Abstract: Analytical Photo-positioning Apparatus, as a vehicle-borne instrument, works in the field.Customers require its superior reliability and high availability.Once the instrument breaks down, the operator is able to repair it in a little time (generally no less than 45 seconds).With the aim to improve the availability of the instrument, its design of maintainability should be referred while its reliability being enhanced. Based on the discussion of the designs aiming at improving the reliability of the electrical part of the instrument, the self-detection issues are discussed, and the design of maintainability is enlarged with the Markov producing method.