I've just received a long awaited winder for my 503CW body. Together with the 50c back this makes an awesome machine... except the back only fires about 2 times out of 3 when using the winder! This is most bizarre. The tab mechanism that fires the exposure moves in the exact same way as far as the eye can tell: same speed, same distance. And in manual mode without the winder, I cannot reproduce this behaviour, the back always fires.
Has anyone come across these symptoms before? Is there a cure?