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Control sequence and waveform of OPF motor are as follows.

(1) Timing chart

(2) Wave form

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(1) Timing chart

(2) Wave form

This unit is equipped with two FANs to prevent the developing devices and Power Supply Unit (PSU) from overheating during
printing.
The FAN rotates at high speed (Approx. 3000rpm) while printing .
After printing is finished, FAN rotates at low speed (Approx.2200rpm) while predetermined period.

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For the control of FAN speed, comparator IC (IC601) is used. 
This IC compares (+) side input level and (-) side input level.
If (+) side input level is bigger than (-) side input level, output of this IC is "OPEN".
If (+) side input level is less than (-) side input level, it outputs "L" level.

When IC300_pinAC31 is "H", Q628 turned on and input level of IC601_pin6 becomes almost 0V.
And since IC601_pin5 is 3.3V, output of IC601_pin7 becomes "OPEN".  
When IC300_pinAD34 is "H", both Q630 and Q631 are turned on, then 24V is supplied to FAN through R661.
Therefore FAN rotates with full speed.

When IC300_pinAC31 is "L", Q628 turned off and input level of IC601_pin6 is determined by the voltage of between R694.
If voltage between R694 is less than 3.3V, and when IC300_pinAD34 is "H", output of IC601_pin7 becomes "H".
Then both Q630 and Q631 are turned on.  So voltage between R694 rises gradually.
When the voltage of R694 exceeds 3.3V, output of IC601_pin7 becomes "L".
Then both Q630 and Q631 are turned off.  So voltage between R694 falls gradually.
By repeating these sequence, voltage between R694 is controlled almost 3.3V.
On the other hand, if FAN voltage is represented Vo and voltage between R694 is represented VL, VL is shown as below for-
mula.

VL=Vo*R694/(R693+R694) 

→ Vo=VL*(R693+R694)/R694

Since each values are as follows, Vo is determined almost 10(V).

VL=3.3(V), R693=160(Kohm), R694=75(Kohm)
Vo=3.3*(160K+75K)/75K=10.3(V)

Therefore FAN rotates with half speed.

When IC300_pinAD34 is "L", both Q630 and Q631 are turned off, then FAN stops.

During the FAN rotation, the pulse signal is output from pin 2 of FAN1 as the rotation detect signal.
If the period of the pulse is wider than prescribed value, it is judged that FAN error occurred.
Then display shows "Call Service 4"(Fuser FAN Error) CALL SERVICE 4 (P.138).

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The control sequence is same as FAN1.  Please refer to the explanation in FAN1 Control (P.47).
If FAN error is occurred,   display shows "Call Service 11"(PSU FAN Error) CALL SERVICE 11 (P.143).