Kenwood TS 790 Service Manual

The Kenwood TS 790 is a high-performance amateur radio transceiver featuring multi-band operation, advanced DSP technology, robust construction, and comprehensive service capabilities. This service manual provides detailed technical information for maintenance, repair, and troubleshooting of the TS 790 model. Below are key sections covering specifications, block diagrams, alignment procedures, circuit descriptions, parts lists, and troubleshooting guides.

1. Technical Specifications 2. Block Diagrams 3. Circuit Descriptions 4. Alignment Procedures 5. Disassembly Instructions 6. Parts List 7. PCB Layouts 8. Voltage Charts 9. Troubleshooting Flowcharts 10. Service Notes 11. Safety Precautions

Technical Specifications

Complete technical specifications and performance characteristics of the Kenwood TS 790 transceiver.

Parameter	Specification
Frequency Range	1.8-30 MHz (amateur bands)
Mode	SSB, CW, AM, FM, Digital
Output Power	100W (SSB/CW), 40W (AM)
Receiver Sensitivity	0.15μV for 10dB S+N/N
Selectivity	2.4kHz/-6dB (SSB), 500Hz/-6dB (CW)
Power Supply	13.8V DC ±15%
Current Drain	Receive: 1.5A, Transmit: 22A max
Dimensions	240(W) × 95(H) × 260(D) mm
Weight	3.8 kg
Temperature Range	-10°C to +60°C

Block Diagrams

Detailed system block diagrams showing signal flow and major components.

RF Section Block Diagram: Shows antenna input through RF amplifier and mixer stages.
IF Section Block Diagram: Displays intermediate frequency processing and filtering.
Audio Section Block Diagram: Illustrates audio amplification and processing circuits.
Power Supply Block Diagram: Details voltage regulation and distribution.
Control System Block Diagram: Shows microprocessor control and interface circuits.

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

Circuit Descriptions

Detailed explanations of major circuit sections and their operation.

Receiver Front End: RF amplifier, first mixer, and bandpass filtering.
IF System: Crystal filters, IF amplifiers, and detector circuits.
Transmitter Chain: Microphone amp, modulator, driver, and final amplifier.
Power Supply: Voltage regulators, protection circuits, and filtering.
Control Circuits: Microprocessor, display driver, and interface logic.

CAUTION! High voltages present in transmitter sections - discharge capacitors before servicing.

Alignment Procedures

Receiver Alignment: RF amplifier tuning, IF alignment, BFO adjustment.
Transmitter Alignment: Carrier insertion, modulation balance, power output calibration.
VCO Alignment: PLL loop filter adjustment, VCO tracking calibration.
Filter Alignment: Crystal filter center frequency and bandwidth adjustment.
Meter Calibration: S-meter, power output, and SWR meter calibration.
Test Equipment Required: Signal generator, oscilloscope, frequency counter, power meter, dummy load.
Alignment Points: Test points TP1-TP12 as marked on PC boards.

Disassembly Instructions

Step-by-step procedures for disassembling the transceiver for service access.

Procedure: Remove bottom cover, front panel, main board, and RF shield sections.

Front Panel Removal: Remove 6 screws from rear panel, disconnect ribbon cables carefully.

Main Board Access: Remove 8 mounting screws, lift board from chassis carefully.

RF Shield Removal: Unsolder shield connections at designated points.

Parts List

Complete component listing with part numbers and specifications.

Part Number	Description	Qty
X10-1230-01	Main PCB Assembly	1
X20-1450-02	Front Panel Assembly	1
2SC2879	RF Power Transistor	2
MA72356	PLL IC	1
YF-455S	455kHz Crystal Filter	3
TC4025	Microprocessor	1
LA1235	IF Amplifier IC	1
RD06HVF1	Driver Transistor	1
100μF/16V	Electrolytic Capacitor	15
1N4007	Rectifier Diode	8

PCB Layouts

Detailed printed circuit board layouts and component placement diagrams.

Main Board Top Side: Component placement and trace routing.
Main Board Bottom Side: Solder side component locations.
Front Panel Board: Display and control interface layout.
Power Supply Board: Regulator and filter component placement.
RF Board: High frequency circuit layout and shielding.

Tip: Use mirror for viewing bottom side component designations.

Voltage Charts

Reference voltage measurements at key test points under various operating conditions.

Receiver Mode Voltages: +13.8V at TP1, +8V at TP2, +5V at TP3

Transmit Mode: +13.8V at final amplifier supply, +12V at driver stage.
Standby Mode: +5V at microprocessor, +3.3V at memory circuits.
Test Points: TP1-TP20 with expected voltage ranges and tolerances.
Current Measurements: Normal operating currents for each major section.

WARNING! High voltage present in power supply section - use isolation transformer.

Troubleshooting Flowcharts

Systematic diagnostic procedures for common failure modes.

Symptom	Possible Cause	Corrective Action
No power	Power supply fault	Check fuse F1, regulator IC201, diodes D101-D104
No receive audio	Audio amp fault	Check IC301, speaker connections, volume control
No transmit	PA fault	Check final transistors Q501-Q502, driver Q401
Frequency error	PLL fault	Check reference oscillator X101, VCO tuning
Display problems	Display driver	Check LCD connections, driver IC601

Reset Procedure: Hold FUNC + PWR during power-on for factory reset.

Service Notes

Important service tips and known issues with recommended solutions.

Known Issues: Intermittent display (replace ribbon cable), RF output degradation (check final transistors), memory corruption (replace backup battery).

Safety Precautions

Essential safety information for service personnel.

High Voltage Warning: Dangerous voltages present in power supply and transmitter sections. Always discharge capacitors before servicing. Use insulated tools. Work on grounded anti-static mat. Follow lockout/tagout procedures.

CAUTION! RF radiation hazard during transmitter testing - use dummy load.

For technical support: Kenwood Service Department 1-800-950-5005