Kenwood VGS-1 Service Manual

VOICE GUIDE & STORAGE UNIT

VGS-1

SERVICE MANUAL

CONTENTS

CIRCUIT DESCRIPTION

Recording/Playback Operation .................................................................... 2

I/O Ports ......................................................................................................... 2

Beat Shift Circuit ........................................................................................... 3

Amateur Transceiver Identification ............................................................. 3

SEMICONDUCTOR DATA

MCU : HD6433024D01TE (IC2) ...................................................................... 4

Reset IC : S-80930CNNBG80 (IC1) ................................................................ 5

Analog Switch : TC7W66FK (IC53, IC54)......................................................5

Bus Switch with Level Shifting : TC7MBD3244AFK (IC57) ........................ 5

COMPONENTS DESCRIPTION ......................................................................... 6

PARTS LIST ........................................................................................................ 6

PC BOARD

ACCESSORY UNIT (X42-3250-60) ................................................................ 8

SCHEMATIC DIAGRAM.....................................................................................9

TERMINAL FUNCTION .................................................................BACK COVER

VGS-1

CIRCUIT DESCRIPTION

Recording/Playback Operation

■ Recording

The audio signal input from the AI pin (CN1 pin 12) passes through a buffer amplifier (IC52 2/2) and goes to an antialiasing filter amplifier (IC52 1/2).

The audio signal is amplified by approx. 30 times by IC52 1/2 and unwanted signal components exceeding 4kHz are cut by an LPF.

The amplified audio signal is input to pin 78 of the MCU (IC2 : Micro Controller Unit).

The MCU converts the audio signal to a digital data (by 8kHz/8-bit sampling) and writes it into a flash memory (IC3, IC5).

When the input level of the AI pin is 100mVp-p, the MCU input becomes approx. 3Vp-p, and the maximum S/N can be achieved.

If a signal exceeding 100mVp-p is input to the AI pin, it is clipped by IC52 so that the MCU input does not exceed 3Vpp to protect the MCU against over-voltage input.

■ Playback and Prerecorded Voice

The audio signal saved in flash memory (IC3, IC5) is converted to an analog signal by the MCU (IC2) and output as a playback signal from pin 84.

This playback signal passes through two LPFs to cut harmonic components and is input to the attenuator circuit.

The attenuator circuit consists of analog switch ICs (IC53, IC54) and division resistors (R64, R66, R67, R71, R72).

The signal attenuated by the attenuator circuit is converted to a low impedance by an output buffer (IC55), then output from the AO pin (CN1 pin 11).

IC3, IC5

FLASH

X30

IC52

Buffer

– +

IC55

Buffer

–

LPF amp

IC53,IC54

ATT

– +

IC52

Fig. 1 Signal flow

AN0

X1 X1

– +

IC51

LPF

IC51

LPF

MCU

–

IC2

DA0

IC53 IC54

R64

R66

R67

R71

R72

Fig. 2 ATT circuit

■ Attenuator Circuit Control Table

95pin 96pin 97pin 98pin

PA2 PA3 PA4 PA5

ATT1 ATT2 ATT3 ATT4

Vol0 Lo Lo Lo Lo 100%

Vol1 Hi Lo Lo Lo 69%

Vol2 Lo Hi Lo Lo 55%

Vol3 Hi Hi Lo Lo 44%

Vol4 Lo Lo Hi Lo 36%

Vol5 Lo Hi Hi Lo 28%

Vol6 Lo Lo Lo Hi 15%

Vol7 Lo Lo Hi Hi 12%

I/O Ports

The VGS-1 is a 3V system unit, but it can be adapted to both 3V and 5V systems for external connection devices with an 8-bit CMOS bus switch (IC57).

IC57 can convert levels from 3V to 3V, from 3V to 5V, or from 5V to 3V.

■ If the External Device is a 3V System

It can be connected without a pull-up resistor.

■ If the External Device is a 5V System

If the external connection device is a 5V system, the VGS1 output ports (BUSY, SO, PLAY) must to be pulled up to 5 V. The waveform may become irregular due to IC57 output capacity and pull-up resistance.

BUSY and PLAY are Hi/Lo logic output ports and are not much affected by pull-up resistance.

Even when 3V or 5V is input to an input port, the IC57 output is 3V.

■ Attenuator Circuit

An attenuator circuit with division resistors is built by controlling four analog switches of IC53 and IC54 with pins 95 to 98 of the MCU (IC2).

The output level is changed in 8 steps with 4-bit data.

• UART Control

For UART control, the maximum communication speed is 115200 bps, and SO pull-up resistor recommends approx 10kΩ.

• Synchronous Control

SO is not used for synchronous control.

Only PLAY and BUSY must to be pulled up.

CIRCUIT DESCRIPTION

RV1

RV2

RV3

RV4

Accessory unit Foil side view

VGS-1

IC57

External device

Pull-up resistor

Fig. 3 External device, pull-up resistor

■ AI Input Port

If input exceeds 100mVp-p, the input signal is clipped and

distortion occurs.

It is necessary to make setting so that no signals exceed-

ing 100mVp-p are input.

If the input level lowers, S/N decreases, so the maximum

input not exceeding 100mVp-p must be used.

■ AO Output Port

When recording is performed with a 100mVp-p input, the

playback output becomes an approx. 2.8Vp-p level.

If Prerecorded Voice is generated, the output is approx

2Vp-p.

IC2

C11

R17

MCU

C10

R18

R19

6667

C12

XTAL EXTAL

IC2 94 pin

PA1 High : Normal Low : Shift

Fig. 4 Beat shift circuit

Amateur Transceiver Identification

The VGS-1 can be set as an amateur transceiver or a Land

Mobile Radio transceiver in the factory.

When it is used as a Land Mobile Radio transceiver, internal data in the VGS-1 is changed to suit the Land Mobile Radio transceiver, so it cannot be used as an amateur transceiver.

The VGS-1 set as a Land Mobile Radio transceiver can be identified because the RV4 land on the PCB is at High level. The default is Low level.

Beat Shift Circuit

To prevent VGS-1 clock oscillation for the MCU (IC2) from causing spurious reception to transceivers to which VGS-1 is connected, the clock oscillator (11.0592MHz) has a beat shift circuit with a transistor switch (Q1).

■ Beat Shift Circuit Off

Pin 94 of the MCU (IC2) goes Low level, Q2 turns off, and Q1 turns on because a 5V bias is applied to its base. In this condition, C10 is shorted, so the oscillation frequency is unchanged.

■ Beat Shift Circuit On

Pin 94 of the MCU goes High level, Q2 turns on, and Q1 turns off because its base is pulled down to GND. In this condition, C10 is connected in series to the crystal oscillator and the oscillation frequency increases by approx. 150ppm.

Fig. 5 RV4

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