Customer has Panasonic DBS system. On one extension the microphone has stopped working in a weird way. When using speakerphone, can hear fine but microphone is not picking up anything. Mute light is off - toggle mute and light goes on/off but doesn't change it. Pick up handset and that works fine.

Looking at possible things, I found #51 for headset mode. When I hit that, then it swaps! The microphone of the speakerphone works, but we can't hear anything... not even a dial tone. Again, pick up the handset and that works fine. Used #51 to toggle it back and it went back to the old microphone dead but speaker works.

No, there is no actual headset. Phone is a VB-44230. User told me she swapped with two other phones (that worked elsewhere) and got same results, so I think it must be programming related. Then again, with the #51 toggle I get the microphone working (but not speaker) which means the microphone does physically work anyway.

Any thoughts?