Panasonic KX-TC2105RUB / KX-TC2105RUS / KX-TC2105RUT / KX-TC2105RUW Service Manual ▷ View online
14.2. Power Supply Circuit
The power supply to the CPU and RF IC from AC Adaptor (+12V) is shown in the diagram below.
The base unit power supply is DC12V. The handset power is supplied from DC 3.6V battery (Nickel-Cadmium battery) which
is installed in the handset.
is installed in the handset.
Power supply for transmitter is turned on by pressing "TALK" key on the handset. During the stand-by mode, the unit stops
transmitting but receives the signal.
During on-hook condition (the handset is placed on the base unit), backup power for memory of the last dialed number is
supplied through the battery (DC 3.6V Nickel-Cadmium in the handset). The memory of this unit is not backed up by the current
from the telephone line.
from the telephone line.
The base unit DC power supply is regulated by Q101, D103. The CPU power is supplied from IC401. IC401 detects AC Adaptor
power failure and maintains the unit security code.
power failure and maintains the unit security code.
<Fig. 1>
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KX-TC2105RUB / KX-TC2105R US / KX-TC2105R UT / KX-TC2105RUW
14.3. Reset Circuit
After power supply from AC adaptor, the reset signal for CPU is making in IC401. Refer to the below waveform.
<Fig. 2>
<Fig. 3>
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KX-TC2105RUB / KX-TC2105R US / KX-TC2105R UT / KX-TC2105RUW
14.4. Charge Circuit
Circuit Operation:
When charging the handset on the base unit, the charge current is as follows;
DC12V
→
L101
→
D102
→
L103
→
CH+(Base)
→
+CONTACT J601(Handset)
→
L602
→
D602
→
CN1-1
→
Battery
→
CN1-2
→
-CONTACT J602(Handset)
→
CH-(Base)
→
L104
→
Q102
→
R104
In this way, the CPU on both units detects the fact that the battery is charged.
The charge current is controlled by switching Q103 of Base Unit. The battery is charged in normal mode for 9 hours and then
in trickle mode.
in trickle mode.
14.5. Telephone Line Interface
Function:
•
•
•
•
Bell signal detection
•
•
•
•
ON/OFF hook and pulse dial circuit
•
•
•
•
Side tone circuit
Bell signal detection and OFF HOOK circuit:
In the idle mode, Q301 is open to cut the DC loop current and decrease the ring load. When ring voltage appears at the Tip (T)
and Ring (R) leads (When the telephone rings), the AC ring voltage is transferred as follows:
•
•
•
•
JK1 TIP
→
P0301
→
L301
→
R334
→
C322
→
Q309
→
IC201 Pin30
•
•
•
•
JK1 RING
→
L302
→
R333
→
C321
→
C323
→
Q309
→
IC201 Pin30
When the CPU detects a ring signal and press the “TALK” key on the handset, Q302 turns on and then Q301 turns on,
thus providing an off-hook condition (active DC current flow through the circuit) and the following signal flow is for the loop
current.
•
•
•
•
Tip
→
P0301
→
L301
→
D303
→
Q301
→
R303
→
Q302
→
D306
→
L302
→
Ring
ON HOOK Circuit:
Q302 is open, Q301 is disconnected as to cut the DC loop current and to cut the voice signal. The unit is consequently in an
on-hook condition.
on-hook condition.
Pulse Dial Circuit:
CPU (Hook) turns Q302 ON/OFF to make the pulse dialing via Q301.
Make/Break ratio when dialing with the Handset 40% : 60%
Side Tone Circuit:
Basically this circuit prevents the TX signal from feeding back to RX signal.
As for this unit, TX signal feed back from Q304 is canceled by the side tone circuit C312, C313, R317, R318 and R319.
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KX-TC2105RUB / KX-TC2105R US / KX-TC2105R UT / KX-TC2105RUW
14.6. Transmitter/Receiver
Base Unit and Handset mainly consist of RF (Radio Frequency) IC and CPU.
Base Unit and Handset transmit/receive voice signal and data signal through the antenna on carrier frequency.
Signal Path:
*Refer to CDL TX/RX in SIGNAL ROUTE (P.41).
14.6.1. Base to Handset
Circuit Operation:
The voice signal input from the TEL LINE interface goes to RF IC as shown in BLOCK DIAGRAM (BASE UNIT) (P.31).
In the talk mode (off-hook) condition, the telephone line voice signal passes through D303, Q301, C313, R320 and C315.
The signal goes through the compressor of RF IC, and it is output to transmitter circuit.
The signal of the data sent to the handset is applied in the anode of the variable capacitor diode (VARICAP : DV401).
The capacitor of VARICAP is changing in accordance with the voice signal from telephone line interface or TX DATA signal from
CPU. Therefore, the carrier frequency which is generated by TX VCO will be changed, and Frequency modulated RF
signal is generated and amplified by RF AMP (Q405, T403). It passes through the Duplexer DPX401 and is radiated from
Antenna.
Antenna.
The signal is transmitted from the base unit and received by the handset antenna and amplified by RF amplifier (Q801) through
DPX1 as shown in BLOCK DIAGRAM (HANDSET) (P.38). And then it is converted to 10.7 MHz and 450 KHz Intermediate
frequency by RF IC and related components.
frequency by RF IC and related components.
The demodulated audio signal is output from RF IC (DET OUT) and passed through "Expander" process to reduce noise, then
voice signal amplified by "Receiver amplifier" is output to receiver (REC1).
The receiver loudness is adjustable by using "LOUD" key on the handset.
TX data (to Handset):
CPU (VTX) becomes low to turn on the transmission power transistor Q805, and CPU (TX-data) sends data signal. It is
FM-modulated by TX VCO and driven by RF AMP, then transmitted to the handset.
14.6.2. Handset to Base
Circuit Operation:
The voice signal from the handset user is picked up by the microphone (MIC), then it passes through "Compressor"
process to reduce noise as shown in BLOCK DIAGRAM (HANDSET) (P.38). And the voice is FM-modulated by
VARICAP (DV1).
The carrier frequency is generated by TX VCO. The transmitter power transistor Q805 is turned on/off by CPU (VTX).
The carrier signal is amplified by RF AMP and sent to the handset duplexer and antenna.
The signal of 39 MHz band (39.775~40.000 MHz) which is input from ANT is filtered at DPX401 as shown in
BLOCK DIAGRAM (BASE UNIT) (P.31), then it is input to RF IC.
The signal input to RF IC is converted through Mixer inside of RF IC, RF filter (CF1, CF2) and Expander.
The signal is transmitted from the handset and received by the base unit antenna and amplified by RF amplifier Q401, then
it is converted to10.7 MHz and 450 KHz Intermediate by RF IC. The demodulated audio signal is output from RF IC
(DET OUT) and passed through "Expander" process to reduce noise, then voice signal is led to LINE AMP. The signal passes
through TELEPHONE INTERFACE and Tel-line.
through TELEPHONE INTERFACE and Tel-line.
RX data (from Handset):
The data signal from handset (ex: Talk, ACK, COM) is also included in 39 MHz band same as the voice data. After second if
filter, the data signal is made square shape by data limiting AMP of the RF IC. RX data is output to CPU (RX Data).
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KX-TC2105RUB / KX-TC2105R US / KX-TC2105R UT / KX-TC2105RUW
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