You should not see any AC voltage when the line is idle. By setting your meter to the AC setting, it's just reading the DC voltage and effectively doubling it, giving you a false reading.

It sounds like the 90 volts that you are detecting during the ring cycle is fine. There is an issue of AC frequency though. U.S. straight-line ringers are designed to respond to 17-33 Hz. Being in Europe, there's a good chance that the frequency of the 90 volts is outside of this range.

I do need to ask these questions:

You had mentioned that you were using 2565HKM sets before. Did the ringers work properly in these sets? If so, we may just have an internal wiring issue.

Is the Call Director set new or is it one that was used? If used, there's a good chance that a diode may have been used in the ringer wiring as a field modification.

Let us know and we can dig further.

Ed Vaughn, MBSWWYPBX