Port Allocations; Power Supply Circuits; Uhf Pll Circuit (Pll Unit); Voltage Lines - Icom IC-821H Service Manual

4-3-2 UHF PLL CIRCUIT (PLL UNIT)
The UHF PLL circuit generates the 1 st LO frequency, and
the signals are applied to the 1 st mixer circuits in the RF-B
unit. The PLL circuit consists of a VCO, prescaler and DDS
circuits.
The signal generated at the UHF VCO circuit (05, D4, D10)
is amplified at the buffer-amplifiers (06, 09), then applied to
the prescaler circuit (IC9). The prescaler circuit divides the
applied signal, and outputs it to the UHF DDS circuit (IC6)
via the buffer-amplifier (08).
The pulses output from the UHF DDS circuit are converted
into DC voltage at the loop filter circuit (IC7a) and then
applied to the UHF VCO circuit.
The output DC voltage from the loop filter circuit is also
applied to the RF-B unit to control the tuned bandpass filter.
4-4 POWER SUPPLY CIRCUITS
4-4-1 VOLTAGE LINES
Line
Description
HVF
The voltage from the external power supply
passed through the internal fuse (PA-B unit, F1).
The same voltage as the HVF line (external
13.8 V
power supply) which is controlled by the
[POWER) switch.
Common 9 V converted from the 13.8 V line by
9V
the 9 V regulator circuit (MAIN unit, IC25). The
output voltage is applied to the PLL,
demodulator and +5 regulator circuits, etc.
Common 5 V converted from the 13.8 V line by
5V
the 5 V regulator circuit (PLL unit, IC11). The
output voltage is used in the PLL unit only.
Common - 5 V converted from the 13.8 V line
-5V
by the - 5 V DC-DC convertor circuit (MAIN
unit, IC26). The output voltage is applied to the
AGC, APC and ALC circuits, etc.
Common 5 V converted from the 9 V line by the
M+5
5 V regulator circuit (MAIN unit, IC27). The
output voltage is applied to the BFO circuits and
optional units, etc.
Common 5 V converted from the 13.8 V line by
F+5
the F+5 regulator circuit (DISPLAY unit, IC13).
The output voltage is used in the DISPLAY and
SW-A units.
8 V for transmitter circuits which is converted
T8V
from the 9 V line by the T8 generator circuit
(MAIN unit, Q36, Q45).
8 V for receiver circuits which is converted from
R8V
the 9 V
lin~
by the R8 generator circuit (MAIN
unit, Q37, Q41).
9 V for transmitter circuits, particularly the PA-A
PAT9
unit, which is converted from the 9 V line by the
PAT9 generator circuit (MAIN unit, Q42, Q45).
9 V for transmitter circuits, particularly the PA-B
PBT9
unit, which is converted from the 9 V line by the
PBT9 generator circuit (MAIN unit, Q43, Q44).
4-7
4-5 PORT ALLOCATIONS
4-5-1 CPU (DISPLAY UNIT, IC1)
Pin
Port
Description
number name
9 RES
Input port for reset signal.
Outputs control signal for speech
15
LCOMP compressor circuit.
"High": Compressor ON
19 SCK1 Output port for serial clock signal.
21
S01
Output port for serial data.
22 SCK2
Output port for serial clock signal for
PLL circuits.
23 STPA
Output port for strobe signals for VHF
DDS circuit (PLL unit, IC1).
24 S02
"Output port for serial data for PLL
circuits.
25 STPB
Output port for strobe signals for UHF
DDS circuit (PLL unit, IC6).
Input port for unlock signal from UHF
32 LCTB
PLL circuit.
"High": When PLL-B is unlocked.
Input port for unlock signal from VHF
33 LCTA
PLL circuit.
"High": When PLL-A is unlocked
Input port for optional speech
37 VBUSY
synthesizer busy signal.
"High": During speech
40-43
KR1-
Input ports for key matrix.
KR4
44-51
KS1-
Outputs strobe signals for key matrix.
KS8
Outputs AF mute signal to the squelch
52 AFMM
control gate (MAIN unit, IC16b/d) for
MAIN band.
Outputs AF mute signal to the squelch
53
AFMS
control gate (MAIN unit, IC25b/c/d) for
SUB band.
54 MT8A
Outputs control signal for VH F
transmitter circuits in RF-A unit.
Outputs control signal for VH F
MR8A
receiver circuits in RF-A unit while
55
VHF signals are being received on the
MAIN band.
Outputs control signal for VHF
SR8A
receiver circuits in RF-A unit while
56
VHF signals are being received on the
SUB band.
57 MT8B
Outputs control signal for UHF
transmitter circuits in RF-B unit.
Outputs control signal for UHF
MR8B
receiver circuits in RF-B unit while
58
UHF signals are being received on the
MAIN band.
Outputs control signal for UHF
SR8B
receiver circuits in RF-B unit while
59
UHF signals are being received on the
SUB band.
78 BEEP
Outputs beep audio signals.