This fault should first check the aperture ring plate opening and closing. Trial hand toggle aperture ring, found that the opening and closing are very flexible, aperture of mechanical part, no problem, the fault should be out in the aperture of the automatic control circuit. Check the light meter, motor and drive pipe Q701 abnormality was not found, check the aperture control abnormal voltage comparator IC704 6 feet. What is the foot abnormal voltage caused by? Check IC704 and peripheral device not found problem, aperture aperture adjustment potentiometer VR701, found that the dynamic and poor contact between set pieces, causing IC703 pet-name ruby feet output aperture aperture status information feedback properly to IC703 11 feet, cause IC703 cannot compare to reference voltage, the output control voltage abnormal IC704 6 feet. After the replacement VR701 troubleshooting.pwtservice manual download site