Are you sure you have it connected properly? I can't see how your phone works at all without the unit powered.

As to your question, without taking actual voltage and current readings on you phone's T&R both with the TBB connected in the line and not connected and again connected with the unit powered I have no idea what's going on. Maybe someone at Viking tech support can answer that. I didn't design it.

All the advice given here ASSUMES that the loop voltage and current is low. So you go out and spend money on a TBB and now you call that into question. A proper diagnoses should be done first to determine what the situation is then decide what to do about it. Not just throw equipment at it by the seat of our pants.

-Hal

CALIFORNIA PROPOSITION 65 WARNING: Some comments made by me are known to the State of California to cause irreversible brain damage and serious mental disorders leading to confinement.