电源问题求诊

我有一块5V40A（200W）的电源，安装前用万用表测量输出端正负极电阻值为“零”，不知是否正常，没敢使用。如果属于不正常，请问是什么问题？如何修理？请各位前辈给诊断一下并赐给疗方，谢啦！

量的时间长一点,如果还是0,就说明是开关电源输出部分有短路,很好修的.一个一个量,排除法.

[whitepad]***400;200;400,200;;** m21,20 l22,19,38,19,40,20,42,22,43,24,44,25,44,27 e|********* m23,45 l24,44,25,42,28,41,30,40,31,39,37,39,38,38,42,37,45,37,47,35,48,36,48,38,47,40,45,42,45,44,44,45,43,47,43,61,45,62,46,63 47,63,49,64,50,65,58,65,59,64,59,63 e|********* m60,23 l61,21,63,20,66,18,92,18 e|********* m58,27 l58,33,59,34,59,46,60,47,60,53,61,54,61,55 e|********* m64,29 l71,29,73,30,82,30,83,31,85,31,90,36,91,38,92,39,93,43,93,71,92,72,91,74,91,75,87,79,86,81,84,82,83,83,81,84,80,85,79,85 78,86,73,86,72,85,70,84,70,83,65,78,65,77,64,77,64,76,62,74,62,73 e|********* m62,40 l85,40 e|********* m62,47 l83,47 e|********* m53,56 l54,56,55,57,56,57,58,58,67,58,69,57,71,55,74,55,75,54,77,53,78,52,81,52,83,50,85,49,86,49,88,48,89,47,90,47,91,46,92,46 93,45,95,45 e|********* m101,39 l103,38,104,37,128,37,129,38,140,38 e|********* m119,20 l119,21,121,24,121,34,122,35,122,43,123,45,123,55,124,57,124,62,123,63,122,65,120,67,119,69,117,69,115,71,113,72,108,72,106,71,104,69,102,69 102,68,101,67,101,65,99,63,99,57 e|********* m104,50 l116,50 e|********* m87,56 l85,58,85,59,83,61,83,63,82,63,80,65,80,66,78,66 e|********* m166,28 l165,29,165,30,164,31,162,35,158,39,158,40,157,41,158,42,160,43,171,43,171,44,172,46,172,49,167,54,165,55,164,56,162,56,161,57,154,57,156,59 158,59,159,60,161,61,162,62,162,63,163,63,164,64,166,64 e|********* m224,30 l223,31,221,32,221,34,217,38,217,39,213,43,212,45,210,46,209,48,207,49,207,50,202,55,202,56,200,57,200,58,199,59 e|********* m197,70 l196,70,195,71,195,72,194,73 e|********* m247,30 l245,32,244,35,239,40,239,41,237,42,236,44,234,45,233,47,232,48,232,49,231,51,230,52,229,54,227,56,227,57,226,58,226,59,225,59 e|********* m217,70 l216,70,215,71,215,72,214,72 e|********* m281,17 l282,18,280,20,279,24,275,28,274,30,270,34,268,35,267,37,265,38,264,40,260,44,258,45,258,47,256,48,255,50,253,51,253,52,252,52,252,53 e|********* m245,63 l244,64,243,64,243,66,242,66,242,67 e|********* m267,117 l267,128,266,129,265,131,265,134,267,136,282,136,283,135,283,117,267,117 e|********* m235,103 l237,101,238,99,238,98,240,97,241,95,248,88,250,87,250,85,251,84,252,82,254,80,255,78,257,78,258,77,259,75,261,75,263,73,265,73,268,72,290,72 291,73,292,73,294,75,297,76,299,77,300,78,302,78,310,86,311,88,313,89,317,93,318,95,321,98,321,99,322,100,323,102,325,104,326,106,327,107,328,109 328,110,329,113,330,114,330,116,331,117,331,135,330,137,329,138,328,140,328,142,327,144,325,146,324,148,320,152,318,153,318,155,317,156,316,158,314,159,306,167 304,167,303,169,301,170,300,170,299,172,297,172,296,173,293,175,291,175,289,177,285,178,283,180,281,180,280,181,276,181,275,182,268,182,267,181,264,179,262,179 260,177,258,176,257,175,255,174,253,172,251,171,251,169,249,167,249,165,247,163,247,160,246,159,245,157,245,156,244,155,243,153,242,152,242,149,240,147,240,145 238,143,238,139,237,137,235,135,235,119,236,118,236,112,237,111,237,107,238,106,238,104,239,103,239,102 e|********0.75; m244,102 l244,101,245,100,245,99,248,96,248,95,251,92,251,91,252,90,253,88,254,87,254,86,255,85,256,85,256,84,258,82,259,82,260,81,262,80,266,80,268,79 269,78,294,78,294,79,295,79,296,80,297,80,298,81,300,82,301,83,301,84,302,84,304,86,306,87,306,88,307,89,307,90,308,91,309,91,309,92,310,92 310,93,311,94,312,96,314,98,314,100,315,100,316,102,317,103,317,105,318,105,319,106,319,107,321,109,321,110,322,111,322,114,323,114,323,118,324,119,324,134 323,134,322,136,320,138,320,139,319,139,319,140,318,140,314,144,313,144,313,145,312,145,312,146,311,147,311,148,310,148,309,150,309,152,308,152,307,153,307,154 306,154,305,155,305,156,302,159,302,160,301,160,301,162,299,163,299,164,298,164,296,166,296,167,294,168,293,169,291,170,289,172,288,172,286,173,286,174,281,174 280,175,274,175,273,176,266,176,266,175,265,174,263,174,263,173,262,172,261,172,261,171,260,170,260,169,257,166,257,165,256,165,256,164,255,164,255,162,254,161 253,161,253,159,252,158,251,158,251,157,250,155,249,155,249,153,248,152,247,152,247,148,246,147,245,147,245,130,244,129,243,127,243,112,244,111,244,109,245,109 245,101 e|********* m268,87 l275,87,275,86,276,85,286,85 e|********* m279,86 l278,87,278,88,277,89,276,91,276,92,274,94,273,94,273,95,272,96,271,98,269,100 e|********* m276,92 l284,92,285,93,285,97,281,101,280,101,279,102,279,103,278,103 e|********* m317,122 l317,130,315,132,315,138 e|********* m306,122 l306,134,308,136,308,137,309,137,309,136,310,135,310,125,309,124,308,124,308,122,307,121,306,121 e|********* m296,118 l296,132,297,132,297,135 e|********* m297,116 l299,116,301,118,301,131,302,132,302,133,303,134 e|********* m295,116 l295,117,290,122,290,128,291,129,291,132 e|********* m320,131 l312,131,311,130,309,129,307,129,307,128,306,127,304,127,302,126,301,125,285,125,285,128,287,130 e|********* m287,162 l288,161,288,155,287,155,286,154,286,151,283,148,282,148,279,145,279,144 e|********* m284,141 l284,149,282,151,282,152,281,152,281,162 e|********* m274,156 l291,156 e|********* m273,149 l272,149,271,148,271,147,270,147,270,146,268,146,267,147,267,158,272,158,273,157,273,148 e|********* m249,110 l249,112 e|********* m243,126 l246,126 e|********* m247,121 l247,132,248,133,248,134,249,134 e|********* m247,124 l248,124 e|********* m247,131 l248,131,248,130,250,128 e|********* m250,112 l250,115,251,116,251,120,252,121,252,141 e|********* m255,123 l255,126,253,128,253,129,254,130,257,130,258,129,258,124,257,123,253,123 e|********* m253,123 l254,123,254,128 e|********* m257,135 l260,135 e|********* m258,131 l262,131,263,130,263,129,264,129,266,127,266,121,265,120,264,120,264,119,263,119,263,118,262,118,260,116,258,116 e|********* m260,125 l262,125 e|********* m254,111 l255,111,255,110,258,110 e|********1.5; m256,78 l253,78,252,79,248,79,247,80,245,80,243,82,241,83,240,83,238,85,236,86,235,86,233,87,232,88,231,88,224,95,224,97,223,97,222,98,222,104,220,106 220,133,221,135,221,139,223,141,223,143,225,145,225,147,226,148,226,151,228,153,228,155,229,155,229,158,230,158,230,159,231,160,232,160,233,161,234,161,235,162 237,162,237,163,246,163 e|********* m226,91 l224,90,224,89,221,89,220,90,218,90,216,92,215,92,214,94,213,95,212,97,212,98,208,102,207,104,207,105,206,106,205,108,205,109,204,110,203,112,203,126 204,127,204,130,206,132,206,134,208,136,208,138,209,139,210,141,211,141,213,143,213,144,215,144,215,145,216,145,217,146,223,146 e|********* m206,99 l202,99,201,100,200,100,199,102,198,103,198,104,197,105,197,107,195,109,195,118,196,119,196,120,197,121,198,123,198,124,200,126,201,126,201,127,202,127 e|********* m194,103 l192,103,192,104,191,104,190,105,190,108,189,110,188,110,188,116,189,116,189,117,194,122,196,122 e|********0.75; m250,85 l245,85,243,86,242,88,239,91,238,91,238,92,237,92,237,93,235,95,234,95,234,97,232,97,232,99,231,99,231,100,230,100,230,101,228,103,228,105,227,105 227,140,229,142,229,147,230,147,230,148,231,149,231,150,232,150,233,151,233,152,234,152,234,153,236,155,237,155,239,157,242,157,243,158 e|********* m224,93 l221,93,220,94,219,94,219,95,218,95,218,96,214,100,214,101,213,101,212,102,212,103,208,107,208,109,206,111,206,126,207,126,207,127,208,129,210,131,210,133 211,133,211,135,212,135,212,136,213,136,214,137,216,137,217,138,218,138 e|********* m204,102 l203,102,202,103,202,105,201,105,199,107,199,108,198,109,198,116,199,117,200,117,200,118,201,119 e|********* m193,106 l193,112 e|********* m220,109 l219,110,218,110,218,111,217,111,217,112,216,112,215,113,215,118,216,119,216,120,217,121,217,122,218,123,218,124 e|********1.5; m264,72 l263,73,260,73,259,74,258,74,258,75,257,76,256,76,255,77,254,77,254,78,253,78,253,79,252,79,248,83,248,84,247,84,247,85,246,85,245,86,245,87 243,89,243,90,241,92,241,97,240,98,239,100,239,101,238,102,237,102,237,104,236,104,235,105,235,118,234,119,233,119,233,129,234,129,234,131,235,132,235,133 236,134,236,136,237,137,237,149,238,150,238,151,239,152,239,154,240,155,240,157,241,157,241,160,242,161,242,162,243,163,243,165,244,166,244,167,245,167,245,168 246,169,246,170,248,172,249,172,249,173,250,173,250,174,251,175,252,175,253,176,254,176,256,178,257,178,257,179,258,179,259,180,259,181,271,181 e[/whitepad]