This paper introduces control tests on a feed positioning system for a large radio telescope. The system is an integration of three subsystems, including a cable trolley subsystem, with a two-degrees-of-freedom orienting mechanism mounted on the trolley, which points a Gough-Stewart mechanism, the third subsystem. The first two subsystems provide a coarse control of the motion of the upper platform of the Gough-Stewart mechanism, while the Gough-Stewart mechanism gives a finer control of the feed-mounted lower platform by actively isolating the vibrations from the upper platform. Standard proportional-integral-derivative controllers with direct terminal feedback from the optical sensors are employed to control the system. Delay-induced dynamic instabilities encountered in the experiments are addressed. A simple error analysis on control with flexible cable is carried to validate the control of the cable-drive architecture. Tests are carried out on a field model of dimension 50 m×50 m×12 m. Typical experiments manifest remarkable positioning ability of the proposed system.