Here’s a general troubleshooting guide that works for all three models:
 

Power and Connectivity

• Issue: Phone not powering on.
  • Solution: Ensure the power adapter is plugged in, or check the PoE (Power over Ethernet) connection.
     
• Issue: No network connection.
  • Solution: Verify that the Ethernet cable is securely connected to the LAN port and the switch/router.

Display Issues

• Issue: Blank or unresponsive screen.
  • Solution: Restart the phone by unplugging and reconnecting it. If using PoE, check the switch.

Registration Issues

• Issue: Phone says "No Service" or fails to register.
  • Solution:
    Check if the SIP account credentials (username, password, and server) are correctly configured.
    Verify network connectivity by testing with another device on the same network.
    Ensure that firewall or NAT settings on the network allow SIP and RTP traffic (typically ports 5060 and 5061 for SIP, and a range for RTP).

Audio Issues

• Issue: No sound or poor audio quality.
  • Solution:
    • Ensure the handset/headset is securely connected.
    • Check for network issues that could cause jitter or packet loss.
    • Use the phone's diagnostic tools to test the audio.
    • Verify that codecs are set correctly (e.g., G.711, G.729).

Firmware and Factory Reset

• Issue: Persistent issues not resolved by restarting.
  • Solution:
    • Check for the latest firmware updates on Yealink’s support site.
    • Perform a factory reset: Navigate to Settings > Advanced Settings (default admin password is often "admin" or "0000") and choose Reset to Factory Settings.
    • Reconfigure the phone after the reset.

Button or Screen Malfunctions

• Issue: Buttons not responding or display glitches.
  • Solution: Ensure the phone isn’t physically damaged. Restart the phone and check for firmware updates.

Logs and Diagnostics

• Access the phone’s web interface by entering its IP address into a browser.
• Navigate to the diagnostics or logs section to gather more details about issues.

Model-Specific Differences

• The T33G has a larger color display compared to the T30P and T31G, but troubleshooting steps are largely the same.
• If troubleshooting a feature exclusive to a model (e.g., Gigabit Ethernet on T31G/T33G), ensure you refer to the specific manual for additional details.