故障现象：仪器能调零，也能校正，但定位时，随着定位旋钮的转动，指针也随之偏转，可是指针总是达不到预定位置时，定位旋钮就已经旋到底不能转动。故障分析与检修：由于此仪器的调零电路和定位电路共用一组稳压电源（电路如图所示），所以根据以上故障现象，初步判断有三种 Symptom: The instrument can be zeroed and can be calibrated. However, when the positioning knob is rotated, the pointer is also deflected. However, when the pointer does not reach the predetermined position, the positioning knob has been rotated to the end and cannot be rotated. Failure analysis and maintenance: Since the zeroing circuit and positioning circuit of this instrument share a set of regulated power supply (the circuit is shown in the figure), according to the above fault phenomena, there are three preliminary judgments.