Hitachi RAC-25JX4, Service Manual

Page: 49 / 119

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6. Power Supply
First, 35V power which operates the indoor unit is generated by the power source section of the outdoor unit and
supplied to the indoor unit through the C and D lines of the connecting cable.
Second, use the DC/DC converter and the 35 V power supply from the outdoor unit to generate 12 V control
power, which drives the stepping motor during the operation.
In addition, use the regulator IC 121 to generate 5 V power required for driving the micro computer and controlling
fan motor.
If the terminal block was overheated due to a connecting cable improper connection, the thermal fuse built in the
terminal block will burnt to shut off the 12 V line and stop the operation of the indoor unit. Then, the outdoor unit
cannot be communicated with the indoor unit and a communication error occurs (the outdoor LD301 will blink 9
times), stop all operations.
Fig. 6-1
Fig. 5-1
Microcomputer
External ROM
SCL
SDA
0V
0V 0V
5V
5V 5V
C401
R404 R403
27
26
1
2
3
4 8
7
6
5
}
IC401 (E 2 PROM)
¥ When power is supplied, the microcomputer reads the data in IC401(E
2
PROM) and sets the
preheating activation value and the rating and maximum speed of the compressor, etc. to their initial
values.
¥ Data of self-diagnosis mode is stored in IC401; data will not be erased even when power is turned
off.
5. Initial Setting Circuit (IC401)