I got this as part of a package deal for some other items. I have gone through every channel, and they all work with either a line in audio source or the mic XLR inputs. Channel 4's L/R Mix button could use a cleaning, but the channel works. My understanding is this came out of a church. And here I'm just passing it along. The manual and information is widely available on the internet. I used to daydream about having one of these back in the '90s LOL