Balanve wheel doesn't move

[BlueHarp]

Hi,
I got a FB 80 movement (F for Förster), which balance wheel doesn't want to move. The wheel train moves freely, the pallet fork swings easily, and the balance wheel moves the pallet fork when I make it rotate. I feel that the balance wheel "wants" to move, but something is wrong and I can't determine what.

https://1drv.ms/i/s!AmSEWqSryKqAlGuMl-Ld9xZZ9ouf?e=KzDl4e

Edited June 13, 2023 by BlueHarp

[nickelsilver]

It could literally be a dozen things (as a start). Take out the fork and put the balance back in and see if it's free. If it is, then there's an issue between the balance and fork. If not, it could be a bent pivot, contamination in the jewels, a piece of dust clamped under a bridge reaching over acting as a brake. Your hairspring looks OK in the pic, but if it's out of flat it can touch the balance arms stopping it from moving.

[BlueHarp]

That's it : the hairspring is out of flat and it touches the balance arms !