常見電腦電源故障分析

1、電源無輸出

當電(dian)(dian)源(yuan)在有(you)負載情況(kuang)下，測(ce)量(liang)不出(chu)各輸(shu)出(chu)端(duan)的直流電(dian)(dian)壓時即認為(wei)電(dian)(dian)源(yuan)無(wu)輸(shu)出(chu)。這時應先打開電(dian)(dian)源(yuan)檢(jian)查保險(xian)絲，通過(guo)保險(xian)絲熔斷情況(kuang)來分析故障范圍。

1)保險絲熔(rong)斷并發黑 說明有嚴重(zhong)短路現象，應重(zhong)點檢查(cha)整流濾波和功率(lv)逆(ni)變電路。

(1)交(jiao)流(liu)濾(lv)波電(dian)(dian)容C3、C4因交(jiao)流(liu)浪涌(yong)電(dian)(dian)壓擊穿而(er)短路，有(you)(you)些ATX電(dian)(dian)源交(jiao)流(liu)濾(lv)波電(dian)(dian)路比較(jiao)復雜，應檢查是否有(you)(you)短路的(de)元(yuan)件。

(2)交(jiao)流(liu)主回路(lu)(lu)橋式整(zheng)流(liu)電(dian)(dian)路(lu)(lu)中(zhong)某個(ge)二極管擊(ji)穿。損壞原(yuan)因：由(you)于(yu)直流(liu)濾波電(dian)(dian)容C5、C6一般為330μF或470μF的大容量(liang)電(dian)(dian)解電(dian)(dian)容，瞬間充(chong)電(dian)(dian)電(dian)(dian)流(liu)可達20A以(yi)上(shang)。所以(yi)瞬間大容量(liang)的浪(lang)涌電(dian)(dian)流(liu)易造成整(zheng)流(liu)橋中(zhong)某個(ge)性能(neng)略差的整(zheng)流(liu)管燒壞。另外交(jiao)流(liu)浪(lang)涌電(dian)(dian)壓(ya)也會擊(ji)穿整(zheng)流(liu)二極管而(er)短路(lu)(lu)。

(3)整流(liu)濾波電(dian)(dian)(dian)路中的直(zhi)流(liu)濾波電(dian)(dian)(dian)容C5、C6擊穿，甚至發(fa)生爆(bao)裂現(xian)象(xiang)。損壞(huai)原因(yin)：由于大容量的電(dian)(dian)(dian)解(jie)電(dian)(dian)(dian)容耐壓一(yi)般為(wei)200V左右，而實際(ji)工(gong)作電(dian)(dian)(dian)壓達(da)到(dao)150V左右，接近額定值(zhi)。因(yin)此(ci)，當輸入電(dian)(dian)(dian)壓產(chan)生波動或某些電(dian)(dian)(dian)解(jie)電(dian)(dian)(dian)容質(zhi)量較差(cha)時，就(jiu)容易發(fa)生擊穿電(dian)(dian)(dian)容現(xian)象(xiang)。另外當電(dian)(dian)(dian)解(jie)電(dian)(dian)(dian)容發(fa)生漏電(dian)(dian)(dian)時，就(jiu)會嚴重發(fa)熱而爆(bao)裂。

(4)直流變換電(dian)路中的(de)功率(lv)開(kai)關(guan)晶體管VT1、VT2和換向二極管VD1、VD2擊穿損壞(huai)。損壞(huai)原因：由于整流濾波后(hou)的(de)輸出電(dian)壓一(yi)般高(gao)達300V左右，逆(ni)變功率(lv)開(kai)關(guan)管的(de)負(fu)載(zai)又是(shi)感(gan)性負(fu)載(zai)，漏感(gan)所(suo)形(xing)成的(de)電(dian)壓峰(feng)值(zhi)可能接近于600V，而(er)VT1、VT2的(de)耐(nai)(nai)壓Vceo只有450V左右。因此當輸入(ru)電(dian)壓偏高(gao)時，某(mou)些(xie)耐(nai)(nai)壓偏低的(de)開(kai)關(guan)管將被擊穿。所(suo)以(yi)可選擇(ze)耐(nai)(nai)壓更高(gao)的(de)功率(lv)開(kai)關(guan)管。

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2)保險絲熔(rong)斷(duan)但不(bu)發黑 說明不(bu)是短路引起保險絲熔(rong)斷(duan)。

(1)通電(dian)(dian)瞬(shun)間燒斷保險，多為瞬(shun)間的(de)大(da)電(dian)(dian)流(liu)將保險沖斷，如開機(ji)時直流(liu)濾波電(dian)(dian)容的(de)充(chong)電(dian)(dian)電(dian)(dian)流(liu)。

(2)使用過(guo)程中(zhong)燒斷保險(xian)，多為負載過(guo)大所致。

3)保(bao)險(xian)(xian)絲(si)未熔斷 如電(dian)(dian)源無輸出。而保(bao)險(xian)(xian)絲(si)完好，則應檢查(cha)電(dian)(dian)源控制(zhi)線(xian)路中是(shi)否(fou)有開路、短(duan)路現(xian)象，以及過壓、過流保(bao)護電(dian)(dian)路是(shi)否(fou)動作，輔助電(dian)(dian)源是(shi)否(fou)完好等。

(1)交(jiao)流(liu)輸入回(hui)路(lu)的(de)限(xian)流(liu)電(dian)(dian)(dian)(dian)阻THR開路(lu)，此時測不到300V直流(liu)電(dian)(dian)(dian)(dian)壓(ya)。開關(guan)電(dian)(dian)(dian)(dian)源采用(yong)220V直接(jie)整(zheng)流(liu)濾(lv)波電(dian)(dian)(dian)(dian)路(lu)，當接(jie)通交(jiao)流(liu)電(dian)(dian)(dian)(dian)壓(ya)時會有較大的(de)浪涌(yong)電(dian)(dian)(dian)(dian)流(liu)(電(dian)(dian)(dian)(dian)容充電(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)流(liu))，浪涌(yong)電(dian)(dian)(dian)(dian)流(liu)易(yi)造成限(xian)流(liu)電(dian)(dian)(dian)(dian)阻或保險絲(si)熔斷。

(2)輔(fu)助(zhu)電(dian)(dian)(dian)源無+5V電(dian)(dian)(dian)壓(ya)輸(shu)出。應重點檢(jian)查輔(fu)助(zhu)電(dian)(dian)(dian)源電(dian)(dian)(dian)路中的相關元(yuan)件(jian)，如(ru)輔(fu)助(zhu)電(dian)(dian)(dian)源電(dian)(dian)(dian)路VT15振(zhen)蕩管損壞(huai)，VZ16穩壓(ya)管、VD30、VD41二極管擊穿短路，限流電(dian)(dian)(dian)阻R72或啟(qi)動電(dian)(dian)(dian)阻R76斷路等。

(3)脈寬調制芯片(pian)TL494損壞，電(dian)(dian)壓比較器LM393損壞。另外如IC10、VT7短(duan)路(lu)，會使IC1的4腳的電(dian)(dian)壓為高電(dian)(dian)平，而處于待(dai)機狀態(tai)。

(4)直流輸出端有(you)短路，此(ci)時(shi)(shi)短路保護會起作用。其(qi)現象是(shi)開機瞬(shun)間(jian)電源指示(shi)亮，然(ran)后馬(ma)上又熄滅。應仔細(xi)檢查(cha)±5V、±12V線路是(shi)否(fou)有(you)破損或電路板上有(you)擊穿的器件。一般最為常見(jian)+5V直流回路的肖(xiao)特基二級管被擊穿。 (5)直流輸出過壓，此(ci)時(shi)(shi)過壓保護會起作用。此(ci)時(shi)(shi)應檢查(cha)+5V、+12V自動(dong)(dong)穩壓控制電路是(shi)否(fou)損壞，使自動(dong)(dong)穩壓控制失(shi)效。

2、受控啟動后直流電源無輸出

(1)T2原邊VT3、VT4推動管損壞，R54電阻(zu)阻(zu)值變大。

(2)半橋功(gong)率變換電路(lu)開關管(guan)VT1、VT2至少(shao)有一個開路(lu)。

(3)防偏磁(ci)電容C8容量變(bian)小(xiao)或開路(lu)。

3、電源有輸出，但開機不自檢

這主(zhu)要是因為電(dian)源的(de)PW-OK信號延(yan)遲(chi)時間不(bu)夠(gou)或無(wu)(wu)輸(shu)出造成的(de)。開機后(hou)，用電(dian)壓表測量PW-OK的(de)輸(shu)出端(電(dian)源插頭的(de)8腳)有無(wu)(wu)+5V。此時應(ying)檢查比(bi)較器LM393是否損壞。如因延(yan)時不(bu)夠(gou)，則應(ying)檢查延(yan)時電(dian)路中的(de)電(dian)阻R104和(he)電(dian)容C60。

4、電源負載能力差

電(dian)(dian)源(yuan)負載(zai)能力差主(zhu)要(yao)表(biao)現為：電(dian)(dian)源(yuan)在(zai)輕負載(zai)情況下，如只向系統板、軟驅供電(dian)(dian)時(shi)(shi)，能正常工(gong)(gong)作(zuo)(zuo)，而在(zai)配上大(da)硬盤、擴充其(qi)他設備時(shi)(shi)，往往電(dian)(dian)源(yuan)工(gong)(gong)作(zuo)(zuo)就不正常。這種情況一般(ban)是功率變換電(dian)(dian)路(lu)的開關管(guan)VT1、VT2性能不好(hao)，濾波電(dian)(dian)容(rong)器C5、C6容(rong)量(liang)(liang)不足。更換濾波電(dian)(dian)容(rong)時(shi)(shi)應注意2個電(dian)(dian)容(rong)的容(rong)量(liang)(liang)和耐壓值必(bi)須一致。

5、電源輸出電壓不準

如(ru)果只有(you)一(yi)檔(dang)電(dian)(dian)壓(ya)偏離額(e)定值，而(er)其他各檔(dang)電(dian)(dian)壓(ya)均正常，則是(shi)該檔(dang)電(dian)(dian)壓(ya)的(de)集成穩壓(ya)電(dian)(dian)路(lu)(lu)或(huo)整(zheng)流二極管(guan)(guan)損(sun)(sun)壞。如(ru)全部偏離額(e)定值，則是(shi)由IC1的(de)1、2腳誤差放大(da)器，R39、C32誤差放大(da)器負反饋回路(lu)(lu)，取樣電(dian)(dian)阻R33、R34、R35、構成+5V、+12V自動穩壓(ya)控制(zhi)電(dian)(dian)路(lu)(lu)有(you)故(gu)障。 在(zai)(zai)更換(huan)電(dian)(dian)源電(dian)(dian)路(lu)(lu)中的(de)二級管(guan)(guan)時要注(zhu)意，因為逆(ni)變器工(gong)作(zuo)頻率較(jiao)高，一(yi)般大(da)于20kHz，另(ling)外負載(zai)電(dian)(dian)流也(ye)較(jiao)大(da)，故(gu)電(dian)(dian)源中+5V檔(dang)采用(yong)肖特基高頻整(zheng)流二極管(guan)(guan)SBD，其余各檔(dang)也(ye)采用(yong)恢(hui)復特性(xing)的(de)高頻整(zheng)流二極管(guan)(guan)FRD。所以在(zai)(zai)更換(huan)時要盡可能找(zhao)到(dao)相同(tong)類型的(de)整(zheng)流二極管(guan)(guan)，以免再次損(sun)(sun)壞。

6、風扇不轉或發生響聲

計算機(ji)電(dian)源(yuan)的(de)風(feng)(feng)(feng)扇(shan)(shan)通常(chang)采用接在(zai)+12V直流輸(shu)出(chu)端(duan)的(de)直流風(feng)(feng)(feng)扇(shan)(shan)。如果電(dian)源(yuan)輸(shu)入(ru)輸(shu)出(chu)一(yi)切(qie)正常(chang)，而風(feng)(feng)(feng)扇(shan)(shan)不轉，多為風(feng)(feng)(feng)扇(shan)(shan)電(dian)機(ji)損壞。如果發出(chu)響聲，其(qi)原因之一(yi)是(shi)由(you)于機(ji)器(qi)長期(qi)的(de)運(yun)轉或運(yun)輸(shu)過(guo)程中的(de)激烈振動引起風(feng)(feng)(feng)扇(shan)(shan)的(de)4個固定螺釘松(song)動;其(qi)二是(shi)風(feng)(feng)(feng)扇(shan)(shan)內部灰塵太(tai)多或含油(you)(you)軸承缺油(you)(you)，只要及時清理或加入(ru)適量的(de)高(gao)級潤滑油(you)(you)，故障就可排(pai)除(chu)。