Retrofitting of an industrial robot consists on verifying the usability conditions of each component of the robot, replacing obsolete ones, especially electronics and control. This work describes the replacement of the analog sensors (resolvers and tachometers) of a retrofitted ASEA IRB6 robot by digital sensors (incremental optical encoders). The advantages of such replacements are assessed through the use of tachometers and encoders for speed feedback. The control architecture based on a CAN-bus is also presented.