Mbox 3: no signal going to left channel in L/R master

[mrsminss]

Following an upgrade to El Capitan, I'm not getting any sound out of the left output (not just playing from ProTools but in anything I run through the Mbox). As the attached image shows, this seems to be happening at source, i.e. it ain't the headphones - the signal going out of returns 1 and 2 are as should be, but they're only coming out of the R channel in the master mix.

Have messed about with Audio Midi Setup and settings in the Mbox controller (limited though both are) to no avail. Is this a driver problem? Is it time to get a new interface?

Any ideas would be grateful received.

With thanks,

James

[Darryl Ramm]

Oh another brave El Capitan user. Now why did you ever upgrade to that?

Did you do an in-situ upgrade or a full new clean OS X install (like Avid recommends for OS X upgrades)?

What exact driver version are you running? You do an uninstall and reinstall of that driver after the OS X (in-situ) upgrade?

Some tests to try...

Try is to use hardware monitoring of a source and see if you can get that to come out of both output channels.
Pan both software returns to the left and see if anything come out on the L main out. That at least hints at where internally things are screwed up, even if you can't do anything about it...
Boot back to your saved previous OS X image and test if it still works there. You did make a bootable backup right?
Test on another computer.
Install a clean OS X version (ideally not El Crapitan) on a spare drive or partition, install just the correct driver version for the Mbox 3 and test if that works from iTunes or similar.