Sharp R-871M Service Manual ▷ View online
871M - 5
OPERATION SEQUENCE
SENSING FIRE OPERATION
The oven will stop its operation when there is a fire in the
oven cavity in microwave cooking condition.
LSI measures the voltage across the temperature measure-
ment circuit intermittently within a 32-second time base once
the oven is started in the microwave cooking mode. The oven
will stop its operation when the difference of the voltages is
more than 0.69 volts in microwave cooking condition.
oven cavity in microwave cooking condition.
LSI measures the voltage across the temperature measure-
ment circuit intermittently within a 32-second time base once
the oven is started in the microwave cooking mode. The oven
will stop its operation when the difference of the voltages is
more than 0.69 volts in microwave cooking condition.
1. Within a 32-second base, first the thermistor is energized
for 3 seconds. After 2 seconds since the thermistor is
energized, the voltage across the temperature
measurement circuit is measured. And after 21 seconds
since the thermistor is cut off, the convection motor
operates for 10 seconds.
energized, the voltage across the temperature
measurement circuit is measured. And after 21 seconds
since the thermistor is cut off, the convection motor
operates for 10 seconds.
2. The oven carries out the procedure above again. If the
second voltage is 0.69V higher than the first voltage, LSI
judges it is a fire in the oven cavity and stops the oven.
judges it is a fire in the oven cavity and stops the oven.
3. When sensor cooking, the sensing fire operation is not
carried out until the oven senses the steam from food.
Because food cannot be cooked well by rotating the
convection fan at that time. After sensing the steam, the
sensing fire operation is started.
Because food cannot be cooked well by rotating the
convection fan at that time. After sensing the steam, the
sensing fire operation is started.
CONVECTION
MOTOR
THERMISTOR
Sensing
Voltage
ON
OFF
ON
OFF
ON
OFF
0 2
20
30 32
64 (sec.)
3 sec.
Sensing the voltage across temperature measurement circuit.
4. When LSI judges it is fire in the oven cavity, LSI will switch
off the relays to the power transformer, fan motor and
convection motor and LSI stops counting down. And then
the damper is closed so that the fresh air does not come
into the oven cavity.
convection motor and LSI stops counting down. And then
the damper is closed so that the fresh air does not come
into the oven cavity.
MICROWAVE OUTPUT POWER (IEC-705)
The power output of this oven is rated using the method specified by IEC-705. Full details of how to carry out this
procedure can be found in the Sharp Technical Training notes which is available from Sharp Parts Centre
(part number SERV-LITMW01).
procedure can be found in the Sharp Technical Training notes which is available from Sharp Parts Centre
(part number SERV-LITMW01).
The IEC-705 procedure must be carried out using laboratory-type procedures and equipment. These requirements
make the procedure unsuitable for routine performance checks.
make the procedure unsuitable for routine performance checks.
Note: The following test method gives an indication of the output power only, it cannot be used to establish the actual/
rated output power. If the true output power is required, then the IEC-705 test method must be used.
Alternative simplified method:
1. Place 2 litres of cold water (between 12
1. Place 2 litres of cold water (between 12
°
C and 20
°
C) in a suitable container.
2. Stir the water and measure the temperature in
°
C. Note temperature as T1.
3. Place the container in the microwave and heat the water for 2 minutes on full power.
4. When the 2 minutes is completed, remove the container and stir the water. Note the water temperature as T2.
5. Calculate the output power using the following formula:
4. When the 2 minutes is completed, remove the container and stir the water. Note the water temperature as T2.
5. Calculate the output power using the following formula:
R.F. Power Output = (T2 - T1) x 80.
MICROWAVE LEAKAGE TEST
This oven should be tested for microwave leakage on completion of any repair or adjustment, following the procedure
described in the Sharp Technical Training notes (part number SERV-LITMW01). The maximum leakage permitted in
BS EN 60335-2-25 is 50W/m
described in the Sharp Technical Training notes (part number SERV-LITMW01). The maximum leakage permitted in
BS EN 60335-2-25 is 50W/m
2
(equivalent to 5mW/cm
2
), however it is not normal to detect any significant leakage,
therefore, any leakage which is detected should be investigated.
It is essential that only leakage detectors with current calibration traceable to the National Physical Laboratories are
used.
Suitable leakage detectors :
CELTEC A100
APOLLO X1
APOLLO X1
OUTPUT POWER TEST PROCEDURE
871M - 6
PROCEDURE
LETTER
A
TOUCH CONTROL PANEL ASSEMBLY TEST
COMPONENT TEST
B
KEY UNIT TEST
If the display fails to clear when the STOP/CLEAR pad is depressed, first verify the flat ribbon
cable is marking good contact, verify that the door sensing switch (stop switch) operates properly;
that is the contacts are closed when the door is closed and open when the door is open. If the
door sensing switch (stop switch) is good, disconnecct the flat ribbon cable that connects the key
unit to the control unit and make sure the door sensing switch is closed (either close the door or
short the door sensing switch connecter). Use the Key unit matrix indicated on the control panel
schematic and place a jumper wire between the pins that correspond to the STOP/CLEAR pad
marking momentary contact. If the control unit responds by clearing with a beep the key unit is
faulty and must be replaced. If the control unit does not respond, it is a faulty and must be
replaced. If a specific pad does not respond, the above method may be used (after clearing the
control unit) to determine if the control unit or key pad is at fault.
cable is marking good contact, verify that the door sensing switch (stop switch) operates properly;
that is the contacts are closed when the door is closed and open when the door is open. If the
door sensing switch (stop switch) is good, disconnecct the flat ribbon cable that connects the key
unit to the control unit and make sure the door sensing switch is closed (either close the door or
short the door sensing switch connecter). Use the Key unit matrix indicated on the control panel
schematic and place a jumper wire between the pins that correspond to the STOP/CLEAR pad
marking momentary contact. If the control unit responds by clearing with a beep the key unit is
faulty and must be replaced. If the control unit does not respond, it is a faulty and must be
replaced. If a specific pad does not respond, the above method may be used (after clearing the
control unit) to determine if the control unit or key pad is at fault.
The touch control panel consists of circuits including semiconductors such as LSI, ICs, etc. Therefore,
unlike conventional microwave ovens, proper maintenance can not be performed with only a voltmeter and
ohmmeter.
In this service manual, the touch control panel assembly is divided into two units, Control Unit and Key Unit,
and troubleshooting by replacement is described according to the symptoms indicated.
1. Key Unit Note : Check key unit ribbon connection before replacement.
unlike conventional microwave ovens, proper maintenance can not be performed with only a voltmeter and
ohmmeter.
In this service manual, the touch control panel assembly is divided into two units, Control Unit and Key Unit,
and troubleshooting by replacement is described according to the symptoms indicated.
1. Key Unit Note : Check key unit ribbon connection before replacement.
The following symptoms indicate a defective key unit. Replace the key unit.
a) When touching the pads, a certain pad produces no signal at all.
b) When touching a number pad, two figures or more are displayed.
c) When touching the pads, sometimes a pad produces no signal.
b) When touching a number pad, two figures or more are displayed.
c) When touching the pads, sometimes a pad produces no signal.
2. Control Panel
The following symptoms indicate a defective control unit. Before replacing the control unit.
perform the key unit test (Procedure P) to determine if control unit is faulty.
perform the key unit test (Procedure P) to determine if control unit is faulty.
2-1 In connection with pads
a) When touching the pads, a certain group of pads do not produce a signal.
b) When touching the pads, no pads produce a signal.
b) When touching the pads, no pads produce a signal.
2-2 In connection with indicators
a) At a certain digit, all or some segments do not light up.
b) At a certain digit, brightness is low.
c) Only one indicator does not light up.
d) The corresponding segments of all digits do not light up; or they continue to light up.
e) Wrong figure appears.
f) A certain group of indicators do not light up.
g) The figure of all digits flicker.
b) At a certain digit, brightness is low.
c) Only one indicator does not light up.
d) The corresponding segments of all digits do not light up; or they continue to light up.
e) Wrong figure appears.
f) A certain group of indicators do not light up.
g) The figure of all digits flicker.
2-3 Other possible troubles caused by defective control unit.
a) Buzzer does not sound or continues to sound.
b) Clock does not operate properly.
c) Cooking is not possible.
d) Proper temperature measurement is not obtained.
b) Clock does not operate properly.
c) Cooking is not possible.
d) Proper temperature measurement is not obtained.
G11
G7
G2
G5. 9
G12
G10
G8
G6
G4
G3
G1
10 min.
10 sec.
PIZZA
1 min.
CAKE
GRILL
TIMER
Info
Kg / Lb
g
• oz
Kg
• Lb
LESS
MORE
STOP/
CLEAR
AUTO
COOK
RICE/
PASTA
OVEN
CHIPS
MIXED
GRILL
CHICKEN
PTNS
AUTO
DEFROST
BAKED
POTATOES
BREAKFAST
START
CLOCK
AUTO
MINUTE
AUTO START
DUAL
CONVECTION/
GRILL
CONVECTION
TEMPERATURE
MICROWAVE
POWER
LEVEL
CARRY OUT 4R CHECKS
TEST PROCEDURES
871M - 7
TEST PROCEDURES
PROCEDURE
LETTER
COMPONENT TEST
C
RELAY TEST
To protect the electronic circuits, this model is provided with a fine foil pattern added to the input
circuiton the PWB, this foil pattern acts as a fuse. If the foil pattern is open, follow the troubleshooting
guide given below for repair.
Problem: POWER ON, indicator does not light up.
circuiton the PWB, this foil pattern acts as a fuse. If the foil pattern is open, follow the troubleshooting
guide given below for repair.
Problem: POWER ON, indicator does not light up.
CARRY OUT 3D CHECKS.
STEPS
OCCURANCE
CAUSE OR CORRECTION
1
The rated AC voltage is not present at
Check supply voltage and oven power cord.
Power terminal of CPU connector (CN-A).
2
The rated AC voltage is present at primary
Low voltage transformer or secondary circuit defective.
side of low voltage transformer.
Check and repair.
3
Only pattern at "a" is broken.
*Insert jumper wire J1 and solder.
(CARRY OUT 3D CHECKS BEFORE REPAIR)
4
Pattern at "a" and "b" are broken.
*Insert the coil RCILF2003YAZZ between "c" and "d".
(CARRY OUT 3D CHECKS BEFORE REPAIR)
D
PROCEDURES TO BE TAKEN WHEN THE FOIL PATTERN ON THE PRINTED WIRING
BOARD (PWB) IS OPEN.
CARRY OUT 3D CHECKS.
Remove the outer case and check voltage between Pin Nos. 1 and 3 of the 4 pin connector (E) on the
control unit with an A.C. voltmeter.
The meter should indicate 230-240 volts, if not check oven circuit.
control unit with an A.C. voltmeter.
The meter should indicate 230-240 volts, if not check oven circuit.
Relay Test
Check voltage at the relay coil with a D.C. voltmeter during the microwave cooking operation. convection
cooking operation or grill operation.
Check voltage at the relay coil with a D.C. voltmeter during the microwave cooking operation. convection
cooking operation or grill operation.
DC. voltage indicated ............. Defective relay.
DC. voltage not indicated ....... Check diode which is connected to the relay coil. If diode is good,
DC. voltage not indicated ....... Check diode which is connected to the relay coil. If diode is good,
control unit is defective.
RELAY SYMBOL
OPERATIONAL VOLTAGE
CONNECTED COMPONENTS
RY1
Approx. 24.0V D.C.
Oven lamp / Turntable motor
RY2
Approx. 18.0V D.C.
High voltage transformer
RY3
Approx. 18.0V D.C.
Grill heating element (Top grill)
RY4
Approx. 18.0V D.C.
Bottom heating element
RY5
Approx. 24.0V D.C.
Fan motor
RY6
Approx. 24.0V D.C.
Convection fan motor
CARRY OUT 4R CHECKS.
NOTE: *At the time of these repairs, make a
visual inspection of the varistor for
burning damage and examine the
transformer with tester for the pres-
ence of layer short circuit (check
primary coil resistance).
If any abnormal condition is de-
tected, replace the defective parts.
burning damage and examine the
transformer with tester for the pres-
ence of layer short circuit (check
primary coil resistance).
If any abnormal condition is de-
tected, replace the defective parts.
CARRY OUT 4R CHECKS.
CN - E
CN - D
D25
a
b
c
d
VRS1
CN - A
RY6
(J1)
1
3
5
31
871M - 8
TOUCH CONTROL / DESCRIPTION OF LSI
TOUCH CONTROL PANEL ASSEMBLY
OUTLINE OF TOUCH CONTROL PANEL
The touch control section consists of the following units as
shown in the touch control panel circuit.
shown in the touch control panel circuit.
(1) Key Unit
(2) Control Unit
(2) Control Unit
The principal functions of these units and signals communi-
cated among them are explained below.
cated among them are explained below.
Key Unit
The key unit is composed of a matrix, signals generated in the
LSI are sent to the key unit from P11 - P17.
When a key pad is touched, a signal is completed through the
key unit and passed back to the LSI through P20 - P23 to
perform the function that was requested.
LSI are sent to the key unit from P11 - P17.
When a key pad is touched, a signal is completed through the
key unit and passed back to the LSI through P20 - P23 to
perform the function that was requested.
Control Unit
Control unit consists of LSI, power source circuit, synchroniz-
ing signal circuit, ACL circuit, buzzer circuit, temperature
measurement circuit, indicator circuit, encoder circuit, and
back light circuit.
ing signal circuit, ACL circuit, buzzer circuit, temperature
measurement circuit, indicator circuit, encoder circuit, and
back light circuit.
1) LSI
This LSI controls the key strobe signal, relay driving signal
for oven function and indicator signal.
for oven function and indicator signal.
2) Power Source Circuit
This circuit generates voltage necessary in the control
unit.
unit.
Symbol
Voltage
Application
VC
-5.2V
LSI(IC1)
3) Synchronizing Signal Circuit
The power source synchronizing signal is available in
order to compose a basic standard time in the clock circuit.
It accompanies a very small error because it works on
commercial frequency.
order to compose a basic standard time in the clock circuit.
It accompanies a very small error because it works on
commercial frequency.
4) ACL
A circuit to generate a signals which resets the LSI to the
initial state when power is supplied.
initial state when power is supplied.
5) Buzzer Circuit
The buzzer is responsive to signals from the LSI to emit
audible sounds (key touch sound and completion sound).
audible sounds (key touch sound and completion sound).
6) Door Sensing Switch (Stop Switch)
A switch to "tell" the LSI if the door is open or closed.
7) Relay Circuit
To drive the magnetron, heating element, fan motor,
turntable motor and light the oven lamp.
turntable motor and light the oven lamp.
8) Back Light Circuit
A circuit to drive the back light (Light emitting diodes LD1
- LD5).
- LD5).
9) Indicator Circuit
This circuit consists of 7-digits, 30-segments and 4-
common electrodes using a Liquid Crystal Display.
common electrodes using a Liquid Crystal Display.
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