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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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Check to the SP-Phone Rx/Tx signal routes. (Refer to Check Sheet for Signal Route (P.114)).

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Check the following parts first: F101, D101-D104, C106, Q101and IC101.
This comes from our experience with experimental tests. For example: power supply and lightning surge voltage test, withstanding
voltage test, intentional short circuit test, etc.

If you find a melted fuse in the unit, do not turn on the power until you locate and repair the faulty parts (except for the fuse);
otherwise the fuse will melt again and you cannot pinpoint the faulty point.

In most cases, the symptom is that nothing is output. It is more likely that the fault is in the primary side rather than the secondary
side. Check the primary side first.

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