Firstly, excuse what will be a simple question to some of you but I've only just ventured into the realms of 6x6 from 645 so my knowledge here is limited.
I have a 501CM with two fairly recent A12 backs - I know the way these work and so far have no problems. I have, however, just bought an old A12 back off ebay - The back has a round winder - no handle and a magnetic flip out disc with an ASA id disc on it - where you would normally put a part of a film box to tell you what film is in it. ser no. TH61663
Visually everything looks fine and all the mechanisms work. My question is, how do you get the film to wind on the correct amount so that it stops and the number 1 appears? If I don't turn the winder anti-clockwise to drop the number 1 into the window the winder just carries on - turning the winder anti-clockwise drops the number 1 in at any time so the film will be out of sync.