Sharp AR-810 (serv.man18) Service Manual ▷ View online
AR-651/810 FUSER UNIT 14 - 9
(5) Error detection during warming up (2)
If the output voltage of either the center thermistor or side thermistor (rear) does not go over
approx. 1.9V(100°C) even in a certain period of time after it has exceeded 40°C or if it does not
go over approx. 3.2V(150°C) even in a certain period of time after it has exceeded 100°C, the “Call for
service” [C44] is displayed
(6) Error detection during warming up (3)
If the output voltage of the thermistor does not go over approx. 4.0V(200°C) even in a certain period of
time after it has exceeded 150°C, the “Call for service” [C44] is displayed.
(7) Abnormality detection during standby/copying
If the output voltage of either the center thermistor or side thermistor (rear) becomes 0.5V or lower for
more than 0.5 sec., the “Call for service” [C43] is displayed, and if that of the side thermistor (front)
becomes 0.5V or lower for more than 0.5 sec., the “Call for service” [C45] is displayed.
(8) Fuser roller thermistor error status counter
• To enhance the safety of the fuser unit, CPU provides the following protection: When the third [C41]
error has occurred after two consecutive [C41] errors, even if an operator turns OFF the power and
back ON, the IH coil is not turned ON and error [C41] is displayed immediately.
However, if the copier becomes ready successfully with the fuser roller thermistor error status counter
“1” or below, the counter is cleared to “0”.
Note: If the heater is not turned ON and either of the error code [C41] to [C45] is still displayed even though the
thermistor, thermostat and IH coil have been repaired and the power is turned ON, check the code “400”
in the mode (08) to set the thermistor/heater status counter to “0”.
Reference
* The fuser roller thermistor error status counter does never have values other than 0 ~ 19 entered.
• If the fuser lamp does not turn ON and the “Call for service” [C41] is displayed immediately after
the power is turned ON, check the fuser roller thermistor error status counter. If it is “2” or over,
be sure to check the thermistor, thermostat and IH coil. Reset the counter to “0” (code “400” in
the (08) mode) after repairing them, then turn ON the power.
• If the fuser roller thermistor error status counter is “20” or over (e.g., 21), there is a possibility
that data in BCRAM or BCRAM itself may have been ruined due to causes such as leakage from
the chargers. Check the bias, high-voltage transformers and charge wires to see if any of them
is defective, and also look through all the data in the BCRAM.
쩹
쩸
AR-651/810 FUSER UNIT 14 - 10
14. 4. 6. Detection of open-circuited thermistors
A thermistor is a device which resistance decreases when it detects a high temperature. If the fuser roller
thermistor is open-circuited, the control circuit finds that the fuser roller temperature is extremely low and
keeps turning ON the IH coil. As a result, the fuser roller temperature rises, possibly activating the thermostat,
which is a safety protection device. To prevent this, CPU works to detect if the thermistor is open-circuited
or not.
* The following is a circuit diagram of the thermistor open-circuit detection circuit common with the center
and side thermistors.
· The input voltage is obtained by dividing the resistor
1, thermistor, resistor 2 and resistor 3.
· The temperature of the fuser roller surface changes.
The resistance of the thermistor changes.
The input voltage changes.
· The main CPU detects this change of the input
voltage to decide if the thermistor is abnormal or not.
Thermistor
Main CPU
R1
+5
R2
R3
C
R4
AR-651/810 FUSER UNIT 14 - 11
14. 5. Fuser Motor Drive
14. 5. 1. Outline of operation
(1) The LGC transmits control signals for the fuser motor rotation (HTRMT:Motor rotation command).
(2) The excited phase switching unit excites each phase on the fuser motor. Fuser motor rotates.
(3) Hall elements A to C are used to detect the rotation position of the motor (or rotor).
(4) The excited phase switching unit switches the excitation for each phase. (By repeating steps (2)
through (4) above, the motor keeps rotating.)
(5) An FG pulse is generated by the rotation of the fuser motor.
(6) The phases and velocities of the FG pulse and the reference frequency from the LGC are compared,
and the differences are added up. In addition to this are added the fluctuations in the supply voltage
(Signal generation).
(7) The switching timing for the excited phase switching unit is changed to match the signal obtained in
step (6). That is, control ensures that the FG pulse and reference frequency are equal. The fuser
motor rotates at a constant speed (locked range state).
(8) When the HTRML signal changes to “H” level, the fuser motor stops rotating.
(9) During standby, the HTRML level changes to “L” if the temperature of the pressure roller drops below the
reference temperature, and the fuser motor rotates at a low speed.
+5.1V
+36A
W
V
U
A
C
B
M/DC-HTR-340N
Reference
frequency
(HTRCK)
Control
signal
HTRML
HTRMT
HTRMT
Wave
shaping
Phase
comparator
Speed
comparator
Difference
Current
detecting
circuit
detecting
circuit
Rotation
control
Excited
phase
switching
unit
Rotor
position
detection
position
detection
Fuser motor
FG pulse
U, V, W : Phase
A, B, C : Hall element
Difference
AR-651/810 FUSER UNIT 14 - 12
14. 5. 2. Control signals
(1) HTRCK signal (LGC
→
MOT:Input)
This signal is a reference clock signal for the fuser motor to rotate at a fixed speed.
The frequency of the reference clock is 1247.6Hz.
(2) HTRML signal (LGC
→
MOT:Input)
This signal switches low-speed fuser motor rotation ON/OFF. When the signal is “L”, the fuser motor
rotates at a low speed.
(3) HTRMT signal (LGC
→
MOT:Input)
This signal is the fuser motor ON/OFF control signal. When the signal changes to “L”, the fuser motor
is turned ON.
Signal level for motor circuit
Signal
“H” level
“L” level
HTRCK
Reference clock (1247.6Hz)
HTRMT
Motor OFF
Motor low-speed ON
HTRML
Motor OFF
Motor ON
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