I have an 816 w/a 160 (door bell) card. The door bell rings on my KX-T7433 phones but not my KX-T7420 phones. I tried switching the phones to make sure the extensions were programmed correctly, and they were. What else can it be? These are two 7433 which work anywhere and three 7420 which light up but do not ring(only for door bell) anywhere. Thanks in advance for your help.

As I'm sure you know, the ringing is indicative
to the port programming and not the phone.
Do the 7420 sets work normally in all other aspects?
I suspect that it may just be the ring switch is in the off position.
Gem

Yes the phone works when a normal phone call comes in on a CO. The switch is set to ring.

Programs #607/608 establish door phone ringing assignments. 607 for day, 608 for night.