140GH2F3D10KJMT以太網(wǎng)模塊
工業(yè)電路板維修技巧
不能過分依賴在線測試儀
1.功能測試不能代替參數(shù)測試
2. 功能測試僅能測試到器件的截止區(qū)，放大區(qū)和飽和區(qū)，但無法了解此時(shí)的工作頻率的高低和速度的快慢。
3. 對數(shù)字芯片而言，僅知道有高低電平的輸出變化，但無法查出它的上升和下降沿的變化速度。
4. 對于模擬芯片，它處理的是模擬的變化量。其受電路的元器件的分布，解決信號方案的不同的影響，是錯(cuò)綜復(fù)雜的。就目前的在線測試技術(shù)，要解決模擬芯片在線測試是不可能的。所以，這項(xiàng)功能測試的結(jié)果，僅能供參考。
5. 大多數(shù)的在線測試議，在對于電路板上的各類芯片進(jìn)行功能測試后，均會給出“測試通過”或“測試不通過”。那么它為什么不給出被測器件是否有問題呢？這就是這類測試儀的缺撼。因?yàn)樵诰€測試時(shí)，所受影響（干擾）的因素太多。要求在測試前采取不少的措施（如斷開晶振，去掉CPU和帶程序的芯片，加隔離中斷信號等等），這樣做是否均有效，值得研究。至少，目前的測試結(jié)果有時(shí)不盡人意。
6. 了解在線測試儀的讀者，均知道有這么一句行話。“在線測試時(shí)不通過的芯片不一定是損壞的；測試通過的芯片一定是沒有損壞的。”它的解釋為，如器件受在線影響或抗干擾時(shí)，結(jié)果可能不通過，對此不難理解。那么，是否損壞的芯片在進(jìn)行測試時(shí)，均會得出“不通過”呢？回答確實(shí)不能肯定。筆者與同行均遇到過，明明芯片已損壞了（確切地說換上這個(gè)芯片板子就不工作了），但測試結(jié)果是通過的。權(quán)威解釋為這是測試儀自身工作原理（后驅(qū)動技術(shù)）所致。故此我們不能過分依賴在線測試儀（盡管各廠家宣傳的很玄）的作用，否則將使維修電路板的工作誤入歧途。
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140GH2F3D10KJMT以太網(wǎng)模塊
