Yamaha M4 power amp's output LED got stuck

Accidentally left my M4 on last night (it's been happening since the lamps burnt out, and I haven't had time to swap them out...) When I came back i was scared because the right level output meter was stuck between -5 and 0 which is pretty loud. However there was no sound coming out of it and I assume anything that loud I would have heard even if sleeping... Anyway I tested it out and the left level meter still responds fine. In fact, I can see the right side getting lighter and darker as it should, but all those bars are still filled up. How the heck do I get it to go back down so the level meter works properly again? Sorry the pictures are so bad. It was hard to get a shot of it.