cisco expansion module 7915 not working

With two Expansion Modules, you need a power supply unit (separate orderable item). Note Use of a non-Cisco certified power supply unit might not work and voids the Cisco Unified IP Phone Expansion Module 7915 product warranty.

The power of the Cisco Unified Communications family of products extends throughout the enterprise by delivering powerful, converged voice solutions with the new Cisco Unified IP Phone Expansion Module 7915 extending capabilities to wideband audio phones (Figure 1).

Data Sheets (All Cisco Unified IP Phone 7900 Series Data Sheets).

Cisco Unified Communications Manager 6.1 and later. Cisco Unified IP Phone Expansion Module 7915.

Cisco Unified IP Phone 7915 and 7916 Expansion Module Quick Reference for Cisco Unified Communications Manager Express 4.3 and Later (PDF - 89 KB).