most likely cause is that it's already cocked. you might want to check whether it's cocked or released before going after the wind mechanism. i don't have any notes on this model, sorry ...
I would suggest that the second curtain didn't complete it's run.
Pretty common on this model. Try moving the shutter curtain gently a millimeter or two toward the rewind side of the camera. This model can complete the exposure, drop the mirror back down, but not release the wind lock. Releasing the wind lock is the end of the cycle on this model.
