Hitachi RAS-25WX8 Manuel De Maintenance page 140

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.
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.
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35V
ICP2
12V power circuit
ICP1
(20V zener)
ICP1
35V
0V
manuals search engine
indoor DC fan motor
5V power
circuit
ZD121
0V
Lock
Q111
S D
S: Source
G
D: Drain
OK
G: Gate
IC111
Prohibited
(between gate (G) and 0V)
Prohibited
– 139 –
M
12V line
5V power line