Very unlettered German
As Hans-Henning suggested, it can mean that the control processor can be completely exchanged during maintezncance. However, since the author has muddled his German syntax rather badly, another possible meaning is:
"The control processor can be exchanged during operations". This proceeds from the assumption that the author used "Im Service" in the english sense of "in service", i.e. while in operation.
Hopefulkly your context will give you a clue which explanation is more likely.