Kenwood TK-5210 Service Manual page 17

TK-5210
3-5. Audio Amplifier Circuit
• AF signal
The AF signal from CODEC (IC406) is amplified by IC407
and goes through IC408.
The AF signal goes through a DAC (IC411), an AF amplifier
(IC603), and an AF switch (IC604), and is routed to audio
power amplifier (IC601), where the signal is amplified and
output to the internal speaker.
• Audio circuit
CODEC (IC406) 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 (IC407) removes quantization noise from the audio
signal output of the CODEC.
The switch (IC408) 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 (IC411) 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 (IC603) amplifies the audio signal so that the
audio signal level at the final stage amplifier is appropriate.
The volume levels of the 8Ω internal speaker and 16Ω
external speaker are matched using the EXT AFC.
The switch (IC604) adjusts the signal path so that the
audio signal is output to the audio amplifier (IC602) for
external speakers when optional external speakers are
connected. If no external speakers are connected, the audio
signal is output to the audio amplifier (IC601) for the internal
speaker.
IC601 and IC602 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 IC601.
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 IC602.
IC8
DSP
IC406
CODEC
16
CIRCUIT DESCRIPTION
TX-RX (X57-682 A/5)
BEEPS/ BEEP/
SCSW voice announce
IC408
IC411
SW DAC
IC407
LPF
Scrambler board
Fig. 4 Audio circuit diagram
3-6. Squelch Circuit
It amplifies the demodulated noise signal from FM IC
(IC204) 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).
IC403 Q412
LPF AMP Noise AMP
Fig. 5 Squelch circuit
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) (IC603)
• Switch (Int/ext) (Q410)
• Switch (Mic mute) (Q406)
• AGC (IC405, D402, D403)
• Switch (Scrambler board) (Q407)
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 (IC603). 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 (Q410) 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 (Q406) cuts off audio
signals from the main, sub and external microphones.
AGC (IC405, D402, D403) 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 (IC406)
is not clipped.
If an optional scrambler board is installed, the switch
CONTROL (X57-682 B/5)
EXT AFC INT AFC EXT AFC
IC603 IC604 IC601
AMP SW AMP
IC602
AMP
D404 IC5
DET CPU
INT SP
universal connector
EXT SP