B&K 507

How do I get my headphones to work after I plug them into my B&K 507? They work fine on other equip. Just not with the 507 & everything else on it works fine.
If memory serves, B&K still answers their phone with a live human being instead of a recording device which is terrific. Plus they have in house people to answer just this kind of question.

Good luck,
Thank you Larry... I'll call them. Mike