Kenwood TK-885, Руководство по обслуживанию

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TK-885
CIRCUIT DESCRIPTION /
Key Matrix Circuit
The TK-885 front panel has ten keys. Each of them is con-
nected to a cross point of a matrix of the KEY1 to KEY7 ports
of the microprocessor. The KEY5 to KEY7 ports are always
high, while the KEY1 to KEY4 ports are always low.
The microprocessor monitors the status of the KEY1 to
KEY7 ports. If the state of one of the ports changes, the
microprocessor assumes that the key at the matrix point cor-
responding to that port has been pressed. Unused points
(KEY1 to KEY7) are also used for foot switch (FSW) input.
Encode
The QT, DQT signals are output from LSDO of the CPU
(IC511) and go to the D/A converter (IC5) of the TX-RX unit.
The DTMF and single/5-tone signals are output from HSDO
of the CPU and goes to the audio processor (IC504). An MSK
signal is output from the audio processor according to the
data (AFDAT) from the CPU. The signal is summed with a
MIC/MSK signal by the audio processor (IC504), and the re-
sulting signal passes through an analog switch (IC506) and
goes to the TX-RX unit (MO).
MO is summed with the external pin DI line by the sum-
ming amplifier (IC3) and the resulting signal goes to the D/A
converter (IC5). The D/A converter (IC5) adjusts the MO level
and the balance between the MO and TO levels. Part of a TO
signal is summed with an output signal from pin 3 (MO) of
IC5 and the resulting signal goes to the MD pin of the VCO.
This signal is applied to a varicap diode in the VCO for direct
FM modulation.
Fig. 12 Key matrix circuit /
Fig. 13 Encode /
IC511
CPU
KEY7
KEY6
KEY5
KEY4
KEY3
KEY2
KEY1
(CLEAR)
A
D CALL SYS
DOWN
SYS
UP
B C
VOL
UP
VOL
DOWN
FSW
Q511
X1
VCXO
IC5
D/A
A1
VCO
IC3
SUM
AMP
IC506
Analog
SW
IC504
Audio
processor
IC300
PLL
MB
MD
MO
TO
HT
DI
MIC
TX-RX UNIT
AFDAT
LSDO
HSDO
IC511
CPU