After some more troubleshooting I found the problem. The lever from the wind solenoid was gummed up. It’s supposed to return by spring force but didn’t.
I removed it, cleaned the shaft and added a drop of oil. After reassembly, the tape transport works as it should.
I must say, this Beocord is the most service-friendly tape recorder I have come across. The service manual leaves something to be desired, though.
In the first picture, my assistant points to the lever in question.
In the second picture, you see the entire lever. It’s the one on top of the gear. (wind solenoid removed)
