Kenwood TK-5310 Service Manual Download Page 17

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TK-5310

CIRCUIT DESCRIPTION

3-5. Audio Amplifier Circuit

•

AF signal

The AF signal from CODEC (IC454) is amplified by IC456

and goes through IC458.

The AF signal goes through a DAC (IC462), an AF amplifier

(IC705), and an AF switch (IC701), and is routed to audio
power amplifier (IC702), where the signal is amplified and
output to the internal speaker.

•

Audio circuit

CODEC (IC454) extracts the audio signal from the receive

signal in the detection circuit in FM mode. The signal is then
deemphasized and output as a decoded audio signal in P25
mode.

LPF (IC456) removes quantization noise from the audio

signal output of the CODEC.

The switch (IC458) stops the audio signal of the CODEC to

prevent the mixing of BEEP, voice announcement and audio
signal when the BEEP or voice announcement is output from
the CPU. If an optional scrambler board is installed, the audio
path is adjusted so that the audio signal goes through the
scrambler board.

DAC (IC462) controls the voltage amplitude level of the

audio signal according to the volume position of the
transceiver. This determines the volume level output from
the speaker.

The amplifier (IC705) amplifies the audio signal so that the

audio signal level at the final stage amplifier is appropriate.

The volume levels of the 8

Ω

internal speaker and 16

Ω

external speaker are matched using the EXT AFC.

The switch (IC701) adjusts the signal path so that the

audio signal is output to the audio amplifier (IC703) for
external speakers when optional external speakers are
connected. If no external speakers are connected, the audio
signal is output to the audio amplifier (IC702) for the internal
speaker.

IC702 and IC703 output is BTL (Bridge Tied Load).

•

AF control

Speaker switching is performed by the CPU (IC5) using

INT AFC or EXT AFC. First, the logic level at the speakers
switching terminal (SSW) on the universal connector is fed to
the CPU. The CPU then outputs data based on this input.

When there is no SP-MIC installed, this logic level

becomes high. When the INT AFC is high, the EXT AFC goes
low, so the AF signal is only fed to the amplifier for the
internal speaker (INT SP) of IC702.

However, when a SP-MIC has been connected, this logic

level becomes low, so the INT AFC goes low and the EXT
AFC goes high. In this case, the AF signal is fed only to
amplifier for the external speaker (EXT SP) of IC703.

3-6. Squelch Circuit

It amplifies the demodulated noise signal from FM IC

(IC304) after filtering through BPF circuit. Then, the amplified
signal is converted to DC signal by the detection circuit. The
converted signal is fed to the CPU (IC5).

4. Transmitter System

4-1. Audio Band Circuit

The audio band circuit of the transmitter system consists

of the following:
• Microphone (Main)
• Microphone (Sub)
• N/C amplifier (Noise canceling mic amplifier) (IC705)
• Switch (Int/ext) (Q455)
• Switch (Mic mute) (Q452)
• AGC (IC452, D450, D451)
• Switch (Scrambler board) (Q454)
• Switch (VGS-1) (IC450)

This transceiver has two types of microphones: main and

sub. The main microphone is located at the front of the
cabinet and the sub microphone is located at the rear of the
cabinet. The audio signal input from these microphones is
synthesized by the N/C amplifier (IC705). The audio signal
from the main microphone is synthesized in normal phase
and the audio signal from the sub microphone is synthesized
in opposite phase. So if the same audio signal is applied in the
same phase to the main and sub microphones, it is cancelled
by the N/C amplifier. If audio signal is input to only the main or
sub microphone, it is not cancelled, but output from the N/C
amplifier.

This prevents ambient noise from entering the audio band

circuit at the next or subsequent stages.

When an optional external speaker microphone is

installed, the Int/ext switch (Q455) cuts off the audio signal
from the main and sub microphones and sends only the audio
signal from the external microphone to the next stage.

The microphone mute switch (Q452) cuts off audio

signals from the main, sub and external microphones.

AGC (IC452, D450, D451) is an amplifier that reduces gain

automatically by greatly increasing the attenuation when the
audio signal of a certain level or higher is present. It controls
the gain so that the audio signal input to the CODEC (IC454)
is not clipped.

Fig. 4

Audio circuit diagram

Fig. 5

Squelch circuit

IC451

BPF AMP

Q460

Noise AMP

D453

DET

IC5

CPU