一台NBC-200型半自动CO_2弧焊机,采用6只平板型ZP200A硅整流二极管组成的三相桥式整流电路。在一次故障中,有两只二极管损坏,维修时拆开风冷散热器,将损坏的二极管取出,换上与损坏二极管型号规格相同的新的二极管,修理后,焊机只能在中小电流档工作,一切换到大电流档工作,新换的二极管即损坏。此种现象多次重复发生,类似现象还发生在其它几台焊机上。究竟是什么原因导致二极管 A NBC-200 semi-automatic CO_2 arc welding machine, using six flat-type ZP200A silicon rectifier diodes composed of three-phase bridge rectifier circuit. In a fault, there are two diodes damaged, the maintenance of the air-cooled radiator removed, remove the damaged diode, replace the same with the damaged diode model of the new diode, repair, welding only in small and medium current file Work, all switched to the work of large current file, the new diode is damaged. This phenomenon repeated many times, a similar phenomenon also occurred in several other welding machine. What exactly led to the diode