In an approach recently proposed for the yield enhancement of programmable gate arrays (PGA's), an initial placement of a circuit is first obtained using a standard technique such as simulated annealing on a defect-free PGA. In the next step, this placement is reconfigured so that the circuit is mapped onto the defect-free portion of a defective PGA chip with the same architecture. We first formulate the reconfiguration aspect of this approach as a problem of shifting pebbles on a graph. We present efficient reconfiguration algorithms for this pebble shift problem. Using these algorithms as heuristics, we develop a yield enhancement system not only for PGA's, but also for programmable Wafer Scare Integrated (WSI) processor arrays. We evaluate the heuristic algorithms using the measures of routability and total wire length of the reconfigured placement of the circuit. Based on this evaluation, we establish proper reconfiguration strategies.>