KENWOOD VGS1
Service Manual

VGS-1
CIRCUIT DESCRIPTION
VGS-1 IC57 O 5V O I
IC2 94 pin R17 PA1 High : Normal Low : Shift

External device 5V
XTAL

IC2 MCU C10 Q1

EXTAL 66 X1

Pull-up resistor Pull-up resistor

67

C12

R18

R19 5V

I

Q2

Fig. 4 Fig. 3 External device, pull-up resistor

Beat shift circuit

� 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 exceeding 100mVp-p are input. If the input level lowers, S/N decreases, so the maximum input not exceeding 100mVp-p must be used.

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.

� 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.

C11

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).

Accessory unit Foil side view

� Beat Shift Circuit Off

Pin 94 of the MCU (IC2) goes Low level, Q2 turns off, and
RV4

RV3 RV2 RV1

Q1 turns on because a 5V bias is applied to its base. In this condition, C10 is shorted, so the oscillation frequency is unchanged.

Fig. 5 RV4

� 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.

3