Kenwood TM 261A Service Manual

The Kenwood TM 261A is a 2-meter FM transceiver designed for amateur radio operations. This service manual provides comprehensive technical information for maintenance, repair, and service procedures. The radio features 45W output power, 50 memory channels, CTCSS/DTCS encode/decode, and rugged construction suitable for mobile and base station use.

1. Technical Specifications 2. Block Diagrams 3. Circuit Description 4. Alignment Procedures 5. Disassembly Instructions 6. Troubleshooting Guide 7. Parts List 8. PCB Layouts 9. Wiring Diagrams 10. Service Notes 11. Firmware Information

Technical Specifications

Complete technical specifications and performance characteristics of the Kenwood TM 261A transceiver.

Parameter	Specification
Frequency Range	144-148 MHz (USA version)
Output Power	45W High / 5W Low
Power Supply	13.8V DC ±15%
Current Consumption	Receive: 0.5A, Transmit: 10A max
Modulation	16F3 (FM)
Channel Spacing	20/25 kHz
Memory Channels	50 + 1 call channel
CTCSS/DTCS	50 CTCSS tones, 104 DTCS codes
Dimensions	140(W) x 40(H) x 170(D) mm
Weight	1.1 kg

Block Diagrams

System block diagrams showing signal flow and major circuit blocks.

RF Section Block Diagram: Shows receiver front-end and transmitter final stages.
IF Section Block Diagram: 21.4 MHz and 455 kHz IF stages with filtering.
Audio Section Block Diagram: Audio processing and amplification circuits.
Control Section Block Diagram: Microprocessor control and interface circuits.
Power Supply Block Diagram: Voltage regulation and distribution.

WARNING! High voltage present in RF power amplifier section. Use proper safety precautions.

Circuit Description

Detailed circuit analysis of major functional blocks.

Receiver Circuit: Dual conversion superheterodyne with 21.4 MHz and 455 kHz IF.
Transmitter Circuit: Exciter stages and 45W RF power amplifier.
PLL Circuit: Frequency synthesizer with TCXO reference.
Audio Circuit: Microphone preamp, audio power amplifier, and squelch circuits.
Control Circuit: Microprocessor and display driver circuits.

CAUTION! Static sensitive components. Use anti-static precautions when servicing.

Alignment Procedures

Receiver Alignment: RF amplifier, mixer, and IF stages alignment.
Transmitter Alignment: Power amplifier bias and modulation adjustment.
PLL Alignment: VCO and reference oscillator adjustment.
Squelch Alignment: CTCSS and carrier squelch threshold adjustment.
Audio Alignment: Deviation and audio frequency response adjustment.
Test Equipment Required: Spectrum analyzer, frequency counter, oscilloscope, power meter.
Alignment Points: All test points and adjustment locations marked on PCBs.

Disassembly Instructions

Step-by-step disassembly procedure for complete unit teardown.

Front Panel: Remove knobs, front bezel screws, and separate control head.

Main Unit: Remove bottom cover, heat sink, and main PCB assembly.

Remove all external knobs and connectors.
Remove bottom cover screws (8 places).
Separate upper and lower case halves.
Remove main PCB mounting screws.
Disconnect all internal wiring harnesses.
Remove RF shield covers as needed.

Tip: Document cable routing and connector positions during disassembly.

Troubleshooting Guide

Systematic troubleshooting procedures for common failure modes.

Symptom	Possible Cause	Corrective Action
No power	Power supply, fuse, regulator	Check DC input, replace fuse F1 (10A), test voltage regulators.
No receive audio	Audio IC, speaker, squelch	Check IC501 audio amplifier, test speaker, adjust squelch.
No transmit	PA transistor, PTT circuit	Test Q17 PA transistor, check PTT switch circuit.
Frequency error	TCXO, PLL circuit	Adjust TCXO X1, check PLL lock voltage.
Display problems	Display driver, connections	Check LCD connections, test display driver IC.

Parts List

Complete component listing with part numbers and descriptions.

Semiconductors: Transistors, ICs, diodes with manufacturer part numbers.
Passive Components: Resistors, capacitors, inductors with values and tolerances.
Mechanical Parts: Connectors, hardware, knobs with Kenwood part numbers.
PCB Assemblies: Complete assembly part numbers for service replacement.
Special Components: TCXO, crystals, filters with specific frequency data.

WARNING! Use only genuine Kenwood replacement parts for proper performance and safety.

PCB Layouts

Printed circuit board layouts for all major assemblies.

Main PCB: Component side and solder side views with reference designators.

Control PCB: Front panel control and display board layout.

Wiring Diagrams

Complete wiring diagrams and cable harness information.

Internal Wiring: All internal cable connections and pin assignments.

External Connections: Microphone, power, and accessory connector pinouts.

Service Notes

Important service information and technical updates.

Service Bulletins: Factory service updates and modifications.
Common Failures: Known issues and recommended repairs.
Test Procedures: Performance verification after repair.
Calibration: Final adjustment and calibration standards.

CAUTION! RF exposure hazard during transmitter testing. Maintain safe distance.

Firmware Information

Microprocessor firmware and programming data.

Component	Firmware Version	Function
Main CPU	Ver 1.2	System control and user interface
Display Driver	Ver 1.0	LCD control and backlight
PLL Data	N/A	Frequency programming data
Memory Backup	Lithium battery	Channel memory retention

Reset Procedure: Power on while holding [F] and [V/M] keys to reset microprocessor.

Service Support: Kenwood authorized service centers only.