Hitachi RAS-18SX8 Manuel De Maintenance page 127
2. Control power circuit
FU1 3A fuse
AC220V-230V
・ An AC power supply from the power plug passes through the 3 A fuse, varistor (VA001), and noise filter circuit and rectified
and smoothed by DB1 and C003 to become a DC current 311 V to 325 V. It is then supplied to the two-way valve drive circuit,
indoor fan motor drive circuit, and switching power circuit.
・ The switching power circuit, as controlled by IC001, drives the primary winding of the transformer (T001) to produce a
specified voltage at the output winding. [The output terminal (pin ①) of IC001 has a switching voltage as shown in Fig. 2-1
but it changes in voltage peak and oscillation period depending on the power load. While on standby for a remote control
signal, in particular, the oscillation frequency is lowered to a level as low as 20 kHz or so to reduce the standby power.]
・ The outputs of the output windings of the transformer is rectified and smoothed to become DC voltages at primary 18.5 V,
12 V, and 8.5 V respectively. The primary 18.5 V is supplied to the drive circuit of the indoor fan motor, the 12 V is supplied
to each vane motor and to the drive circuits of the cleaner drive motor and other equipment, and the 8.5 V is adjusted to a
stable 5 V by the 3-terminal regulator IC (IC101) and supplied to the microcomputer peripheral circuit.
・ The drive circuit of the two-way valve controls energization of the two-way valve coil, thereby controlling the freezing cycle.
Check
If a failure in a part or circuit has produced an abnormal current in the power supply, the 3 A fuse will melt down to
prevent further damage. If the 3 A fuse melts down, check the indoor fan motor, switching electrical circuit, and other
components and replace any defective part.
Check
If an abnormally high voltage is applied to the power supply, the 3 A fuse and varistor (VA001) will prevent further
damage. If a high voltage results in the 3 A fuse melted down, the varistor (VA001) should have deteriorated and
destroyed. Therefore replace it at the same time.
Caution
The primary circuit of the transformer (T001) has a voltage to ground. Guard against electric shocks.
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Two-way
Indoor fan
valve coil
motor
Ｆ Ｍ
D001
TH001
NF1
1 2 3 4
8
IC001
6
DB1
9
7
10
D133
Primary 0 V
Primary 18.5 V
Two-way valve
control circuit
Pin
%8
of microcomputer
manuals search engine
T001
C126
L151
D102
D101
D131
R134
R104
R123
C101
12V
R122
PC102
PC101
3
14
R236
IC683
Switching power circuit
Fig. 2-1
– 160 –
8.5V
12V
D103
I
O
IC101
R10 3 C107
G
R127
C127
K
IC102
R
A
5V
0V
