this is a common problem with aux cards on
the onyx vs. However, it's a good indicator in your case that your getting anything at all. Ussually when the aux card is bad you get nothing at all. Try this, at ext 300 (operators set, if cos set to 30) lift handset press PGM# key dial 0 dial 4, hang up.This resets your com port to 9600 n 8 1.
If this doesn't work make sure you have a good ground first, then if so disconnect it
and try without. Also if you have an expanded system (more than 1 cabinet) power down disconnect mod cord from slave aux restore power and try again.

good luck