I have a couple of extensions (301 & 325) that can make calls with no issues however when receiving calls the caller cannot be heard on ext but extension caller can hear the person on the extension. Both were in use about 3 years ago and working fine, to my knowledge there have been no changes made to the system aside from just disconnecting the phones from the lines and not using them. I am a tech geek but know little about this system. I have worked with (making some changes to programing from console) on an SX-100 and helped install but not program an SX-200.

Is it the same for internal and external calls?

Please provide a little more detail. When you write that the extensions in question can make calls with no issues, are those extensions able to complete both internal extension to extension calls as well as outgoing calls with audio transmission OK both ways? This is critical to know as the process for receiving calls and making calls uses the same circuits.

Rcaman