Brace yourselves for the sillies:
Up till then, he'd only needed the "play " buttons.
There's an old joke about bands ( Bay City Rollers, when I first heard it
)
Manager walks into the dressing room to find the guitarist in tears. On asking what the problem is " It's the drummer, he's altered the tuning on one of my guitar strings ".
Manager asks why that's a problem, and is told " He won't tell me which one it is"!
I can talk.
I used my little Behringer mixer, and couldn't work out why the mics were fine, but I had to wind the line input up to the top.
Might have helped if I hadn't had the attenuator buttons pressed on the line channels, knocking 14db off the pre amp.