Kenwood TS 940 Service Manual

The Kenwood TS 940 is a high-performance amateur radio transceiver featuring all-mode operation (SSB, CW, AM, FM, RTTY), 100W output power, built-in antenna tuner, general coverage receiver (100kHz-30MHz), digital frequency display, memory channels, IF shift, noise blanker, and comprehensive DSP filtering. Below are key sections for technical specifications, maintenance procedures, alignment instructions, troubleshooting, and schematics.

1. Technical Specifications 2. Block Diagrams 3. Circuit Descriptions 4. Alignment Procedures 5. Maintenance & Repair 6. Troubleshooting Guide 7. Parts List 8. Schematics 9. Mechanical Assembly 10. Safety Precautions 11. Service Notes

Technical Specifications

Complete technical specifications for the Kenwood TS 940 transceiver system.

Parameter	Specification
Frequency Range	Receive: 100kHz-30MHz; Transmit: 1.8-30MHz (amateur bands)
Modes	SSB, CW, AM, FM, RTTY
Output Power	100W PEP (SSB), 100W DC (CW), 40W (AM), 100W (FM)
Power Supply	13.8V DC ±15%, 22A max
Receiver Sensitivity	SSB/CW: 0.25μV for 10dB S/N; AM: 3μV for 10dB S/N
IF Frequencies	1st IF: 69.0115MHz; 2nd IF: 8.83MHz; 3rd IF: 455kHz
Filtering	SSB: 2.4kHz; CW: 500Hz; AM: 6kHz; RTTY: 500Hz
Antenna Impedance	50 ohms unbalanced
Dimensions	420(W) × 155(H) × 370(D) mm
Weight	Approx. 15 kg

Block Diagrams

System block diagrams showing signal flow and major circuit sections.

Overall System Block Diagram: Shows complete signal path from antenna to audio output.
Receiver Block Diagram: Detailed RF/IF stages, mixer circuits, and demodulation.
Transmitter Block Diagram: Exciter stages, driver, and final amplifier sections.
Power Supply Block Diagram: Voltage regulation and distribution circuits.
Control System Block Diagram: Microprocessor and interface circuits.

NOTE! Refer to schematics for detailed component-level information.

Circuit Descriptions

Detailed descriptions of major circuit sections and their operation.

RF Amplifier Circuit: Front-end protection and pre-amplification.
Mixer Stages: First and second mixer circuits with local oscillators.
IF Amplification: Multiple IF stages with crystal filtering.
Demodulator Circuits: Product detectors for SSB/CW, AM detector, FM discriminator.
Transmitter Circuits: Microphone amp, balanced modulator, driver, and final amplifier.
Power Supply: Switching and linear regulation circuits.
Control Circuits: Microprocessor, display driver, and interface logic.

CAUTION! High voltages present in transmitter and power supply sections.

Alignment Procedures

Step-by-step alignment instructions for optimal performance.

Receiver Alignment: RF stages, mixer injection levels, IF amplifier gains.
Transmitter Alignment: Carrier suppression, sideband balance, power output.
VCO Alignment: PLL loop filter adjustments for stable frequency synthesis.
Filter Alignment: Crystal and mechanical filter adjustments.
Display Calibration: Frequency counter and meter calibrations.

Maintenance & Repair

Routine maintenance procedures and component replacement guidelines.

Preventive Maintenance: Regular cleaning, connector inspection, cooling system check.

Component Replacement: Transistor substitution guidelines, IC replacement procedures.

Board-Level Repair: Circuit board removal and installation procedures.

WARNING! Always disconnect power and discharge capacitors before servicing.

Troubleshooting Guide

Systematic troubleshooting procedures for common problems.

Symptom	Possible Cause	Corrective Action
No power	Power supply fault, fuse blown	Check DC input, replace fuse F1 (8A), verify power supply operation
No receive audio	Audio amp failure, speaker connection	Check IC501 (audio power amp), verify speaker connections
Poor sensitivity	RF amp fault, AGC circuit	Check Q1-Q3 (RF amps), verify AGC voltage levels
No transmit output	Driver/Final amp failure, relay issues	Check Q12-Q14 (driver/final), verify relay RL1 operation
Frequency instability	VCO/PLL fault, reference oscillator	Check TCXO (X1), verify PLL lock voltages
Display problems	Display driver, microprocessor	Check IC801 (display driver), verify microprocessor clock

Parts List

Complete component listing with part numbers and specifications.

Semiconductors: Transistors, diodes, integrated circuits with Kenwood part numbers.

Passive Components: Resistors, capacitors, inductors with values and tolerances.

Mechanical Parts: Knobs, connectors, hardware, and mechanical assemblies.

NOTE: Use exact replacement parts for proper performance and safety.

Schematics

Complete circuit diagrams for all sections of the transceiver.

Main Receiver/Transmitter Schematic: Complete RF/IF and modulation circuits.
Power Supply Schematic: DC-DC converter and voltage regulation circuits.
Control Circuit Schematic: Microprocessor, display, and interface circuits.
Filter Networks: Crystal and mechanical filter circuits.
Panel Controls: Front panel switches, potentiometers, and indicators.

WARNING! High voltage sections clearly marked - exercise extreme caution.

Mechanical Assembly

Disassembly and reassembly procedures with exploded views.

Chassis Removal: Step-by-step chassis extraction for internal access.

Board Replacement: Circuit board removal and installation procedures.

Front Panel: Control assembly and display module servicing.

CAUTION! Handle circuit boards carefully to avoid static damage.

Safety Precautions

Critical safety information for service personnel.

Electrical Safety: High voltages present in power supply and transmitter sections.

RF Exposure: Proper handling during transmitter testing and alignment.

Component Safety: High-temperature components and proper heat sinking.

WARNING! Always use isolation transformer when servicing AC-powered sections.

Service Notes

Technical service bulletins and field modification information.

Factory Updates: Recommended modifications for improved performance.

Common Issues: Known problems and verified solutions.

Test Points: Key voltage and signal measurement points.

Service Contacts: Kenwood authorized service centers and technical support.