High Telephone line noise with missing door opening via “DTMF” issues and causing terrible audibility from the visitor to the tenant?

Tip and Ring bi-directional signalling is not differential or in-ground current noise issue:

  • Install a 0.1 μF capacitor in series to the Tip. Then line test:
  • - If the signal/noise improves then Line is unbalance. Request Line Card change-out; OR
  • Disconnect Tip and Ring from the module. Measure the voltage (potential) between Tip and Chassis ground. If voltage exceeds 2.0-2.5 volts:
  • - then run a 10 AWG/Stranded cable from the telephone access unit to the communication demarcation point to ensure voltage drops to approximately 0 potential difference; OR
  • Change out the power supply. Ensure the power supply ground is connected to the power ground and not the communication ground.

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