Atik One 6.0 filter wheel out of position

[solo05]

Hi

I have just managed to buy a second hand One 6.0 and was carrying out tests to make sure all is well with the unit.

Cooling, camera and hub all fine.  Then I tried the filter wheel.  It moves round but sometimes it leaves the hole half across the sensor, on the next move it then moves to a correct position although not the one I have chosen. It is as if the mechanical index is out of sync.  Is this even possible ?  Could the previous owner have put it back incorrectly when removing his filters ready for sale.  There is little information to be found about how this thing is meant to be put back together.

I would ask the previous owner but it came from Germany 

Any help would be appreciated.

Thanks
Steve