KX-TG8421RUB, KX-TG8421RUN, KX-TG8421RUT, KX-TG8421RUW, KX-TG8422RUB, KX-TG8422RUN, KX-TGA840RUB, KX-TGA840RUN, KX-TGA840RUT, KX-TGA840RUW - Panasonic Telephone Service Manual (repair manual). Page 3

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1 Safety Precautions----------------------------------------------- 4

1.1. For Service Technicians --------------------------------- 4

2 Warning -------------------------------------------------------------- 4

2.1. Battery Caution--------------------------------------------- 4
2.2. About Lead Free Solder (Pbf: Pb free)--------------- 4
2.3. Discarding of P.C. Board--------------------------------- 5

3 Specifications ----------------------------------------------------- 6
4 Technical Descriptions ----------------------------------------- 7

4.1. Block Diagram (Base Unit) ------------------------------ 7
4.2. Circuit Operation (Base Unit) --------------------------- 8
4.3. Block Diagram (Handset)-------------------------------11
4.4. Circuit Operation (Handset)----------------------------12
4.5. Circuit Operation (Charger Unit) ----------------------13
4.6. Signal Route -----------------------------------------------14

5 Location of Controls and Components ------------------16

5.1. Controls -----------------------------------------------------16

6 Installation Instructions ---------------------------------------17

6.1. Connections------------------------------------------------17
6.2. Battery-------------------------------------------------------17

7 Operating Instructions-----------------------------------------19

7.1. Programmable Settings ---------------------------------19
7.2. Registering a Handset to a Base Unit---------------22
7.3. Copying Phonebook Entries ---------------------------23
7.4. Dialling Mode ----------------------------------------------23
7.5. Error Messages -------------------------------------------23
7.6. Troubleshooting-------------------------------------------24
7.7. For Service Hint-------------------------------------------29

8 Service Mode -----------------------------------------------------30

8.1. Engineering Mode ----------------------------------------30
8.2. Copying Phonebook Items when Repairing -------34
8.3. How to Clear User Setting------------------------------36

9 Troubleshooting Guide ----------------------------------------37

9.1. Troubleshooting Flowchart -----------------------------37
9.2. Troubleshooting by Symptom (Base Unit and

Charger Unit) ----------------------------------------------49

9.3. Troubleshooting by Symptom (Handset) -----------53

10 Disassembly and Assembly Instructions ---------------57

10.1. Disassembly Instructions -------------------------------57
10.2. How to Replace the Handset LCD -------------------61

11 Measurements and Adjustments---------------------------62

11.1. Equipment Required -------------------------------------62
11.2. The Setting Method of JIG (Base Unit) -------------62
11.3. Adjustment Standard (Base Unit)---------------------64
11.4. Adjustment Standard (Charger Unit)-----------------65
11.5. The Setting Method of JIG (Handset) ---------------66
11.6. Adjustment Standard (Handset) ----------------------68
11.7. Things to Do after Replacing IC or X'tal ------------69
11.8. RF Specification-------------------------------------------71
11.9. How to Check the Handset Speaker or

Receiver ----------------------------------------------------72

11.10. Frequency Table (MHz) ---------------------------------72

12 Miscellaneous ----------------------------------------------------73

12.1. CPU Data (Base Unit) -----------------------------------73
12.2. CPU Data (Handset)-------------------------------------75
12.3. How to Replace the Flat Package IC----------------77
12.4. How to Replace the LLP (Leadless Leadframe

Package) IC------------------------------------------------79

12.5. Terminal Guide of the ICs, Transistors and

Diodes ------------------------------------------------------ 81

13 Schematic Diagram -------------------------------------------- 83

13.1. For Schematic Diagram -------------------------------- 83
13.2. Schematic Diagram (Base Unit)---------------------- 84
13.3. Schematic Diagram (Base Unit_Operation) ------- 86
13.4. Schematic Diagram (Handset)------------------------ 88
13.5. Schematic Diagram (Charger Unit)------------------ 90

14 Printed Circuit Board ------------------------------------------ 91

14.1. Circuit Board (Base Unit_MAIN) --------------------- 91
14.2. Circuit Board (Base Unit_Operation)---------------- 93
14.3. Circuit Board (Handset) -------------------------------- 94
14.4. Circuit Board (Charger Unit)--------------------------- 96

15 Exploded View and Replacement Parts List ----------- 97

15.1. Cabinet and Electrical Parts (Base Unit) ----------- 97
15.2. Cabinet and Electrical Parts (Handset)------------- 98
15.3. Cabinet and Electrical Parts (Charger Unit) ------- 99
15.4. Accessories and Packing Materials --------------- 100
15.5. Replacement Part List -------------------------------- 103