I think that the Main Body PCB does not deliver the voltage if it does not detect a load - e.g. when a crevasse tool is connected. I found that when I used the mini-brush (also motorised) it started to spin. This meant that the main unit was okay and the fault was with the brush head.
I dismantled the brush head and found that one of the wires connecting to the motor, through the articulated joint had broken. There was enough play in the wire to allow me to solder the broken wire back together. I'm not sure how long this will last though as the wire moves around when the head rotates. I guess at some point I will have to replace the whole wire.
I have also had the problem whereby the dust accumulates at the contacts from the main unit to the dust canister. A pair of tweezers and some rubbing (isopropyl) alcohol soon sorted that.