故障现象开机后,描笔向下单偏,将基线调节电位器顺时针调到头或将增益电位器逆时针调到头时,描笔可勉强回到中心位置,当描笔在中心位置时,定标基本正常,机器在封闭状态(ＲＥＳＥＴ)时,描笔调节正常。分析与故障排除　心电图机在封闭状态下前级信号对地短路,ＩＣ309输入为0电平, Symptom After power on, when the pen is down to single bias, when the base potentiometer is turned clockwise or the gain potentiometer is turned counterclockwise, the pen can barely return to the center position. When the pen is in the center position, The standard is basically normal. When the machine is in the closed state (RESET), the pen adjustment is normal. Analysis and troubleshooting ECG machine in the closed state before the signal short-circuit to the ground, IC309 input is 0 level,