New Customer has a DHS system from 20 years ago. All the phones (8)once rang for incoming calls now only 2 ring. The phones ring on transfer and switch phones and they ring at the stations that work. Any suggestions beside time for a new phone system lol.

Its past time. That being said system could be in a different attendant mode, or it lost programming. However if some of the ports have failed to work, then a component of the system has gone bad. Customer should get a new one, Summit 80 is a really good unit.

Maybe 2 COs ring is default

Have you looked at the receive and ring assignments in programming?