My customer has an SL1100 with 10 analog trunks and 20 digital stations. Recently they're complaining that sometimes one party or the other can't be heard at all. This is happening on at least 7 of the 10 lines and on just about every station, so it's not happening on just one of the CO cards or one of the digital station cards. They do use Plantronics headsets, but they report that it's also happening with handsets.

The trunks are all from Consolidated Communications via analog copper beyond SLC-96 systems. Their tech verified that the trunks all test good and that they derive from separate SLC-96 systems and/or from multiple line cards within the systems, so it's unlikely that a single bad card or system on their end is at fault. He also reports that there are no other customer complaints at these systems. Ball's back in my court.

I'm thinking that the main board in the KSU must be at fault. I'm not sure if that's replaceable or if I have to replace the entire KSU. Any other ideas and input?