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01 整機不工作

整機不工作的(de)故(gu)障表現為通電(dian)后放大器(qi)無(wu)(wu)任何顯(xian)示，各(ge)功能鍵均(jun)失效(xiao)，也無(wu)(wu)任何聲音，像未通電時一樣。

檢修時首(shou)先應(ying)檢查電(dian)(dian)源電(dian)(dian)路。可(ke)用萬用表(biao)測量電(dian)(dian)源插頭兩(liang)端的(de)直流電(dian)(dian)阻(zu)值(zhi)(電(dian)(dian)源開關應(ying)接通)，正常(chang)時應(ying)有(you)數百(bai)歐(ou)姆(mu)的(de)電(dian)(dian)阻(zu)值(zhi)。若測得阻(zu)值(zhi)偏小許多，且電(dian)(dian)源變壓器嚴重發熱(re)，說明電(dian)(dian)源變壓器的(de)初級回路有(you)局部短(duan)路處；

若(ruo)測(ce)得(de)阻值(zhi)為(wei)無窮大(da)，應(ying)檢查保險(xian)絲是否熔斷、變(bian)(bian)壓器初級繞組是否開路(lu)、電(dian)(dian)源(yuan)(yuan)(yuan)線與插頭之間有無斷線。有的機器增(zeng)加了溫度(du)保護裝置，在電(dian)(dian)源(yuan)(yuan)(yuan)變(bian)(bian)壓器的初級回(hui)路(lu)中(zhong)接(jie)入了電(dian)(dian)流保險(xian)絲(通常安(an)裝在電(dian)(dian)源(yuan)(yuan)(yuan)變(bian)(bian)壓器內部(bu)，將變(bian)(bian)壓器外部(bu)的絕緣(yuan)紙去掉即可(ke)見到(dao))，它損壞后也會使電(dian)(dian)源(yuan)(yuan)(yuan)變(bian)(bian)壓器初級回(hui)路(lu)開路(lu)。

若(ruo)電(dian)(dian)(dian)(dian)(dian)(dian)源插(cha)頭(tou)兩(liang)端阻值正(zheng)(zheng)常，可通電(dian)(dian)(dian)(dian)(dian)(dian)測量電(dian)(dian)(dian)(dian)(dian)(dian)源電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)各輸出電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)是否(fou)正(zheng)(zheng)常。對于采(cai)用系統(tong)控(kong)制微(wei)處理器或邏輯控(kong)制電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)的放大(da)器，應著重檢(jian)查該(gai)控(kong)制電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)的供電(dian)(dian)(dian)(dian)(dian)(dian)電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)(通常為+5V)是否(fou)正(zheng)(zheng)常。如無(wu)+5V電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)，應測量三端穩壓(ya)集成電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)7805的輸入端電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)是否(fou)正(zheng)(zheng)常，若(ruo)輸入端電(dian)(dian)(dian)(dian)(dian)(dian)壓(ya)不正(zheng)(zheng)常，應檢(jian)查整流、濾(lv)波電(dian)(dian)(dian)(dian)(dian)(dian)路(lu)。

若7805輸(shu)入端電(dian)(dian)(dian)壓正(zheng)(zheng)常，而(er)輸(shu)出端無十5V電(dian)(dian)(dian)壓或電(dian)(dian)(dian)壓偏(pian)低，可斷開(kai)負載看(kan)+5V電(dian)(dian)(dian)壓能否恢復(fu)正(zheng)(zheng)常。若+5V電(dian)(dian)(dian)壓正(zheng)(zheng)常，則故障在負載電(dian)(dian)(dian)路；若+5V電(dian)(dian)(dian)壓仍(reng)不正(zheng)(zheng)常，則故障在7805本身。若系(xi)統控制電(dian)(dian)(dian)路的+5V供電(dian)(dian)(dian)電(dian)(dian)(dian)壓正(zheng)(zheng)常，應再檢查微處理器(qi)的時鐘及(ji)復(fu)位信號是(shi)否正(zheng)(zheng)常、鍵控與顯示驅動(dong)電(dian)(dian)(dian)路有無損壞(huai)。

02 噪(zao)聲大

放大器的噪聲有交(jiao)流聲、爆裂聲、感應噪聲和白(bai)噪聲等。

檢(jian)修(xiu)時，應(ying)先判(pan)斷噪聲來自于前級(ji)還(huan)是來自于后級(ji)電路。可把前、后級(ji)的(de)信號(hao)連接插頭(tou)取(qu)下，若噪聲明(ming)顯變小，說明(ming)故障(zhang)在前級(ji)電(dian)路；

反之(zhi)，故(gu)障在后(hou)級(ji)電路。交(jiao)(jiao)流聲(sheng)是(shi)指(zhi)聽感低沉、單(dan)調而(er)穩(wen)定的(de)100Hz交(jiao)(jiao)流哼聲(sheng)，主要(yao)是(shi)電源(yuan)部分濾波(bo)不良所(suo)致，應著重(zhong)檢查電源(yuan)整流、濾波(bo)和穩(wen)壓元件有無(wu)損壞。前、后(hou)級(ji)放大電路電源(yuan)端(duan)的(de)退耦電容虛焊或失效，也會(hui)產生一種類(lei)似交(jiao)(jiao)流聲(sheng)的(de)低頻(pin)振蕩噪(zao)聲(sheng)。

感應(ying)(ying)噪(zao)聲是成(cheng)分較復雜(za)且刺耳的(de)交(jiao)流聲，主要是前級電(dian)(dian)(dian)路(lu)中的(de)轉換(huan)開關(guan)(guan)、電(dian)(dian)(dian)位器(qi)接地不(bu)良(liang)或(huo)(huo)信號連(lian)線屏蔽(bi)不(bu)良(liang)所(suo)致。爆裂聲是指間斷(duan)的(de)“劈啪(pa)”、“咔咔”聲，在前級電(dian)(dian)(dian)路(lu)中，應(ying)(ying)檢查(cha)信號輸(shu)入(ru)插(cha)頭與插(cha)座(zuo)、轉換(huan)開關(guan)(guan)、電(dian)(dian)(dian)位器(qi)等是否接觸(chu)不(bu)良(liang)，耦合(he)電(dian)(dian)(dian)容有無虛焊(han)、漏電(dian)(dian)(dian)等。后級放大電(dian)(dian)(dian)路(lu)應(ying)(ying)檢查(cha)繼電(dian)(dian)(dian)器(qi)觸(chu)點是否氧化、輸(shu) 入(ru)耦合(he)電(dian)(dian)(dian)容有無漏電(dian)(dian)(dian)或(huo)(huo)接觸(chu)不(bu)良(liang)。

另(ling)外，后級電(dian)路(lu)中的差(cha)分輸入管(guan)(guan)或恒流管(guan)(guan)軟擊穿，也會(hui)產(chan)生(sheng)類似電(dian)火(huo)花(hua)的“咔咔”噪(zao)聲(sheng)。白噪(zao)聲(sheng)是指(zhi)無規(gui)則的連續(xu)“沙沙”聲(sheng)，通(tong)常(chang)是由前(qian)、后級放(fang)大電(dian)路(lu)中的輸入級晶體管(guan)(guan)、場效(xiao)應管(guan)(guan)或運放(fang)集(ji)成電(dian)路(lu)的性(xing)能不良(liang)產(chan)生(sheng)的本(ben)底噪(zao)聲(sheng)，檢修(xiu)時，可用同規(gui)格的元件代換試之(zhi)。

03 音量輕(qing)

所謂音輕故(gu)障，是指(zhi)音頻(pin)信號在放(fang)大(da)傳輸(shu)過(guo)程(cheng)中(zhong)，因某個(ge)放(fang)大(da)級放(fang)大(da)量變化或在某個(ge)環(huan)節被(bei)衰減(jian)，使(shi)放(fang)大(da)器的(de)(de)增益下降或輸(shu)出(chu)功率變小(xiao)。檢修時，首先應檢查(cha)信號源(yuan)和(he)音箱是否(fou)正常，可用替換的(de)(de)辦(ban)法(fa)來檢查(cha)。然(ran)后檢查(cha)各類轉(zhuan)換開關(guan)和(he)控制(zhi)電位器，看(kan)音量能(neng)否(fou)變大(da)。

若以上各部分均正(zheng)常，應(ying)判斷出(chu)故障(zhang)是(shi)在(zai)前級(ji)還(huan)是(shi)在(zai)后級(ji)電(dian)路(lu)。對(dui)于某一個聲道音輕，可將(jiang)其前級(ji)電(dian)路(lu)輸出(chu)的信號交換輸入到另一(yi)聲(sheng)道的后(hou)級(ji)電路，若音箱的聲(sheng)音大小不(bu)變，則故障(zhang)在(zai)后(hou)級(ji)電路；

反之，故(gu)障(zhang)在前級電路(lu)(lu)。后級放大電路(lu)(lu)造成的(de)音輕，主要有輸(shu)出功(gong)率不足和增益不夠(gou)兩種原因(yin)。可用適當(dang)加大輸(shu)入信(xin)號(例如(ru)將收錄機輸(shu)出給揚(yang)聲器(qi)的(de)信(xin)號直(zhi)接加至后級功(gong)放電路(lu)(lu)的(de)輸(shu)入端(duan)，改變收錄機的(de)音量，觀察功(gong)放輸(shu)出的(de)變化)的(de)方(fang)法來判斷是(shi)哪種原因(yin)引起的(de)。