Dismantled conveyor unit. Couldn't figure out why the belt was slipping. The tension was fine, and adjusting it made no difference. Dismantling the thing revealed that some swine person had managed to stick a piece of chalk into the mechanism (that would've taken a bit of effort on behalf of the idiot perpetrator), which had been crushed at the rollers, and was spread about inside, making everything slippy, rather than grippy.

Extra - some of the little darlings other handy work. It's not difficult putting rubbish in the bins. Roof and gutters could do with some attention here, as could all the others with various vegetation starting to take hold in strange places elsewhere.