Hi,
I have one of those and they are so simple that it is strange that you have problems with winding.
I only had problems with winding when I used a "modified" 120 spool (cutted the edges of). A modified
120 spool won't work on these cameras, and after the second shot the camera won't wind easily and
you are then forcing the simple mecanism. Get a real 620 spool and respool 120 film, then it works
smoothly.
Another problem I had was that the lens was quite foggy, and it needed a serious cleaning. That was
an easy repair also, as the three element lens is easy to unscrew. The bellows of my camera were
perfect also, no holes, no light leaking. The results you can get with this simple camera are amazing,
as you all know, cameras don't matter.
Regards,
César.