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9

The circuit controls the automatic switching of the transmitted and received signals, to and from the telephone line, when the
unit is used in the handsfree mode.

The speakerphone can only provide a one-way communication path.
In other words, it can either transmit an outgoing signal or receive an incoming signal at a given time, but cannot do both simul-
taneously. Therefore, a switching circuit is necessary to control the flow of the outgoing and incoming signals.
This switching circuit is contained in IC601 and consists of a Voice Detector, TX Attenuator, RX Attenuator, Comparator and
Attenuator Control. The circuit analyzes whether the TX(transmit) or the RX(receive) signal is louder, and then it processed the
signals such that the louder signal is given precedence.
The Voice Detector provides a DC input to the Attenuator Control corresponding to the TX signal.
The Comparator receives a TX and a RX signal, and supplies a DC input to the Attenuator Control corresponding to the RX sig-
nal.
The Attenuator Control provides a control signal to the TX and the RX attenuator to switch the appropriate signals on and off.
The Attenuator Control also detects the level of the volume control to automatically adjust for changing ambient conditions.

1. Transmission signal path:

The input signal from the microphone is sent through the circuit via the following path: MIC 

→ Pin 9 of IC601 → Pin 10 of IC601

→ Pin 3 of IC601 → Pin 4 of IC601 → R601 → C602 → Q108 → Tel line.

2. Reception signal path:

Signals receive from the telephone line are outputted at the speaker via the following path:Tel line 

→ Q108 → Q109 → C112 →

R600 

→ C603 → Pin 27 of IC601 → Pin 26 of IC601 → Pin 19 of IC601 → Pin 15 of IC601 → Speaker.

3. Transmission/Reception switching

The comparison result between TX and RX outputs as a DC level of Pin 25 of IC601.TX level is high ...... Pin 25 = Pin 21 -
6mVRX level is high ...... Pin 25 = Pin 21 - 150mVComparator output is connected to the attenuator control inside of IC601.

4. Voice detector

The output of the mic amp (Pin 10 of IC601) is supplied to Pin 13 of IC601 as a control signal for the voice detector.

5. Attenuator control

The attenuator control detects the setting of the volume control through Pin 24 of IC601 to automatically adjust for changing
ambient conditions.

10

This circuit is used for to initialize the microcomputer when it incorporates batteries.

When the batteries is inserted into the unit, then the voltage is regulated by IC304 and power is supplied to the CPU. The set
can operate beyond point A in the circuit voltage diagram.

VCC

Battery

GND

Reset

Power

Down

A

Vcc

Reset

CPU Reset

Power down

11

Refer to the Operating Instructions.

You can download and refer to the Operating Instructions (Instruction book) on TSN Server.

Refer to the Operating Instructions.

You can download and refer to the Operating Instructions (Instruction book) on TSN Server.

Refer to the Operating Instructions.

You can download and refer to the Operating Instructions (Instruction book) on TSN Server.

If the current password is forgotten, follow the below procedure, you will be able to establish new password

Press  MUTE
Enter “10349276”

Press 

12

SYMPTOM

CURE

Dead

Check IC801, X801, X802

Can't hear the voice from handset.

Check Q109, Q405, Q406.

No voice transmit.

Check Q424, Q108.

Can't tone dial.

Check IC801, R921, R922, R923, R924, R925 and C923.

Can't pulse dial

Check Q101, Q103, Q104.

Can’t auto redial

Check IC201, Q201.

No rings.

Check D3, D4, D5, D6, IC1 and Q1.

Can’t speak with the speakerphone.

Check IC601

Can't hold.

Check Q107.

Can't speak with the handset.

Check handset jack

Can't speak with the headset.

Check headset jack

Can’t change the volume for speakerphone.

Check IC801, IC601, R661, R662, R663

Can't change the volume for handset.

Check IC801, Q491, Q492, Q493, R403, R404, R412

No volume handset or speakerphone.

Check IC801, Q108, Q401.

YES

YES

YES

YES

NO

NO

NO

Can a pulse sound
be monitored?

Does the voltage across
Tip(T) and Ring(R) rapidly
switch between 48V and 10V?

Check TEL line Jack.

Do pulses (3 Vp-p) appear
at Pin22 of IC801?

Do  pulses (0.6 Vp-p) appear
at base of Q103?

Check Q101,Q103.

Check Dial mode.

Check Q204