I had a same problem, mechanism-wheel on the lens, that choosing different exposure settings, skip one toot, and because that wheel with different exposures inside lens was out of alignment and didn't let enough light to hit film. Simple fix, just dial exposure gear all a way up inside camera. Its black plastic cylindric gear on lens mechanism and choosing wheel on outside of camera all way on first position when closing camera. Basically camera needed simple recalibration. 15 minutes fix. Be careful when you working with open camera, there is condenser that running flash, it hit me, give me little shake on finger :) nothing major and dangerous, just unexpected.