Kenwood TR 751E Service Manual

The Kenwood TR 751E is a high-performance amateur radio transceiver featuring 2-meter VHF operation, 50W output power, advanced DSP filtering, multiple operating modes including FM, CW, and SSB, built-in CTCSS/DCS encode/decode, wide frequency coverage from 140-150 MHz, memory channels with scanning capabilities, and robust construction for reliable field operation. Below are key sections for technical specifications, circuit descriptions, alignment procedures, troubleshooting, and maintenance.

1. Technical Specifications 2. Circuit Description 3. Block Diagram 4. Alignment Procedures 5. Voltage Measurements 6. Component Layout 7. Troubleshooting Guide 8. Parts List 9. Maintenance Schedule 10. Safety Precautions 11. Warranty Information

Technical Specifications

Key electrical and mechanical specifications for the Kenwood TR 751E transceiver.

Parameter	Specification
Frequency Range	140-150 MHz (RX/TX)
Output Power	50W (High), 10W (Low)
Operating Modes	FM, CW, SSB
Sensitivity	0.16 μV for 12 dB SINAD (FM)
Selectivity	Wide/Narrow (15 kHz/7.5 kHz)
Power Supply	13.8V DC ±15%
Current Drain	Receive: 0.8A, Transmit: 12A max
Antenna Impedance	50 ohms
Dimensions	165(W) × 55(H) × 200(D) mm
Weight	1.8 kg

Circuit Description

Detailed description of major circuit blocks and their functions.

RF Amplifier Stage: Pre-amplifies received signals and provides transmit power amplification
Mixer Circuit: Converts RF signals to intermediate frequency (IF)
IF Amplifier: Provides main signal amplification and selectivity
DSP Processor: Digital signal processing for filtering and noise reduction
PLL Synthesizer: Frequency generation and stability control
Audio Circuits: Microphone preamp, audio power amplifier, and speaker output
Power Supply Regulation: Voltage regulation and protection circuits

WARNING! High voltages present in power amplifier section. Use appropriate safety precautions.

Block Diagram

System overview showing signal flow and major components.

Receiver Chain: Antenna → RF Amp → 1st Mixer → IF Filter → 2nd Mixer → DSP → Audio
Transmitter Chain: Microphone → Audio Amp → Modulator → Driver → Power Amp → Antenna
Control System: CPU → Display → Keypad → PLL → Memory
Power Supply: DC Input → Regulators → Protection Circuits → All Sections

Alignment Procedures

Step-by-step alignment instructions for optimal performance.

PLL Alignment: Adjust VC1 for zero beat at 145.000 MHz
Receiver Alignment: Set signal generator to 145.000 MHz, adjust L1 for maximum S-meter reading
Transmitter Alignment: Connect wattmeter, adjust L3 for 50W output at 145.000 MHz
Modulator Balance: Adjust VR1 for minimum distortion on modulation meter
Squelch Adjustment: Set VR2 for squelch closure at 0.2 μV input

CAUTION! Use calibrated test equipment. Follow procedures exactly.

Voltage Measurements

Reference voltage measurements at key test points.

Test Point	Voltage (DC)	Description
TP1	+8.0V	Receiver supply voltage
TP2	+5.0V	Logic circuit supply
TP3	+13.8V	Power amplifier supply
TP4	-8.0V	Negative supply for mixers
TP5	+3.3V	DSP processor supply

Component Layout

Physical location of major components on PC boards.

Main Board: IC1 (CPU), IC2 (DSP), Q1-Q3 (RF transistors), FL1-FL3 (filters)
Front Panel: Display, keyboard, potentiometers, indicator LEDs
Power Supply Board: Regulators, protection diodes, filter capacitors
RF Unit: Mixers, oscillators, power amplifier module

Troubleshooting Guide

Common problems and their solutions.

Symptom	Possible Cause	Corrective Action
No power	Blown fuse, power cable	Check F1 (10A), verify 13.8V at input
No transmit	PA transistor, PLL unlock	Check Q5, measure PLL lock voltage at TP6
Poor reception	RF amplifier, antenna	Test Q1, verify antenna connection
Display issues	Ribbon cable, contrast	Reseat J1, adjust VR3 for contrast
Audio distortion	Modulator, audio IC	Check IC4, adjust modulation balance

Parts List

Critical replacement components and their part numbers.

Part Number	Description	Qty
2SC1971	RF Power Transistor	1
2SK241	RF Amplifier FET	2
TA7310P	Audio Power IC	1
MB1501	PLL IC	1
10.7MHz	Ceramic Filter	3

Maintenance Schedule

Recommended maintenance intervals and procedures.

Every 6 months: Clean internal dust, check fan operation
Annual: Verify transmitter output power and modulation
2 years: Replace electrolytic capacitors in power supply
5 years: Complete alignment and performance verification

Note: More frequent maintenance may be required in harsh environments.

Safety Precautions

Important safety information for service technicians.

WARNING! Disconnect power before servicing. High voltages present even when powered off. Use anti-static precautions when handling semiconductors. Ensure proper grounding of test equipment.

Warranty Information

Warranty terms and service contact information.

Kenwood TR 751E carries a 3-year warranty from date of purchase. Warranty covers defects in materials and workmanship. Service available through authorized Kenwood service centers. For technical support, contact Kenwood Corporation at 1-800-950-5005 or visit www.kenwood.com.