Panasonic KX-TCD953RUB (serv.man2) Service Manual ▷ View online
6.2. THE LINE INTERFACE SECTION
6.2.1. INTRODUCTION
This section consists of the telephone line interface, bell detector, hookswitch, pulse dialing circuits, audio circuits, DC mask & line
impedance circuits, power supplies, and battery charger circuits.
impedance circuits, power supplies, and battery charger circuits.
6.2.2. TELEPHONE LINE INTERFACE (SEE Fig. 21)
The telephone line is connected (via 2 or 3 jumpers selected for country of destination) to a bridge rectifier D8. Surge suppressor
SA3 protects against excessive line voltages. Test points are TP14 (A), TP13 (B). Bridge rectifier D8 provides for lines of either
polarity. The output of D8 is “Line +” (TP50) and “Line -” which is ground.
SA3 protects against excessive line voltages. Test points are TP14 (A), TP13 (B). Bridge rectifier D8 provides for lines of either
polarity. The output of D8 is “Line +” (TP50) and “Line -” which is ground.
6.2.3. BELL DETECTOR (SEE Fig. 21)
The AC ringing signal is detected by optocoupler IC2, using its internal diode in conjunction with D4. DC from the line is blocked
by C2. The other components D2, D3, and R3 reduce current and increase the circuit impedance in line with national requirements.
When ringing is detected IC2 will turn on, and the RING line (TP76) will be dragged to a low voltage.
by C2. The other components D2, D3, and R3 reduce current and increase the circuit impedance in line with national requirements.
When ringing is detected IC2 will turn on, and the RING line (TP76) will be dragged to a low voltage.
Circuit Diagram
Fig. 21
6.2.4. CLIP CIRCUITS (SEE Fig. 21)
The caller ID signal is detected by IC4.
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6.2.5. HOOKSWITCH (AND PULSE DIALING) (SEE Fig. 22)
T8 is the hookswitch, driven by T9. When the phone is “off-hook”, the HOOK control signal from the BBIC will be a high logic level
(+3V), and both transistors will be on, thus T8 will “loop” the line. The zenner diode D10 protects transistors T13 against transient
line voltages.
(+3V), and both transistors will be on, thus T8 will “loop” the line. The zenner diode D10 protects transistors T13 against transient
line voltages.
6.2.6. PULSE DIALING (SEE Fig. 22)
During pulse dialing the hookswitch (T8, T9) is used to generate the pulses using the HOOK control signal, which is set high during
pulses. To force the line impedance low during the “pause” intervals between dial pulses, the PAUSE-DIAL signal turns on T11,
(increases current), thus reducing line impedance (see 8.3.10. BATTERY CHARGER)
pulses. To force the line impedance low during the “pause” intervals between dial pulses, the PAUSE-DIAL signal turns on T11,
(increases current), thus reducing line impedance (see 8.3.10. BATTERY CHARGER)
6.2.7. AUDIO CIRCUITS (SEE Fig. 22)
The line output signal from the BBIC RXAF is amplified by T13. The RXAF line is DC coupled to T13 thus making it work as a
current limiter (typically < 8mA). The emitter load of T13 is complex to achieve the correct frequency response, since the line load
is also complex. The line input signal TXAF is taken from the junction of R41 and R70. Phase cancellation of the line output audio
occurs at this point, so that only incoming line audio should be passed to the BBIC on TXAF.
current limiter (typically < 8mA). The emitter load of T13 is complex to achieve the correct frequency response, since the line load
is also complex. The line input signal TXAF is taken from the junction of R41 and R70. Phase cancellation of the line output audio
occurs at this point, so that only incoming line audio should be passed to the BBIC on TXAF.
Circuit Diagram
Fig. 22
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6.2.8. POWER SUPPLIES (SEE Fig. 23)
The AC Adaptor for the KX-TCD953 / KX-TCD958 consists of two separate isolated DC supplies providing a +8 V supply for the
base circuitry, and a 9 V supply only for the charger circuit. The isolation is because the main base circuitry is connected to the
telephone line, so potentially hazardous voltages may be present, while the charger circuitry has charge contacts that could be
touched by the operator, so the two supplies must be kept separate. The 8 V supply from the AC Adaptor is connected via J2 pin
1 (TP90) +8 V, and J2 pin 2 (TP89) ground. The unregulated +8 V supply is fed to the first regulator.This regulator IC7 provides
a regulated output pin 2 (TP91) of +4.0 V (called +4V). The second regulator IC11 is fed with +4V and provides the stable +3.2V
supply (TP95). During power-up this regulator generates a RESET signal (TP94) which is used to reset the microcontroller and
BBIC.
base circuitry, and a 9 V supply only for the charger circuit. The isolation is because the main base circuitry is connected to the
telephone line, so potentially hazardous voltages may be present, while the charger circuitry has charge contacts that could be
touched by the operator, so the two supplies must be kept separate. The 8 V supply from the AC Adaptor is connected via J2 pin
1 (TP90) +8 V, and J2 pin 2 (TP89) ground. The unregulated +8 V supply is fed to the first regulator.This regulator IC7 provides
a regulated output pin 2 (TP91) of +4.0 V (called +4V). The second regulator IC11 is fed with +4V and provides the stable +3.2V
supply (TP95). During power-up this regulator generates a RESET signal (TP94) which is used to reset the microcontroller and
BBIC.
The regulator IC6 provides a regulated output pin 2 (TP109) of +6.0V.
6.2.9. BATTERY CHARGER (SEE Fig. 23)
The 9 V supply from the AC Adaptor is connected via J2 pin 6 (TP82) positive, and J2 pin 5 (TP78) negative. The constant current
battery charger circuit is made up of T14 and T15 (series pass transistor) and associated components. Charging detector circuit
T16 switches on when a charging current flows through R64 and D11, and turns on IC6. The charge contacts are charge current
flows in via J5 (TP88), through T15, R63, AC ADAPTOR 4V supply, R64, D11, and out of J5 (TP84).
battery charger circuit is made up of T14 and T15 (series pass transistor) and associated components. Charging detector circuit
T16 switches on when a charging current flows through R64 and D11, and turns on IC6. The charge contacts are charge current
flows in via J5 (TP88), through T15, R63, AC ADAPTOR 4V supply, R64, D11, and out of J5 (TP84).
Circuit Diagram
Fig. 23
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6.3. Speakerphone (SEE BLOCK DIAGRAM Fig.18 and SCHEMATIC
DIAGRAM[BASE UNIT])
The extra circuitry for the TCD953/958 speakerphone circuit comprises a microphone, a speaker, a speakerphone codec IC10 and
a speaker amplifier IC14.However, note that the majority of the speakerphone functionality is contained within the existing BBIC
IC101. This includes the switching between microphone and speaker path, echo suppression and cancelling, etc. The
speakerphone codec IC10 only provides analogue-to-digital conversion and digital-to-analogue conversion.
a speaker amplifier IC14.However, note that the majority of the speakerphone functionality is contained within the existing BBIC
IC101. This includes the switching between microphone and speaker path, echo suppression and cancelling, etc. The
speakerphone codec IC10 only provides analogue-to-digital conversion and digital-to-analogue conversion.
A bi-directional serial data link is provided between the speakerphone codec IC10 and the BBIC IC101. The 8.0 kHz strobe signal
STRO from IC101 pin 39 (TP46) is a synchronising pulse for this data link, and the 2.3 MHz clock ICLK from IC101 pin 44 (TP47)
is the clock for the serial data link, and is also the sampling clock for the analogue-to-digital converter (ADC) and digital-to-analogue
converter (DAC) in the speakerphone codec IC10.
STRO from IC101 pin 39 (TP46) is a synchronising pulse for this data link, and the 2.3 MHz clock ICLK from IC101 pin 44 (TP47)
is the clock for the serial data link, and is also the sampling clock for the analogue-to-digital converter (ADC) and digital-to-analogue
converter (DAC) in the speakerphone codec IC10.
The DC supply to the speakerphone codec IC10 pin 6, is a 3.1V supply, derived from the regulator IC6 (TP185). The DC supply
to the speakerphone amplifier IC14 pin 6, is a 6.4V supply, derived from the regulator IC5 (TP109).
to the speakerphone amplifier IC14 pin 6, is a 6.4V supply, derived from the regulator IC5 (TP109).
6.3.1. Path from Telephone Line to Speaker
Audio from the telephone line passes via the normal signal path of J1 tel-line connector (TP13 and TP14), D8 bridge rectifier
(TP45), T3/T5 current limiter (TP50), T8 hookswitch (TP55), and R41 (TP123), to BBIC IC101 pin 58 (TP121).In the BBIC it is
converted from an analogue audio signal into digital data in the BBIC´s internal codec. Additionally, the speakerphone switching
and echo suppression functions are contained within the BBIC.An eight level speaker volume control is provided, and the
functionality for this is also contained within the BBIC.The digital data is sent from the BBIC IC101 pin 46 to IC10 speakerphone
codec pin 10 (TP25), via the serial data link. In the speakerphone codec IC10, the data is converted back to analogue audio, and
fed from IC10 pin 5 (TP178) and to the speaker amplifier IC14 pin 4 (TP179). The audio signal is amplified in IC14, and the push-
pull audio output is sent from IC14 pins 5 and 8 to the speaker (TP101) and (TP102).
(TP45), T3/T5 current limiter (TP50), T8 hookswitch (TP55), and R41 (TP123), to BBIC IC101 pin 58 (TP121).In the BBIC it is
converted from an analogue audio signal into digital data in the BBIC´s internal codec. Additionally, the speakerphone switching
and echo suppression functions are contained within the BBIC.An eight level speaker volume control is provided, and the
functionality for this is also contained within the BBIC.The digital data is sent from the BBIC IC101 pin 46 to IC10 speakerphone
codec pin 10 (TP25), via the serial data link. In the speakerphone codec IC10, the data is converted back to analogue audio, and
fed from IC10 pin 5 (TP178) and to the speaker amplifier IC14 pin 4 (TP179). The audio signal is amplified in IC14, and the push-
pull audio output is sent from IC14 pins 5 and 8 to the speaker (TP101) and (TP102).
6.3.2. Path from Microphone to Telephone Line
DC bias for the microphone is provided from the BBIC IC101 pin 57 (TP170) (positive bias) and pin 51 (TP171) (negative bias). The
bias is fed to the microphone via R89 and R82 (positive bias) and R90 and R83 (negative bias). The balanced audio signal from
the microphone is fed to the speakerphone codec IC10 pins 19 and 18 via R82 (TP172), R87, R99, and R83 (TP173), R88, and
R100.
bias is fed to the microphone via R89 and R82 (positive bias) and R90 and R83 (negative bias). The balanced audio signal from
the microphone is fed to the speakerphone codec IC10 pins 19 and 18 via R82 (TP172), R87, R99, and R83 (TP173), R88, and
R100.
The analogue signal is converted into a digital signal in the speakerphone codec (IC10), and the digital signal on IC10 pin 11
(TP37), is fed via the serial data link to the BBIC IC101 pin 45. The speakerphone switching and echo suppression functions are
contained within the BBIC. The digital data is converted again into an analogue signal in the BBIC´s internal codec.
(TP37), is fed via the serial data link to the BBIC IC101 pin 45. The speakerphone switching and echo suppression functions are
contained within the BBIC. The digital data is converted again into an analogue signal in the BBIC´s internal codec.
The analogue signal is fed from IC101 pin 63 (TP119), via T13 audio amplifier (TP55), T8 hookswitch (TP50), T3/T5 current limiter
(TP45), D8 bridge rectifier, to J1 tel. line connector (TP13 and TP14), and out to the telephone line.
(TP45), D8 bridge rectifier, to J1 tel. line connector (TP13 and TP14), and out to the telephone line.
6.4. Keyboard
The TCD953 is fitted with a keyboard which provides the user with comprehensive speakerphone facilities, and includes a full
numeric keypad for dialling out.The keyboard is mounted on a separate pcb (2AP board), and is connected to the main pcb via J3
connector.
numeric keypad for dialling out.The keyboard is mounted on a separate pcb (2AP board), and is connected to the main pcb via J3
connector.
Additional circuitry for the keyboard comprise a tri-state latch (IC9) and tri-state buffer (IC8), both mounted on the main
pcb.Keyboard scan pulses and LED drive signals are fed from the BBIC address/data bus to the keyboard via latch IC9 and
connector J3.Key press information from the keyboard is fed via J3 and the tri-state buffer IC8 to the BBIC address/data bus
pcb.Keyboard scan pulses and LED drive signals are fed from the BBIC address/data bus to the keyboard via latch IC9 and
connector J3.Key press information from the keyboard is fed via J3 and the tri-state buffer IC8 to the BBIC address/data bus
The DC supply to IC8 pin20, and IC9 pin 20, is a 3.1V supply, derived from the regulator IC6 (TP185).
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