VX2 wont start

Hello, we are a Institute from the RWTH Aachen. 

We have 4 VX2's. 

We want to start with one. And change the Batteries against litium cells. The old PB ones were completely dead. 

I wanted to test the rest of the electronics. So I hooked up a PSU to the scooter with 52V and 10 Amps. Lights works. But the Speedo does not turn on properly. In the first line are only black boxes. 

1. switched they key on

2. swtiched the kill switch on. 

3. pulled the right brake. 

nothing happens. 

I read the sevcon over CAN. The throttle signal arrives there but the motor wont spin. The gree LED isn't blinking. 

Is there something more I can try?