In this paper, two units’ Parallel system was considered in which both units operate simultaneously. The system is subjected to two types of failures. Type I failure is minor and occur with the failure of a single component and is checked by minimal repairs, while type II failure is catastrophic in which both components failed and the system is replaced. It is assumed that when one component is receiving minimal repair treatment other non failed component will receive some preventive maintenance action like oiling, greasing, etc. The system is also replaced preventively at the age P t . The aim is to modify an existing model that addressed the problem of replacing the system preventively before failure or at failure .The paper discusses and subsequently obtained the optimum replacement times P t that minimize the expected cost numerically.Keywords: Structural dependence, replacement, minimal repair, preventive maintenance
