I'm always dropping handhelds - this time was terminal. Luckily a spare unit was to hand. The switch for the feedback on/off had shattered cutting all the power so logically it was an easy fix. It sat on the back of the bench for quite a while, but with the first show of the season looming I thought it best to take a deep breath and get on with it.
The switch is one of the standard small DPDT sliders which I keep in stock for 9mm point control.
The wires were unsoldered from the smashed switch and cleaned up as best that I could - not easy with less than 25mm to play with. A new switch had the poles tinned and I set about very carefully re-soldering the wires with the whole unit clamped gently in the bench vice. When all were attached I plugged the unit into the back of a Gaugemaster cased controller and it worked first time.