Greetings to all. New member here, with what I hope is a stupid question.

I just bought a Sinar Pan Tilt head from B&H Photo as an early foray into LF photography. I know they are elusive, so I struck while the iron was hot.

It arrived yesterday, and seems to be in very good condition. It pans just as I would expect. I am, however, unable to get it to tilt. It seems to be stuck at horizontal, even after I loosen the collar locking screw.

Am I missing a necessary step or action?

Any wisdom gratefully received. I look forward to participating in less niggling topics in the future!