Sharp AR-651 (serv.man17) Service Manual ▷ View online
AR-651/810 FUSER UNIT 14 - 5
D1
T1
C1
C3
CPU
Tr2
(IGBT)
IGBT
drive
C2
Tr1
IGBT
drive
14. 4. 2. Heating principle of IH coil
The magnetic field is generated by applying a high frequency current to the IH coil inside the fuser roller,
which then produces the eddy current in it. When the eddy current flows, the Joule heat is generated by the
resistance element of the fuser roller, which is then heated. In the IH coil method, the thermal efficiency is
higher than the lamp method because the fuser roller is directly heated.
IH coil is divided into two parts to decrease the temperature difference between the center and both ends
of the fuser roller.
Current flowing inside the
fuser roller
fuser roller
[Block diagram of high frequency power supply (IH control board)]
IH coil
Fuser roller
Monitoring input current
Monitoring input current
Current input
Voltage
input
input
I/F circuit on LGC board
Photocoupler
Smoothing circuit
Control circuit for high frequency current
[Image of current flowing from A to B]
Current flowing on the surface of the fuser roller
High frequency
power source
power source
Side IH coil
Magnetic field
Eddy current
B
A
Center IH coil
AR-651/810 FUSER UNIT 14 - 6
14. 4. 3. IH control circuit interface
The IH control circuit uses a photocoupler as an insulator against the secondary circuit.
The interface signals are as followed.
Number
Signal
Direction
Definition
J552-1
IH2ON
HOST to IH OFF signal when the roller ends are heated abnormally
J552-2
5V
J552-3
H1PWR1
HOST to IH Electric power setting
J552-4
H1PWR2
J552-5
H1PWR3
J552-6
H2PWR1
J552-7
H2PWR2
J552-8
H2PWR3
J553-1
IH1ON
HOST to IH ON/OFF signal
J553-2
SG
J553-3
IHDUTY
HOST to IH ON duty signal
J553-4
IHERR1
HOST to IH Error signal
J553-5
IHERR2
AR-651/810 FUSER UNIT 14 - 7
14. 4. 4. IH control circuit abnormalities
The IH output is stopped when an abnormality occurs in the IH control circuit.
(1) When the power voltage of the copier is too high or too low
IH output is stopped to protect the IGBT when the input voltage, which is higher or lower than specified
range, is applied to the copier. This is an error [C47].
(2) When the AC is not applied to the IH control circuit
The error that the AC is not applied to the IH control circuit properly is [C47]. The same error occurs
when the thermostat is either activated or blown.
(3) When the temperature of the IGBT is too high
Normally, the IGBT is forcibly cooled down as it becomes hot while the power is supplied to the IH
control circuit. The error [C48] is occurred when this cooling operation is not sufficient and the IGBT
becomes too hot.
(4) When the temperature detection sensor of the IH control circuit is malfunctioning
The error [C49] occurs when the temperature detection sensor is malfunctioning or the IH coil is not
connected properly.
(5) When the ON/OFF of IH coil becomes out of control
When an abnormality occurs at the IH control circuit and the ON/OFF of the IH coil becomes out of
control, CPU decides the error code and counter value of the fuser roller thermistor error status after
detecting the abnormal temperature at the thermistor.
* Abnormal temperature
Center thermistor
: 230°C
Side thermistor (rear) : 240°C
Side thermistor (front) : 270°C
AR-651/810 FUSER UNIT 14 - 8
14. 4. 5. Temperature detecting section
To keep the fuser roller at a certain temperature, the center thermistor and side thermistor (rear) detect the
temperature of the fuser roller and control ON/OFF of the IH coil. Outputs from the thermistors are used to
detect abnormalities of the fuser roller temperature.
(1) Relation between the thermistor output voltage and surface temperature of the fuser roller:
Approx. 4.0V when the temperature is 200°C
Approx. 3.8V when the temperature is 183°C, and approx. 3.7V when the temperature is 177°C.
(2) Temperature control for the surface of the fuser roller:
(3) Temperature control for both ends of the fuser roller
During the multiple copying, the temperature of both ends of the fuser roller (where a paper does not
pass on) generally becomes higher than that of the other areas (where a paper does pass on). The side
thermistor (front) detects the temperature of the ends, in this case, it controls the center IH coil and
side IH coil to unify the fuser roller temperature.
(4) Error detection during warming up (1)
If the output voltage of either the center thermistor or side thermistor (rear) does not go over approx.
0.5V(40°C) even in a certain period of time after the heater has turned ON, the “Call for service” [C41]
is displayed.
C
ON
ON
ON ON ON ON
ON ON
ON
ON
OFF
OFF
0
0
0
65
81
81 65
81
0
65
0
AR-810
Temperature
Fusing control
200°C and above
IH coil turned OFF
183~200°C
IH coil turned ON
Normal copy speed
177~183°C
Copying continued but the copy speed lowered (AR-810 only)
Below 177°C
Copying interrupted and back to the ready
Temperature
of fuser roller
Herter
177
183
200
Copy speed
(A4/LT)
Warming-up
Ready (200°C) During copying
Ready
During
copying
During
waiting
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