Hi there, my son moved to a flat which has a faulty Urmet Digivoice 1138/3 door telecom system. The buzzer and door release do not work. However, if you pickup the handset, you could communicate with the outside entry unit fine. We tried to replace the telecom with the new Urmet 1138/4 but we seem to have the same problem. Any suggestions on how to troubleshoot the problem would be highly appreciated.