故障现象一：机器处于封闭状态，无定标，无心电波形，其他功能正常。分析检修：观察封闭指示灯亮，正常时应处于熄灭状态，从现象分析，故障出在封闭控制电路。首先测该部分电路中INST控制信号为低电平，正常工作状态下应为高电平，而此电平是由IC215C非门6脚出的，它受控于前 Symptom 1: The machine is in a closed state, no calibration, no ECG waveform, and other functions are normal. Analytical overhaul: Observe that the closed indicator light is on. Normally it should be in the extinguished state. From the phenomenon analysis, the fault is in the closed control circuit. First of all, the INST control signal in this part of the circuit is measured to be low level, which should be high level under normal operating conditions. This level is controlled by the IC215C NOT gate 6 foot.