故障现象：开机，功能选择开关无论在任何位置，热笔均不热，并且调节笔温电位器，热笔也不热。分析检修：测热笔电阻呈开路状态，说明热笔内加热丝烧断，换新热笔，通电。功能选择开关在准备位时，没有多长时间热笔发红，且笔温电位器不受调。立刻关机。笔温加热电路，其工作 Symptoms: Power on, function selection switch No matter what the position, the heat pen is not hot, and adjust the pen temperature potentiometer, heat pen is not hot. Analytical overhaul: The thermal pen resistance is in an open state, which indicates that the heating wire is blown in the hot pen, the new hot pen is used, and the power is turned on. When the function selection switch is in the preparation position, it does not take much time for the heat pen to turn red, and the pen temperature potentiometer is not adjusted. Shut down immediately. Pen temperature heating circuit, its work