萬用表測試SMT元件的一個小竅門
有些貼片元件非常細小，用普通萬用表表筆測試檢修時很不方便，一是容易造成短路，二是對涂有絕緣涂層的電路板不便接觸到元件管腳的金屬部分。這里告訴大家
六、電(dian)路(lu)板公共電(dian)源短路(lu)故障(zhang)的檢修方法(fa)

七、一塊小橡皮，解決大問題
工業控制用到的板卡越來越多，很多板卡采用金手指插入插槽的方式.由于工業現場環境惡劣，多塵、潮濕、多腐蝕氣體的環境易使板卡產生接觸不良故障，很多朋友可能通過更換板卡的方式解決了問題，但購買板卡的費用非常可觀，尤其某些進口設備的板卡。其實大家不妨使用橡皮擦在金手指上反復擦幾下，將金手指上的污物清理干凈后，再試機，沒準就解決了問題！方法簡單又實用。
八、時好時壞電氣故障的分析
各種(zhong)時好時壞電(dian)氣(qi)故(gu)障從概率大(da)小(xiao)來講大(da)概包括以下幾種(zhong)情況：

1、打開機箱蓋查看內存條是否安裝或者松動；
2、拔掉內存條開機后報警聲是否相同；
3、清除COMS（可能設置有錯誤）或者更換BIOS；
4、打開機箱蓋查看電源是否與計算機底板或主板連接正常，底板與主板接插處是否松動，開機底板或主板是否上電，ATX電源是否接線有誤；
5、拔掉內存條開機是否報警；
6、更換CPU或主板。

二、

具體方法如下：

  1、在(zai)檢修中應(ying)首先檢查電源電路是否(fou)正常(chang),然后(hou)再檢查其他部分(fen)。

電(dian)源故障有(you)以下幾(ji)種情況(kuang):

(1)無電(dian)(dian)(dian)源(yuan)電(dian)(dian)(dian)壓(ya)或電(dian)(dian)(dian)源(yuan)電(dian)(dian)(dian)壓(ya)低。數控系統(tong)(tong)常采用±5V、±12V、±15V、±24V ,少數采用+ 3. 3V。而(er)電(dian)(dian)(dian)源(yuan)電(dian)(dian)(dian)壓(ya)的不正常,即會引起系統(tong)(tong)工作異常。

(2)用(yong)電(dian)(dian)壓表檢(jian)測(ce)電(dian)(dian)源(yuan)電(dian)(dian)壓正常,但用(yong)示波(bo)(bo)器檢(jian)測(ce)發現電(dian)(dian)壓波(bo)(bo)形紋波(bo)(bo)大。通常是電(dian)(dian)源(yuan)濾波(bo)(bo)電(dian)(dian)容開路，整(zheng)流二極管不良(liang)或虛焊造成的，有時(shi)是某(mou)元件擊穿(chuan)損壞(huai)造成電(dian)(dian)源(yuan)負載過重。

(3)系統剛開機時正常,工(gong)作一(yi)(yi)段(duan)時間后電(dian)源(yuan)電(dian)壓下降(jiang)。這通常是(shi)穩壓電(dian)路或大功率三(san)極管(guan)不良。在溫度升高后引(yin)起電(dian)源(yuan)電(dian)壓下降(jiang),也可能是(shi)某一(yi)(yi)元件虛焊，溫度升高后出(chu)現接觸(chu)不良。

無電(dian)(dian)(dian)(dian)源(yuan)(yuan)電(dian)(dian)(dian)(dian)壓或(huo)(huo)電(dian)(dian)(dian)(dian)源(yuan)(yuan)電(dian)(dian)(dian)(dian)壓嚴重降低時(shi)(shi),會引(yin)起(qi)(qi)系(xi)統(tong)中(zhong)斷或(huo)(huo)停止工作(zuo),這(zhe)種故障易(yi)檢測和(he)發現。當(dang)電(dian)(dian)(dian)(dian)源(yuan)(yuan)帶(dai)負(fu)(fu)(fu)載(zai)(zai)能力(li)(li)下降或(huo)(huo)濾(lv)波(bo)電(dian)(dian)(dian)(dian)路(lu)失效(xiao)時(shi)(shi),卻(que)是難以(yi)判斷的(de)。它會使系(xi)統(tong)突(tu)然停止工作(zuo),引(yin)起(qi)(qi)設備的(de)突(tu)發事(shi)故,造成(cheng)設備及人員傷害,務必(bi)引(yin)起(qi)(qi)高度重視。如一臺由FANUC 3MA組成(cheng)的(de)加(jia)工中(zhong)心(xin),開機后(hou)CRT無任何顯示。用(yong)萬用(yong)表檢測系(xi)統(tong)電(dian)(dian)(dian)(dian)源(yuan)(yuan)板A14B - 0067 - B002 - 01 ,發現+ 5V電(dian)(dian)(dian)(dian)源(yuan)(yuan)電(dian)(dian)(dian)(dian)壓為3. 75V ,去掉(diao)負(fu)(fu)(fu)載(zai)(zai)檢測, +5V電(dian)(dian)(dian)(dian)源(yuan)(yuan)為+ 4. 95V。說明電(dian)(dian)(dian)(dian)源(yuan)(yuan)帶(dai)負(fu)(fu)(fu)載(zai)(zai)能力(li)(li)低或(huo)(huo)負(fu)(fu)(fu)載(zai)(zai)有短(duan)路(lu)存在 。經檢查負(fu)(fu)(fu)載(zai)(zai)正(zheng)常(chang)(chang)。說明電(dian)(dian)(dian)(dian)源(yuan)(yuan)帶(dai)負(fu)(fu)(fu)載(zai)(zai)能力(li)(li)下降。經檢查更(geng)換C36濾(lv)波(bo)電(dian)(dian)(dian)(dian)容,系(xi)統(tong)正(zheng)常(chang)(chang)工作(zuo)。

2、時鐘電路

時鐘(zhong)電路主(zhu)(zhu)要是(shi)在系(xi)統(tong)主(zhu)(zhu)板上(shang),它是(shi)大(da)規模集成電路賴以(yi)工(gong)作(zuo)的(de)基本條件。它是(shi)以(yi)晶體振蕩器(俗稱晶振)為基礎,在電路中產(chan)生恒(heng)定的(de)方波信號 。晶體停(ting)振,就像人的(de)心(xin)臟(zang)停(ting)止跳動一(yi)(yi)(yi)樣,使(shi)系(xi)統(tong)處于癱瘓狀態。晶振工(gong)作(zuo)正常后,系(xi)統(tong)電路才能在CPU的(de)指(zhi)揮下按晶振時鐘(zhong)的(de)節拍工(gong)作(zuo)。晶振的(de)數(shu)量(liang)和(he)頻率隨數(shu)控系(xi)統(tong)的(de)不同(tong)(tong)而有所不同(tong)(tong),但一(yi)(yi)(yi)般至少(shao)有一(yi)(yi)(yi)個,其余電路所需(xu)的(de)不同(tong)(tong)的(de)時鐘(zhong)頻率由分頻電路或另外的(de)晶振來解(jie)決。

晶(jing)(jing)振(zhen)(zhen)(zhen)的(de)(de)損壞(huai)率較高(gao),其(qi)(qi)(qi)故障常(chang)見(jian)有(you)以下幾(ji)種: (1)晶(jing)(jing)振(zhen)(zhen)(zhen)漏(lou)電(dian)(dian)損壞(huai)。可(ke)用(yong)(yong)萬用(yong)(yong)表(biao)P×10 K擋測量,若(ruo)其(qi)(qi)(qi)電(dian)(dian)阻為(wei)無(wu)窮(qiong)(qiong)大(da),則為(wei)正常(chang);若(ruo)有(you)阻值則為(wei)漏(lou)電(dian)(dian)。(2)晶(jing)(jing)振(zhen)(zhen)(zhen)內(nei)部開路。用(yong)(yong)萬用(yong)(yong)表(biao)測其(qi)(qi)(qi)電(dian)(dian)阻雖(sui)無(wu)窮(qiong)(qiong)大(da),但(dan)在電(dian)(dian)路中(zhong)不能(neng)產生振(zhen)(zhen)(zhen)蕩(dang)脈沖。(3)晶(jing)(jing)振(zhen)(zhen)(zhen)變(bian)質使其(qi)(qi)(qi)參(can)數改變(bian)。只有(you)用(yong)(yong)示波(bo)器和頻率計才能(neng)檢測。晶(jing)(jing)振(zhen)(zhen)(zhen)雖(sui)能(neng)振(zhen)(zhen)(zhen)蕩(dang),但(dan)其(qi)(qi)(qi)時(shi)(shi)(shi)(shi)鐘頻率偏離(li)其(qi)(qi)(qi)標稱值,此(ci)(ci)時(shi)(shi)(shi)(shi)雖(sui)有(you)振(zhen)(zhen)(zhen)蕩(dang)脈沖,但(dan)由于(yu)脈沖數量錯誤,系統電(dian)(dian)路也不能(neng)工作。此(ci)(ci)時(shi)(shi)(shi)(shi)只有(you)用(yong)(yong)頻率計才能(neng)準確測出其(qi)(qi)(qi)偏差。(4)在實(shi)際時(shi)(shi)(shi)(shi)鐘電(dian)(dian)路中(zhong),晶(jing)(jing)振(zhen)(zhen)(zhen)的(de)(de)兩端到(dao)地均接有(you)一個幾(ji)皮法到(dao)幾(ji)十(shi)皮法的(de)(de)瓷片電(dian)(dian)容(rong),該(gai)電(dian)(dian)容(rong)漏(lou)電(dian)(dian)、變(bian)質而引起的(de)(de)時(shi)(shi)(shi)(shi)鐘電(dian)(dian)路的(de)(de)故障也較為(wei)常(chang)見(jian)。檢測晶(jing)(jing)振(zhen)(zhen)(zhen)的(de)(de)好壞(huai)用(yong)(yong)示波(bo)器和頻率計測量,萬用(yong)(yong)表(biao)很(hen)難判定(ding)其(qi)(qi)(qi)好壞(huai)。

如一臺由FANUC 6M控(kong)制的(de)加工中(zhong)心,工作一段時間(jian)后(hou),突然(ran)CRT黑屏,機(ji)床無動作。關掉電(dian)源(yuan)(yuan),再(zai)送上電(dian)源(yuan)(yuan),機(ji)床又能工作一段時間(jian)。檢查電(dian)源(yuan)(yuan)一切正常。故障可能在系統主板上。經檢修主板A16B - 1000 - 0220/ 04A ,發現兩個晶(jing)振中(zhong) 的(de)一個16. 3840MHz晶(jing)振內部接觸不良,更換后(hou)使用至今未再(zai)發生同類故障。

3、復位電路

復(fu)(fu)(fu)(fu)(fu)位電(dian)(dian)(dian)(dian)路也是存(cun)在(zai)于系(xi)統(tong)主板上的(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)路,它是大規(gui)模數字集成電(dian)(dian)(dian)(dian)路特有(you)的(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)路。微處理(li)器(qi)、接口電(dian)(dian)(dian)(dian)路等(deng)(deng)都有(you)復(fu)(fu)(fu)(fu)(fu)位端(duan)子。復(fu)(fu)(fu)(fu)(fu)位電(dian)(dian)(dian)(dian)路產(chan)生的(de)(de)(de)(de)(de)復(fu)(fu)(fu)(fu)(fu)位脈沖(chong)把程(cheng)序計數器(qi)清零，使CPU從存(cun)儲器(qi)中(zhong)調出初(chu)始化(hua)文件,對各控(kong)制芯片(pian)端(duan)口進行(xing)初(chu)始化(hua)。如果復(fu)(fu)(fu)(fu)(fu)位電(dian)(dian)(dian)(dian)路不良,系(xi)統(tong)會(hui)發生紊亂、死機等(deng)(deng)故障(zhang)。一般(ban)用(yong)示波(bo)器(qi)觀察(cha)復(fu)(fu)(fu)(fu)(fu)位脈沖(chong)時(shi),應(ying)反復(fu)(fu)(fu)(fu)(fu)通斷電(dian)(dian)(dian)(dian)源(yuan),在(zai)開關每次(ci)接通的(de)(de)(de)(de)(de)瞬間觀察(cha)復(fu)(fu)(fu)(fu)(fu)位脈沖(chong)。復(fu)(fu)(fu)(fu)(fu)位脈沖(chong)應(ying)為理(li)想的(de)(de)(de)(de)(de)矩形方波(bo)。若無復(fu)(fu)(fu)(fu)(fu)位脈沖(chong),應(ying)檢(jian)查復(fu)(fu)(fu)(fu)(fu)位電(dian)(dian)(dian)(dian)路中(zhong)的(de)(de)(de)(de)(de)電(dian)(dian)(dian)(dian)阻、電(dian)(dian)(dian)(dian)容、晶(jing)體管等(deng)(deng)。集成電(dian)(dian)(dian)(dian)路復(fu)(fu)(fu)(fu)(fu)位端(duan)應(ying)為規(gui)則(ze)的(de)(de)(de)(de)(de)低或高(gao)電(dian)(dian)(dian)(dian)平(ping),否則(ze),應(ying)為復(fu)(fu)(fu)(fu)(fu)位電(dian)(dian)(dian)(dian)路故障(zhang)或集成電(dian)(dian)(dian)(dian)路損壞。如一臺(tai)使用(yong)PLASMA數控(kong)系(xi)統(tong)的(de)(de)(de)(de)(de)大型加工中(zhong)心,系(xi)統(tong)不能啟動(dong),CRT無報警顯示。經(jing)檢(jian)查±5V、±12V、±24V電(dian)(dian)(dian)(dian)源(yuan)電(dian)(dian)(dian)(dian)壓(ya)正 常(chang),時(shi)鐘電(dian)(dian)(dian)(dian)路正常(chang)。懷疑是系(xi)統(tong)主板的(de)(de)(de)(de)(de)問題,在(zai)檢(jian)查復(fu)(fu)(fu)(fu)(fu)位電(dian)(dian)(dian)(dian)路時(shi),發現CPU復(fu)(fu)(fu)(fu)(fu)位端(duan)無復(fu)(fu)(fu)(fu)(fu)位脈沖(chong)。進一步檢(jian)查發現復(fu)(fu)(fu)(fu)(fu)位端(duan)一個3. 3k/ 0. 5W電(dian)(dian)(dian)(dian)阻開路,更(geng)換后(hou)系(xi)統(tong)啟動(dong)正常(chang)。