Kenwood TH 22AT Service Manual

The Kenwood TH 22AT is a compact 2-meter amateur radio transceiver featuring 5W output power, 200 memory channels, CTCSS/DTCS encode/decode, wide frequency coverage (136-174MHz), alphanumeric display, built-in VOX, and multiple scanning functions. Below are key sections for technical specifications, circuit descriptions, alignment procedures, troubleshooting, and maintenance.

1. Technical Specifications 2. Block Diagram & Circuit Description 3. Disassembly Instructions 4. Alignment Procedures 5. PCB Layout & Schematics 6. Parts List 7. Troubleshooting Guide 8. Maintenance & Calibration 9. Firmware Information 10. Regulatory Compliance 11. Service Notes

Technical Specifications

Key technical parameters and operating characteristics of the TH 22AT transceiver.

Parameter	Specification
Frequency Range	136-174 MHz (Rx/Tx)
Output Power	5W (High), 1W (Low)
Memory Channels	200 (10 scan edges)
Modulation	16KΦF3E (FM)
Power Supply	13.8V DC ±15%
Current Drain	1.3A (Tx max), 150mA (Rx max)
Dimensions	58(W) × 110(H) × 31.5(D) mm
Weight	Approx. 300g
Antenna Impedance	50Ω
Operating Temperature	-10°C to +60°C

Block Diagram & Circuit Description

Functional block diagram and detailed circuit descriptions for each section.

RF Unit: Double conversion superheterodyne receiver with 45.05MHz first IF
PLL Circuit: TC5082P synthesizer with 5.12MHz reference oscillator
Audio Circuit: MC34119P audio power amplifier with built-in VOX
Power Supply: 3-terminal regulator IC for stable voltage supply
Control Circuit: Microprocessor-based control system with EEPROM

WARNING! High voltage present in some circuits; discharge capacitors before servicing.

Disassembly Instructions

Step-by-step procedure for disassembling the transceiver for service.

Remove battery pack and antenna
Remove 6 screws from rear case (2.5mm hex)
Separate front and rear cases carefully
Disconnect flex cables from main board
Remove shield covers as needed for access

CAUTION! Handle flex cables gently to avoid damage. Use proper anti-static precautions.

Alignment Procedures

Receiver Alignment: Adjust L1, L2, L3 for maximum sensitivity at 146MHz
Transmitter Alignment: Adjust L4, L5 for maximum power output
PLL Adjustment: Verify lock voltage and frequency accuracy
Modulation Balance: Adjust VR1 for proper deviation (5kHz)
Squelch Adjustment: Set threshold using VR2
Required Equipment: Signal generator, oscilloscope, power meter, frequency counter
Test Points: TP1 (PLL lock), TP2 (modulation), TP3 (RF power)

PCB Layout & Schematics

Complete printed circuit board layouts and detailed schematic diagrams.

Main Board: Double-sided PCB with plated-through holes. Component side shows IC placement, solder side shows trace routing.

Key ICs: IC1 (CPU), IC2 (PLL), IC3 (RF amp), IC4 (Audio), IC5 (Regulator)

Test Points: Clearly marked on PCB for voltage and signal measurements.

Parts List

Complete component listing with manufacturer part numbers.

Reference	Description	Part Number
IC1	Microprocessor	M38503F
IC2	PLL Synthesizer	TC5082P
IC3	RF Power Transistor	2SC3102
IC4	Audio Amplifier	MC34119P
Q1	VCO Transistor	2SC4226
D1-D4	Switching Diodes	1SS216
L1-L5	Adjustable Coils	KDR-A12

Troubleshooting Guide

Systematic approach to diagnosing and repairing common problems.

Symptom	Possible Cause	Corrective Action
No power	Power supply, fuse, regulator	Check DC input, measure IC5 output, replace if necessary
No transmit	PLL unlock, RF circuit	Verify PLL lock voltage, check IC3 bias, measure RF output
Poor reception	RF front end, IF alignment	Check L1-L3 alignment, measure receiver sensitivity
Display issues	LCD connector, CPU	Reseat flex cable, check CPU operation, replace LCD if needed
Audio problems	Speaker, audio IC, VOX	Check speaker continuity, measure IC4 output, adjust VOX level

Maintenance & Calibration

Regular maintenance procedures and calibration schedules.

Clean exterior with isopropyl alcohol and soft cloth
Check battery contacts for corrosion
Verify frequency accuracy annually
Calibrate power output every 2 years
Update firmware as needed

Tip: Use factory calibration equipment for accurate adjustments.

Firmware Information

Microprocessor firmware versions and programming procedures.

Current Version: V1.2 (EEPROM data included)

Programming: Requires Kenwood programming cable and software. EEPROM contains channel and configuration data.

Regulatory Compliance

FCC Part 15 and Part 97 compliance information. CE marking requirements. Manufacturer: Trio-Kenwood Corporation. For technical support, contact authorized Kenwood service centers.

Service Notes

Important service tips and special procedures.

Use only Kenwood genuine parts for replacements
RF power transistor requires thermal compound when replaced
PLL adjustment requires stable 13.8V power supply
Display contrast can be adjusted via internal potentiometer
Memory backup battery: CR2032 (typical life 5 years)

Service Centers: Authorized Kenwood service facilities only. Technical support available at www.kenwood.com