Hitachi RAS-18YH6 Service Manual page 74

CHECKING THE INDOOR UNIT ELECTRICAL PARTS
1. Power does not come on (no operation)
Is AC220-230V being generated
between terminals A and B on the
indoor unit terminal board?
Yes
1
Is DC35V or 20V being generated
between terminals C and D on the
indoor unit terminal board?
Yes
Is the control voltage being
generated normally?
12V line: 12V or 7V
5V line: 5V
Yes
Do the air deflectors perform initial
operation when the power supply is
turned on after off?
No
Is the microcomputer reset input
(pin7) "Hi"?
Yes
Is the microcomputer clock signal
10MHz at pins 0 and A being
generated normally?
Yes
Replace the control P.W.B.
: When not in operation, the unit will enter into a low-power standby state, possibly causing a voltage drop to the 12V and 35V lines
1
as shown below.
25V - 20V
No
Is AC220-230V being generated at
AC outlet?
No
Is AC220-230V being generated
between terminals A and B on the
outdoor unit terminal board?
Is DC35V is being generated between
terminals C and D on the outdoor unit
terminal board?
Are C and D connection cables
reversed?
No
Yes
No
No
12V - 7V
Yes
Yes
No
No
Perform final operation check.
– 72 –
No
Check AC outlet and breaker, and
repair any defective part.
Check the power cable, power
switch, and terminal board, and
repair any defective part.
No
Check the indoor/outdoor unit
connection cable, and correct any
defective section (wrong connection,
incomplete insertion).
Yes
Yes
Connect the cables correctly.
Check the outdoor unit power circuit,
and repair any defective part.
Check according to the proper method
for checking the power circuit.
Check the wireless light receiving unit.
Check the reset circuit, and repair
any defective section.
Replace the microcomputer and
oscillator.