Remove casing, electricity observation aperture cannot move. Check the light ring plate no distortion, no dust, suspect malfunction with the aperture of the automatic control circuit. Check the light meter, automatic control circuit of Q701, R725 are normal; Check IC704, found that the voltage of 0 v 5 foot, the foot voltage provided by IC330 7 feet. The measured voltage IC330C 7 foot also to 0 v. According to this judgment was not damaged, IC330 is capacitance C311 breakdown. Check the IC330 and capacitance C311 respectively. Found C311 breakdown, resulting in no voltage IC330 7 feet. That cause IC704 5 feet no voltage, IC704 cannot be compared with the benchmark level, lead to the 7 feet no control voltage output, cause Q701 in the off state, causing the aperture ring cannot be opened. After replacing C311 fault disappear.hFqservice manual download site