Doesn't look like the spring is working..?

Spring snapped? 👿

Take it bits or LBS and order one.

There be another one just behind to compare it too. It be looking like there be no spring left attached or it be snapped. Best you be finding some buried treasure to fund a new one.

I thought it was the spring gone.
I was looking behind, but since this one is XTR on rapid shifters, and the one behind is on a road bike, I was wondering if it could be different.

Cheers, I'm off to scour my tool box, or a trip to the LBS tomorrow (not holding breath for parts though, they don't carry them here in China)

That happend to the girlfriends mech the spring hadn't snapped just popped inside, I took it apart put it back together and it's still working. There's a small allen key grub screw that you have to undo to get the jockey wheel cage off.

Might not be the spring it might be a small bit of metal on the back that stops the derailleur spinning round. I had this problem with the same derailleur, snapped my chain and couldnt work how to thread the chain back through as the derraileur gave no tension. If you unbolt the derailleur from the frame, flip it over then try and rotate the cage through 360 you should see where the metal stop has been damaged.
I managed to bodge two old ones to make a half decent good one, otherwise its 'kerching' time at LBS

yeah, some how, I've managed to round off the metal stop. I've botched together something, shall see how it'll hold off, otherwise it'll be a long & slow walk to the LBS

[edit, actually, I'd just ride my cross bike there, but not looking forward to spending [s]that amount of[/s] money]