電子設備中(zhong)使用著大(da)量各種類型的電子元(yuan)(yuan)器(qi)件，設備發生(sheng)故(gu)障大(da)多是由于電子元(yuan)(yuan)器(qi)件失效或(huo)損壞引起的。因此(ci)怎么正確檢測電子元(yuan)(yuan)器(qi)件就(jiu)顯得尤其重(zhong)要，這也是電子維修(xiu)人員必須掌(zhang)握的技能。下面是部分常見電子元(yuan)(yuan)器(qi)件檢測經驗和技巧，供(gong)大(da)家參考(kao)。
1．測整流電橋(qiao)各腳的極性(xing)
萬用表置R×1k擋，黑(hei)表筆(bi)(bi)(bi)接(jie)橋(qiao)(qiao)(qiao)堆(dui)(dui)的(de)(de)(de)任(ren)意引腳(jiao)，紅表筆(bi)(bi)(bi)先后測其(qi)余三(san)只腳(jiao)，如果讀(du)(du)數均(jun)為無窮大，則(ze)黑(hei)表筆(bi)(bi)(bi)所接(jie)為橋(qiao)(qiao)(qiao)堆(dui)(dui)的(de)(de)(de)輸(shu)出正(zheng)極，如果讀(du)(du)數為4～10kΩ，則(ze)黑(hei)表筆(bi)(bi)(bi)所接(jie)引腳(jiao)為橋(qiao)(qiao)(qiao)堆(dui)(dui)的(de)(de)(de)輸(shu)出負極，其(qi)余的(de)(de)(de)兩引腳(jiao)為橋(qiao)(qiao)(qiao)堆(dui)(dui)的(de)(de)(de)交(jiao)流輸(shu)入端。
2．判斷晶振(zhen)的好壞
先(xian)用萬用表(R×10k擋)測(ce)晶(jing)振(zhen)兩端的(de)電(dian)(dian)阻值，若為無(wu)(wu)窮大，說明晶(jing)振(zhen)無(wu)(wu)短路或漏電(dian)(dian)；再將試電(dian)(dian)筆(bi)插(cha)入市電(dian)(dian)插(cha)孔內，用手指捏(nie)住晶(jing)振(zhen)的(de)任一引腳，將另(ling)一引腳碰觸試電(dian)(dian)筆(bi)頂端的(de)金屬部(bu)分(fen)，若試電(dian)(dian)筆(bi)氖泡發紅，說明晶(jing)振(zhen)是好的(de)；若氖泡不亮，則說明晶(jing)振(zhen)損壞。
3．單向晶閘(zha)管檢測
可用萬用表(biao)的(de)(de)(de)R×1k或R×100擋測量(liang)任(ren)意兩極(ji)(ji)之問的(de)(de)(de)正、反(fan)向電阻(zu)(zu)(zu)，如果(guo)找到一對極(ji)(ji)的(de)(de)(de)電阻(zu)(zu)(zu)為低阻(zu)(zu)(zu)值(zhi)(100Ω～lkΩ)，則此時(shi)(shi)黑(hei)表(biao)筆(bi)所(suo)接的(de)(de)(de)為控制(zhi)極(ji)(ji)，紅表(biao)筆(bi)所(suo)接為陰極(ji)(ji)，另一個(ge)極(ji)(ji)為陽極(ji)(ji)。晶閘管共(gong)有3個(ge)PN結，我們可以通過測量(liang)PN結正、反(fan)向電阻(zu)(zu)(zu)的(de)(de)(de)大(da)小(xiao)來判(pan)別它的(de)(de)(de)好壞。測量(liang)控制(zhi)極(ji)(ji)(G)與陰極(ji)(ji)[C)之間(jian)的(de)(de)(de)電阻(zu)(zu)(zu)時(shi)(shi)，如果(guo)正、反(fan)向電阻(zu)(zu)(zu)均為零或無窮大(da)，表(biao)明(ming)控制(zhi)極(ji)(ji)短路(lu)或斷路(lu)；測量(liang)控制(zhi)極(ji)(ji)(G)與陽極(ji)(ji)(A)之間(jian)的(de)(de)(de)電阻(zu)(zu)(zu)時(shi)(shi)，正、反(fan)向電阻(zu)(zu)(zu)讀數均應很(hen)大(da)；
{測(ce)量(liang)陽極(ji)(A)與陰極(ji)(C)之間的電阻(zu)時，正(zheng)、反向(xiang)電阻(zu)都應很大。
4．雙(shuang)向晶閘管的極性識(shi)別
雙向晶(jing)(jing)閘管(guan)有主(zhu)(zhu)電(dian)(dian)(dian)極(ji)(ji)1、主(zhu)(zhu)電(dian)(dian)(dian)極(ji)(ji)2和控(kong)制極(ji)(ji)，如(ru)果用萬用表R×1k擋測量(liang)兩(liang)個(ge)主(zhu)(zhu)電(dian)(dian)(dian)極(ji)(ji)之(zhi)間的電(dian)(dian)(dian)阻(zu)(zu)，讀(du)數應近似(si)無窮(qiong)大(da)，而控(kong)制極(ji)(ji)與任一個(ge)主(zhu)(zhu)電(dian)(dian)(dian)極(ji)(ji)之(zhi)間的正、反(fan)向電(dian)(dian)(dian)阻(zu)(zu)讀(du)數只(zhi)有幾十歐。根據(ju)這一特(te)性，我們很容(rong)易通過(guo)測量(liang)電(dian)(dian)(dian)極(ji)(ji)之(zhi)間電(dian)(dian)(dian)阻(zu)(zu)大(da)小(xiao)，識別(bie)出雙向晶(jing)(jing)閘管(guan)的控(kong)制極(ji)(ji)。而當黑表筆接主(zhu)(zhu)電(dian)(dian)(dian)極(ji)(ji)1。紅表筆接控(kong)制極(ji)(ji)時(shi)所(suo)測得(de)的正向電(dian)(dian)(dian)阻(zu)(zu)總是要比(bi)反(fan)向電(dian)(dian)(dian)阻(zu)(zu)小(xiao)一些(xie)，據(ju)此我們也很容(rong)易通過(guo)測量(liang)電(dian)(dian)(dian)阻(zu)(zu)大(da)小(xiao)來(lai)識別(bie)主(zhu)(zhu)電(dian)(dian)(dian)極(ji)(ji)1和主(zhu)(zhu)電(dian)(dian)(dian)極(ji)(ji)2。
5．檢(jian)查(cha)發光(guang)數碼管的好(hao)壞
先將(jiang)萬(wan)用表(biao)置R×10k或R×l00k擋，然(ran)后將(jiang)紅表(biao)筆與數(shu)碼管(以共陰數(shu)碼管為例(li))的“地”引出端相連，黑表(biao)筆依次接(jie)數(shu)碼管其他引出端，七段均應分別發光，否則說明數(shu)碼管損壞。
6．判別(bie)結型場效應管的電極
將(jiang)萬用(yong)表(biao)置于(yu)R×1k擋，用(yong)黑表(biao)筆(bi)接觸(chu)假定(ding)(ding)為(wei)柵極(ji)(ji)G的(de)管(guan)(guan)腳(jiao)，然后用(yong)紅(hong)(hong)表(biao)筆(bi)分別(bie)接觸(chu)另外兩個(ge)管(guan)(guan)腳(jiao)，若(ruo)阻(zu)(zu)值(zhi)均(jun)比較小(xiao)(5～10 Ω)，再將(jiang)紅(hong)(hong)、黑表(biao)筆(bi)交換測(ce)(ce)量一次。如阻(zu)(zu)值(zhi)均(jun)大(∞)，說(shuo)明(ming)都是(shi)反向(xiang)電阻(zu)(zu)(PN結反向(xiang))，屬N溝(gou)道管(guan)(guan)，且黑表(biao)筆(bi)接觸(chu)的(de)管(guan)(guan)腳(jiao)為(wei)柵極(ji)(ji)G，并說(shuo)明(ming)原先假定(ding)(ding)是(shi)正確的(de)。若(ruo)再次測(ce)(ce)量的(de)阻(zu)(zu)值(zhi)均(jun)很小(xiao)，說(shuo)明(ming)是(shi)正向(xiang)電阻(zu)(zu)，屬于(yu)P溝(gou)道場(chang)效應(ying)管(guan)(guan)，黑表(biao)筆(bi)所接的(de)也是(shi)柵極(ji)(ji)G。若(ruo)不出(chu)(chu)現上述(shu)情況，可(ke)以(yi)調換紅(hong)(hong)、黑表(biao)筆(bi)，按上述(shu)方法進行測(ce)(ce)試，直至(zhi)判斷出(chu)(chu)柵極(ji)(ji)為(wei)止。一般結型場(chang)效應(ying)管(guan)(guan)的(de)源(yuan)極(ji)(ji)與漏(lou)極(ji)(ji)在制造時是(shi)對稱(cheng)的(de)，所以(yi)，當(dang)柵極(ji)(ji)G確定(ding)(ding)以(yi)后，對于(yu)源(yuan)極(ji)(ji)S、漏(lou)極(ji)(ji)D不一定(ding)(ding)要(yao)判別(bie)，因為(wei)這兩個(ge)極(ji)(ji)可(ke)以(yi)互換使(shi)用(yong)。源(yuan)極(ji)(ji)與漏(lou)極(ji)(ji)之(zhi)間的(de)電阻(zu)(zu)為(wei)幾千歐。
7．三極(ji)管電極(ji)的判別
對于(yu)一只型號標示(shi)不(bu)清或無標志的(de)三極(ji)管(guan)，要想分(fen)辨出(chu)它(ta)們(men)的(de)三個(ge)電(dian)(dian)(dian)極(ji)，也可用萬用表(biao)(biao)(biao)測(ce)(ce)試(shi)。先將(jiang)萬用表(biao)(biao)(biao)量(liang)(liang)程開關撥在R×100或R×1k電(dian)(dian)(dian)阻擋上。紅表(biao)(biao)(biao)筆(bi)任(ren)意(yi)接觸三極(ji)管(guan)的(de)一個(ge)電(dian)(dian)(dian)極(ji)，黑表(biao)(biao)(biao)筆(bi)依(yi)次(ci)接觸另外兩(liang)個(ge)電(dian)(dian)(dian)極(ji)，分(fen)別測(ce)(ce)量(liang)(liang)它(ta)們(men)之間的(de)電(dian)(dian)(dian)阻值，若測(ce)(ce)出(chu)均為(wei)幾百歐低電(dian)(dian)(dian)阻時，則紅表(biao)(biao)(biao)筆(bi)接觸的(de)電(dian)(dian)(dian)極(ji)為(wei)基極(ji)b，此管(guan)為(wei)PNP管(guan)。若測(ce)(ce)出(chu)均為(wei)幾十至(zhi)上百千(qian)歐的(de)高電(dian)(dian)(dian)阻時，則紅表(biao)(biao)(biao)筆(bi)接觸的(de)電(dian)(dian)(dian)極(ji)也為(wei)基極(ji)b，此管(guan)為(wei)NPN管(guan)。
在(zai)判別(bie)出(chu)管(guan)(guan)型和(he)基(ji)極(ji)b的(de)基(ji)礎上(shang)，利用(yong)三極(ji)管(guan)(guan)正向(xiang)電(dian)(dian)流(liu)放(fang)(fang)大(da)系數比(bi)(bi)反向(xiang)電(dian)(dian)流(liu)放(fang)(fang)大(da)系數大(da)的(de)原理確定集(ji)電(dian)(dian)極(ji)。任意假定一個電(dian)(dian)極(ji)為c極(ji)，另(ling)一個電(dian)(dian)極(ji)為e極(ji)。將(jiang)(jiang)萬用(yong)表(biao)量(liang)程開關撥在(zai)R×1k電(dian)(dian)阻擋上(shang)。對(dui)于：PNP管(guan)(guan)，令紅(hong)(hong)表(biao)筆接(jie)c極(ji)，黑表(biao)筆接(jie)e極(ji)，再用(yong)手同時捏一下管(guan)(guan)子(zi)的(de)b、c極(ji)，但不能(neng)使b、c兩(liang)極(ji)直接(jie)相碰，測出(chu)某(mou)一阻值。然(ran)后兩(liang)表(biao)筆對(dui)調進行第二次(ci)(ci)測量(liang)，將(jiang)(jiang)兩(liang)次(ci)(ci)測的(de)電(dian)(dian)阻相比(bi)(bi)較(jiao)，對(dui)于：PNP型管(guan)(guan)，阻值小的(de)一次(ci)(ci)，紅(hong)(hong)表(biao)筆所接(jie)的(de)電(dian)(dian)極(ji)為集(ji)電(dian)(dian)極(ji)。對(dui)于NPN型管(guan)(guan)阻值小的(de)一次(ci)(ci)，黑表(biao)筆所接(jie)的(de)電(dian)(dian)極(ji)為集(ji)電(dian)(dian)極(ji)。
8．電位(wei)器的好壞判別
先測(ce)電(dian)(dian)位(wei)(wei)(wei)器(qi)的(de)(de)(de)(de)標(biao)(biao)稱(cheng)(cheng)阻(zu)(zu)值(zhi)。用(yong)(yong)萬(wan)(wan)用(yong)(yong)表的(de)(de)(de)(de)歐姆擋測(ce)“1”、“3”兩(liang)端(設“2”端為活(huo)動(dong)(dong)觸(chu)點(dian))，其讀數(shu)應(ying)為電(dian)(dian)位(wei)(wei)(wei)器(qi)的(de)(de)(de)(de)標(biao)(biao)稱(cheng)(cheng)值(zhi)，如萬(wan)(wan)用(yong)(yong)表的(de)(de)(de)(de)指針不動(dong)(dong)、阻(zu)(zu)值(zhi)不動(dong)(dong)或阻(zu)(zu)值(zhi)相差很多(duo)，則表明該電(dian)(dian)位(wei)(wei)(wei)器(qi)已(yi)損壞。再檢查電(dian)(dian)位(wei)(wei)(wei)器(qi)的(de)(de)(de)(de)活(huo)動(dong)(dong)臂與(yu)電(dian)(dian)阻(zu)(zu)片的(de)(de)(de)(de)接(jie)觸(chu)是否良好(hao)。用(yong)(yong)萬(wan)(wan)用(yong)(yong)表的(de)(de)(de)(de)歐姆擋測(ce)“1”、“2”或“2”、“3”兩(liang)端，將電(dian)(dian)位(wei)(wei)(wei)器(qi)的(de)(de)(de)(de)轉軸(zhou)按逆時針方向旋至(zhi)接(jie)近“關”的(de)(de)(de)(de)位(wei)(wei)(wei)置(zhi)，此時電(dian)(dian)阻(zu)(zu)應(ying)越小越好(hao)，再徐徐順時鐘旋轉軸(zhou)柄，電(dian)(dian)阻(zu)(zu)應(ying)逐漸增大，旋至(zhi)極端位(wei)(wei)(wei)置(zhi)時，阻(zu)(zu)值(zhi)應(ying)接(jie)近電(dian)(dian)位(wei)(wei)(wei)器(qi)的(de)(de)(de)(de)標(biao)(biao)稱(cheng)(cheng)值(zhi)。如在電(dian)(dian)位(wei)(wei)(wei)器(qi)的(de)(de)(de)(de)軸(zhou)柄轉動(dong)(dong)過(guo)程中萬(wan)(wan)用(yong)(yong)表指針有跳動(dong)(dong)瑚象，描踢(ti)活(huo)動(dong)(dong)觸(chu)』點(dian)接(jie)觸(chu)不良。
9．測量大容量電容的(de)漏電電阻(zu)
用(yong)500型(xing)萬(wan)用(yong)表置于R×10或R×100擋(dang)(dang)，待指(zhi)針指(zhi)向最(zui)大值時，再立(li)即(ji)改用(yong)R×1k擋(dang)(dang)測量，指(zhi)針會在較短時間(jian)內穩(wen)定，從而讀出漏(lou)電(dian)電(dian)阻阻值。
10．判別紅外(wai)接收頭(tou)引(yin)腳(jiao)
萬用表(biao)置R×1k擋，先假(jia)設接(jie)(jie)收頭的(de)某腳(jiao)(jiao)為(wei)接(jie)(jie)地(di)端(duan)(duan)，將其與黑(hei)表(biao)筆(bi)(bi)相接(jie)(jie)，用紅表(biao)筆(bi)(bi)分別測(ce)(ce)量另(ling)兩(liang)腳(jiao)(jiao)電(dian)阻，對比兩(liang)次所(suo)測(ce)(ce)阻值(zhi)(一(yi)般在(zai)4～7k Q范圍)，電(dian)阻較(jiao)小(xiao)的(de)一(yi)次其紅表(biao)筆(bi)(bi)所(suo)接(jie)(jie)為(wei)+5V電(dian)源引腳(jiao)(jiao)，另(ling)一(yi)阻值(zhi)較(jiao)大的(de)則(ze)(ze)為(wei)信號(hao)引腳(jiao)(jiao)。反之，若用紅表(biao)筆(bi)(bi)接(jie)(jie)已(yi)知地(di)腳(jiao)(jiao)，黑(hei)表(biao)筆(bi)(bi)分別測(ce)(ce)已(yi)知電(dian)源腳(jiao)(jiao)及(ji)信號(hao)腳(jiao)(jiao)，則(ze)(ze)阻值(zhi)都(dou)在(zai)15kΩ以上，阻值(zhi)小(xiao)的(de)引腳(jiao)(jiao)為(wei)+5V端(duan)(duan)，阻值(zhi)偏大的(de)引腳(jiao)(jiao)為(wei)信號(hao)端(duan)(duan)。如果測(ce)(ce)量結果符合(he)上述阻值(zhi)則(ze)(ze)可判斷該接(jie)(jie)收頭完好。
11．判斷(duan)無符(fu)號電(dian)解(jie)電(dian)容極性
先將電容短路放(fang)電，再(zai)(zai)將兩引(yin)線(xian)(xian)做好A、B標記，萬用(yong)表置(zhi)R×100或R×1k擋(dang)，黑表筆(bi)接(jie)A引(yin)線(xian)(xian)，紅(hong)表筆(bi)接(jie)B引(yin)線(xian)(xian)，待指針靜止不動后(hou)讀數(shu)(shu)，測完后(hou)短路放(fang)電；再(zai)(zai)將黑表筆(bi)接(jie)B引(yin)線(xian)(xian)，紅(hong)表筆(bi)接(jie)A引(yin)線(xian)(xian)，比較兩次(ci)讀數(shu)(shu)，阻值較大(da)的一(yi)次(ci)黑表筆(bi)所接(jie)為(wei)正(zheng)極，紅(hong)表筆(bi)所接(jie)為(wei)負極。
12．測發(fa)光二(er)極管
取一個容量大于(yu)100“F的電(dian)解電(dian)容器(容量越(yue)大，現象越(yue)明顯)，先用萬用表(biao)(biao)(biao)R×100擋對其充(chong)(chong)電(dian)，黑表(biao)(biao)(biao)筆(bi)接電(dian)容正(zheng)極(ji)(ji)，紅(hong)表(biao)(biao)(biao)筆(bi)接負(fu)極(ji)(ji)，充(chong)(chong)電(dian)完畢后，黑表(biao)(biao)(biao)筆(bi)改(gai)接電(dian)容負(fu)極(ji)(ji)，將被測發光(guang)(guang)(guang)(guang)二極(ji)(ji)管接于(yu)紅(hong)表(biao)(biao)(biao)筆(bi)和(he)電(dian)容正(zheng)極(ji)(ji)之間。如果(guo)(guo)發光(guang)(guang)(guang)(guang)二極(ji)(ji)管亮后逐漸熄滅，表(biao)(biao)(biao)明它是好的。此時紅(hong)表(biao)(biao)(biao)筆(bi)接的是發光(guang)(guang)(guang)(guang)二極(ji)(ji)管的負(fu)極(ji)(ji)，電(dian)容正(zheng)極(ji)(ji)接的是發光(guang)(guang)(guang)(guang)二極(ji)(ji)管的正(zheng)極(ji)(ji)。如果(guo)(guo)發光(guang)(guang)(guang)(guang)二極(ji)(ji)管不亮，將其兩端對調(diao)重新接上(shang)測試，還不亮，表(biao)(biao)(biao)明發光(guang)(guang)(guang)(guang)二極(ji)(ji)管已損壞(huai)。
13.光電耦合器檢測
萬用(yong)表(biao)選用(yong)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)R×100擋(dang)，不得(de)選R×10k擋(dang)，以防電(dian)(dian)(dian)(dian)(dian)池電(dian)(dian)(dian)(dian)(dian)壓過高擊穿發(fa)(fa)光(guang)(guang)二(er)極(ji)管(guan)。紅、黑(hei)表(biao)筆接(jie)(jie)輸(shu)入(ru)端，測(ce)(ce)正(zheng)、反(fan)向(xiang)(xiang)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)，正(zheng)常時正(zheng)向(xiang)(xiang)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)為(wei)數十(shi)(shi)歐(ou)姆，反(fan)向(xiang)(xiang)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)幾千歐(ou)至幾十(shi)(shi)千歐(ou)。若正(zheng)、反(fan)向(xiang)(xiang)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)相近(jin)，表(biao)明發(fa)(fa)光(guang)(guang)二(er)極(ji)管(guan)已損壞。萬用(yong)表(biao)選電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)R×1擋(dang)。紅、黑(hei)表(biao)筆接(jie)(jie)輸(shu)出(chu)端，測(ce)(ce)正(zheng)、反(fan)向(xiang)(xiang)電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)，正(zheng)常時均接(jie)(jie)近(jin)于∞，否(fou)則受(shou)(shou)光(guang)(guang)管(guan)損壞。萬用(yong)表(biao)選電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)R×10擋(dang)，紅、黑(hei)表(biao)筆分別接(jie)(jie)輸(shu)入(ru)、輸(shu)出(chu)端測(ce)(ce)發(fa)(fa)光(guang)(guang)管(guan)與(yu)受(shou)(shou)光(guang)(guang)管(guan)之間的(de)絕緣電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)(有條件(jian)應用(yong)兆歐(ou)表(biao)測(ce)(ce)其(qi)絕緣電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)，此時兆歐(ou)表(biao)輸(shu)出(chu)額定電(dian)(dian)(dian)(dian)(dian)壓應略低于被測(ce)(ce)光(guang)(guang)電(dian)(dian)(dian)(dian)(dian)耦合器所允(yun)許(xu)的(de)耐壓值)，發(fa)(fa)光(guang)(guang)管(guan)與(yu)受(shou)(shou)光(guang)(guang)管(guan)問絕緣電(dian)(dian)(dian)(dian)(dian)阻(zu)(zu)(zu)(zu)(zu)正(zheng)常應為(wei)∞。
14．光敏電阻的(de)檢(jian)測
將(jiang)萬用表撥到R×1kΩ擋，把光敏電(dian)阻(zu)的受光面(mian)與入射光線保持(chi)垂直(zhi)，于是(shi)在萬用表上(shang)直(zhi)接測得(de)的電(dian)阻(zu)就是(shi)亮阻(zu)。再把光敏電(dian)阻(zu)置于完全黑(hei)暗的場所，這時(shi)萬用表所測出的電(dian)阻(zu)就是(shi)暗阻(zu)。如果(guo)亮阻(zu)為幾(ji)(ji)千歐至(zhi)幾(ji)(ji)十(shi)干(gan)歐，暗阻(zu)為幾(ji)(ji)至(zhi)幾(ji)(ji)十(shi)兆歐，說(shuo)明光敏電(dian)阻(zu)是(shi)好(hao)的。
15．激光二(er)極管損壞判別(bie)
拆下激光(guang)二極管(guan)(guan)，測(ce)量(liang)其(qi)阻值(zhi)(zhi)(zhi)，正(zheng)常(chang)情況下反向(xiang)阻值(zhi)(zhi)(zhi)應為無窮(qiong)大，正(zheng)向(xiang)阻值(zhi)(zhi)(zhi)在20kΩ～40kΩ。如果(guo)所測(ce)的正(zheng)向(xiang)阻值(zhi)(zhi)(zhi)已超過50kΩ，說(shuo)明(ming)激光(guang)二極管(guan)(guan)性能已下降；如果(guo)其(qi)正(zheng)向(xiang)阻值(zhi)(zhi)(zhi)已超過90kΩ，說(shuo)明(ming)該管(guan)(guan)已損壞，不能再使用了。
