伟大领袖毛主席教导说: “对于物质的每一种运动形式,必须注意它和其他各种运动形式的共同点。但是,尤其重要的,成为我们认识事物的基础的东西,则是必须注意它的特殊点,就是说,注意它和其他运动形式的质的区别。”SBR-4型包裹收寄机,和其它由继电器电路构成的设备一样,机内电路都是直流电路。完成一直流电的回路,继电器就吸动;出了故障,可用万用电表沿回路逐段查找。但是, Chairman Mao, the great leader, taught that: “For every form of movement in matter, attention must be paid to its commonalities with other forms of movement, but it is of particular importance that what becomes the basis for our understanding of things must be noted Its special point, that is, to pay attention to the qualitative difference between it and other forms of movement. ”SBR-4 parcel send and receive devices, and other devices composed of the relay circuit, the circuit is the DC circuit. Completion of the circuit has been flowing, the relay on the suction; out of trouble, the multimeter can be used along the loop to find paragraph. but,