Through KTI test on 1#RAM we discovered the fault from DQ14.By checking up the maintenance picture we dicovered that it was R15 that corresponded with the fault.R15 was detected abnormal by apparatus( the measured value was 260 ohm while the normal value is 15 ohm).Breakdown vestiges were found on the R15 by the 300X microscope which should have been led by the excessive current.