I'm sorry to hear that you're having this issue with your TV.
I'd recommend calling the service technician and reporting that this stopped working, as you noted, after it was serviced.
If you're not able to find resolve, post back here with your transaction number from the call to Samsung and let me know. While I can't promise a resolution, I can definitely have your situation reviewed. But dealing directly with the technician is the fastest (and probably best) way to resolve the issue quickly.
When I purchased my LN55C750 it had AMP and I liked it.
My 3D emitter was recently repaired by a Local Samsung Tech and oddly now the AMP menu is greyed out. The Tech hit some wierd combination of buttons on the remote and went into a service menu. Besides that, all he did was remove the back panel and reconnect the wire to the emitter (which had come loose).
What are the requirements for the AMP menu to be highlighted? It is currently greyed out and set to off.
Thanks in advance