往往靜下心來，或者(zhe)干脆休息一小會兒，多角度的思(si)考(kao)和(he)(he)排除故(gu)(gu)障，往往會有意想不(bu)到(dao)的效果。