This paper considers output based tracking control for an experimental underactuated H-drive manipulator. This manipulator can be transformed into a so-called second-order chained form by a coordinate- and feedback transformation. An observer is proposed to solve the output feedback problem for systems in second-order chained form. For the designed observer global stability of the closed loop system is proved. Due to friction in the unactuated rotational joint the closed loop system is no longer asymptotically stable, but with a heuristic modification of the observer both the tracking and observer errors are bounded. Experimental results show the validity of this approach.