R2B0N7N3N3A0A冗余模塊
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,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?!彼慕忉尀?,如器件受在線影響或抗干擾時,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,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。
R2B0N7N3N3A0A冗余模塊
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