Low voice call out on only 1 of 9 Avaya phones need help

[billpeters]

I have an Avaya Partner intercom system model PACS R7.0 91I. I have a low sound voice call out on only 1 of 9 Avaya phones. It hears loud and clear on incoming voice, but outgoing voice is very soft for all intercom recipients and all outside calls. It affects all lines on this one phone. It has happened suddenly without any known accident to the phone. Volume is set to high. I have unplugged all lines and replugged them with no change.
I need help on how to fix. Thanks,
billpeters

 

[TouchToneTommy]

The handset is bad
The handset cord is bad
The phone is bad
The extension port on the control unit is bad

Pick one and replace the bad component

Trade handsets with a known good phone. Problem clears with the different handset, and the other phone is now bad? Get a new handset

Trade handset cords (but keep the handsets as original) with a known good phone. Problem clears with the new handset cord and the other phone is now bad? Get a new handset cord

Swap the entire phone with a known good phone. Problem clears with the exchange, and the phone at a new location is bad? get a new phone

At the control unit, swap the cord plugged into the bad extension number with the cord from a known good location. Old location with a different extension number is good, change to a different, available extension number or replace the control unit.

 

[billpeters]

Thanks, You are correct. I had already tried exchanging the handset and discovered a different handset worked. I am getting another tomorrow.

billpeterd