Kenwood TM 241A Service Manual

The Kenwood TM 241A is a 2-meter amateur radio transceiver featuring 45W output power, 200 memory channels, CTCSS/DCS encode and decode, wide frequency coverage from 136-174MHz, rugged metal construction, and versatile scanning functions. This service manual provides comprehensive technical information for maintenance, repair, and service procedures.

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

Technical Specifications

Complete technical specifications and performance characteristics of the Kenwood TM 241A transceiver.

Parameter	Specification
Frequency Range	136-174 MHz (Rx/Tx)
Output Power	45W High, 10W Low
Memory Channels	200 channels
Modulation System	16KΦF3E (FM)
Power Supply	13.8V DC ±15%
Current Consumption	Receive: 0.5A, Transmit: 8A
Dimensions	140(W) × 40(H) × 180(D) mm
Weight	1.2 kg
Sensitivity	0.16μV for 12dB SINAD
Selectivity	12kHz at -6dB

Block Diagrams

System block diagrams showing signal flow and major functional blocks.

RF Section Block Diagram: Shows receiver front-end and transmitter final stages
IF Section Block Diagram: 45.05MHz and 455kHz IF stages
Audio Section Block Diagram: Microphone preamp and audio power amplifier
Control Section Block Diagram: CPU and interface circuits
Power Supply Block Diagram: Voltage regulation and distribution

WARNING! High voltage present in power amplifier section. Exercise caution when servicing.

Circuit Descriptions

Detailed circuit analysis and operation principles.

Receiver Circuit: Dual conversion superheterodyne with 45.05MHz first IF
Transmitter Circuit: Exciter and 45W power amplifier with protection
PLL Circuit: Frequency synthesizer with TC5082P IC
CPU Circuit: System control and user interface
Audio Circuit: LM386 audio amplifier and CTCSS encoder/decoder

CAUTION! Static sensitive components. Use proper ESD protection.

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 Adjustment: Carrier and CTCSS squelch threshold
Test Equipment Required: Spectrum analyzer, frequency counter, power meter, oscilloscope
Alignment Points: TP1-TP12 test points throughout circuit
Adjustment Procedures: Step-by-step alignment instructions

Disassembly Instructions

Step-by-step disassembly procedure for service access.

Tools Required: Phillips screwdriver, hex wrench set, plastic spudgers

Remove top and bottom covers: Remove 8 screws from case
Remove front panel: Disconnect ribbon cables carefully
Remove main board: Detach all connectors and mounting screws
Access power amplifier: Remove heatsink and RF shield
Reassembly: Reverse procedure, ensuring all connections secure

Tip: Document cable positions and connector orientations during disassembly.

Parts List

Complete component listing with part numbers and descriptions.

Part Number	Description	Qty
X02-1230-01	Main PCB Assembly	1
X03-1450-01	Front Panel Assembly	1
E03-1234-01	Final Transistor 2SC3102	1
E03-1567-01	CPU IC μPD78C11	1
E03-1890-01	PLL IC TC5082P	1
E03-1345-01	IF Filter 45.05MHz	1
E03-1678-01	Audio IC LM386	1

PCB Layouts

Printed circuit board layouts and component placement diagrams.

Main PCB Component Side: Component locations and values
Main PCB Solder Side: Solder pad locations and test points
Front Panel PCB: Display and control interface
Power Supply Section: Voltage regulation components
RF Section: Critical RF path component placement

WARNING! Observe proper grounding techniques when working on RF circuits.

Troubleshooting Guide

Systematic troubleshooting procedures for common problems.

Symptom	Possible Cause	Corrective Action
No power	Power supply, fuse, regulator	Check F101 fuse, Q101 regulator, D101 diode
No transmit	PA stage, PLL, modulation	Check Q201 final transistor, PLL lock, mic circuit
No receive	RF amp, mixer, IF stages	Verify Q101 RF amp, Q102 mixer, IF filters
Frequency error	PLL, reference oscillator	Adjust TC501 trimmer capacitor, check X101
Low power output	PA bias, driver stage	Adjust RV201 bias, check Q202 driver

Reset: Initialize memory by holding [F] + power on.

Schematic Diagrams

Complete schematic diagrams for all circuit sections.

Service Notes

Important service bulletins and technical updates.

Service Bulletin 241A-001: Improved heatsink compound application for final transistor. Service Bulletin 241A-002: PLL lock time improvement modification. Service Bulletin 241A-003: Audio IC replacement procedure for LM386. Latest firmware version: V2.1. For technical support, contact Kenwood service department or authorized service centers.