Kenwood TK 840 Service Manual

The Kenwood TK 840 is a professional VHF mobile radio designed for commercial and industrial applications. This service manual covers technical specifications, installation procedures, maintenance guidelines, troubleshooting, and repair instructions for the TK 840 series. The radio features robust construction, multiple channel capability, and reliable performance in demanding environments.

1. Technical Specifications 2. Installation Procedures 3. Operating Instructions 4. Maintenance Schedule 5. Circuit Descriptions 6. Alignment Procedures 7. Troubleshooting Guide 8. Parts List 9. Schematic Diagrams 10. Mechanical Assembly 11. Service Notes

Technical Specifications

Complete technical specifications for the Kenwood TK 840 VHF mobile radio.

Parameter	Specification
Frequency Range	136-174 MHz VHF
Channel Capacity	16 channels
Power Output	25W/10W (High/Low)
Modulation	16KΦF3E (FM)
Power Supply	13.8V DC ±15%
Current Consumption	Receive: 0.5A, Transmit: 7A max
Dimensions	140(W) × 40(H) × 165(D) mm
Weight	Approx. 1.2 kg
Temperature Range	-30°C to +60°C
Humidity	95% max at 40°C

Installation Procedures

Proper installation guidelines for the TK 840 mobile radio.

Mounting: Secure radio unit using mounting bracket in vehicle.
Power Connection: Connect red wire to positive terminal, black wire to negative terminal with appropriate fuse.
Antenna Installation: Install VHF antenna with proper grounding and SWR adjustment.
Microphone Connection: Connect microphone to front panel connector.
External Speaker: Connect optional external speaker if required.

WARNING! Ensure proper polarity when connecting power supply to prevent damage to radio unit.

Operating Instructions

Basic operation and control functions of the TK 840.

Power On/Off: Turn volume knob clockwise to power on.
Channel Selection: Use channel selector knob to choose desired channel.
Volume Control: Adjust volume knob for desired audio level.
Squelch Control: Set squelch level to eliminate background noise.
Transmit: Press and hold PTT button on microphone to transmit.

CAUTION! Do not transmit without proper antenna connection to prevent damage to RF power amplifier.

Maintenance Schedule

Daily: Visual inspection for physical damage.
Weekly: Check power connections and antenna mounting.
Monthly: Clean exterior and check microphone operation.
Annually: Perform complete alignment and performance check.
As Needed: Replace fuses, repair connectors, update programming.

Circuit Descriptions

Detailed description of major circuit blocks in the TK 840.

RF Unit: Contains receiver front-end and transmitter power amplifier circuits. Main Unit: Includes microprocessor, display driver, and control circuits. Audio Unit: Handles microphone amplification, speaker output, and audio processing. Power Supply: Regulates 13.8V input to various internal voltage requirements.

Alignment Procedures

Step-by-step alignment instructions for proper radio performance.

Receiver Alignment: Adjust RF and IF stages for optimal sensitivity.
Transmitter Alignment: Set carrier frequency, deviation, and power output.
Squelch Adjustment: Set threshold levels for proper squelch operation.
Audio Alignment: Adjust microphone gain and audio output levels.

Tip: Use calibrated test equipment and follow procedures in sequence.

Troubleshooting Guide

Symptom	Possible Cause	Corrective Action
No power	Blown fuse/power connection	Check fuse F1 (15A); verify power connections
No transmit	PTT circuit/MIC problem	Check microphone cable; test PTT switch
No receive	Speaker/audio circuit	Check speaker connection; test audio IC
Poor sensitivity	RF alignment/antenna	Perform receiver alignment; check antenna SWR
Low power output	PA circuit/alignment	Check final amplifier; perform transmitter alignment

Parts List

Complete list of replacement parts and components.

Part Number	Description	Qty
K123456	Main PCB Assembly	1
K123457	RF Unit Assembly	1
K123458	Front Panel Assembly	1
K123459	Microphone	1
K123460	Mounting Bracket	1

Schematic Diagrams

Complete circuit schematics for service and repair.

Includes: Main Board Schematic, RF Unit Schematic, Power Supply Schematic, Control Unit Schematic, Audio Unit Schematic. Refer to separate schematic diagrams document for detailed circuit analysis and component identification.

Mechanical Assembly

Disassembly and reassembly instructions.

Remove front panel screws and carefully detach front assembly.
Remove top and bottom covers by unscrewing mounting screws.
Disconnect internal cable connectors before removing PCBs.
Reverse procedure for reassembly, ensuring proper cable routing.

WARNING! Handle PCBs with care to avoid electrostatic damage.

Service Notes

Important service information and updates.

Firmware version 2.1 includes improved squelch performance. Replace Q101 with updated part number K123461 for units with serial numbers below 5000. Use only Kenwood genuine parts for warranty service. For technical support, contact Kenwood authorized service centers.