Panasonic KX-TG7841S User manual

© Panasonic System Networks Co., Ltd. 2013
Unauthorized copying and distribution is a violation
of law.
ORDER NO. KM41302655CE
F13
Telephone Equipment
Model No. KX-TG7841S
KX-TG7842S
KX-TG7843S
KX-TG7844S
KX-TG7845S
KX-TG365SK
KX-TG7871S
KX-TG7872S
KX-TG7873S
KX-TG7874S
KX-TG7875S
KX-TG385SK
KX-TGA680S
KX-TGA20B
Link-to-Cell Cellular Convergence
Solution
B: Black Version
S: Silver Version
(for U.S.A.)
(Handset)
KX-TGA680 KX-TG7841/7871
(Base Unit)
(Charger Unit)
Model No Base Unit Handset Charger Unit Expandable
KX-TG7841
1 (TG7841) 1 (TGA680) Up to 6
KX-TG7842
1 (TG7841) 2 (TGA680) 1 Up to 6
KX-TG7843
1 (TG7841) 3 (TGA680) 2 Up to 6
KX-TG7844
1 (TG7841) 4 (TGA680) 3 Up to 6
KX-TG7845
1 (TG7841) 5 (TGA680) 4 Up to 6
KX-TG365
1 (TG7841) 5 (TGA680) 4 Up to 6
KX-TG7871
1 (TG7871) 1 (TGA680) Up to 6
KX-TG7872
1 (TG7871) 2 (TGA680) 1 Up to 6
KX-TG7873
1 (TG7871) 3 (TGA680) 2 Up to 6
KX-TG7874
1 (TG7871) 4 (TGA680) 3 Up to 6
KX-TG7875
1 (TG7871) 5 (TGA680) 4 Up to 6
KX-TG385
1 (TG7871) 5 (TGA680) 4 Up to 6
KX-TGA680*
1 (TGA680) 1
Configuration for each model
*KX-TGA680 is also an optional accessory, which contains a
handset and a charger.

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KX-TG7841/KX-TG7842/KX-TG7843/KX-TG7844/KX-TG7845/KX-TG365SK/KX-TG7871/KX-TG7872/KX-TG7873/KX-TG7874/KX-TG7875/KX-TG385SK/KX-TGA680
WARNING
This service information is designed for experienced repair technicians only and is not designed for use by the general
public. It does not contain warnings or cautions to advise non-technical individuals of potential dangers in attempting
to service a product. Products powered by electricity should be serviced or repaired only by experienced professional
technicians. Any attempt to service or repair the product or products dealt with in this service information by anyone
else could result in serious injury or death.
IMPORTANT SAFETY NOTICE
There are special components used in this equipment which are important for safety. These parts are marked by
in the Schematic Diagrams, Circuit Board Diagrams, Exploded Views and Replacement Parts List. It is essential that
these critical parts should be replaced with manufacturer’s specified parts to prevent shock, fire or other hazards.
Do not modify the original design without permission of manufacturer.
IMPORTANT INFORMATION ABOUT LEAD FREE, (PbF), SOLDERING
If lead free solder was used in the manufacture of this product, the printed circuit boards will be marked PbF.
Standard leaded, (Pb), solder can be used as usual on boards without the PbF mark.
When this mark does appear, please read and follow the special instructions described in this manual on the
use of PbF and how it might be permissible to use Pb solder during service and repair work.
LWhen you note the serial number, write down all 11 digits. The serial number may be found on the bottom of the unit.
LThe illustrations in this Service Manual may vary slightly from the actual product.

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KX-TG7841/KX-TG7842/KX-TG7843/KX-TG7844/KX-TG7845/KX-TG365SK/KX-TG7871/KX-TG7872/KX-TG7873/KX-TG7874/KX-TG7875/KX-TG385SK/KX-TGA680
TABLE OF CONTENTS PAGE PAGE
1 Safety Precautions----------------------------------------------- 5
1.1. For Service Technicians --------------------------------- 5
2 Warning-------------------------------------------------------------- 5
2.1. Battery Caution--------------------------------------------- 5
2.2. About Lead Free Solder (PbF: Pb free)-------------- 5
2.2.1. Suggested PbF Solder ------------------------------ 6
2.3. Discarding of P. C. Board-------------------------------- 6
3 Specifications ----------------------------------------------------- 7
4 Technical Descriptions ----------------------------------------- 8
4.1. Circuit Configuration of TG78xx Series
Phones------------------------------------------------------- 8
4.2. US-DECT Description------------------------------------ 9
4.2.1. TDD Frame Format ---------------------------------- 9
4.2.2. TDMA system------------------------------------------ 9
4.2.3. Signal Flowchart in the Radio Parts-------------10
4.3. Block Diagram (Base Unit_Main)---------------------11
4.4. Tel Interface Circuit---------------------------------------12
4.5. Block Diagram (Base Unit_RF Part)-----------------13
4.6. Circuit Operation (Base Unit)--------------------------14
4.6.1. BBIC (Base Band IC: IC501) ---------------------14
4.6.2. Flash Memory (IC502)------------------------------14
4.6.3. Flash Memory (IC601)------------------------------14
4.6.4. EEPROM (IC611)------------------------------------14
4.6.5. Bluetooth Unit (IC721)------------------------------14
4.6.6. Power Supply Circuit/Reset Circuit--------------15
4.6.7. Telephone Line Interface---------------------------17
4.6.8. Parallel Connection Detect Circuit/Auto
Disconnect Circuit -----------------------------------18
4.6.9. Calling Line Identification (Caller ID)/Call
Waiting Caller ID-------------------------------------19
4.7. Block Diagram (Handset)-------------------------------21
4.8. Block Diagram (Handset_RF Part)-------------------22
4.9. Circuit Operation (Handset)----------------------------23
4.9.1. Outline--------------------------------------------------23
4.9.2. Power Supply Circuit/Reset Circuit--------------23
4.9.3. Charge Circuit ----------------------------------------24
4.9.4. Battery Low/Power Down Detector--------------24
4.9.5. Speakerphone----------------------------------------24
4.10. Behavior of Electric Power Failure-------------------25
4.11. Circuit Operation (Charger Unit)----------------------25
4.12. Signal Route-----------------------------------------------26
5 Location of Controls and Components ------------------28
6 Installation Instructions---------------------------------------28
7 Operating Instructions-----------------------------------------28
8 Test Mode ----------------------------------------------------------29
8.1. Engineering Mode----------------------------------------29
8.1.1. Base Unit ----------------------------------------------29
8.1.2. Handset ------------------------------------------------31
9 Service Mode -----------------------------------------------------33
9.1. How to Clear User Setting (Handset Only)---------33
10 Troubleshooting Guide----------------------------------------34
10.1. Troubleshooting Flowchart-----------------------------34
10.1.1. Check Power------------------------------------------35
10.1.2. Check Record ----------------------------------------36
10.1.3. Check Playback -------------------------------------39
10.1.4. Check Battery Charge------------------------------39
10.1.5. Check Link---------------------------------------------40
10.1.6. Check the RF part -----------------------------------42
10.1.7. Registering a Handset to the Base Unit-------46
10.1.8. Deregistering a Handset---------------------------46
10.1.9. Check Handset Transmission--------------------47
10.1.10. Check Handset Reception------------------------47
10.1.11. Check Caller ID ------------------------------------- 47
10.1.12. Check BT Communication------------------------48
11 Disassembly and Assembly Instructions---------------50
11.1. Disassembly Instructions-------------------------------50
11.1.1. Base Unit----------------------------------------------50
11.1.2. Handset------------------------------------------------52
11.1.3. Charger Unit------------------------------------------53
11.2. How to Replace the Base unit LCD ----------------- 54
11.3. How to Replace the Handset LCD-------------------56
12 Measurements and Adjustments --------------------------57
12.1. Equipment Required ------------------------------------57
12.2. The Setting Method of JIG-----------------------------57
12.2.1. Connections (Base Unit) --------------------------57
12.2.2. Connections (Handset) ----------------------------58
12.2.3. How to install Batch file into P.C.----------------59
12.2.4. Commands--------------------------------------------60
12.3. Adjustment Standard (Base Unit)--------------------61
12.3.1. Bottom View ------------------------------------------61
12.4. Adjustment Standard (Handset)---------------------- 62
12.4.1. Component View ------------------------------------ 62
12.5. Things to Do after Replacing IC or X'tal------------63
12.5.1. How to download the data ------------------------63
12.6. Frequency Table------------------------------------------ 66
12.7. Bluetooth Frequency Table----------------------------67
13 Miscellaneous----------------------------------------------------68
13.1. How to Replace the LLP (Leadless Leadframe
Package) IC ----------------------------------------------- 68
13.1.1. Preparation--------------------------------------------68
13.1.2. Caution-------------------------------------------------68
13.1.3. How to Remove the IC-----------------------------68
13.1.4. How to Install the IC --------------------------------69
13.2. How to Replace the Flat Package IC ---------------70
13.2.1. Preparation--------------------------------------------70
13.2.2. How to Remove the IC-----------------------------70
13.2.3. How to Install the IC --------------------------------71
13.2.4. How to Remove a Solder Bridge----------------71
13.3. Terminal Guide of the ICs, Transistors and
Diodes ------------------------------------------------------72
13.3.1. Base Unit----------------------------------------------72
13.3.2. Handset------------------------------------------------ 72
14 Schematic Diagram --------------------------------------------73
14.1. For Schematic Diagram --------------------------------73
14.1.1. Base Unit (Schematic Diagram (Base
Unit_Main)) ------------------------------------------- 73
14.1.2. Handset (Schematic Diagram
(Handset_Main))-------------------------------------73
14.2. Schematic Diagram (Base Unit_Main)--------------74
14.3. Schematic Diagram (Base Unit_RF)---------------- 76
14.4. Schematic Diagram (Base Unit_Operation)-------77
14.5. Schematic Diagram (Base Unit_USB Charge) ---78
14.6. Schematic Diagram (Base Unit_LED) --------------78
14.7. Schematic Diagram (Handset_Main) ---------------80
15 Printed Circuit Board ------------------------------------------83
15.1. Circuit Board (Base Unit_Main) ----------------------83

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KX-TG7841/KX-TG7842/KX-TG7843/KX-TG7844/KX-TG7845/KX-TG365SK/KX-TG7871/KX-TG7872/KX-TG7873/KX-TG7874/KX-TG7875/KX-TG385SK/KX-TGA680
15.1.1. Component View ------------------------------------83
15.1.2. Bottom View ------------------------------------------84
15.2. Circuit Board (Base Unit_Operation)----------------85
15.3. Circuit Board (Base Unit_USB Charge)------------86
15.4. Circuit Board (Base Unit_LED)-----------------------86
15.5. Circuit Board (Handset_Main) ------------------------87
15.5.1. Component View ------------------------------------87
15.5.2. Bottom View ------------------------------------------88
16 Exploded View and Replacement Parts List-----------89
16.1. Cabinet and Electrical Parts (Base Unit)-----------89
16.2. Cabinet and Electrical Parts (Handset)-------------90
16.3. Cabinet and Electrical Parts (Charger Unit)-------91
16.4. Accessories and Packing Materials -----------------92
16.4.1. KX-TG7841S -----------------------------------------92
16.4.2. KX-TG7842S -----------------------------------------93
16.4.3. KX-TG7843S -----------------------------------------94
16.4.4. KX-TG7844S -----------------------------------------95
16.4.5. KX-TG7845S -----------------------------------------96
16.4.6. KX-TG365SK-----------------------------------------97
16.4.7. KX-TG7871S -----------------------------------------98
16.4.8. KX-TG7872S -----------------------------------------99
16.4.9. KX-TG7873S --------------------------------------- 100
16.4.10. KX-TG7874S --------------------------------------- 101
16.4.11. KX-TG7875S --------------------------------------- 102
16.4.12. KX-TG385SK--------------------------------------- 103
16.4.13. KX-TGA680S--------------------------------------- 104
16.5. Replacement Parts List------------------------------- 105
16.5.1. Base Unit-------------------------------------------- 105
16.5.2. Handset---------------------------------------------- 107
16.5.3. Charger Unit ---------------------------------------- 109
16.5.4. Accessories and Packing Materials----------- 109
16.5.5. Screws ------------------------------------------------110
16.5.6. Fixtures and Tools----------------------------------110

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KX-TG7841/KX-TG7842/KX-TG7843/KX-TG7844/KX-TG7845/KX-TG365SK/KX-TG7871/KX-TG7872/KX-TG7873/KX-TG7874/KX-TG7875/KX-TG385SK/KX-TGA680
1 Safety Precautions
1.1. For Service Technicians
•Repair service shall be provided in accordance with repair technology information such as service manual so as to
prevent fires, injury or electric shock, which can be caused by improper repair work.
1. When repair services are provided, neither the products nor their parts or members shall be remodeled.
2. If a lead wire assembly is supplied as a repair part, the lead wire assembly shall be replaced.
3. FASTON terminals shall be plugged straight in and unplugged straight out.
•ICs and LSIs are vulnerable to static electricity.
When repairing, the following precautions will help prevent recurring malfunctions.
1. Cover plastic parts boxes with aluminum foil.
2. Ground the soldering irons.
3. Use a conductive mat on worktable.
4. Do not grasp IC or LSI pins with bare fingers.
2Warning
2.1. Battery Caution
Risk of explosion if battery is replaced by an incorrect type. Dispose of used batteries according to the instructions.
Attention:
A nickel metal hydride battery that is recyclable powers the product you have purchased.
Please call 1-800-8-BATTERY (1-800-822-8837) for information on how to recycle this battery.
2.2. About Lead Free Solder (PbF: Pb free)
Note:
In the information below, Pb, the symbol for lead in the periodic table of elements, will refer to standard solder or solder that
contains lead.
We will use PbF solder when discussing the lead free solder used in our manufacturing process which is made from Tin (Sn),
Silver (Ag), and Copper (Cu).
This model, and others like it, manufactured using lead free solder will have PbF stamped on the PCB. For service and repair
work we suggest using the same type of solder.
Caution
• PbF solder has a melting point that is 50 °F ~ 70 °F (30 °C ~ 40 °C) higher than Pb solder. Please use a soldering iron with
temperature control and adjust it to 700 °F ± 20 °F (370 °C ± 10 °C).
• Exercise care while using higher temperature soldering irons.:
Do not heat the PCB for too long time in order to prevent solder splash or damage to the PCB.
• PbF solder will tend to splash if it is heated much higher than its melting point, approximately 1100 °F (600 °C).
• When applying PbF solder to double layered boards, please check the component side for excess which may flow onto the
opposite side (See the figure below).
Component
Component
pin
Solder
Remove all of the
excess solder
(Slice View)

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KX-TG7841/KX-TG7842/KX-TG7843/KX-TG7844/KX-TG7845/KX-TG365SK/KX-TG7871/KX-TG7872/KX-TG7873/KX-TG7874/KX-TG7875/KX-TG385SK/KX-TGA680
2.2.1. Suggested PbF Solder
There are several types of PbF solder available commercially. While this product is manufactured using Tin, Silver, and Copper
(Sn+Ag+Cu), you can also use Tin and Copper (Sn+Cu), or Tin, Zinc, and Bismuth (Sn+Zn+Bi). Please check the
manufacturer's specific instructions for the melting points of their products and any precautions for using their product with other
materials.
The following lead free (PbF) solder wire sizes are recommended for service of this product: 0.3 mm, 0.6 mm and 1.0 mm.
2.3. Discarding of P. C. Board
When discarding P. C. Board, delete all personal information such as telephone directory and caller list or scrap P. C. Board.
0.3 mm X 100 g 0.6 mm X 100 g 1.0 mm X 100 g

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KX-TG7841/KX-TG7842/KX-TG7843/KX-TG7844/KX-TG7845/KX-TG365SK/KX-TG7871/KX-TG7872/KX-TG7873/KX-TG7874/KX-TG7875/KX-TG385SK/KX-TGA680
3 Specifications
Note:
(*1) KX-TG7841/KX-TG7842/KX-TG7843/KX-TG7844/KX-TG7845/KX-TG365SK
(*2) KX-TG7871/KX-TG7872/KX-TG7873/KX-TG7874/KX-TG7875/KX-TG385SK
Design and specifications are subject to change without notice.
Note for Service:
•Operation range: Up to 300 m outdoors, Up to 50 m indoors, depending on the condition.
•Analog telephone connection: Telephone Line
•Optional headset: KX-TCA60, KX-TCA93, KX-TCA400, KX-TCA430
•Optional Range extender: KX-TGA405
•Optional Key detector: KX-TGA20
Power source
Receiving Method
Oscillation Method
Detecting Method
Tolerance of OSC Frequency
Modulation Method
ID Code
Ringer Equivalence No. (REN)
Dialing Mode
Redial
Speed Dialer
Power Consumption
Operating Conditions
Dimensions (W x D x H)
Mass (Weight)
AC Adaptor
(PNLV226Z, 120 V AC, 60 Hz) (*1)
(PNLV234Z, 120 V AC, 60 Hz) (*2)
Super Heterodyne
PLL synthesizer
Quadrature Discriminator
10.368 MHz ±100 Hz
Frequency Modulation
40 bit
0.1B
Tone (DTMF)/Pulse
Up to 48 digits
Up to 24 digits (Phonebook)
Standby: Approx. 1.2 W
Maximum: Approx. 4.5 W (*1)
Maximum: Approx. 8.5 W (*2)
0 ˚C - 40 ˚C (32 ˚F – 104 ˚F)
20 % – 80 % relative air humidity
(dry)
Approx. 178 mm × 115 mm × 101 mm
Approx. 350 g
Rechargeable Ni-MH battery
AAA (R03) size (1.2 V 400 mAh)
Super Heterodyne
PLL synthesizer
Quadrature Discriminator
13.824 MHz ±100 Hz
Frequency Modulation
40 bit
Tone (DTMF)/Pulse
Up to 48 digits
Up to 24 digits (Phonebook)
8 days at Standby,
10 hours at Talk
0 ˚C - 40 ˚C (32 ˚F – 104 ˚F)
20 % – 80 % relative air humidity
(dry)
Approx. 48
mm × 31 mm × 168 mm
Approx. 130 g
Base Unit Handset Charger
AC Adaptor
(PNLV233-AZ, 120 V AC, 60 Hz)
Standby: Approx 0.1 W
Maximum: Approx 1.8 W
0 ˚C - 40 ˚C (32 ˚F – 104 ˚F)
20 % – 80 % relative air humidity
(dry)
Approx. 72 mm × 73 mm × 39 mm
Approx. 100 g
Duplex procedure:
TDMA (Time Division Multiple Access)
Channel spacing:
1.728MHz (DECT 6.0)
1.0MHz(Bluetooth)
Bit rate:
1.152Mbit/s (DECT 6.0)
1.0 Mbit/s (Bluetooth)
Modulation:
GFSK (Gaussian Frequency Shift Keying)
RF transmission power:
115 mW (max/DECT6.0)
Voice coding:
USB Charger: (*2)
ADPCM 32 kbit/s (DECT 6.0)
CVSD/PCM 64kbit/s (Bluetooth)
PCM 64kbit/s(BT_IC)
■
■
■
■
■
■
■
■Standard:
DECT 6.0 (Digital Enhanced Cordless
Telecommunications 6.0)
■Number of channels:
60 Duplex Channels (DECT 6.0)
79 Duplex channels(Bluetooth)
Bluetooth wireless technology 2.1
■Frequency range:
1.92 GHz to 1.93 GHz (DECT 6.0)
2.402 GHz to 2.48 GHz (Bluetooth)
Output voltage: DC 5 V
Output current: 500 mA

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KX-TG7841/KX-TG7842/KX-TG7843/KX-TG7844/KX-TG7845/KX-TG365SK/KX-TG7871/KX-TG7872/KX-TG7873/KX-TG7874/KX-TG7875/KX-TG385SK/KX-TGA680
4 Technical Descriptions
4.1. Circuit Configuration of TG78xx Series Phones
TG78xx consists of DECT cordless telephone and Bluetooth Module.
Both voices of transmission and reception are transferred by PCM.
BBIC on DECT side controls the cordless telephone system, which makes control data communication with BT_IC on BT
Module in serial data.
DECT6.0
Bluetooth
Headset
Bluetooth Devices
Cellular Phone
(For Link to Cell
communication)
TGA680
Handset
PSTN DC
5.5V
BBIC
FLASH IC601
(TAM)
EEPROM IC611
(Data)
TEL I/F POWER
QSPI FLASH
IC502
(Program)
Main PCB
Audio signal
(PCM)
Control/Data
Bluetooth Bluetooth
signal
(UART)
BT_Module
(IC721)
(IC501)
MIC
SPEAKER

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KX-TG7841/KX-TG7842/KX-TG7843/KX-TG7844/KX-TG7845/KX-TG365SK/KX-TG7871/KX-TG7872/KX-TG7873/KX-TG7874/KX-TG7875/KX-TG385SK/KX-TGA680
4.2. US-DECT Description
The frequency range of 1.92 GHz-1.93 GHz is used. Transmitting and receiving carrier between base unit and handset is same
frequency. Refer to Frequency Table (P.66).
4.2.1. TDD Frame Format
4.2.2. TDMA system
This system is the cycles of 10 ms, and has 6 duplex paths, but maximum duplex communication path is 5 because of dummy
bearer use.
In 1 slot 417 μs, the 10 ms of voice data is transmitted.
•2 - Handsets Link
Traffic Bearer
A link is established between base unit and handset.
The state where duplex communication is performed.
Handset doesn't make up duplex in no free RF channels because of interference. (*1)
Dummy Bearer
Base unit sends Dummy-data to the all stand-by state handsets.
Handsets receive that data for synchronization and monitoring request from the base unit.
Base unit doesn't send Dummy bearer in no free RF channels because of interference. (*1)
Note:
(*1) It is a feature under FCC 15 regulation and for interference avoidance.
In the case of checking RF parts, it is better in least interference condition.
417 μs (available) 417 μs (blind)
5 ms 5 ms
Up Link ( Handset ->Base Unit ) Down Link ( Base Unit ->Handset )
DATA rate : 1.152 Mbps
RX1 RX2 RX3 RX4 RX5 RX6 TX1 TX2 TX3 TX4 TX5 TX6
RX1 RX2 RX3 RX4 RX5 RX6 TX1 TX2 TX3 TX4 TX5 TX6
TX RX
RXTX
Traffic Bearer Dummy bearer
Base unit
Handset 1
(Stand by)
Handset 2
(Link)
Handset 3
(Link)

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KX-TG7841/KX-TG7842/KX-TG7843/KX-TG7844/KX-TG7845/KX-TG365SK/KX-TG7871/KX-TG7872/KX-TG7873/KX-TG7874/KX-TG7875/KX-TG385SK/KX-TGA680
4.2.3. Signal Flowchart in the Radio Parts
Reception
Base unit:
A voice signal from TEL line is encoded to digital data and converted into a 1.9GHz modulated radio signal by BBIC(IC501).
The RF signal, after which is amplified in BBIC, is fed to selected antenna.
Handset:
As for a handset RF, RF signal is received in one antenna.
BBIC down-converts to 864 kHz IF signal from RX signal and demodulates it to digital data "RXDATA".
BBIC (IC1) converts RXDATA into a voice signal and outputs it to speaker.
Transmission
Handset:
A voice signal from microphone is encoded to digital data and converted into a 1.9GHz modulated radio signal by BBIC(IC1).
The RF signal, after which is amplified in BBIC, is fed to an antenna.
Base unit:
As for a base unit RF, RF signal is received in two antennas.
BBIC (IC501) compares RF signal levels and selects the antenna to be used. Then BBIC down-converts to 864 kHz IF signal
from RX signal in the selected antenna, and demodulates it to digital data "RXDATA".
BBIC (IC501) converts RXDATA into a voice signal and outputs it to TEL line.

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KX-TG7841/KX-TG7842/KX-TG7843/KX-TG7844/KX-TG7845/KX-TG365SK/KX-TG7871/KX-TG7872/KX-TG7873/KX-TG7874/KX-TG7875/KX-TG385SK/KX-TGA680
4.3. Block Diagram (Base Unit_Main)
KX-TG7841/7842/7843/7844/7845/365/7871/7872/7873/7874/7875/385 BLOCK DIAGRAM (Base Unit_Main)
SIDE_TONE CIRCUIT
Crystal 10.368MHz
TR_RLY
TIP
RING
TEL_JACK
VRF
/
VPA
RF_Block
IC501 BBIC
DC5.5V+ GND
DC_JACK
+
-
CHARGE
3
4
2
1
D1
0
1
CHARGE DETECT
Q
7
0
1
Q141
Q161
REGULATOR
IC302
Power Down DET
Power supply at AC failure
KEY PAD
LED
VBAT
PDN_DET
CHARGE_DET
IC611
LCD
IC502
IC751
IC601
IC721 BT Module
Q301
+1.8V +3.0V
AVD/VDD
QSPI
CIDINp CIDINn
P3_6 MICh
LSRp
RF_VDD
Q302
+2.4V
VDD_PA
ANT1 ANT2

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KX-TG7841/KX-TG7842/KX-TG7843/KX-TG7844/KX-TG7845/KX-TG365SK/KX-TG7871/KX-TG7872/KX-TG7873/KX-TG7874/KX-TG7875/KX-TG385SK/KX-TGA680
4.4. Tel Interface Circuit
TX AMP
SIDE TONE
RX AMP
CONTROL CIRCUIT
CALLER ID DETECT
BELL DETECT
P101
R141
R142
3
4
2
1
C101 D101
Q141
C102
R101 C103
R102
SA101
TIP
RING
REGULATOR
C104
C105
C106
R103
R105
C107
R104
C108
R106

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KX-TG7841/KX-TG7842/KX-TG7843/KX-TG7844/KX-TG7845/KX-TG365SK/KX-TG7871/KX-TG7872/KX-TG7873/KX-TG7874/KX-TG7875/KX-TG385SK/KX-TGA680
4.5. Block Diagram (Base Unit_RF Part)
KX-TG7841/7842/7843/7844/7845/365/7871/7872/7873/7874/7875/385 BLOCK DIAGRAM (Base Unit_RF Part)
10.368
MHz
IC501 RF block
TXDATA
ANT1
ANT1
RF_TXp RF_TXn RF_RXp RF_RXn
ANT2
ANT2
Control
Logic
RXDATA
Mixer
Demodulator
D802
PLL
3856-3843MHz
/3859-3845MHz
Modulator

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KX-TG7841/KX-TG7842/KX-TG7843/KX-TG7844/KX-TG7845/KX-TG365SK/KX-TG7871/KX-TG7872/KX-TG7873/KX-TG7874/KX-TG7875/KX-TG385SK/KX-TGA680
4.6. Circuit Operation (Base Unit)
General Description:
(BBIC, Flash Memory, EERROM) is a digital speech/signal processing system that implements all the functions of speech
compression, record and playback, and memory management required in a digital telephone answering machine.
The BBIC system is fully controlled by a host processor. The host processor provides activation and control of all that functions
as follows.
4.6.1. BBIC (Base Band IC: IC501)
•Voice Message Recording/Play back
The BBIC system uses a proprietary speech compression technique to record and store voice message in Flash Memory.
An error correction algorithm is used to enable playback of these messages from the Flash Memory.
•DTMF Generator
When the DTMF data from the handset is received, the DTMF signal is output.
•Synthesized Voice (Pre-recorded message)
The BBIC implements synthesized Voice, utilizing the built in speech detector and a Flash Memory, which stored the vocabulary.
•Caller ID demodulation
The BBIC implements monitor and demodulate the FSK/DTMF signals that provide CID information from the Central Office.
•Digital Switching
The voice signal from telephone line is transmitted to the handset or the voice signal from the handset is transmitted to the
Telephone line, etc. They are determined by the signal path route operation of voice signal.
•Block Interface Circuit
RF part, LED, Key scan, Speaker, Telephone line.
4.6.2. Flash Memory (IC502)
Main program data is stored.
4.6.3. Flash Memory (IC601)
Following information data is stored.
•Voice signal
ex: Pre-recorded Greeting message, Incoming message
4.6.4. EEPROM (IC611)
Following information data is stored.
•Settings
ex: message numbers, ID code, Flash Time, Tone/Pulse
4.6.5. Bluetooth Unit (IC721)
Use for Bluetooth communication.
RF part
ADPCM
Analog
Front
End
&
Multi-
plexer
TEL
Line
Interface
Digital
Speech
Processor
Caller ID
Modem
Digital TAM System
Flash Memory IC601
Host CPU
BBIC (IC501)
TDD & TDMA
with FHSS
Processor ADPCM
PCM OUT
MIC
SP
PCM IN
Keys/ LEDs
/ Charge
EEPROM
IC611
Flash Memory
(Program)
IC502
Bluetooth Unit

15
KX-TG7841/KX-TG7842/KX-TG7843/KX-TG7844/KX-TG7845/KX-TG365SK/KX-TG7871/KX-TG7872/KX-TG7873/KX-TG7874/KX-TG7875/KX-TG385SK/KX-TGA680
4.6.6. Power Supply Circuit/Reset Circuit
The power supply voltage from AC adaptor is converted to VBAT (3.0V) in IC302. And +3.0V for peripherals and analog part is
insulated from VBAT by Doubler of BBIC.
Circuit Operation:
+5.5V
+5.5V +3.0V
+3.0V
+1.8V
+3.0V_CP
IC501
IC302 IC502
BBIC
AC Adaptor 3.0V
REGULATOR
QSPI FLASH
VDD3
VDD1
VDD4
+3.0V_CP2 IC601
TAM FLASH
IC611
D610
VDD5
EEPROM
LCD
RF Part
LEDs
Q301
Bluetooth
unit
+2.4V
VDD2
Q302
IC721
Q661 LCD BLT
LCD_BLT (pin59_IC501)
Startmonitor
(IC501 57pin)
VDDC (1.2 V)
VBAT
Reset (RSTN)
(IC501_77pin)
BBIC chip initialize
(CKM/STM)

16
KX-TG7841/KX-TG7842/KX-TG7843/KX-TG7844/KX-TG7845/KX-TG365SK/KX-TG7871/KX-TG7872/KX-TG7873/KX-TG7874/KX-TG7875/KX-TG385SK/KX-TGA680
4.6.6.1. Charge Circuit
The voltage from the AC adaptor is supplied to the charge circuits.
D361 R372
D362 R371
CHARGE+
R373
C351
F301 DCP
CHARGE-
( )
+5.5V
DCM
K A

17
KX-TG7841/KX-TG7842/KX-TG7843/KX-TG7844/KX-TG7845/KX-TG365SK/KX-TG7871/KX-TG7872/KX-TG7873/KX-TG7874/KX-TG7875/KX-TG385SK/KX-TGA680
4.6.7. Telephone Line Interface
Telephone Line Interface Circuit:
Function
• Bell signal detection
• ON/OFF hook and pulse dial circuit
• Side tone circuit
Bell (RINGING) signal detection and OFF HOOK circuit:
In the idle mode, Q141 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:
L1T →C105 →R105 →R110 →R11 1→R112 →BBIC pin18(RINGING)
When the CPU (BBIC) detects a ring signal, Q141 turns on, thus providing an off-hook condition (active DC current flow through
the circuit). Following signal flow is the DC current flow.
T →D101 →Q141 →Q161 →R163 →D101 →P101 →R
ON HOOK Circuit:
Q141 is open, Q141 is connected as to cut the DC loop current and to cut the voice signal. The unit is consequently in an on-
hook condition.
Pulse Dial Circuit:
Pin 19 of BBIC turns Q141 ON/OFF to make the pulse dialing.
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 Q161 is
canceled by the canceller circuit of BBIC.
C172
C171
R166
R178
RX
Pin25 of IC501
TX
Pin27 of IC501
R160
+
C164 C161
C167
R165
R162
TP9
C173
C165
R161
R164
C184
C107 C103
C113
C163
Q151
EB
C
R151
R163
C168
C186
C111
R110
C110
R112 C181
R109
C109
Q141
Q142
C101
P101
L1T
L1R
D101
C102
1
2
3+
~~
_
4
R145
C142
C152
R152
AK
D142
R141
BE
C
E
BC
R144
R131
R133
C132
R142
(3216)
SA101
TP10
R111
RA101
RA101
C108
R103
R105 C105
C106
C104
R106
R101
R102R104
HOOK
Pin19 of IC501
CIDOUT
Pin24 of IC501
LSRn
Pin28 of IC501
RINGING
Pin18 of IC501
CIDINn
Pin23 of IC501
CIDINp
Pin21 of IC501

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KX-TG7841/KX-TG7842/KX-TG7843/KX-TG7844/KX-TG7845/KX-TG365SK/KX-TG7871/KX-TG7872/KX-TG7873/KX-TG7874/KX-TG7875/KX-TG385SK/KX-TGA680
4.6.8. Parallel Connection Detect Circuit/Auto Disconnect Circuit
Function:
In order to disable call waiting and stutter tone functions when using telephones connected in parallel, it is necessary to have a
circuit that judges whether a telephone connected in parallel is in use or not. This circuit determines whether the telephone
connected in parallel is on hook or off hook by detecting changes in the T/R voltage.
Circuit Operation:
Parallel connection detection when on hook:
When on hook, the voltage is monitored at pin 32 of IC501. There is no parallel connection if the voltage is
0.54 V or higher, while a parallel connection is deemed to exist if the voltage is lower.
Parallel connection detection when off hook:
When off hook, the voltage is monitored at pin 17 of IC501; the presence/absence of a parallel connection is determined by
detecting the voltage changes.
If the Auto disconnect function is ON and statuses are Hold, receiving ICM, OGM transmitting, BBIC disconnects the line after
detecting parallel connection is off hook.
Q141
Q161
R141
R142
R153
R131R133
Q142
R151
R145
C132
Pin 32 of IC501
ADC0
Pin 17 of IC501
PARADET
HOOK
Pin 19 of IC501
C101
D101
C102
SA101
P101
TEL JACK
3
4
2
1
R163
L1T
L1R
R152
C152
R121

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KX-TG7841/KX-TG7842/KX-TG7843/KX-TG7844/KX-TG7845/KX-TG365SK/KX-TG7871/KX-TG7872/KX-TG7873/KX-TG7874/KX-TG7875/KX-TG385SK/KX-TGA680
4.6.9. Calling Line Identification (Caller ID)/Call Waiting Caller ID
Function:
Caller ID
The caller ID is a chargeable ID which the user of a telephone circuit obtains by entering a contract with the telephone company
to utilize a caller ID service. For this reason, the operation of this circuit assumes that a caller ID service contract has been
entered for the circuit being used. The data for the caller ID from the telephone exchange is sent during the interval between the
first and second rings of the bell signal. The data from the telephone exchange is a modem signal which is modulated in an FSK
(Frequency Shift Keying) * format. Data "1"is a 1200 Hz sine wave, and data "0"is a 2200 Hz sine wave. There are two types of
the message format which can be received: i.e. the single message format and plural message format. The plural message
format allows to transmit the name and data code information in addition to the time and telephone number data.
*: Also the telephone exchange service provides other formats.
1st Ring
2 sec Silent interval 4 sec
2nd Ring
2 sec
0.5 s 575 ms min 0.5 s
DATA
0.1 Vrms
STD Ring / 20 Hz
Tip-Ring
DATA in
A
BDATA out
1200 Hz
=DATA "1"
1 bit=833 µs
2200 Hz
=DATA "0 "
70 Vrms
month day hour minute number
201348700035161504
Single message format
Plural message format
1st Ring
2 sec
718 ms 2nd Ring
0.5 s
DATA
month day hour minute number
20134870003516 16
DATA CODE NAME
201 John Smith 04

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KX-TG7841/KX-TG7842/KX-TG7843/KX-TG7844/KX-TG7845/KX-TG365SK/KX-TG7871/KX-TG7872/KX-TG7873/KX-TG7874/KX-TG7875/KX-TG385SK/KX-TGA680
Call Waiting Caller ID
Calling Identity Delivery on Call Waiting (CIDCW) is a CLASS service that allows a customer, while off-hook on an existing call,
to receive information about a calling party on a waited call. The transmission of the calling information takes place almost
immediately after the customer is alerted to the new call so he/she can use this information to decide whether to take the new
call.
Function:
The telephone exchange transmits or receives CAS and ACK signals through each voice RX/TX route. Then FSK data and
MARK data pass the following route.
Telephone Line →P101 →C105, C106 →R105, R106 →RA101 →IC501(23, 21).
If the unit deems that a telephone connected in parallel is in use, ACK is not returned even if CAS is received, and the
information for the second and subsequent callers is not displayed on the portable handset display.
CAS
CAS: CPE Alerting Signal
Dual Tone of 2130 Hz, 2750 Hz
-15 dBm (900 ohm load)
80 5 ms
MARK DATA
0~500 ms 58~75 ms about 300 ms
(be changed by
Information Volume)
Continuance Signal
of 1200 Hz (Data "1") "FSK"
ACK: Acknowledged Signal
DTMF
"D"
ACK
0~100 ms 60 5 ms
Telephone Exchange Cordless phone
Cordless phone
Signal Flow
Signal Flow
Telephone Exchange
Call Waiting Format
CIDOUT
Pin 24
RA101
C110
R110
R109
RA101
CIDINn
Pin 23
CIDINp
Pin 21
LSRn
Pin 28
C109
C107 C103
C108
R103
R105 C105
C106
C104
R106
R101
R102R104
P101
L1T
L1R
SA101
IC501