Panasonic KX-FC379CX, Service Manual

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7.7.8. Digital Speakerphone
The digital speakerphone has different features from the analog speakerphone.
The analog speakerphone switches between Tx or Rx. Either Tx or Rx is able to pass through a telephone line or speaker,
depending on the Tx and Rx signal (voice) level. The higher-level signal (either TX or RX) can pass through the route.
Therefore, you never hear the other party´s voice while you are talking. However, the digital speakerphone allows you to hear
the other party´s voice while you are talking. So both Tx and Rx are active at the same time. There is also a difference in the
troubleshooting procedures between the two types.
At the start of communication, during the initial 2~3 correspondences, the digital speakerphone performs half-duplex operation,
alternating between transmission (Tx) and reception (Rx). Then duplex communication becomes available.
Learning occurs during the initial 2~3 correspondences in order to set the appropriate parameters for duplex communication.
You cannot check the digital speaker phone by the signal route test mentioned in the Analog Board Section because the level
is always changing as stated above.
Therefore, there is a service function for this troubleshooting. In this service mode, you can set the mute to either Tx or Rx. Then
you can check the signal route of the speaker phone Tx or the speaker phone Rx without any disturbances.
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