Panasonic KX-TCD961GB Service Manual ▷ View online
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2.6 LOCATOR KEY (SEE Fig. 19-1)
The keyboard “Locator (Page)” button is connected to pin 10 of the IC501. When pressed the base transmits a mes-
sage to the handset, which then beeps.
2.7 FACTORY SERIAL PORT (SEE Fig. 19-1)
In order to communicate with the handset during manufacture and servicing (using a PC) a serial data link has been
provided. Serial data input/output is provided on J102 (TP152), and a ground is provided on J103. The bi-directional
serial data line is split into two at IC101 pin 27 (input) and pin 26 (output). Data rate is 9600 baud J103. D105
provides ESD protection, and R117 and C146 provide RF de-coupling.
2.8 BUZZER CIRCUIT (SEE Fig.19-1)
A square-wave signal from IC101 pin 41 (TP103) is used to sound the buzzer via switching transistor T101 (TP101).
Various tones and cadences are used dependent on function.
2.9 AUDIO PATH-RX AUDIO-LINE INPUT (SEE Fig. 19-1)
Audio from the Line Interface TXAF enters the BBIC on pin 58. R111 and C113 are to balance the
(differential) audio input of IC101, and C110 and C112 are for RF de-coupling. In the BBIC audio passes through the
gain-controlled line input amplifier, into the ADC part of the codec, where it is sampled and turned into digital data. The
burst mode controller then processes this raw data (called the B-field) performing encryption and scrambling, adding
the various other fields that go together to produce the GAP standard DECT frame, assigning to a time slot and
channel etc. The data then passes through the gaussian filter to emerge on pin 22 as TRADAT, .
2.10 AUDIO PATH - TX AUDIO - LINE OUTPUT (SEE Fig. 19-1)
Audio from the receiver RECDAT enters the BBIC on pin 20 and passes through the clock recovery circuit. The burst
mode controller separates out the B-field data, and performs de-encryption and de-scrambling as required. It then
goes to the DAC part of the codec where data is turned back into analogue audio. The audio signal is amplified by the
gain-controlled line output amplifier, and balanced audio is output on pin 63, and fed as RXAF to the Line Interface.
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Circuit Diagram
Fig. 19-2
2.11 OFF HOOK LED (SEE Fig. 19-2)
When the Handset is in “Talk” mode, the Off-Hook LED D502 is switched on by transistor T504 (on), using a control
line from pin 32 of IC501.
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REV-POL
LINE-SENS
TP23
TP24
3. THE LINE INTERFACE SECTION (SEE BLOCK DIAGRAM Fig. 18)
3.1 INTRODUCTION
This section consists of the telephone line interface, bell detector, charge-pulse detector, hook switch, pulse dialing
circuits, audio circuits, DC mask & line impedance circuits, power supplies, and battery charger circuits.
3.2 TELEPHONE LINE INTERFACE (SEE Fig. 20)
The telephone line is connected (via 2 or 3 jumpers selected for country of destination) to a L1 and L2. Surge sup-
pressor SA3 protects against excessive line voltages. Test points are TP13 (A), TP14 (B) and TP15 (E).
A 16 kHz notch filter L3, L5, C5 and C26 blocks the 16 kHz “charge pulse” signal from the rest of the line input cir-
cuitry.
Bridge rectifier D8 provides for lines of either polarity. The output of D8 is “Line +” (TP17) and “Line –” which is ground.
3.3 EARTH RECALL (SEE Fig. 20)
For countries that require Earth Recall facilities, relay RLY1 is provided to short the E line to the A or B lines. The relay
is energized when transistor T2 is switched on by a high level on the EARTH control line from the BB-IC IC101. D1
will quench the large back-emf voltage that would otherwise occur across the relay coil when T2 turns off.
3.4 BELL DETECTOR (SEE Fig. 20)
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 will be dragged to a low voltage.
Fig. 20
Circuit Diagram
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Fig. 21
Circuit Diagram
3.5 CHARGE PULSE DETECTOR (SEE Fig. 20)
The 16 kHz charge pulse (billing pulse) signal is detected by IC3A, which forms a sharp 16 kHz bandpass filter. If a
16 kHz charge pulse is present, a large 16 kHz output from IC3A will switch comparator IC3B, which output a 16 kHz
square wave. This will cause transistor T18 to switch, sending the 16 kHz square wave signal CHARGE-PULSE to the
BBIC. The BBIC will check the frequency and pulse length to determine if it is a valid charge pulse.
3.6 CLIP CIRCUITS (SEE Fig. 20)
The caller ID signal is detected by IC4.
3.7 HOOK SWITCH (AND PULSE DIALING) (SEE Fig. 21)
T8 is the hook switch, driven by T9. When the phone is “off-hook”, the HOOK control signal from the BBIC will be a
high logic level (+3V), and all three transistors will be on, thus T8 will “loop” the line. The zener diode D10 protects
transistors T11 to T13 against transient line voltages.
3.8 PULSE DIALING (SEE Fig. 21)
During pulse dialing the hook switch (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, which turns on T12 harder (increases current).
3.9 AUDIO CIRCUITS (SEE Fig. 21)
The line output signal from the BBIC RXAF (IC101 pin 63) 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 achieved the correct
frequency response, since the line load (for Germany) is also complex.
The line input signal TXAF (IC101 pin 58) 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.
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