You may not want to do this but the repair manual for the RB's is online. I downloaded mine and if you just enter in Mamiya Rb67 repair manual in a search engine, you will find it. Not the easiest to understand, and if you want to see if you can fix it yourself, give it a try. It could be something as simple as a screw that came loose and got jammed in the works somewhere. I would also try tipping it upside down and lightly tapping it to see if you can shake something lose. Otherwise, I think we are talking a pro repair shop. Best of luck with it. Ric.