Hitachi RAK-18QXB Service Manual page 52

2. Reset Circuit
Timing chart
pin of IC501 supply voltage
pin of IC501 output voltage
or pin of microcomputer
Reset circuit is to initialize the indoor unit microcomputer when switching ON the power or after recovering from power
failure.
Microcomputer operates when
Waveform of each part when switching ON the power and when shutting down is shown in the Fig. 2-2.
After switching ON the power,
rises and reaches approximately 4.4V or higher.
Then, resetting will be cancelled and microcomputer starts operating.
After shutting down the power,
falls and reaches approximately 4.2V or lower.
Then, the microcomputer will be in reset condition.
5V
2
5 1
3
IC501
Fig.2-1
Voltage
5 . 0V
RES canceling voltage
4 . 4V
Voltage
5.0V
Fig.2-2
pin of the indoor unit microcomputer (reset input) is "Lo" for resetting and "Hi" for heating.
pin of IC501 supply voltage and
pin of IC501 supply voltage and
- 52 -
R503
R502
0V
pin of microcomputer becomes Hi when DC5V line
pin of microcomputer becomes Lo when DC5V line
Reset
11
Microcomputer
RES detecting voltage
4 . 2V