Yaesu FT-51R Technical Supplement

Introduction

This manual provides the technical information necessary for servicing the FT-51R Dual-Band handheld amateur transceiver. Servicing this equipment requires expertise in handling surface-mount chip components. Attempts by non-qualified persons to service this equipment may result in permanent damage not covered by the warranty, and may be illegal in some countries.

Two PCB layout diagrams are provided for each double-sided board in this transceiver. Each side of the board is referred to by the type of the majority of components installed on that side ("leaded" or "chip-only"). In most cases one side has only chip components, and the other has either a mixture of both chip and leaded components (trimmers, coils, electrolytic capacitors, ICs, etc.), or leaded components only.

Yaesu Musen assumes no liability for damage that may occur as a result of typographical or other errors. Cooperation in pointing out any inconsistencies in the technical information would be appreciated. Yaesu Musen reserves the right to make changes in this transceiver in the interest of technological improvements, without notification to the owners.

Specifications

General

Receiver

Transmitter

Chip Component Information

This section details common chip components, including ceramic capacitors, tantalum capacitors, and resistors, providing their typical dimensions (L, W, H) and marking conventions. It also describes the factory process for installing chip components using robots and adhesive resin.

Manual replacement of chip components is explained, emphasizing the need for specialized tools like a temperature-controlled soldering iron, tweezers, and solder wick. Precautions include avoiding forceful removal to prevent board damage, never reusing removed components, and limiting soldering time to 3 seconds or less to protect components and the board.

The procedure for installing a replacement chip involves applying a small amount of solder to one land, positioning the chip with tweezers, soldering the first electrode, then soldering the second electrode, ensuring no bridging occurs.

Transceiver Disassembly and PCB Access

This section outlines the steps for disassembling the transceiver to access internal components and Printed Circuit Boards (PCBs). It details procedures for removing the CNTL Unit, Contact Unit, 144-Mother Unit, and 430-Mother Unit.

Key steps include removing the dial lock nut, rear panel screws (noting different thread types), separating transceiver halves, and disconnecting ribbon cables. Caution is advised when prying components to avoid damaging delicate surface-mounted parts.

The manual also covers Lithium Backup Battery Replacement, specifying the Yaesu part number for the replacement cell and detailing the desoldering and replacement process, including the use of an insulating seal.

Exploded View & Miscellaneous Parts

This section provides an exploded view illustration and lists miscellaneous parts such as screws, rubber knobs, and padding. It notes that non-designated parts are only available as part of a designated assembly.

Alignment

The FT-51R is factory aligned, but this section details procedures for realignment if components are replaced. It emphasizes that unauthorized attempts may void the warranty and recommends servicing by authorized Yaesu technicians.

Required Test Equipment: RF Signal Generator, Deviation Meter, In-line Wattmeter, Dummy Load (50Ω and 8Ω), Regulated DC Power Supply, Frequency Counter, AF Signal Generator, AC Voltmeter, DC Voltmeter, VHF/UHF Sampling Coupler, SINAD Meter.

Alignment Preparation & Precautions: Use a dummy load for transmission tests, ensure ambient temperature is stable (20°C-30°C), allow equipment to reach room temperature, and warm up test equipment thoroughly. Signal levels are referenced to 0 dBµ = 0.5 µV.

Procedures include:

• Alignment Power Connections: Details on connecting power using hook-on clips to specific test points.
• PLL & Transmitter Alignment: Adjustments for PLL reference frequency and transmitter power output for both VHF and UHF bands.
• Interstage Transformer Alignment: Procedures for tuning transformers on the 144-Mother Unit and 430-Mother Unit for optimal SINAD sensitivity.
• Internal System Alignment Routine: A software-driven alignment process accessed via button combinations, covering S-meter calibration, squelch thresholds, and Tx deviation adjustments for both VHF and UHF.
• CPU Reset: Instructions for performing soft and hard CPU resets to restore factory defaults.

Circuit Description

The FT-51R's electronics are divided into three main boards: 144-MHz Mother Unit, 430-MHz Mother Unit, and the Control Unit, supported by minor boards. The description details the function of various circuit blocks.

Key Sections Described:

• Antenna Duplexer: Filters VHF/UHF signals to allow independent operation on shared antenna.
• VHF/UHF Reception: Describes signal path from antenna through filters, RF amplifiers, mixers, IF stages, and detectors, including PLL frequency synthesis.
• VHF/UHF Squelch Control: Explains how noise detection and carrier presence activate squelch and control indicator LEDs.
• VHF/UHF Single-Band Dual Receive: Details how signals are sampled and processed for dual reception.
• AF Output: Describes audio processing, tone generation (CTCSS, DTMF), volume control, and amplification stages.
• Transmitter Stages: Covers speech input, modulation, frequency modulation of VCOs, RF amplification stages (PA modules), and automatic power control (APC).
• Transmit/Receive Switching: Explains the PTT switch operation and control signals for switching between transmit and receive modes.
• PLL Frequency Synthesizer: Details the Voltage-Controlled Oscillator (VCO), phase comparator, and reference oscillator for frequency generation and locking.
• Power-On Sequencing: Describes the initial power-up sequence involving the microprocessor and voltage regulators.

Block Diagram

The block diagram illustrates the overall architecture of the FT-51R, showing the main units and their interconnections. It highlights the flow of signals and control between the CNTL Unit, 144-Mother Unit, 430-Mother Unit, VCO Units, KEY Unit, MIC Unit, and CONTACT Unit.

Interconnection Diagram

This diagram details the physical and electrical connections between the various circuit boards, including connectors like J1001, J2001, J3001, J6001, J6002, J6003, J7001, J5001, and J4001, specifying signal lines such as power, ground, RF signals, and control data.

Board Unit Schematics, Layout & Parts

This extensive section provides detailed schematics, component layout diagrams, and comprehensive parts lists for each major unit of the FT-51R transceiver.

CNTL Unit

Contains schematics, parts layout, and a detailed parts list for the control circuitry, including microprocessors, memory, audio ICs, and interface components.

144-Mother Unit

Includes schematics, parts layout, and a detailed parts list for the 144 MHz VHF circuitry, featuring RF amplifiers, mixers, IF stages, PLL components, and transmitter power amplifiers.

430-Mother Unit

Provides schematics, parts layout, and a detailed parts list for the 430 MHz UHF circuitry, similar in function to the 144-Mother Unit but for the UHF band.

144-VCO Unit

Contains schematics, parts layout, and a parts list for the Voltage-Controlled Oscillator (VCO) circuit specific to the 144 MHz band.

430-VCO Unit

Includes schematics, parts layout, and a parts list for the Voltage-Controlled Oscillator (VCO) circuit specific to the 430 MHz band.

KEY Unit

Details the circuitry for the front panel keys and switches, including schematics, parts layout, and a parts list.

MIC Unit

Covers the microphone circuitry, including schematics, parts layout, and a parts list for the microphone element.

CONTACT Unit

Provides schematics, parts layout, and a parts list for the unit that interfaces between the main boards and other modules.