Hitachi RAC-18YH4, Service Manual

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6-2. Reset Circuit
The reset circuit initializes the microcomputer program when Power is “ON” from “OFF”.
Low voltage at pin 48 resets the microcomputer , and HI activates the microcomputer.
Fig. 6-7 shows the reset circuit and Fig. 6-8 shows waveform at each point when power is turned on and
off.
When power is turned on, 12V line and 5V line voltages rise and 12V line voltage reaches 10.9V an
reset voltage input to pin 48 of microcomputer is set to Hi .
Reset voltage will be hold “Hi” until the 12V line voltage drops to 9.90V even though the power shuts
down.
Fig. 6-7
Fig. 6-8
−
MAIN P.W.B.
Microcomputer
RESET OUT.
RESET
56
48
C204
0V
R252
1
0V
8
2
3
IC5(1/2)
+
5V
D208 R287
C215
R284 R286
C215
R285
C226
R292
R289
R288
0V 0V 0V 0V
12V
12V line
12V line
5V line
5V line
Reset volage
Reset volage
Time
Time
10.9V
9.9V
12
6
0
12
6
0
Power is ON Voltage (V)
Power is OFF Voltage (V)