Hi Simon,
I apologize for the delay. I'm working (hard )on other project. I just got through the forum today.
To begin, you must dismantle the whole gimbal. Then check all the parts and make sure there are no problems with the wires.
If you have everything ok, the problem may be on the motherboard. In my case, the problem was a burned motor controller. But attention, the replacement of each electronic component, is not easy. You will need good repair equipment.
Thanks