１故障现象与主机联机不打印，脱机自检正常。２故障分析初步诊断为接口电路故障，故障原因可能是操作人员带电插拨接口连接器所致。３查接口信号①各引线的信号标准如表１；②检测结果，绝大多数信号都符合标准，唯独引线５为０．７３ｖ、即数据４为低电平。③看数据输入电路 1 failure phenomenon does not print online with the host, off-line self-test normal. 2 Fault Analysis The initial diagnosis of the interface circuit failure, the cause of the malfunction may be due to the operator plug-in interface connector. 3 check the interface signal ① The signal standard of each lead is as shown in Table 1; ② The test result, the vast majority of signals are in line with the standard, except that the lead 5 is 0.73v, that is, the data 4 is low. ③ look at the data input circuit