Panasonic KX-TCD951EB / KX-TCD955EC Service Manual ▷ View online
25
KX-TCD951EB/KX-TCD955EC
3. THE LINE INTERFACE SECTION (SEE BLOCK DIAGRAM Fig. 19)
3.1 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.
3.2 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), TP21 (S) and TP15 (E).
Bridge rectifier D8 provides for lines of either polarity.
The output of D8 is “Line +” (TP50) and “Line –” which is ground.
3.3 EARTH RECALL (SEE Fig. 21)
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 energised when transistor T2 is switched on by a high level on the E A R T H control line (TP77) 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. 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 the wall plug inside. 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
LINE-SENSE
REV-POL
S
B
A
E
PULSE_DIAL
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KX-TCD951EB/KX-TCD955EC
Fig. 22
Circuit Diagram
3.5 CLIP CIRCUITS (SEE Fig. 21)
The caller ID signal is detected by IC4.
3.6 HOOKSWITCH (AND PULSE DIALING) (SEE Fig. 22)
T8 is the hookswitch, driven by T9. When the phone is “off-hook”, the H O O K 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 zenner diode D10 protects
transistors T11 to T13 against transient line voltages.
3.7 PULSE DIALING (SEE Fig. 22)
During pulse dialing the hookswitch (T8, T9) is used to generate the pulses using the H O O K 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), thus reducing line impedance
(see section 3.10)
3.8 AUDIO CIRCUITS (SEE Fig. 22)
The line output signal from the BBIC R X A F (TP120) is amplified by T13. The R X A F 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 fre-
quency response, since the line load (for UK) is also complex.
The line input signal TXAF (TP123) 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.
RxAF
TxAF
HOOK
PULSE DIAL
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KX-TCD951EB/KX-TCD955EC
3.9 POWER SUPPLIES (SEE Fig. 23)
The AC Adaptor for the KX-TCD951EB / KX-TCD955EC 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 IC6 is fed with +4V and provides the stable +3.0V supply (TP95). During power-up this
regulator generates a RESET signal (TP94) which is used to reset the microcontroller and BBIC.
3.10 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 the “Charging” LED D12. The charge contacts are J3 (TP89) positive and J4 (TP88) negative.
Charge current flows in via J4, through T15, R63, AC Adaptor 9 V supply, R64, D11, and out via J3.
Circuit Diagram
VUNREG
RESET
Fig. 23
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KX-TCD951EB/KX-TCD955EC
Fig. 24
BLOCK DIA
GRAM RF UNIT (HANDSET)
Doubler
1.89GHz
BPF
TR Switch
RF
Amp
112.32MHz
BPF
BPF=Bandpass Filter
LPF=Low Pass Filter
LPF=Low Pass Filter
Mixer
Phase-Lock-Loop
Tx
Buffer
PA
Switch
P.A.
SAW
BPF
IF
Amp
RSSI
DC
Comp
IF
Amp
Det.
VCO
Buff.
DC Contr.
Rx/Tx
3V
Reg.
3V
Data
LPF
945MHz
1.89GHz
10.368MHz
4V-FILT
SLICE OUT 31
SLICE CTRL 30
SLICE CTRL 30
RSSI 32
SYS CLOCK 34
PLL ENABLE 22
PLL DATA 21
PLL CLOCK 20
PLL PD 12
PLL DATA 21
PLL CLOCK 20
PLL PD 12
Vcc OC 18
RF ON 8
RF ON 8
Rx DATA
29
Tx DATA
19
Vcc PA (4V)
5
,
4
PLL PWR DWN
17
Tx/Rx SWITCH
2
PA RAMP
39
RF1
49
NC
42
GND
43
GND
44
GND
45
GND
46
GND
47
GND
48
RF1
49
GND
15
NC
14
NC
13
PLL PD
12
NC
11
GND
10
GND
9
9
RF ON
8
8
GND
7
7
GND
6
6
Vcc PA
5
5
Vcc PA
4
4
GND
3
3
Tx/Rx SWITCH
2
2
GND
1
1
GND 26
GND
27
GND
28
Rx DATA
29
SLICE CTRL
30
SLICE OUT
31
RSSI
32
GND
33
SYS CLOCK
34
GND
35
GND
36
GND
37
GND
38
PA RAMP
39
GND
40
GND
41
GND 25
GND 24
GND 23
GND 24
GND 23
PLL ENABLE 22
PLL DATA 21
PLL CLOCK 20
Tx DATA 19
Vcc OC 18
PLL PWR DWN 17
NC 16
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