Dear Friends,

My cuckoo clock, an Azura, has a cuckoo that sings if I move the hands backwards, or if I pull the little string which allows me to advance the hours the cuckoo sings. But if I move the hands forwards there is just a "Thunk", and the cuckoo only opens the door a tiny crack.

You can see the mechanism in this video, where I advance the hands clockwise, then anti-clockwise:

How can I repair it?

Thanks for your time! (and expertise)