我们现场一个S7-400H 硬冗余PLC控制系统，最近有异常报警。
刚开始
master PLC 外部故障报警 总线故障报警 冗余错误报警 处于RUN状态
standby PLC 外部故障报警 总线故障报警 冗余错误报警 以太网模块报警 处于STOP状态
A从站有一块AO模块报警,有一个IM153-2模块报SF灯
B从站有一个IM153-2模块报SF灯常亮

经过诊断
1、更换了standby PLC侧的故障以太网模块之后，也重新定义了这块以太网模块地址，物理地址和IP地址跟之前的以太网地址一样。以太网模块恢复正常，
2、更换了A从站的AO模块，重新拔插了AO模块底座，A从站恢复正常
3、将standby PLC上电，RUN，等待几分钟之后，standby PLC恢复RUN状态。

具体情况如下：
standby PLC左侧：报警灯为BUS2F和REDF
Master PLC右侧：报警灯为REDF 运行侧
B分站左侧IM153-2模块报警灯为SF常亮
整个系统正常运行，全部分站IO模块都在正常通讯状态下。

问题如下：
1、 B分站SF灯常亮可能是什么故障呢？IM153-2模块或者底座有问题？
2、 standby PLC左侧：报警灯为BUS2F，是否消除了问题1就可消除
3、 PLC冗余故障，是否是因为问题2导致的，还是说冗余模块有问题？

诊断信息如下：
Event 1 of 120: Event ID 16# 7303
H system (1 out of 2) has gone into redundant mode
Occurred in: Master CPU in rack 1
Startup information:
- Startup without modified system configuration
Update time in ms: 97
Requested OB: CPU redundancy error OB (OB72)
Priority class: 28
Incoming event
12:15:08.787 PM 01/25/2013


Event 2 of 120: Event ID 16# 43E2
Change from update mode to operating mode RUN (redundant mode)
Previous operating mode: UPDATE
Requested operating mode: RUN (redundant mode)
Event occurred in the master CPU in rack 1
Incoming event
12:15:08.749 PM 01/25/2013


Event 3 of 120: Event ID 16# 43E9
Standby CPU: Change from startup mode to update mode
Previous operating mode: STARTUP (warm restart)
Requested operating mode: UPDATE
Event occurred in the standby CPU in rack 0
Incoming event
12:15:08.397 PM 01/25/2013


Event 4 of 120: Event ID 16# 43E1
Change from link-up mode to update mode
Previous operating mode: LINK-UP
Requested operating mode: UPDATE
Event occurred in the master CPU in rack 1
Incoming event
12:15:08.397 PM 01/25/2013


Event 5 of 120: Event ID 16# 43E8
Standby CPU: Change from link-up mode to startup mode
STOP due to: STOP caused by stop switch being activated
Startup information:
- Time for time stamp at the last non backed up power on
- Single processor operation
Current/last startup type:
- Warm restart triggered by switch setting
Permissibility of certain startup types:
- Manual warm restart permitted
Last valid operation or setting of the automatic startup type at power on:
- Warm restart triggered by switch setting
Previous operating mode: LINK-UP
Requested operating mode: STARTUP (warm restart)
Event occurred in the standby CPU in rack 0
Incoming event
12:15:07.876 PM 01/25/2013

谢谢。