I own Martin Logan SL3s. I have no experience with the Cinema TM. But looking at a picture I can see the pannel. I assume you have a single center channel speaker. There should be a noticeable difference when the speaker is plugged in. Have you tried listening with the other speakers turned off to see if you hear a difference? It is possible the pannel is blown but I would think more likely it might just be a fuse. Also make sure that the power cord is tight.
