I have seen this problem from multiple users over the years and have never seen a clear solution.
As an example, I am just looking at things on my Samsung UE46ES6300 and have no issues getting into the service menu. I have the Expert and Advanced menus displayed but both are greyed out. I have seen a comment from an engineer stating that Expert Mode is for use at the Factory when connected directly to the chip.
From what I can see browsing different forums, many users are able to access the Picture_2d menu but it has always been greyed out for me. Does anyone actually know how to make this option accessible?