1、開關電源電壓(ya)輸出低的原因

(1)220V交流電壓輸入和整流濾波電路對開關管供給的作業電壓不行，超出脈(mo)寬調整電路控制(zhi)規劃。

(2)負載電路存在過(guo)流引起開關電源負載加重而(er)導致輸出電壓下降。

(3)開(kai)／關(guan)機切換錯誤(wu)，行掃描電(dian)路剛開(kai)始(shi)作業瞬間，開(kai)關(guan)電(dian)源(yuan)即處(chu)于待機狀況，此(ci)類缺(que)點適(shi)用于無(wu)準備電(dian)源(yuan)的機器，CPU電(dian)源(yuan)取自同一(yi)個電(dian)源(yuan)，非副(fu)電(dian)源(yuan)供給。

(4)開／關機(ji)接(jie)口電路結束因缺點處于開機(ji)與待(dai)機(ji)之間的狀況，然后導致開關電源輸出電壓低于正(zheng)常值(zhi)高于待(dai)機(ji)值(zhi)。

(5)保護電路結束(shu)因缺(que)點進(jin)入導通狀(zhuang)況，使電源進(jin)入弱振(zhen)狀(zhuang)況，引起開(kai)關(guan)電源輸出電壓(ya)下降(jiang)。

(6)整流(liu)輸出(chu)電(dian)(dian)路中(zhong)二極管和(he)濾波電(dian)(dian)容、限流(liu)電(dian)(dian)阻損壞引起輸出(chu)電(dian)(dian)壓低。

(7)脈寬(kuan)調制電(dian)(dian)路缺點(dian)，不能(neng)對(dui)開關(guan)電(dian)(dian)源輸出(chu)電(dian)(dian)壓(ya)的改變作(zuo)出(chu)正確的呼應，對(dui)開關(guan)管基極電(dian)(dian)壓(ya)調整方(fang)向不對(dui)，然后構(gou)成(cheng)開關(guan)電(dian)(dian)源輸出(chu)電(dian)(dian)壓(ya)低。

(8)正(zheng)(zheng)反饋電(dian)路中(zhong)的正(zheng)(zheng)反饋電(dian)阻值改變，續流二極管性能蛻變或恒流源缺點，使正(zheng)(zheng)反饋量缺乏(fa)，導致振動(dong)周(zhou)期變長，振動(dong)頻率下降(jiang)，然后引起開關電(dian)源輸出電(dian)壓低。

(9)它激式(shi)開(kai)關電(dian)源因未得到行逆(ni)程脈(mo)沖(chong)而作業于低頻狀況，構成輸(shu)出(chu)電(dian)壓低。

2、判別問題的(de)方法與(yu)過程

從上述剖(pou)析的原因(yin)看出，引起電壓(ya)低(di)的原因(yin)涉(she)及到了開關電源本身的各個部(bu)分和與開關電源相關的全部(bu)電路，在檢修時應先(xian)縮(suo)小(xiao)缺點規劃。

(1)檢測(ce)開(kai)關(guan)管(guan)(guan)c極電(dian)壓，承認(ren)開(kai)關(guan)管(guan)(guan)供電(dian)正(zheng)常。

(2)依據開關電(dian)源(yuan)各(ge)個輸出端電(dian)壓判別缺(que)點。

開(kai)(kai)(kai)關(guan)電(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)有的(de)(de)輸(shu)(shu)出(chu)(chu)端電(dian)(dian)(dian)(dian)(dian)壓(ya)正常(chang)，有的(de)(de)低于正常(chang)值。缺點在(zai)(zai)輸(shu)(shu)出(chu)(chu)電(dian)(dian)(dian)(dian)(dian)壓(ya)低的(de)(de)這個整(zheng)(zheng)(zheng)流(liu)輸(shu)(shu)出(chu)(chu)電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)，應對電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)中的(de)(de)限流(liu)電(dian)(dian)(dian)(dian)(dian)阻、整(zheng)(zheng)(zheng)流(liu)二(er)極管、濾波(bo)電(dian)(dian)(dian)(dian)(dian)容進行(xing)檢查(cha)代換，若限流(liu)電(dian)(dian)(dian)(dian)(dian)阻發(fa)燙，說明負(fu)(fu)(fu)載(zai)(zai)(zai)(zai)過流(liu)，查(cha)負(fu)(fu)(fu)載(zai)(zai)(zai)(zai)。開(kai)(kai)(kai)關(guan)電(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)各路(lu)(lu)輸(shu)(shu)出(chu)(chu)均低。這種狀況說明負(fu)(fu)(fu)載(zai)(zai)(zai)(zai)和整(zheng)(zheng)(zheng)流(liu)輸(shu)(shu)出(chu)(chu)電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)均正常(chang)，缺點在(zai)(zai)開(kai)(kai)(kai)關(guan)電(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)的(de)(de)正反饋電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)、脈寬調整(zheng)(zheng)(zheng)、開(kai)(kai)(kai)／待機電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)、保護電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)。輸(shu)(shu)出(chu)(chu)電(dian)(dian)(dian)(dian)(dian)壓(ya)有的(de)(de)下降(jiang)份額(e)大，有的(de)(de)輸(shu)(shu)出(chu)(chu)電(dian)(dian)(dian)(dian)(dian)壓(ya)下降(jiang)份額(e)小。測量效(xiao)果說明缺點在(zai)(zai)輸(shu)(shu)出(chu)(chu)電(dian)(dian)(dian)(dian)(dian)壓(ya)下降(jiang)份額(e)大的(de)(de)電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)。此(ci)刻可(ke)斷開(kai)(kai)(kai)此(ci)路(lu)(lu)負(fu)(fu)(fu)載(zai)(zai)(zai)(zai)，假(jia)設斷開(kai)(kai)(kai)的(de)(de)是行(xing)電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)，應接假(jia)負(fu)(fu)(fu)載(zai)(zai)(zai)(zai)。在(zai)(zai)斷開(kai)(kai)(kai)負(fu)(fu)(fu)載(zai)(zai)(zai)(zai)后(hou)，再測開(kai)(kai)(kai)關(guan)電(dian)(dian)(dian)(dian)(dian)源(yuan)(yuan)各輸(shu)(shu)出(chu)(chu)端電(dian)(dian)(dian)(dian)(dian)壓(ya)，若恢復正常(chang)，可(ke)判別(bie)所斷電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)的(de)(de)負(fu)(fu)(fu)載(zai)(zai)(zai)(zai)有過流(liu)現象。若仍不(bu)正常(chang)，說明缺點在(zai)(zai)該整(zheng)(zheng)(zheng)流(liu)濾波(bo)電(dian)(dian)(dian)(dian)(dian)路(lu)(lu)。

3、斷開主負(fu)載、接上燈泡(pao)，判別是(shi)否負(fu)載缺(que)點

有些(xie)收臺(tai)(tai)圖閃、帶(dai)負(fu)載后電(dian)壓(ya)不穩的機器，難于鑒別(bie)缺點是在電(dian)源(yuan)或是負(fu)載時(shi)，能夠(gou)選用“借法”，用此電(dian)源(yuan)帶(dai)同(tong)(tong)等(deng)標(biao)準、相同(tong)(tong)B+電(dian)壓(ya)的另(ling)一臺(tai)(tai)機器行負(fu)載，進行判別(bie)。

4、保存(cun)發動(dong)、正反饋、軟發動(dong)及負反饋電路

逐個吊(diao)銷各種保護電(dian)(dian)(dian)(dian)路(lu)、待(dai)機控制電(dian)(dian)(dian)(dian)路(lu)結(jie)束(shu)三極管。開機查詢缺點是(shi)否消除，來逐漸縮小缺點規劃(hua)。留心：兼(jian)有穩壓(ya)效(xiao)果的電(dian)(dian)(dian)(dian)路(lu)不能(neng)斷開(例如光電(dian)(dian)(dian)(dian)耦合(he)器)。斷開保護電(dian)(dian)(dian)(dian)路(lu)時(shi)，須慎重，并采納防止電(dian)(dian)(dian)(dian)壓(ya)升高的辦(ban)法。

5、選用替代(dai)(dai)法、檢(jian)修脈(mo)寬調整(zheng)電路(lu)(lu)（用克己(ji)取樣(yang)電路(lu)(lu)替代(dai)(dai)原(yuan)取樣(yang)電路(lu)(lu)，判別缺點規(gui)劃）

(1)代換(huan)后，電壓恢復正常，說明缺(que)點(dian)在取樣(yang)電路及光耦電路。

(2)電(dian)(dian)壓仍(reng)(reng)低(di)，則斷(duan)開原取樣電(dian)(dian)路(lu)(lu)B+接入點(dian)(dian)(dian)，假設電(dian)(dian)壓還低(di)，則檢查(cha)B+濾波(bo)電(dian)(dian)容，承認良好后(hou)，能夠(gou)圈定缺點(dian)(dian)(dian)在熱底板部(bu)分(fen)。先查(cha)軟發動電(dian)(dian)路(lu)(lu)是(shi)否對開關管(guan)B極分(fen)流了。仍(reng)(reng)不可，查(cha)正(zheng)反饋、負反饋電(dian)(dian)路(lu)(lu)。查(cha)熱底板部(bu)分(fen)的(de)負反饋方法同檢查(cha)電(dian)(dian)壓高(gao)的(de)方法附近，選(xuan)用迫(po)使B+輸(shu)出高(gao)的(de)思路(lu)(lu)(留心：改變(bian)作業點(dian)(dian)(dian)不能構(gou)成(cheng)B+過高(gao)擴展缺點(dian)(dian)(dian))。

總(zong)之(zhi)，在電(dian)(dian)源的修補中(zhong)，當電(dian)(dian)壓不穩時可選(xuan)用逆向思(si)維，電(dian)(dian)壓高時使之(zhi)變低，電(dian)(dian)壓低時使之(zhi)變高，必(bi)要時可選(xuan)用人為(wei)改(gai)變作業(ye)點(dian)電(dian)(dian)壓。以(yi)利(li)于查找缺(que)點(dian)點(dian)，在于修補人員活絡把握(wo)。