Hitachi RAF-25FX8 Service Manual page 142

［Other Caution］
1.Cautions for ICP (IC protector)
(1) Be careful not to short-circuit during servicing.
→If short-circuited, ICP will instantaneously open.
(2) If ICP Opens, remove cause, and then replace ICP.
→If repair is incomplete, ICP may open again.
35V
2. CN3 (Power), CN10 (Fan Motor), CN13 (Temporary switch-P.W.B.) and CN4 (Indicating P.W.B.) are connectors
with lock mechanism: Release lock with finger before disconnecting.
3. Do not touch the following parts during voltage and waveform check; ICP1 may be blown or Q111
may be damaged:
Q111 is MOS-FET and its gate terminal is a high input resistor, If tester probe, etc, touches gate (G), gate drive
●
circuit and 0V line, Q111 will be turned on continuously, over-current will flow, and ICP1 may be blown, causing
trouble in Q111.
When switching waveform of Q111 is to be observed, measure gate (G) and drain (D) with source (S) as base
point.
4. Do not connect/disconnect CN10 (fan motor connector) when power is being supplied to P.W.B.: Over-current
will flow to fan motor and P.W.B. (microcomputer, IC, etc.) and cause malfunction. Always connect/
disconnect CN10 with power turned off.
ICP2
12V power circuit
ICP1
ZD121
(20V zener)
Lock
ICP1
35V
IC111
0V
indoor DC fan motor
12V line
5V power
5V power line
circuit
0V
Q111
S D
S: Source
G
D: Drain
OK
G: Gate
Prohibited
(between gate (G) and 0V)
Prohibited
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M