Hitachi RAS-25JX4 Service Manual page 83

ther Cautions
(1) Cautions concerning ICP (IC Protector)
1. Use due caution for short circuit in servicing.
Short circuit will open the ICP immediately.
2. When the ICP opens, remove the cause of this phenomenon and replace the ICP.
If the remedy is improper, the ICP may open again.
(2) The CN3 (power suppy) and CN7 (temperature fuse) and CN10 (fan motor) and CN11 (ventilation fan motor) are the
connectors with lock mechanism.
Press the lock with your fingers to unlock and remove the connector.
(3) When checking the voltage and waveform, do not connect the probes to the forbidden areas show below. Touching them
may cause the ICP1 and ICP3 blowout and Q111 and Q911 failure.
35V line
The Q111 and Q911 is a MOS-FET and its gate terminal is a high impedance. When a probe such as a multimeter is
contacted with the gate G , the Q111 and Q911 may have the continuous ON state to supply overcurrent in the circuit,
causing the ICP1 and ICP3 blowout and Q111 and Q911 failure.
When checking the switching waveform of the Q111 and Q911, set the source S to the base and measure the gate G and
drain D .
(4) During power feeding to the P.W.B., do not remove and insert the CN10 (fan motor connector) and CN11 (Vertilation fan
motor connector). Failure to do so may cause overcurrent to the fan motor and P.W.B.s (microcomputer, IC and the like)
and a failure may occur. To remove or insert the CN10 and CN11, be sure to shut off the power.
35V line
ICP2
12V Power circuit
ICP1
20V
Zener Diode
Ventilation fan motor
12V Power circuit
ICP3
Press here
Unlock
Lock
R121
ICP1
+
_
0V
R920
R921
ICP3
5V
ZD121
Power circuit
0V
Q111
S
OK
R114
Q113
Q112
8 5
R115
7 2
Forbidden Forbidden
6 3 area area
1 4
OK
Q911
S
OK
R914
Q913
Q912
8 5
R915
7 2
Forbidden Forbidden
3
6
area area
1 4
88
M
Indoor unit fan motor
12V line
5V line
M
Ventilation fan motor
OK
D
G
Forbidden area (Gate(G)-0V)
D
G
Forbidden area (Gate(G)-0V)