I recently bought a Mamiya ZE Quartz with a Mamiya-Sekor E f/1.7 50mm lens that I recently found at an antique store. It's either been abused or been used a lot, but it's seen better days.
For some reason when I take the lens off and I look through it, its aperture is closed to f/16 even when I move the dial to f/1.7. It also only shoots in f/16 when it's attached to the camera. I read somewhere that the aperture is adjusted electronically because of the metal contacts on the body and on the lens but I'm not really sure since I've never shot with a Mamiya and I haven't tried it with batteries yet.