Stephan, ( Ich werde auf Englisch antworten, damit jeder es lesen und/oder kommentieren kann.)
You are a silver member, so you can view the data of the bolab 4 yourself via products>beolab>beolab4.
I don’t think you will find somewhere else a specific repair to the applier PCB nor the specific electronic diagram.
The power amplifier is just an IC with some components added, with some knowledge of the matter it is not that difficult to repair, otherwise find someone who can or buy a new output stage print from B&O.
What is broken that you want to repair. ?
.
.