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9

• On hook

Q101 is open, Q101 is connected as to cut DC loop current and cut the voice signal.

• Off hook

Q101 turns on thus providing an off-hook condition (active DC current flow through the circuit) and the following signal flow id for
the DC loop current
T 

→ POS101 → D7 → Q101 → Q108 → R124 → D106 → D10 → R

• Receiving signal flow :

TEL line 

→ POS101 → Q101 → C113 → R125 → C108 → Q109 → Q405 → Q406 → Headset Jack → Handset SP

• Transmission signal flow :

Mic 

→ Q424 → C435 → R437 → Q108 → Pos101 → Tel Line

This circuit is used to sense the status of the line (busy tone or dial tone) during Auto Redial.

D7 

→ Q101 → C201 → R201 → R205 → Pin 5 of IC201 → Pin 1 of IC201 → D202 → R208 → Q201

When the subscriber hangs-up, check the intermittent tone. If cycle tone is detected, the collector of Q201 goes to a low logic.

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

10

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 

MUTE LED Flashing

MUTE LED Off

11

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, C924, R925 and C923.

Can't pulse dial

Check Q101, Q103, Q204.

Can’t auto redial

Check IC201, Q201.

No rings.

Check D3, D4, D5, D6, IC1 and Q1.

Can't hold.

Check Q107.

Can't speak with the handset.

Check handset 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

12

YES

YES

YES

NO

NO

NO

Can the DTMF
sound be monitored?

Does the DTMF signal
appear at base of Q424?

Check Q424,Q108.

Does the DTMF signal
appear at Pin62 of IC801?

Check
R482, C481 and Q406, D401.

Check
R921, R922, R923, C924, 
R925 and C923.

Check IC801, X801 and X802.

YES

YES

YES

YES

NO

NO

NO

NO

Call the unit from
another telephone.

Does a sine wave of
approximately 60V or more
appear across Tip and Ring?

Check the telephone line
and the telephone line cord.

Is the voltage at the anode
and cathod of D1 30V?

Check C1,C2,R1,D1, D2, 
D3, D4, D5 and D6.

Is the voltage across Pins 1
and 5 of IC1 30V

Check IC1.

Does the tone ringer
output signal appear
across Pin 8 and 5 of IC1?

Check
IC1, R2, R3,  R4, C3 and C5.

Check the SW1, Q1 and T1.