故障现象：屏幕扫描垂直方向缺少回波（指部分扫描线无反射波或反射很弱），且图象整体表现灵敏度低。根据故障现象故怀疑可能①发射电路工作不正常，或某些发射电路甚至不工作。②＋125V电源电路故障。③超声探头不良。故采用孤立方法进行判断。①根据扫描回波缺少且灵敏度低 Symptoms: The lack of echoes in the vertical direction of the screen scan (reflecting that some of the scan lines have no reflected waves or weak reflections), and the overall image display sensitivity is low. According to the failure phenomenon, it may be suspected that 1 transmitting circuit is not working properly, or some transmitting circuits do not even work. The 2+125V power supply circuit has failed. 3 Defective ultrasound probe. Therefore, an isolated method is used for judgment. 1 Absence of scan echo and low sensitivity