Power Supply Circuits; Other Circuits - Icom IC-T7H Service Manual

4-4 POWER SUPPLY CIRCUITS

VOLTAGE LINE
DESCRIPTION
LINE
The voltage from the external power supply or
HV
attached battery pack.
The same voltage as the HV line (external power
supply or battery pack) which is controlled by the
VCC
power switch ([POWER] control).
Common 3 V converted from the VCC line by the
+3CPU regulator IC (LOGIC unit; IC2). The out-
VHT2V
put voltage is supplied to the +3C, R3 and T4
regulator circuits, etc.
Common 3 V converted from the VCC line by the
+3C regulator circuit (LOGIC unit; Q4, Q5, Q40
UHT2V
and D3) using the +3CPU regulator (LOGIC unit;
IC2).
3 V for receiver circuit converted from the VCC
line by the R3 regulator circuit (2F unit; Q4, Q5
R3V
and D402).
4 V for transmitter circuit converted from the
VCC line by the T4 regulator circuit (1F unit;
Q702, Q703 and D702). The T4 regulator circuit
+3S
is controlled by the CPU (LOGIC unit; IC1, pin
45) via T4 control regulator circuit (1F unit;
Q704).
• PLL circuit
"VTUNE" signal to VHF
RF circuit (2F unit)
Loop Loop
filter filter
Ref. osc. X1
(15.2 MHz)
"2NDLO" signal to the
FM IF IC (2F unit)
DUAL VCO BOARD
V VCO
Q304, Q305, D303, D304
U VCO
Q301, Q302, D301, D302
8
Phase Programmable
detector counter
Programmable
16
divider
17
3
Phase
Programmable
detector
counter
13
4-5

OTHER CIRCUITS

4-5-1 TONE SQUELCH CIRCUIT (LOGIC UNIT)
A portion of the detected audio signals from the "DETO" line
are passed through the low-pass filter (IC13). The filtered
signal is then applied to the CPU (IC1, pin 4), and is com-
pared with the programmed tone signal. The CPU (IC1) out-
puts control signals to the AF mute and AF regulator circuits
to open the squelch when a matched tone signal is received.
The programmed subaudible tone signal is output from the
CPU (LOGIC unit; IC1, pin 9) directly when transmitting with
a tone.
Buffer Buffer
Q852
Q351
Buffer
Q306
Buffer
Q352
IC851 (PLL IC)
2
Prescaler
3
PSTB
4
Shift register CLK
5
DATA
19
Prescaler
4 - 4
to VHF buffer amp.
D351
circuit
to UHF buffer amp.
circuit
D352