According to this thread there is a little switch that possibly has dirty contacts: https://archivedforum2.beoworld.co.uk/forums/p/45201/326714.aspx#326714
The photos are missing, but the video in the last post still works. I think that you can just about make out the switch between the large white cog and the metal plate about 1:20 mins into the video.
EDIT: Here’s a direct link to the video:
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