[vic0239]

Thanks everyone for the very useful input.

I've attached a better photo of the back of the clock which I think is quite different to UB's and more in line with what Nick was suggesting and what I've experienced in the past working with other clocks.

Returning to my original issue, I wonder if a dab of switch cleaner or isopropyl alcohol in the area of the pin rings might help? It might just be dirt in that mechanism causing intermittent contact. The clock was quite dusty.