Siemens S5-135U/155U System Manual page 234

CPUs, Memory Cards, Memory Submodules, Interface Submodules
Removal
Remove your interface submodule in the following steps:
Step
Note
Since the interface module is secured to the CPU with screws, interference
pulses are given a path to ground via the shield of the CPU.
5-94
Action
1 Switch off the power supply of your PLC.
2 Remove the CPU from the central controller.
3 Slacken the two locking screws of the submodule and pull it out
of the receptacle.
4 Fit another submodule (as already described) or close the
receptacle with its cover. Use the fixing screws of the submodule.
5 Insert the CPU in the central controller.
6 Switch the power supply of your PLC on again.
System Manual
C79000-G8576-C199-06