The beacon drains all electrical power from any technology on the planet, which is why the Doctor, the humans, and the Daleks are stranded there. Yet the Doctor's sonic screwdriver works just fine when he needs it to.
The doctor is disturbed by the Daleks and 'bacteria' before he can replace the boards he has modified. Yet when the doctor and Bellal are retreating through the maze they meet a malfunctioning door and the Doctor determines his meddling is working.