KX-TG2521RUT, KX-TGA251RUT — Panasonic Telephone Service Manual (repair manual). Page 11

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11
KX-TG2521RUT/KX-TGA251RUT
4.3.
Block Diagram (Handset)
SPEAKER
RECEIVER
MIC
CHARGE
CIRCUIT
Q4, Q9, R7Q4,
Q9,
R7
CHARGE
CONTACTS
CHARGE(+)
CHARGE(-)
CHARGE_CTRL
CHARGE
EEPROM
SCL
SDA
BATTERY
TERMINAL
D7
R45
VBAT
BATT+
BATT-
1.8 V
Q2
1.8 V
LCD
CD
RESET
CSB
SDA
 SCL
CPU
Analog
Front
End
D/A
A/D
33
35
15
16
19
20
32
31
57
58
 36
13
43
42
63
54
55
66
ADPCM
Codec
Filter
DSP
Speech
Decoding
Speech
Encoding
BMC
Burst
Decoding
RF PA
ANT1
IC801
Burst
Encoding
RF
PLL
MOD/DEMOD
5
3
4
3
6
7
8
9
2
77
78
75
RXn
RXon
ANT1
DA801
RXp
TXp
TXn
Pon
PSEL
TXon
VDD-PADRY
9
10
XTAL
X1
10.368
MHz
BATTERY
44
ON SWITCH
KEYPAD
Charge
Pump
ROWS
COLUMNS
CP3.0V
CP4.0V
48, 49, 50, 51
22, 23, 24, 25, 26
BBIC
IC1
IC3
 56
52
73
74
80
LDO_CTRL
KX-TGA251 BLOCK DIAGRAM (HANDSET)
LCD-BACK  LIGHT
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KX-TG2521RUT/KX-TGA251RUT
4.4.
Circuit Operation (Handset)
4.4.1.
Outline
Handset consists of the following ICs as shown in Block Diagram (Handset) (P.11).
• DECT BBIC (Base Band IC): IC1
- All data signals (forming/analyzing ACK or CMD signal)
- All interfaces (ex: Key, Detector Circuit, Charge, DC/DC Converter, EEPROM, LCD, RF Power Amp.)
- PLL Oscillator
- Detector
- Compress/Expander
- Reception
• RF Power Amp: IC801
- Amplifier for transmission
• EEPROM: IC3
- Temporary operating parameters (for RF, etc.)
4.4.2.
Power Supply Circuit/Reset Circuit
Circuit Operation:
When power on the Handset, the voltage is as follows;
BATTERY(2.2 V ~ 2.6 V: BATT+) 
→ F1 → Q2 (1.8 V), IC1-43pin (2.5V)
The Reset signal generates IC1 (61 pin) and 1.8 V.
4.4.3.
Charge Circuit
Circuit Operation:
When charging the handset on the Base Unit, the charge current is as follows;
DC+(6.5 V) 
→ R56 → R55 → D22 → CHARGE+(Base) → CHARGE+(Handset) → Q4 → D7→ F1 → BATTERY+... Battery... 
BATTERY- 
→ R45 → GND → CHARGE-(Handset)→ CHARGE-(Base) → GND → DC-(GND)
In this way, the BBIC on Handset detects the fact that the battery is charged.
The charge current is controlled by switching Q9 of Handset.
Refer to Fig.101 in Power Supply Circuit (P.9).
4.4.4.
Battery Low/Power Down Detector
Circuit Operation:
“Battery Low” and “Power Down” are detected by BBIC which check the voltage from battery.
The detected voltage is as follows;
• Battery Low
Battery voltage: V(Batt)   2.25 V ± 50 mV
The BBIC detects this level and "
" starts flashing.
• Power Down
Battery voltage: V(Batt)   2.0 V ± 50 mV
The BBIC detects this level and power down.
4.4.5.
Speakerphone
The hands-free loudspeaker at SP+ and SP- is used to generate the ring alarm.
13
KX-TG2521RUT/KX-TGA251RUT
4.5.
Signal Route
14
KX-TG2521RUT/KX-TGA251RUT
15
KX-TG2521RUT/KX-TGA251RUT
5 Location of Controls and Components
Refer to the Operating Instructions.
Note:
You can download and refer to the Operating Instructions (Instruction book) on TSN Server.
6 Installation Instructions
Refer to the Operating Instructions.
Note:
You can download and refer to the Operating Instructions (Instruction book) on TSN Server.
7 Operating Instructions
Refer to the Operating Instructions.
Note:
You can download and refer to the Operating Instructions (Instruction book) on TSN Server.
7.1.
For Service Hint

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