1 channel quiet in a multiamp

Hi everyone,
i have a Marantz MM9000 5 channel amp that was running fine until just the other day. one of the channels has become significantly quieter than the rest. i have checked to make sure i had the gains turned up the same, and i have tried changing the inputs from the pre to make sure it wasn't a cable/speaker/pre problem.

anyone have any ideas what may be the cause? there is still sound coming out of that channel, but it is much quieter.

if you've eliminated cables and other components and verified it's one channel in the amp, the next thing I'd check for is fuses. I'm not familiar with your amp, but many that I am have rail fuses inside the case - usually on the board. If yours doesn't have fuse holders on the outside, check inside. And even if it does and they check out I'd still check inside before calling for service.
Even though teh little attenuators are set to the same level the one on that channel could be funked up. Try turning the amp off, and sweeping the knob back and forth for about a minute. This can knock of any corrosion that has built up.

Good luck!