Our scale was not very expensive, we have had it for over a decade, and we could probably replace it at very small expense. But that is not the point, is it.
We decided to have a look inside, in case it was something simple and obvious. As with all these things, the hardest part was trying to figure out the magic sequence for getting the top / bottom off so you can look inside.
And we once again have a working kitchen scale – and saved ourselves a couple of quid into the bargain.