Oil pressure is a valuable parameter indicating condition of aircraft lubrication system problem of reducer oil pressure indicator’s value is larger was proposed after installating a new flight data signal adapter and it was pointed out that it was caused by design detect of internal amplifier circuit which leaded to overvoltage damage.The conclusion was made from internal system structure theory,combining modern electronic testing technology and correct analysis method.Fault phenomenon was removed by redesign of amplifier circuit after mechanism analysis, fault reproduction and validation,refering to relevant literature on the circuit design and experimental and mounting reliability verification.Blind decomposition inspection was avoided,and flying safety was guaranteed.