The LCD screen on two Adtran IP 712 phones recently went blank. Other than having a blank LCD screen, the phones seem to be working fine; i.e., phone calls keep coming in and are able to be picked up. The functionality of buttons was not tested.
The Adtran IP 712 phones are accessible through the web GUI using the following formant http://192.168.XXX.XXX/admin. FYI, the default Username = admin and Password = password. In our experience a Reset and Factory Reset via the web GUI did not fix the issue. On one occasion, one of the phones booted up normally but the LCD screen went blank again several minutes later.
We were able to resolve the blank LCD screen for only one of the Adtran IP 712 phones by deleting the User Acct and Phone Config and creating them again (we are using Adtran Netvanta 7100 PBX). The phone was able to boot up normally after that and the blank screen is fixed.
On the second phone the same fix did not work and was eventually replaced. The root cause is still unknown but suspect corrupt firmware and/or missing phone firmware on the Netvant 7100 PBX.