I got the problem solved with the help of a contributor to ifixit & am posting the solution here in case it helps anyone else. In my case the ribbon wire going from the switch to the logic board had somehow become a bit loose & wasn't securely fastened. The ribbon feeds into a small square in the upper right corner of the logic board. I simply pushed down on the square & heard a click. Problem solved. Ifixit has some great photos of the iPod insides that show the components I am referring to.