Kenwood TS 120 Service Manual

The Kenwood TS 120 is a high-performance amateur radio transceiver featuring all-mode operation (SSB, CW, AM), frequency coverage of 1.8-30 MHz, 200W PEP output, built-in power supply, digital frequency display, RF attenuator, noise blanker, VOX, RIT, and comprehensive metering. This service manual provides detailed technical information for maintenance, repair, and alignment procedures.

1. Technical Specifications 2. Block Diagrams 3. Circuit Descriptions 4. Alignment Procedures 5. Troubleshooting Guide 6. Parts List 7. Schematic Diagrams 8. Mechanical Assembly 9. Voltage Charts 10. Test Equipment Requirements 11. Service Notes

Technical Specifications

Complete technical specifications and performance characteristics of the Kenwood TS 120 transceiver.

ParameterSpecification
Frequency Coverage1.8-30 MHz (all amateur bands)
ModesSSB, CW, AM
Output Power200W PEP (SSB), 150W (CW), 50W (AM)
Power SupplyBuilt-in, 100-120V/200-240V AC, 50/60Hz
Frequency Stability±100 Hz after warm-up
Sensitivity0.25 μV for 10 dB S+N/N
Selectivity2.4 kHz (-6 dB), 4.5 kHz (-60 dB)
Image RejectionGreater than 60 dB
IF RejectionGreater than 60 dB
Audio Output2W at 10% distortion

Block Diagrams

System block diagrams showing signal flow and major circuit sections.

  1. RF Section: Front end, RF amplifier, mixer circuits
  2. IF Section: Multiple conversion stages, crystal filters
  3. Audio Section: Audio amplifiers, AGC circuits
  4. Power Supply: Transformer, rectifiers, regulators
  5. Control Section: Microprocessor, display drivers

NOTE! Refer to schematic diagrams for detailed component-level information.

Circuit Descriptions

Detailed descriptions of major circuit functions and operation.

  1. Receiver Circuits: RF input, mixer, IF amplification, detector
  2. Transmitter Circuits: Microphone amp, balanced modulator, driver, PA stages
  3. VFO System: Main VFO, BFO, frequency synthesis
  4. Control Circuits: Mode selection, metering, protection circuits
  5. Power Supply: AC input, rectification, voltage regulation

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

Alignment Procedures

Step-by-step alignment instructions for optimal performance.

Troubleshooting Guide

Systematic troubleshooting procedures for common problems.

SymptomPossible CauseCorrective Action
No powerFuse, power switch, transformerCheck fuse F1 (5A); verify AC input; test power switch
No receiveRF stages, BFO, audio ampCheck voltages; inject signal at various stages; verify BFO operation
No transmitPA stages, driver, mic circuitVerify PTT operation; check PA voltages; test microphone input
Frequency driftVFO stability, reference oscillatorCheck oven operation; verify VFO component stability
Poor sensitivityRF amp, mixer, AGCAlign RF stages; check AGC voltages; verify front end operation

WARNING! High voltages present - use isolation transformer when servicing.

Parts List

Complete component listing with part numbers and descriptions.

Part NumberDescriptionValue/Type
X10-1230-01Main transformerPower supply
X09-1780-05Final transistor2SC2879
X91-1250-10VFO capacitorVariable
X42-1100-03Crystal filter9 MHz
X35-1450-12IF transformerAdjustable

Schematic Diagrams

Complete schematic diagrams for all circuit sections.

  1. Main receiver schematic
  2. Transmitter PA schematic
  3. Power supply schematic
  4. Control circuit schematic
  5. Display and metering schematic

NOTE! Schematics show component values, test points, and voltage references.

Mechanical Assembly

Mechanical drawings and assembly instructions.

Voltage Charts

DC voltage measurements at key test points.

Test PointVoltage (DC)Conditions
TP1 (PA Collector)+24VTransmit mode
TP2 (12V Reg)+12V ±0.5VAll modes
TP3 (8V Reg)+8V ±0.3VAll modes
TP4 (-8V Reg)-8V ±0.3VAll modes
TP5 (VFO Varactor)+4 to +20VTuning

Test Equipment Requirements

Recommended test equipment for service and alignment.

  1. Oscilloscope: 20 MHz minimum bandwidth
  2. RF Signal Generator: 0.1-50 MHz coverage
  3. Frequency Counter: 0.1 Hz resolution
  4. Dummy Load: 50 ohm, 200W capacity
  5. Multimeter: Digital, high impedance
  6. Power Supply: Variable DC for testing

CAUTION! Use proper test equipment rated for high RF power levels.

Service Notes

Important service information and technical updates.

Factory modifications and service bulletins. Common failure points and recommended replacements. Alignment tips and special procedures. Safety precautions for high-voltage sections.

Service Contacts: Kenwood authorized service centers only. Original factory parts recommended for all repairs.

Warranty: Service by unauthorized personnel voids warranty.

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