I bet your revolving adapter is missing the pin that drives the mechanism, it sticks out quite a bit and is prone to breaking off when you are a bit careless with the revolving adapter when it's taken off to use a polaroid back. Attached is a picture of the pin, have a look if it's there. It is supposed to go in a hole that is in the middle on the right side of the camera when viewed from the back. You can use a piece of wire to test the mechanism if the pin is indeed missing. Don't touch the red bars to do that, they are very fragile. Mine broke off once (6 months ago) and I received a new one from Mamiya for less than 15 bucks including postage.