Maurice,
I am very pleased you managed to get your Beovision 3 back working.
At about the time of the introduction of the AVANT B&O concluded that repairing to component level outside a B&O workshop could not really continue mainly because of complexity of the product, so they introduced "Module Swap Kits" where a module and even a chassis would be swapped and sent back to B&O for upgrade and repair by the dealer or B&O service agent.
From that time, circuit diagrams in the service manuals were really limited to wiring or connection diagrams which frustrated those electronics educated people like you and me who had no problems fixing most electronic products to component level.
Clearly, cost also played its part and today a lot of electronic products/component part are thrown away rather than being fixed nearly always because it cheaper, but maybe in the future more people will go back to repairing products now we have finally started to move into recycling.