ZED60 meter doesn't light up for main mix

I have a ZED60. Recently it has developed a strange problem. All the features are working properly and we have sound except for one thing: the meter for the main mix doesn’t light up. The meter is working for channels that have “Listen” pressed in (PFL) but when we disengage PFL on all channels, the meter doesn’t light up. The PFL LED is off (as expected) but the meters don’t light up at all. I haven’t checked to see if the phones work for the main mix yet.

Any ideas? Is it a loose cable inside? Why would PFL metering work, but main metering not work?

After searching the block diagram and manual, I assume one of the three “Phones Select” switches is pressed to listen Record, Aux, or Playback and display it on the meter.
Main Mix is ​​probably only displayed if none of these is pressed.

And yep you have it right. I looked back at my “known good working” photo and sure enough those three buttons are up. Looks like someone pressed them in for some reason. Thanks for that! Meter is working again!