Bronica GS-1 backs

A few months ago I bought a Bronica GS-1 with a 120 and 220 back. The 220 back works fine, but the 120 did not. When I tried to load film into it, it would advance through the entire roll, never stopping and setting the shutter ready for exposure. I would put the back on the camera, and the film advance lever would wind the film all the way through the roll without ever stopping for exposure.

I just bought an "excellent" 120 back from KEH, and it has the exact same problem. It advances the film all the way, wasting the roll, without allowing for any exposures. Again, I've never had a problem with the 220 back.

Does anyone know of a solution to this problem? Is this common? I'm getting fed up with this, especially since 220 film is extremely limited in selection, and I don't see it hanging on much longer. I'd hate for this camera to become worthless because no working 120 backs can be found.

Thanks for any advice.

I have a GS-1 with two 120 backs and I've never had that problem. Without knowing more about your situation, I wonder if trying a different camera body would help isolate the problem.

Check the back/camera interface to see if anything is visibly different between your working 120 and 220 backs, that's how I managed to fix a frame spacing issue on one of my M645 Super backs (Sticky pin was binding, quick bend fixed it). IIRC the shells are common between 120/220 in each variety of G back so you might try the inserts in the shell from the 220 and vice versa to determine if you have a shell issue, an insert issue or a body issue.

Well, I gave up on trying to diagnose the problem and instead tried a 120 roll in the functional 220 back. It works ok. No focus problems that I can see on a roll of transparencies. Now I'm hoping for a refund from KEH for the bad 120 back. Thanks for your help.