If you look at the second photo on this eBay listing you will see F1 to F4 marked on the PCB attached to the transformer. The fuses will be on the other side – probably the small back circular type.
https://www.ebay.co.uk/itm/255201530108
(EDIT: There’s an F5 as well closer to the edge of the PCB)
(EDIT2: There’s a better photo here in a Beoparts listing: https://beoparts.com/category/beosound/beosound-ouverture/#jp-carousel-8289)
