JETStream JT220M, Руководство по обслуживанию

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JT220M
7
CIRCUIT DESCRIPTION

D/A Converter
The D/A converter (U505) is used to adjust MO modulation, AF volume, TV voltage, FC reference
voltage, and PC POWER CONTROL voltage level.
Adjustment values are sent from the CPU as serial data. The D/A converter has a resolution of 256 and
the following relationship is valid.
Power Supply Circuit
When the POWER switch on the display unit is pressed, the power port on the display unit which is
connected to CPU port 25 (POWER), goes low, then CPU port 31 (P13) goes high, Q103 turns on, SBE
SW (Q100) turns on and power (SBE) is supplied to the radio.
When the DC power supplied to the radio, the voltage regulator IC (U1) supply into the CPU VDD and
reset voltage detect IC (U5). U5 will generate signal (RESET) in to the reset terminal on the CPU (U2) to
carry out a power ON reset.
During receiving, the CPU port 72 (P41) output "H" level. Q101 and Q108 turn on. and reception circuit
is supplied by 8V power supply (8R).
When the receiving is at FM, the CUP port 77 (P46) output "L" level. Q106 turns on and supplies 8V
power supply to FM reception circuit (VFM).
During transmitting, CPU port 78 (P47) output "H" level. Q102 and Q104 turn on. Transmitting circuit
output 8V power supply (8T). (See Fig. 15.)
Fig. 15 Power supply circuit
U2
5M
CPU
Q100
SW
Q103
SW
U1
AVR
U5
RST
Q101
SW
Q108
SW
Q106
SW
VAM VFM
Q102
SW
Q104
SW
Q107
SW
Q105
SW
8R
8T
U100
AVR
U101
AVR
5C
8C
RESET
P13
P46
P41
P
4
7
FB
POWER SW
POWER