A study described machine operators' problem-solving actions at a computerized circuit-board assembly machine in a small manufacturing plant located on the West Coast. Participants were a machine operator and his supervisor, both from Vietnam, who were building large prototype boards for a major computer corporation. Over a 6.5 minute interval, the workers confronted two problems with the assembly. First, the robotic arm was unable to pick a component from the feeder; and, second, the component was larger than the place assigned to it on the board. The workers solved the first problem by adapting machine parts so that the arm would place the component correctly and the second by recommending a change in the customer's design plans. For each problem they followed this procedure: notice the problem, hypothesize the source, test the hypothesis, and look for an optimal solution. Fine-grained analysis of the workers' actions on the machine showed they applied perceptual and representational competence during the problem-solving process. This second level of analysis of the workers' collaborative actions on the machine showed that they drew on well-honed perceptions--auditory, visual, and kinesthetic--to discover the trouble and find its source. Throughout the troubleshooting, the workers referred to various kinds of inscriptions; work with numerical inscriptions pervaded the activity. Worker perceptions and representations mutually elaborated on one another. (Contains 30 references.) (YLB)