Autofocus can no longer be repaired
If you have a question regarding a Contax N-mount 17-35, 24-80 or 70-300 lens with an autofocus malfunction, the diagnostic procedure is to see if aperture works and can be controlled from the camera body, for example by testing the depth-of-field preview button. If it does, the diagnosis is a failed autofocus motor. Please be advised that the aperture stepper motor and the focus ultrasonic motor derive power from the same pin on the Contax N mount electrical interface. If one of them works, it means the power supply is fine and the electronic interface is fine. So the other must be a failed motor. Contax is the only one who is able to fix a failed autofocus motor because no one else is able to procure the spare part. They ceased operation in 2015, however, and that means failed autofocus motors are unrepairable, unfortunately.