1.选用电阻比对法确诊电源负载短路缺点
缺点实例:FANUC一BESK伺服驱动板十15V负载软击穿烧保险丝。
咱们修理时,经过开始查看断定缺点因素是负载部分短路,而且用数字表测得十15V对“地”电阻,正常板为1.3KΩ 缺点板为300Ω。因为通电好烧保险丝,底子无法通电查看,所以只能做电阻丈量或拆元件查看。
可是,因为该伺服板的十15V电源与其负载(24只集成元件)的印刷电路成放射型构造,所以,电阻丈量时无法做电路切开别离,而且因为元件多且为直接焊装,也不也许逐个拆开查看。修理的实际操作好不容易,即便缺点解决了,也一般弄得电路板伤痕累累。处理这种既不能做电路切开别离或元件拆开也无法通电查看的缺点,咱们选用电阻比对法查看很便利。确诊查看时,不切开电路也不焊脱元件,而是直接丈量十15V端与各集成元件的有关管脚问的电阻值,同时将缺点板与正常板做对应值对比,即可查出缺点。处理以上缺点时,考虑到元件管脚多,所以首要剖析厚膜块内部电路(图中已标出)和集成块管脚功用图,然后从中筛选出若干首要的测试点,做电阻丈量。当丈量到Q7时,发现其3脚( + 15V)对14脚(输出)电阻为150Ω(正常为6KΩ ,怀疑Q7(LM339)有疑问,替换Q7后,伺服板康复正常,阐明Q7管脚间阻值反常系内部软击穿,从而致使电源短路。
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