Panasonic KX-MB1520FX7 Service Manual page 51

KX-MB1520FX7/KX-MB1520FX8/KX-MB1520FXW/KX-MB1530FX7/KX-MB1530FXW
6.10.3.2. Full Speed Mode
In full speed mode, IC300_pinC8 outputs constant 3.3V.
When 607 is turned on, Vo becomes approx. 22V (approx. 2V drops between R616).
So the voltage between R624 is determined as follows.
VL=Vo*R623/(R623+R624)=22*22K/(150K+22K)=2.8(V)
Since IC504_pin2 is 3.3V and IC504_pin2 is 2.8V, IC504_pin1 is always "L".
Consequently Q607 is always turned on, then approx. 22V is supplied to FAN motor.
Therefore FAN rotates with full speed.
6.10.3.3. FAN stop
When IC300_pinC8 is "L", Q607 is turned off, then FAN motor stops rotation.
6.10.3.4. Control table
FANON1 FAN Operation mode
(IC300_pinC8)
H Full speed
Pulse Half speed
L Stop
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