If you open the clock in the back, you will see a thin wire that starts at the bellows and goes up to the cuckoo. This wire should move the cuckoo up and down while it calls. It is not connected with the cuckoo, but usually ends under the cuckoo’s tail (see picture).

During shipping, this wire may slip above the cuckoo. If this is the case, it may block the cuckoo and the door.

To fix this, you can simply turn the wire around the cuckoo carefully, so it is under the cuckoo’s tail again. This should be quite easy if you open the cuckoo’s door (the cuckoo will move forward when the door is opened).