I am servicing an old NBX 100 system and trying to get the MOH to work. I found a setting that was like "disable MOH input" that was set to yes and I changed to no, and have tried both a mono and stereo plug for the input and even tried a little pre-amp to boost the volume of the input but I get nothing. I'm thinking now that the board that the MOH input is on maybe has failed and needs to be replaced?

Anybody have any thoughts on this?

Make sure in the System Settings -> System wide screen that MOH and MOH on transfer are checked and click Apply.

That should do it. When MOH is enabled you might notice the switch ports just light up nearly solid with traffic. This is because MOH is a multicast. The IT person might mention something.

We have had the occasional system with a bad MOH port too.

A mono plug is best for the input. I have found there is sometimes a "sweet spot" on these NBX jacks.

What are you using for an input?