Kenwood TKR-850 Service Manual page 23

5-6. DSP
The DSP circuit filters transmit/receive audio signal and
encode/decodes signaling (QT, DQT). This circuit consists
of IC618, IC612, IC613, IC614, IC603, IC606, IC608, IC610,
IC616, and IC619.
The receive signal DET is converted from analog to digital
by IC614 with a sampling frequency of 16.128kHz. The digi-
tized audio signal is sent to DSP IC618 to process the signal-
ing signal and audio signal. The processed digital audio sig-
nal is fed to CODEC IC613, converted from digital to analog,
and the analog signal is output from pin 16 (AOUTR). Then,
the audio signal is amplified by IC619 (B/2), passes through
the IC619 (A/2) low-pass filter, and goes to an electronic vol-
ume IC615.
The transmit audio signal coming from IC605 is amplified
by IC610, fed to pin 3 (AINL) of CODEC IC614, and con-
verted from analog to digital at a sampling frequency of
16.128kHz. The digitized transmit audio signal is AGC-pro-
cessed, pre-emphasized and filtered at 300Hz to 3kHz by
DSP IC618, and the resulting signal is fed back to CODEC
IC614, and converted from digital to analog, and the analog
signal is output from pin 15 (AOUTL). The transmit signal
from AOUTL is amplified by IC616 (B/2), passes through the
IC616 (A/2) low-pass filter, and goes to the IC611 (A/2) sum-
ming amplifier.
IC613 is a counter IC and the clock required for the
CODEC and DSP is generated by dividing the 16.515MHz
clock signal produced by DSP IC618.
IC603 and IC606 are interface IC between the CPU oper-
ated at 5.0V and the DSP operated at 3.3V.
5-7. Base-Band Circuit
The base-band circuit switches between the modulation
signal to the transmitter circuit, and remote audio and ad-
justs their levels. This circuit consists of IC605, IC607,
IC611, IC615, and IC617.
Modulation inputs include local microphone input, low-
speed data (LSD), high-speed data (HSD), external audio in-
put (TA), and external data input (TD), and demodulation out-
puts include receive audio output (RA), and receive data out-
put (RD).
The multiplexer (IC605) changes signals, the electronic
volume (IC615) adjusts the level, and the operational ampli-
fier (IC607, IC611, IC617) amplifiers and sums signals.
5-8. RS-232C Circuit
The RS-232C circuit connects the RS-232C serial port of a
personal computer directly to this model to perform FPU
operation. The FPU operation can also be performed by con-
necting a programming cable (KPG-46) to the local micro-
phone on the front panel. But, if the D-sub connector on the
rear panel is used, the programming cable is not required.
The 232C driver IC (IC620) changes the TTL-232C level. The
firmware can only be rewritten with the local microphone on
the front panel.
5-9. Power Supply Circuit
The power supply circuit generates power to operate the
CPU, DSP, flash ROM, bi-directional buffer, and base-band
circuit. This circuit consists of IC624, IC625, IC626, IC627,
IC628, and IC630.
CIRCUIT DESCRIPTION
6. DC Power Supply Circuit
6-1. DC Source Switching Relay Circuit
1. The final unit contains a relay (K1) for switching between
2. Trickle charge circuit
6-2. SB Switching Relay Circuit
1. SB (Switched +B) is supplied through the relay (K1) in the
2. If +B exceeds 18V, the relay is forcibly turned OFF by
the Main DC and Backup Battery.
If an external power source is connected to the Main DC
terminal, the Backup terminal is isolated by the relay. If
the Main DC turns OFF due to power failure, it is
switched to the Backup terminal by the relay.
The CPU monitors which is used, Main DC or Backup
Battery.
If both Main DC and Backup Battery are connected,
trickle charging of 0.5 A max. can be performed from the
Main DC power supply to the Battery.
(The default is OFF. See the Modification section for in-
formation on the modification method.)
The battery is charged from the Main DC with D8, D9 and
R61. If it exceeds 0.5 A, the charging circuit is turned
OFF by D9.
Main
DC
D8
D9
R61
120mA
Land
Backup
battery
16
BUP
IC604
CPU
Fig. 9 DC source switching relay circuit
TX-RX unit A/2.
When S507 (DC source switch) in the display unit is
turned ON, the relay (K1) is turned ON to output SB.
D12 and Q25 to interrupt the power and protect the main
unit.
+B
R165 R166
D12
Q25
Fig. 10 SB switching relay circuit
TKR-850
R54
+B
K1
(Relay)
Final unit (A/2)
TX-RX unit (A/2)
TX-RX unit (B/2)
Q601
K1
SB
Land
(PSW)
Q24
Display unit
S507
(Front panel)
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