Matt:
The buzzers with red leads are for 18 volts; the ones with blue leads are for 10. Obviously, the life span of the 10 volt buzzers will be shortened if used with 18 volts.
The relays on the card form a matrix, almost the same matrix formed by a DTMF dial. For each digit dialed, a different combination of relays are activated. That's probably why you see something from two different digits when you are testing. You should see two separate relays operate for any digit dialed. The fact that you are getting the same response leads me to believe that the card is not bad.
It's not possible for an "out of tune" dial to cause the problem that you are having. If half of a DTMF digit isn't produced, then nothing will register.
You are very, very close to solving this. I am sure that the whole problem revolves around your input terminal for the 10 volts. I'll do my best to look around tomorrow and see if I can get you some more definitive information tomorrow.
