Alt-Out level imbalance

Does anyone know why I have a 6dB difference between the Left and Right outputs of my Alt-Out? Everything is set to centre, I even tested it using the inbuilt SigGen and a multitrack recorder to check the levels. Am I overlooking something? Surely it can’t be a tolerance thing on the physical level knob? Is that a dual-gang pot or is it a single pot and the L&R levels adjusted in software?

It’s a Qu-Pac.

Have you tried other mix outputs routed to the alt out as a test?
Is the main left right out good?
What is the cabling and connectors your using plugged into the alt out?

@John

The best way to rule out anything in setup or software is to backup your show, then carry out a hard reset and test again.
If this fixes it, it could be an output balance setting (routing screen with mix master selected).

A 6dB difference could also be an issue with balanced vs unbalanced i.e. one of the signals is balanced and the other isn’t.
This could be due to cables/connectors (switch the two and see if it follows), but could also be a hardware issue at the sockets (send another mix which has dedicated XLR outputs to the ALT OUT and compare the XLR outputs to the TRS outputs).
If your testing points towards a hardware issue, then please contact your local distributor (https://www.allen-heath.com/where-to-buy/) to arrange a service.

Thanks,
Keith.