DJM 2000 cue master

Hey guys,

I have a DJM 2000 and I have a problem with the volume of the master cue in my headphones.
Basically the volume depends on the volume of master output! I only can get it’s full volume when the master volume is full!!!
In other words, you cannot mix without speakers and just trough your headphones. so annoying please help if you know the problem.

Thank you