Hi, I just received a Canonet QL17 G-III in very nice cosmetic condition, but I bought it "untested", and the shutter doesn't seem to want to fire. I can cock it, I think, with the film advance lever, but pressing the shutter button does not cause anything to happen. I'm hoping there's a step I'm missing or a switch that needs to be set (although I don't see any). Anyone know what the magic solution might be? Thanks!