DDJ-SR Master volume button

Hi guys, 

I've been working with my DDJ-SR for a while without issue ... but today the Master Volume button is not working at all... Serato is not detecting any action on the button, and when I try to map the volume onto another knob, if works. It looks like an hardware failure, but I'd like to confirm. Any thoughts on how to check this or potential solutions ? 

I tried: 

- firmware upgrade to 1.0.8

- connection on another Laptop with Serato (unfortunately Recordbox freezes mon my laptop). 

I'm on a Mac High Sierra. 

Thanks in advanced for your precious help.