Hitachi RAM-18QH5E, Service Manual

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Outdoor DC Fan Motor control circuit
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This model uses DC Fan Motor which is including controller circuit into the Motor shell.
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This DC Fan Motor will rotate by control voltage apply to Vsp input. (Voltage range: 1.7 to 7V DC)
Vsp high : Faster; Vsp low: slower; Vsp lower than 1.7V: stop
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Motor will output FG pulse by following this motor revolution.
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Outdoor Microprocessor will output PWM control signal from FAN CHOP terminal by following the instruction
from indoor Microprocessor.
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This PWM control signal will convert to Vsp voltage by smoothing circuit (Q101 & RC filter)
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Fan motor will start to rotate when Vsp was proceeding over than 1.7V, and generate FG pulse by rotation
speed.
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FG pulse will feed back to Outdoor Microprocessor through PQ102.
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PQ102 is the isolator between Microprocessor circuit and DC Fan Motor circuit, which has to match the
Fan Motor revolution with instructed revolution. Such as...
FG feedback: Faster – Instruction: Slower ... Decrease pulse width
FG feedback: Slower – Instruction: Faster ... Increase pulse width
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FG pulse is also used for Fan Motor fail detection
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Microprocessor will monitor FG pulse 30 seconds after start the fan motor. If there is no signal detected,
it will consider that the Fan Motor was malfunction and stop the operation. In this case, LD301 on control
PWB will blink 12 times. (Fan Motor lock detected)
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R107 and IC4 are used for Fan Motor over current detection.