Kenwood TH-D74E Service Manual page 10

2.1.5.4 Unlock detection circuit
The LD pins (pin 39 of the IC284 and pin 7 of the IC364) of the PLL ICs will output L-level signals when the PLLs are unlocked. The
main MPU (IC702) is in control of the switching timing of transmission and reception by monitoring the output.
CONT PCB
CODEC IC
IC707
DAC
IC671
(To MAIN MPU)
TCXO_VCON
TRIPPLER
Q378,382
BPF
X362
nd
BAND A 2 LOCAL
nd
BAND B 2 LOCAL
2.1.6 Power Supply Circuit
2.1.6.1 DC-IN circuit
The +B power supply will be provided with a constant voltage of 8.3 V through the charging DC-DC driver IC (IC585) and the switching
FET (Q580) when power at 11.0 to 15.9 VDC is supplied to the DC-IN JACK. At the same time, the VINOK pin (pin 5 of IC585) will be
set to a high level.
When the +B voltage is 5.3 V or higher, the output of the comparator IC (IC591) will be fixed to a low level and the collector voltage of
the Q585 will be set to a high level.
When the VINOK pin of the IC585 is set to a high level, the monostable multivibrator IC (IC588) will output a single-pulse signal. When
a battery at 5.5 V or higher is connected, the monostable multivibrator IC (IC588) will output a single-pulse signal.
The EN pin (pin 1) of the DC-DC module (IC584) will be set to a high level when the power switch is pressed or when the single-pulse
signal is input into the logic circuitry consisting of the OR circuit (IC592), AND IC (IC587), and NOT circuit (Q584).
When the EN pin of the IC584 is set to a high level, the IC584 will output a constant voltage of 4.0 V to the 40C power supply, and the
main MPU (IC700) will start.
When the main MPU starts, the main MPU will transmit a charge control instruction to the IC585 and set the 40CS to a high level at
the same time.
The EN pin of the IC584 will be kept at a high level as the 40CS is set to a high level. As a result, the IC584 will output 4.0 V to the
40C continuously, and the main MPU will continue to operating.
1-10 (No.RA044<Rev.001>)
MOD
D366-367
VCO_MOD
LPF
Q391
Freq
LDB
LDA
Q368,369
IC284
BAND B PLL IC
R DIVIDER N DIVIDER
PHASE
DETECTOR
SUB MPU
IC661
LPF
IC364
BAND A PLL IC
R DIVIDER N DIVIDER
PHASE
DETECTOR
Fig.7 VCO-PLL circuit
BUFFER LOCAL AMP
Q389 Q365
VCO B
DIVIDER
FIN AMP 1/2,1/4,1/8
Q364 IC361
LPF
VCO A BUFFER LOCAL AMP
Q386 Q383 Q381
FIN AMP
Q384
LPF
TX AMP
D365 Q361
RF SW
(To TX)
LOCAL AMP
Q363 D364 D361
RF SW RF SW
st
BAND B 1 LOCAL
LOCAL AMP
D378 Q376
st
BAND A 1 LOCAL
RF SW
DOUBLER
Q380 D38
RF SW