Dude u need to tell us if the defect is heavy or light !!
But heres the method
14 coins .. since one of them is not defected..
divide into two groups ..
7 7 findout the defective group. ---------> for this u need to know wheither the defect made the coin heavy or not.
from the 7 make 3 3, 1 will be left out ..
3 3 measure if balanced 1 is defective.
now out of the 3 ..
pick randomily 2
and measure if balanced the left out coin is defective
if unbalanced U NEED TO KNOW IF THE HEAVY ONE IS DEFECTIVE OR THE LIGHTER ONE !!