Cisco 7906G Administration Guide - Page 234

General Troubleshooting Tips Chapter 9 Troubleshooting and Maintenance Table 9-2 Cisco Unified IP Phone Troubleshooting (continued) Summary LCD display issues. Dual-Tone Multi-Frequency (DTMF) delay. Loopback condition. Explanation If the display appears to have rolling lines or a wavy pattern, it might be interacting with certain types of older fluorescent lights in the building. Moving the phone away from the lights, or replacing the lights, should resolve the problem. When you are on a call that requires keypad input, if you press the keys too quickly, some of them might not be recognized. A loopback condition can occur when the following conditions are met: • The SW Port Configuration option in the Network Configuration menu on the phone is set to 10 Half (10-BaseT / half duplex) • The phone receives power from an external power supply. • The phone is powered down (the power supply is disconnected). In this case, the switch port on the phone can become disabled and the following message will appear in the switch console log: HALF_DUX_COLLISION_EXCEED_THRE SHOLD To resolve this problem, re-enable the port from the switch. 9-18 Cisco Unified IP Phone 7906G and 7911G for Cisco Unified Communications Manager 6.1 OL-14585-01