Sharp R-870B User manual

R-870B
TABLE OF CONTENTS Page
CAUTION, MICROWAVE RADIATION.................................................................................................... 1
WARNING.................................................................................................................................................1
PRODUCT SPECIFICATIONS ................................................................................................................ 2
GENERAL INFORMATION.......................................................................................................................2
APPEARANCE VIEW .............................................................................................................................. 3
OPERATION SEQUENCE....................................................................................................................... 4
FUNCTION OF IMPORTANT COMPONENTS ....................................................................................... 8
SERVICING ..............................................................................................................................................8
TROUBLESHOOTING GUIDE ...............................................................................................................10
TEST PROCEDURE.............................................................................................................................. 12
TOUCH CONTROL PANEL ASSEMBLY ..............................................................................................20
COMPONENT REPLACEMENT AND ADJUSTMENT PROCEDURE.................................................. 27
MICROWAVE MEASUREMENT ........................................................................................................... 33
WIRING DIAGRAM................................................................................................................................ 34
PICTORIAL DIAGRAM .......................................................................................................................... 38
POWER UNIT CIRCUIT .........................................................................................................................39
CONTROL PANEL CIRCUIT ..................................................................................................................40
PRINTED WIRING BOARD ....................................................................................................................41
PARTS LIST .......................................................................................................................................... 42
S8837R870BPHR
DOUBLE GRILL
CONVECTION
MICROWAVE OVEN
MODEL R-870B
In interests of user-safety the oven should be restored to its original
condition and only parts identical to those specified should be used.
SERVICE MANUAL
SHARP CORPORATION
DOUBLE GRILL

CONVECTION
Sensor
CRISPYSNACK
PIZZA
AUTO COOK
GRILL
Grilled Fish
RICEMENU
GRILL
SLOW COOK
STOP/CLEAR INSTANTCOOK/START
POWER LEVEL EASYDEFROST
CONVEC
PREHEAT MIX
REHEATDISH STEAMMENU
Grilled Lobster
Steak
Beef
Lamb
Chicken
Cake
Apple Pie
Cookies
SENSORCOOK
ROAST BAKE
HELP
1
2
3
1
2
3
1
2
3
TURNOVER ADD STAND
KG
%
AUTO SENSOR COOK
COVER STIR DEFROST HELP

R-870B

R-870B
1
SERVICE MANUAL
DOUBLE GRILL
CONVECTION
MICROWAVE OVEN
R-870B
GENERAL IMPORTANT INFORMATION
This Manual has been prepared to provide Sharp Corp. Service
engineers with Operation and Service Information.
It is recommended that service engineers carefully study the entire
text of this manual, so they will be qualified to render satisfactory
customer service.
CAUTION
MICROWAVE RADIATION
Service engineers should not be exposed to the microwave
energy which may radiate from the magnetron or other micro-
wave generating devices if it is improperly used or connected.
Allinputandoutputmicrowaveconnections,waveguides,flanges
andgasketsmustbesecured.Neveroperatethedevicewithout
a microwave energy absorbing load attached. Never look into
an open waveguide or antenna while the device is energized.
WARNING
Never operate the oven until the following points are ensured.
(A) The door is tightly closed.
(B) The door brackets and hinges are not defective.
(C) The door packing is not damaged.
(D) The door is not deformed or warped.
(E) There is not any other visible damage with the oven.
Servicing and repair work must be carried out only by trained
service engineers.
Allthe parts marked "*" onpartslistareused at voltages morethan
250V.
Removal of the outer wrap gives access to potentials above 250V.
All the parts marked "∆" on parts list may cause undue microwave
exposure,by themselves, or when theyare damaged, loosened or
removed.
Never operate the Top and/ or Bottom heater with the oven
outer cabinet removed. (Because air flow is eliminated, and the
excess heat generated on adjacent components). It can cause
permanent damage or a fire.
SHARP CORPORATION
OSAKA, JAPAN
PRODUCT SPECIFICATIONS
GENERAL INFORMATION
APPEARANCE VIEW
OPERATING SEQUENCE
FUNCTION OF IMPORTANT
COMPONENTS
SERVICING AND
TROUBLESHOOTING GUIDE
TEST PROCEDURE
TOUCH CONTROL PANEL
COMPONENT REPLACEMENT
AND ADJUSTMENT PROCEDURE
MICROWAVE MEASUREMENT
WIRING DIAGRAM
PARTS LIST

2
R-870B
GENERAL INFORMATION
WARNING
THIS APPLIANCE MUST BE EARTHED
IMPORTANT
THE WIRES IN THIS MAINS LEAD ARE COLOURED IN ACCORDANCE WITH THE FOLLOWING CODE:
GREEN-AND-YELLOW : EARTH
BLUE : NEUTRAL
BROWN : LIVE
PRODUCT DESCRIPTION
SPECIFICATION
ITEM DESCRIPTION
Power Requirements 220 Volts
50 Hertz
Single phase, 3 wire earthed
Power Consumption Microwave cooking 1.6 kW
Top Heater mode 1.3 kW
Grill cooking Bottom heater mode 0.9 kW
Double grill mode 2.1 kW
Convection cooking 2.1 kW
Power Output 900 W nominal of RF microwave energy (measured by method of IEC 705)
Operating frequency 2450 MHz
Grill heater Power Output (Top heater) 1200 W (600 W x 2)
Bottom heater Power Output 800 W
Case Dimensions Width 520 mm
Height 309 mm including foot
Depth 502 mm
Cooking Cavity Dimensions Width 352 mm
Height 207 mm
Depth 368 mm
Turntable diameter 325 mm
Control Complement Touch Control System
Clock (1:00 - 12:59) / Timer (0 - 99 minutes and 99 seconds)
Microwave Power for Variable Cooking
Repetition Rate;
100% ...................................................Full power throughout the cooking time
70%..................................................................... approx. 70% of FULL Power
50%..................................................................... approx. 50% of FULL Power
30%..................................................................... approx. 30% of FULL Power
10%..................................................................... approx. 10% of FULL Power
Mix cooking
Convec. Mix High ..................... 250˚C convection with 30% microwave power
Convec. Mix Low...................... 250˚C convection with 10% microwave power
Grill Mix High.......................................Top heater with 50% microwave power
Grill Mix Low ....................................... Top heater with 10% microwave power
Grill Cooking .............. Top heater mode/ Buttom heater mode/ Double Grill mode
Convection cooking..........................................40˚C to 250˚C temperature control
CRISPY SNACK pad, PIZZA pad, AUTO COOK pads
SENSOR COOK pads, MORE (')/LESS (") pads
HELP pad, GRILL pad, CONVEC pad, PREHEAT pad
MIX pad, SLOW COOK pad, POWER LEVEL pad
EASY DEFROST pad, NUMBERpads, STOP/CLEAR pad
CLOCK pad, INSTANT COOK/START pad
Set Weight Approx. 20 kg

R-870B
3
TOUCH CONTROL PANEL
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5
5
2
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TurntableTurntable
support
High rack
Low rack
Turntable 
motor shaft
Bottom 
heater
APPEARANCEVIEW
1. TOP HEATER SYMBOL
The symbol will light when the top heater is in use.
2. BOTTOM HEATER SYMBOL
The symbol will light when the bottom heater is in use.
3. CONVECTION SYMBOL
The symbol will light during convection cooking.
4. MICROWAVE SYMBOL
The symbol will light during microwave cooking.
A. CRYSPY SNACK PAD: Press to select 5 popular snack menus.
B. PIZZA PAD: Press to select 3 pizza menus.
C. AUTO GRILL PAD: Press to select 3 popular grill menus.
D. AUTO ROAST PAD: Press to select 3 popular roast menus.
E. AUTO BAKE PAD: Press to select 3 popular baking menus.
F. SENSOR RICE MENU PAD: Press to cook rice, congee or porridge.
G. SENSOR REHEAT DISH PAD: Press to reheat dish.
H. SENSOR STEAM MENU PAD
Press to steam fish, meat or dumpling.
I. MORE (') / LESS (") pads
Press to adjust the doneness of food in one minute increments during
cooking or to increase/ decrease the time whilst programming the
automatic operations.
J. HELP PAD
Pressto selectauto start,child lock, languageor demonstrationmodes.
Press to get cooking information.
K. GRILL PAD: Press to select grill cooking.
L. CONVEC PAD
Press to select convection cooking and convection temperature.
M. PREHEAT PAD
Press to preheat the oven prior to cooking.
N. MIX PAD: Press to select mix cooking.
O. SLOW COOK PAD: Press to cook slowly and longer time.
P. POWER LEVEL PAD
Press to select microwave power setting. If not pressed, HIGH power is
automatically selected.
Q. EASY DEFROST PAD
Press to defrost meat by entering weight.
R. NUMBER PADS
Press to enter cooking times, clock time, weight or quantity of food.
S. STOP/CLEAR PAD
Presstoclearduringprogramming.Pressoncetostopoperationofoven
during cooking; Press twice to cancel cooking programme.
OVEN
1. Oven lamp
2. Top heaters (Grill heaters)
3. See through door
4. Door hinges
5. Door safety latches
6. Door seals and sealing surfaces
7. Bottom heater
8. Oven cavity
9. Turntable motor shaft
10.Ventilation openings
11.Waveguide cover
12.Door opening button
13.Control panel
14.Digital display
15.Power supply cord
16.Outer cabinet
17.Ventilation slit
NOTE:
1. Ensurethatthebottomheaterisinthelowest
position as shown the figure, as it is possible
tomove it upand downto help withcleaning.
2. Placetheturntablesupportovertheturntable
motor shaft on the floor of the cavity.
3. Then place the turntable on to the turntable
support.
T. CLOCK PAD
Press to set clock time.
U. INSTANT COOK/START PAD
Pressoncetocookfor1minuteat100%(HIGH
power) or increase by 1 minute multiples each
time this pad is pressed during cooking. Press
to start oven after setting programs.
CRISPY SNACK
PIZZA
AUTO COOK
GRILL
Grilled Fish
RICE MENU
GRILL
SLOW COOK
STOP/ CLEAR INSTANT COOK/START
POWER LEVEL EASY DEFROST
CONVEC PREHEAT MIX
REHEAT DISH STEAM MENU
Grilled Lobster
Steak
Beef
Lamb
Chicken
Cake
Apple Pie
Cookies
SENSOR COOK
ROAST BAKE
HELP
1
2
3
1
2
3
1
2
3
TURNOVER ADD STAND
KG
%
AUTO SENSOR COOK
COVER STIR DEFROST HELP
1
2
3
4
A
C
F
K
J
O
L
P
S
T
B
E
D
H
I
M
G
N
Q
U
R

4
R-870B
OPERATION SEQUENCE
OFF CONDITION
Closing the door activates the 1st. latch switch and 2nd.
interlock relay control switch.
IMPORTANT:
When the oven door is closed, the contacts COM-NC
of the monitor switch must be open. When the mi-
crowave oven is plugged in a wall outlet (220V 50Hz),
the line voltage is supplied to the noise filter and the
control unit.
Figure O-1 on page 34
1. The oven display will show " SHARP MICRO- WAVE
OVEN " .
2. Press the STOP/CLEAR pad. The oven display will
show " : ".
3. Set the clock as follows.
3-1. Press the CLOCK pad once.
3-2. Enter the time of day by perssing the number
pads.
3-3. Start the clock by pressing the CLOCK pad.
NOTE:
1. If you do not set the clock, " : " will appear on the
display. When the operation of the oven is finished, " :
" will appear on the display instead of the time of day.
2. The oven can be also used when the clock is not set.
3. Whentheovendoorisopened,theovenlampdoesnot
come on.
MICROWAVE COOKING CONDITION
100% (HIGH) COOKING
Enteradesiredcookingtimebypressingthenumberpads
and start the oven by pressing START pad.
Function sequence Figure O-2 on page 34
CONNECTED COMPONENTS RELAY
Convection motor RY1
High voltage transformer RY2
Grill heater (Top) RY3
Bottom heater RY4
Fan motor, RY5
Oven lamp, Turntable motor RY6
1. The line voltage is supplied to the primary winding of
thehigh voltagetransformer. The voltage is converted
to about 3.3 volts A.C. output on the filament winding
and high voltage of approximately 2000 volts A.C. on
the secondary winding.
2. The filament winding voltage (3.3 volts) heats the
magnetronfilamentandthehighvoltage(2000volts)is
sentto the voltage doubling circuit,where it is doubled
to negative voltage of approximately 4000 volts D.C..
3. The 2450 MHz microwave energy produced in the
magnetron generates a wave length of 12.24 cm. This
energyischannelledthroughthewaveguide(transport
channel)into the ovencavity, wherethe food isplaced
to be cooked.
4. Whenthecookingtimeisup,asignaltoneisheardand
the relays RY2 + RY5 + RY6 go back to their home
position. The circuits to the oven lamp, high voltage
transformer, fan motor and turntable motor are cut off.
5. Whenthe oven dooris openedduring a cookingcycle,
the switches come to the following condition.
Switch Contact Condition
During Oven Door
Cooking Open(No cooking)
1st. latch switch COM-NO Closed Opened
2nd. interlock relay
control switch COM-NO Closed Opened
Monitor Switch COM-NC Opened Closed
Thecircuittothehighvoltagetransformer,fanmotor,oven
lamp and turntable motor are cut off when the 1st. latch
switch and 2nd. interlock relay control switch are made
open. Shown in the display is remaining time.
6. MONITOR SWITCH CIRCUIT
The monitor switch is mechanically controlled by the
oven door, and monitors the operation of the 1st. latch
switch and the 2nd. interlock relay RY2.
6-1. When the oven door is opened during or after the
cycle of a cooking program, the 1st. latch switch and
2nd. interlock relay control switch must open their
contactsfirst.Afterthatthecontacts(COM-NC)ofthe
monitor switch can be closed.
6-2. When the oven door is closed, the contacts (COM-
NC) of the monitor switch must be opened. After that
thecontactsofthe1st.latchswitchand2nd.interlock
relay control switch are closed.
6-3. Whentheovendoorisopenedandthecontactsofthe
1st. latch switch and the 2nd. interlock relay RY2
remain closed, the fuse M10Awill blow, because the
monitorswitchisclosed andashortcircuitiscaused.
70% (MEDIUM HIGH), 50% (MEDIUM), 30% (ME-
DIUM LOW), 10% (LOW COOKING)
When the microwave oven is preset for variable cooking
power, the line voltage is supplied to the high voltage
transformer intermittently within a 32-second time base
through the relay contact which is coupled with the cur-
rent-limitingrelay RY2.Thefollowing levels of microwave
power are given.
SETTING
Note: TheOn/Offtimeratiodoesnotexactlycorrespond
to the percentage of microwave power, because
approx. 2 seconds are needed for heating up the
magnetron filament.
CONVECTION COOKING CONDITION
PREHEATING CONDITION
SelectpreheatingtemperaturebypressingthePREHEAT
pad. When the START pad is touched, the following
operations occur:
Figure O-3 on page 35
1. The coils of shut-off relays RY1+RY5+RY6 are ener-
gized, the oven lamp, cooling fan motor, turntable
motor and convection motor are turned on.
2. The coil of heater relays RY3+RY4 are energized by
the CPU unit and the main supply voltage is added to
100% 32 sec. ON Approx. 100%
70% 24 sec. ON 8 sec. OFF Approx. 70%
50% 18 sec. ON 14 sec. OFF Approx. 50%
30% 12 sec. ON 20 sec. OFF Approx. 30%
10% 6 sec. ON 26 sec. OFF Approx. 10%

R-870B
5
the top and bottom heaters.
3. When the oven temperature reaches the selected
preheat temperature, the following operations occur:
3-1. The heater relays RY3+RY4 de-energized by the
CPUunittemperaturecircuitandthermistor,opening
the circuit to the top and bottom heaters.
3-2. The oven will continue to function for 30 minutes,
turning the top and bottom heaters on and off, as
needed to maintain the selected preheat tempera-
ture. The oven will shut-down completely after 30
minutes.
CONVECTION COOKING CONDITION
When the preheat temperature is reached, a beep signal
will sound indicating that the holding temperature has
beenreachedintheoven cavity. Open the door and place
the food to be cooked in the oven. Select the cooking
temperature by pressing the CONVEC pad. And then
enter the cooking time by pressing the NUMBER pads.
WhentheSTARTpadistouched,thefollowingoperations
occur:
1. The numbers of the digital read-out start the count
down to zero.
2. Theovenlamp,turntablemotor,coolingfan motor and
convection motor are energized.
3. The relays(RY3 and RY4) are energized (if the cavity
temperature is lower than the selected temperature)
and the main supply voltage is applied to the heating
elementtoreturn to the selectedcookingtemperature.
Thetopheatersand the bottomheaterworkin accord-
ance with the following table while the heaters are
energized.
Selected Temp- Top Heaters Bottom Heater
erature (˚C) Power (%) Power (%)
250 40 40
230 40 40
220 40 40
200 30 70
180 20 70
160 10 70
150 10 70
130 10 60
70 10 40
40 10 30
4. Upon completion of the cooking time, the audible
signal will sound, and oven lamp, turntable motor,
cooling fan motor and convection motor are de-ener-
gized. At the end of the convection cycle, if the cavity
airtemperatureisabove120˚C,thecircuitto(RY5)will
be maintained (by the thermistor circuit) to continue
operationofthecoolingfanmotoruntilthetemperature
drops below 104˚C, at which time the relay will be de-
energized, turning off the fan motor. Relay (RY1) will
however, open as soon as the convection cycle has
ended, turning off the convection fan motor.
GRILL COOKING CONDITIONS
The oven has three grill cooking condition. They are the
TOP HEATER mode, BOTTOM HEATER mode and
DOUBLE GRILL mode.
TOP HEATER MODE
In this mode, the food is cooked by the top heaters. Press
the GRILL pad once and then enter the cooking time by
pressing the number pads. When the START pad is
pressed, the following operations occur:
Figure O-4(a) on page 35
1. The relay RY3 + RY5 + RY6 are energized.
2. The numbers of the digital read-out start the count
down to zero.
3. Then the top heaters, turntable motor, oven lamp and
fan motor are energized.
4. Now, the food is grilled by the top heaters.
5. Uponcompletionof the selectedcookingtime,audible
signal sounds and the contacts of relays RY3 + RY6
are opened, then the top heaters, turntable motor and
oven lamp are de-energized. But the relay RY5 stays
closed and the fan motor operates for 5 minutes. But if
the cooking time is less than 2 minutes the relay RY5
will not stay close.
BOTTOM HEATER MODE
In this mode, the food is cooked by the bottom heater.
PresstheGRILLpadtwiceandthenenterthecookingtime
by pressing the number pads. When the START pad is
pressed, the following operations occur:
Figure O-4(b) on page 36
1. The relay RY4 + RY5 + RY6 are energized.
2. The numbers of the digital read-out start the count
down to zero.
3. Then the bottom heater, turntable motor, oven lamp
and fan motor are energized.
4. Now, the food is grilled by the bottom heater.
5. Uponcompletionof the selectedcookingtime,audible
signal sounds and the contacts of relays RY4 + RY6
areopened, thenthe bottom heating elements, turnta-
ble motor and oven lamp are de-energized. But the
relay RY5 stays closed and the fan motor operates for
5minutes.Butifthecookingtimeislessthan2minutes
the relay RY5 will not stay close.
DOUBLE GRILL MODE
In this mode, the food is cooked by both the top heaters
and bottom heater. Press the GRILL pad three times and
thenenterthe cookingtimeby pressing thenumberpads.
WhentheSTARTpadispressed,thefollowingoperations
occur:
Figure O-4(c) on page 36
1. The relay RY3 + RY4 + RY5 + RY6 are energized.
2. The numbers of the digital read-out start the count
down to zero.
3. Then the top heaters, bottom heater, turntable motor,
oven lamp and fan motor are energized.
4. Now, the food is grilled by the top heaters and the
bottom heater.
5. Upon completion of the selected cooking time, audible
signal sounds and the contacts of relays RY3 + RY4 +
RY6areopened,thenthetopheatingelements,bottom
heatingelement,turntablemotorandovenlamparede-
energized. But the relay RY5 stays closed and the fan
motor operates for 5 minutes. But if the cooking time is
less than 2 minutes the relay RY5 will not stay closed.
MIX COOKING CONDITION
The oven will cook food by supplying top heaters and/or
bottom heater and microwave energy alternately within a
48secondstimebase.Andtheovenhasfourprogrammed
cooking mode.

6
R-870B
CONVEC MIX HIGH MODE AND CONVEC MIX LOW
MODE
Inthese modes,the foodis cookedby the convection and
the microwave energy. Press the MIX pad once for
CONVEC MIX HIGH mode. Press the MIX pad twice for
CONVEC MIX LOW mode. And then enter the cooking
time by pressing the number pads. When the START pad
is pressed, the following operations occur:
Figure O-5(a) on page 37
1. The relay RY1+ RY5 + RY6 are energized.
2. The numbers of the digital read-out start the count
down to zero.
3. Theconvectionmotor,turntablemotor, oven lamp and
fan motor are energized.
4. TherelayRY2andtherelaysRY3+RY4areenergized
alternatelywithina48secondstimebasebythecontrol
unit.
5. The relays RY3 + RY4 are energized (If the cavity
temperature is lower than the selected temperature)
and the main supply voltage is applied to the top and
bottom heaters to return to selected cooking tempera-
ture.Andthehighvoltagetransformeroperatesthrough
the relay RY2 is energized.
6. Therelationshipbetweenthetopheatingelementsand
magnetron operations are as follows.
Note: TheOn/Offtimeratiodoesnotexactlycorrespond
to the percentage of microwave power, because
approx. 2 seconds are needed for heating up the
magnetron filament.
7. Uponcompletionof the selectedcookingtime,audible
signal sounds and the contacts of relays RY1 + RY2 +
RY3 + RY4 + RY6 are opened, then the top heaters,
bottom heater, high voltage transformer, turntable
motor, convection motor and oven lamp are de-ener-
gized. At the end of the convection cycle, if the cavity
air temperature is above 120˚C, the circuit to RY5 will
be maintained (by the thermistor circuit) to continue
operationofthecoolingfanmotoruntilthetemperature
drops below 104˚C, at which time the relay will be de-
energized, turning off the fan motor.
GRILL MIX HIGH MODE AND GRILL MIX LOW MODE
Inthesemodes,thefoodiscookedbythetop heaters and
the microwave energy. Press the MIX pad three times for
GRILL MIX HIGH mode. Press the MIX pad four times for
GRILL MIX LOW mode. And then enter the cooking time
by pressing the number pads. When the START pad is
pressed, the following operations occur:
Figure O-5(b) on page 37
1. The relay RY5 + RY6 are energized.
2. The numbers of the digital read-out start the count
down to zero.
3. The turntable motor, oven lamp and fan motor are
energized.
4. The relay RY2 + RY3 are energized alternately within
a 48 seconds time base by the control unit.
5. The top heaters operate through the relay RY3 is
energized. And the high voltage transformer operates
through the relay RY2 is energized.
6. Therelationshipbetweenthetopheatingelementsand
magnetron operations are as follows.
Note: TheOn/Offtimeratiodoesnotexactlycorrespond
to the percentage of microwave power, because
approx. 2 seconds are needed for heating up the
magnetron filament.
7. Uponcompletionof the selectedcookingtime,audible
signal sounds and the contacts of relaysRY2 + RY3 +
RY6 are opened, then the top heaters, high voltage
transformer, turntable motor and oven lamp are de-
energized. At the end of the convection cycle, if the
cavity air temperature is above 120˚C, the circuit to
RY5 will be maintained (by the thermistor circuit) to
continue operation of the cooling fan motor until the
temperature drops below 104˚C, at which time the
relay will be de0energized, turning off the fan motor.
AUTOMATIC OPERATIONS
This oven has the following automatic operations;
CRISPY SNACK
PIZZA
AUTO GRILL
AUTO ROAST
AUTO BAKE
EASY DEFROST
Theasewill automatically computethecooking modeand
thecookingtime.Andtheovenwillcookordefrostthefood
according to the special cooking sequence.
LIMITATIONS OF POWER OUTPUT IN MANUAL
OPERATION
After the same cooking mode is carried out for more than
the specified cooking time, the power output is automati-
cally reduced by turning the control relays on and off
intermittently, as shown in the table below. This is to
protect the oven door against temperature rising.
16 SEC. 32 SEC.
22 SEC.26 SEC.
22 SEC.26 SEC.
CONVEC MIX LOW mode
CONVEC MIX HIGH mode
MICROWAVE POWER
= APPROX. 30%
MICROWAVE POWER
= APPROX. 10%
40 SEC.8 SEC.
ON
ON
OFF
OFF
OFF
ON
OFF
ON
(MICRO.)
(MICRO.)
CONVEC
OPERATION
250˚C
CONVEC
OPERATION
250˚C
26 SEC. 22 SEC.
GRILL MIX LOW mode
GRILL MIX HIGH mode
MICROWAVE POWER
= APPROX. 50%
MICROWAVE POWER
= APPROX. 10%
40 SEC.8 SEC.
ON
ON
OFF
OFF
OFF
ON
OFF
ON
(MICRO.)
(MICRO.)
TOP
HEATERS
TOP 
HEATERS

R-870B
7
Specified cooking Limited power Time base
Cooking mode time (minutes) output (%) (seconds)
Microwave
100% Power 20 70 32
Top heaters 30 50 48
Bottom heater 15 50 48
Top browner and
10 (Top) 50 48
Bottom browner 10 (Bottom) 50 48
or Oven cooking
NOTE:
1. In case of Automatic operations, the limitations of
power output are not carried out.
2. In case that the STOP/CLEAR pad is pressed or the
oven door is opened during cooking, the limitations of
poweroutputarecarriedoutafterthetotalcookingtime
beyond the specified cooking time.
3. In case of the two or more same cooking modes are
carried out, the limitations of power output are carried
out after the total cooking time beyond the specified
cooking time.
4. Incaseofthetwoormoredifferentcookingmodes are
carried out, the specified cooking time is started to
countfromthepointwhenthecookingmodeischanged.
5. If the cooking mode has the power level display, the
power level is also displayed when the limitations of
power output are carried out.
ABSOLUTE HUMIDITY SENSOR (AH SENSOR)
COOKING CONDITION
In case where the AH sensor is used (SENSOR RICE
MENU, SENSOR REHEAT DISH or SENSOR STEAM
MENU),the foods arecooked inmicrowave cooking mode
without figuring time, power level or quantity. When the
oven senses enough steam from the food, it relays the
information to its microprocessor which will calculate the
remaining cooking time and power level needed for best
results. When the food is cooked, water vapour is devel-
oped. The sensor “senses” the vapour and its resistance
increases gradually. When the resistance reaches the
valuesetaccordingtothemenu,supplementarycookingis
started. The time of supplementary cooking is determined
by experiment with each food category and inputted into
the LSI.
An example of how sensor works:
1. Potatoes at room temperature. Vapour is emitted very
slowly.
2. Heat potatoes. Moisture and humidity is emitted rap-
idly. You can smell the aroma as it cooks. ;
3. Sensor detects moisture and humidity and calculates
cooking time and variable power.
AH SENSOR COOKING SEQUENCE
1. Incasethe AH sensorcookingconditionis started, the
coil of shut-off relays (RY5+RY6) are energized, the
ovenlampandcoolingfanmotorareturnedon,butthe
power transformer is not turned on.
NOTE: TheovenshouldnotbeoperatedonAHSENSOR
COOKING immediately after plugging in the unit.
WaittwominutesbeforecookingonAHSENSOR
COOKING CONDITION.
2. After about 16 seconds, the cook relay (RY2) is ener-
gized.The powertransformer isturned on,microwave
energy is produced and first stage is started. The 16
seconds is the cooling time required to remove any
vapour from the oven cavity and sensor.
(Figure O-2)
NOTE: During this first stage, do not open the door or
touch STOP/CLEAR pad.
3. When the sensor detects the vapour emitted from the
food,thedisplayswitchesovertotheremainingcooking
timeand thetimer counts down to zero.At thistime, the
door may be opened to stir food, turn it or season, etc.
NOTE: In case where a small quantity of food is cooked,
theovenwillstopwithoutdisplayingtheremaining
cooking time. In case of "Reheat Pie" of Sensor
Instant Action, the relay (RY2) is turned off and
power transformer is turned off. And then the
relays (RY3 + RY4) are energized. The top and
bottom heaters are turned on.
4. Whenthetimerreacheszero,anaudiblesignalsounds.
The shut-off relay (RY5+RY6) and cook relay (RY2)
are de-energized and the power transformer, oven
lamp, etc. are turned off.
FIRE SENSING FEATURE (MICROWAVE MODE)
This model incorporates a sensing feature which will stop
the oven's operation if there is a fire in the oven cavity
during microwave cooking. This accomplished by the LSI
repeatedly measures the voltage across the temperature
measurement circuit (thermistor) during it's 32-seconds
timebasecomparingtheobtainedvoltagemeasurements.
Ifthemostrecent voltagemeasuredis700mVgraterthan
the previous voltage measured, the LSI judges it as a fire
inthe oven cavity and switchesoff the relays to the power
transformer,fanmotorturntablemotorandtheovenlamp.
The LSI also stops counting down. Please refer to the
following section for a more detailed description.
Operation
Please refer to the timing diagrams below.
1. Thethermistoroperateswithina32-secondstimebase
and it is energized for three (3) seconds and off for 29
seconds. Two (2) seconds after the thermistor is
energized, the voltage across the temperature meas-
urement circuit is sampled by the LSI and twenty one
(21)secondsafterthethermistoriscutofftheLSIturns
on the cooling fan for six (6) seconds.
2. The above procedure is repeated. If the difference
between the first voltage measured (in step 1) and
the voltage measured when the procedure is repeated
(step 2) is greater than 700mV the LSI makes the
judgment that there is a fire in the oven cavity and will
switch off the relays to the power transformer, fan
MICROWAVE
MICROWAVE
AH SENSOR

8
R-870B
DOOR OPEN MECHANISM
Thedoorcanbeopenedbypushingtheopenbuttononthe
controlpanel.Whentheopenbuttonispushed,theswitch
leverismovedupward,operatingthelatchhead.Thelatch
head is moved upward and released from the latch hook.
Now, the door can be opened.
Figure D-1. Door Open Mechanism
FUNCTION OF IMPORTANT COMPONENTS
1ST. LATCH SWITCH AND 2ND. INTERLOCK
RELAY CONTROL SWITCH
1. Whentheovendoorisclosed,thecontacts(COM-NO)
of each switch must be closed.
2. When the oven door is opened, the contacts (COM-
NO) of each switch must be opened.
MONITOR SWITCH
1. Whenthedoorisclosed,thecontacts(COM-NC)must
be opened.
2. When the door is opened, the contacts (COM-NC)
must be closed.
3. Ifthe oven door is opened and he contacts(COM-NO)
of the 1st. latch switch and 2nd. interlock relay (RY2)
fail to open, the fuse M10A blows immediately after
closing the contacts (COM-NC) of the monitor switch.
CAUTION: BEFORE REPLACING A BLOWN FUSE
M10ATESTTHE1ST.LATCHSWITCH,2ND.
INTERLOCK RELAY (RY2), MONITOR
SWITCH AND MONITOR RESISTOR FOR
PROPER OPERATION. (REFER TO CHAP-
TER “TEST PROCEDURE”).
motor, turntable motor and the oven lamp. The LSI
also stops counting down.
3. Oncethefiresensorfeaturehasshuttheunitdown,the
programmedcookingcyclemayberesumedby press-
ing the "START" pad or the unit may be reset by
pressing the "CLEAR" pad.
IMPORTANT:
During sensor cooking operation, the fire sensing
operationsequence will notbeginuntil the AHsensor
has detected vapours and initiated a sensor cooking
cycle.Thisisbecausetheoperationoftheconvection
fanwouldinterferewiththeAHsensor'svapourdetec-
tion.
ON/OFF TIME RATIO
Ingrillcooking,convectioncookingormixcooking,thetop
heaters,bottomheaterormagnetronoperatewhithina48
secondtimebase.ThefollowingtableistheON/OFFtime
ratio at each power output of the top heaters, bottom
heater or magnetron.
POWER OUTPUT ON TIME OFF TIME
100% 48 sec. 0 sec.
90% 44 sec. 4 sec.
80% 40 sec. 8 sec.
70% 36 sec. 12 sec.
60% 32 sec. 16 sec.
50% 26 sec. 22 sec.
40% 22 sec. 26 sec.
30% 16 sec. 32 sec.
20% 12 sec. 36 sec.
10% 8 sec. 40 sec.
Latch Hook
Latch Heads
Door
1st. Latch Switch
2nd. Interlock
Relay Control
Switch
Monitor Switch
Switch Lever
CONVECTION
MOTOR
THERMISTOR
Sensing 
Voltage
ON
OFF
ON
OFF
ON
OFF
0 2 3 24 30 32 (sec.) 64 (sec.)
3 sec.
Sensing the voltage across temperature measurement circuit.
6 sec.

R-870B
9
NOISE FILTER
The noise filter assembly prevents radio frequency inter-
ference that might flow back in the power circuit.
TOP HEATERS
The top heaters are located on the top of the oven cavity
assembly. The top heaters send out heat to grill foods.
BOTTOM HEATER
Thebottomheaterislocatedontheflooroftheovencavity
assembly.Thebottomheatersendsoutheattogrillfoods.
ONVECTION COOKING SYSTEM
Thisovenisdesignedwithahot air heating systemwhere
food is not directly heated by the top and bottom heaters,
but is heated by forced circulation of the hot air produced
by the top and bottom heaters. The air heated by the top
and bottom heaters is circulated through the convection
passageprovidedontheoutercasingoftheovencavityby
means of the convection fan which is driven by the
convection motor. It then enters the inside of the oven
throughtheventholesprovidedontheleftsideoftheoven.
Next,thehotairheatsthefoodontheturntableandleaves
theovencavitythroughtheventintheovencavityleftside
wall. Without leaving the oven, this hot air is reheated by
the top and bottom heaters, passes through the convec-
tion passage and enters the inside of the oven cavity
again, in a continuing cycle. In this way, the hot air
circulates inside the oven cavity to raise its temperature
and, at the same time, comes into contact with the food
being cooked. When the temperature inside the oven
cavity reaches the selected temperature, the top and
bottom heaters are de-energized. When the temperature
inside the oven cavity drops below the selected tempera-
ture, the top and bottom heaters are energized again. In
this way, the ins ide of the oven cavity is maintained at
approximately the selected temperature. When the con-
vectiontimereaches0,thetopandbottomheatersarede-
energizedandtheconvectionfanstopsoperatingandthe
oven shuts off. Upon completion of the cooking time, the
audiblesignalwillsound,andovenlamp, turntable motor,
coolingfanmotorandconvectionmotorarede-energized.
Attheendoftheconvectioncycle,ifthecavityairtempera-
ture is above 120˚C, the circuit to RY5 will be maintained
(by the thermistor circuit) to continue operation of the
coolingfanmotoruntilthetemperaturedropsbelow104˚C,
atwhichtimetherelaywillbede-energized,turningoffthe
fan motor. Relay RY1 will however, open as soon as the
convectioncyclehasended,turningofftheconvectionfan
motor. This will now cool.
FUSE M10A 250V
1. If the wire harness or electrical components are short-
circuited,thisfuseblowstopreventanelectricshockor
fire hazard.
2. This fuse blows when the 1st. latch switch and 2nd.
interlock relay(RY2)remainclosedwiththeovendoor
open and when the contacts (COM-NC) of monitor
switch closes.
FUSE 15A
If the wire harness or electrical components are short-
circuited,thisfuseblowstopreventanelectricshockorfire
hazard.
HIGH VOLTAGE FUSE 0.75A
Thehighvoltagefuseblowswhenthehighvoltagerectifier
or the magnetron is shorted.
THERMAL CUT-OUT 125˚C (MG)
Thisthermalcut-outprotectsthemagnetronagainstover-
heating. If the temperature goes up higher than 125˚C
because the fan motor is interrupted or the ventilation
openings are blocked, the thermal cut-out will open and
line voltages to the high voltage transformer will be cut off
and the operation of the magnetron will be stopped.
THERMAL CUT-OUT170˚C (OVEN)
The thermal cut-out located on the top of the oven cavity
is designed to prevent damage to the oven if the foods in
the oven catch fire due to over heating produced by
improper setting of the cooking time or failure of control
unit.Underthenormaloperation,theoventhermalcut-out
remains closed. However, when abnormally high tem-
peraturearereachedwithintheovencavity, oven thermal
cut-out will open at 170˚C causing the oven to shut down.
The thermal cut-out will cut back in at 155˚C.
THERMISTOR
The thermistor is a negative temperature coefficient type.
Thetemperatureintheovencavityisdetectedthroughthe
resistance of the thermistor, and then the control unit
causes the heating element relay to operate, thus the
current to the heating element is turned ON/OFF.
MONITOR RESISTOR
The monitor resistor prevents the fuse M10A bursting
when the fuse M10A blows due to the operation of the
monitor switch.
TURNTABLE MOTOR
Theturntablemotordrivestheturntablerollerassemblyto
rotate the turntable.
FAN MOTOR
Thefanmotordrivesabladewhichdrawsexternalcoolair.
Thiscool air isdirected throughthe air vanessurrounding
the magnetron and cools the magnetron. This air is chan-
nelled through the oven cavity to remove steam and
vapours given off from heating food. It is then exhausted
through the exhausting air vents of the oven cavity.
CONVECTION MOTOR
The convection motor drives the convection fan and
provides the heated air.

10
R-870B
When troubleshooting the microwave oven, it is helpful to
followtheSequenceofOperationinperformingthechecks.
Many of the possible causes of trouble will require that a
specifictestbe performed.Thesetests are givenaproce-
dure letter which will be found in the “Test Procedure”
section.
IMPORTANT: If the oven becomes inoperative because
of a blown fuse M10A in the 1st. latch
switch-2nd.interlockrelay(RY2)-monitor
switch - monitor resistor circuit, check the
1st.latchswitch,2nd.interlockrelay(RY2),
monitor switch and monitor resistor be-
fore replacing the fuse M10A.
TROUBLESHOOTING GUIDE
REMEMBER TO CHECK 3D
1) Disconnect the supply.
2) Door opened, and wedged open.
3) Discharge high voltage capacitor.
WARNING: AGAINST THE CHARGE OF THE
HIGH-VOLTAGE CAPACITOR.
The high-voltage capacitor remains charged about
60 seconds after the oven has been switched off.
Wait for 60 seconds and then short-circuit the con-
nection of the high-voltage capacitor (that is, of the
connectingleadofthehigh-voltagerectifier)against
thechassiswiththeuseofaninsulatedscrewdriver.
Sharprecommendthatwhereverpossiblefault-findingis
carriedoutwiththesupplydisconnected.Itmayin,some
cases,benecessarytoconnectthesupplyaftertheouter
case has been removed, in this event carry out 3D
checks and then disconnect the leads to the primary of
the high voltage transformer. Ensure that these leads
remain isolated from other components and the oven
chassis. (Use insulation tape if necessary.) When the
testing is completed carry out 3D checks and reconnect
the leads to the primary of the high voltage transformer.
When all service work is completed and the oven is fully assembled, the microwave power output should be checked
and microwave leakage test should be carried out.
SERVICING
WARNING TO SERVICE PERSONNEL
Microwaveovenscontaincircuitrycapableofproducingveryhighvoltageandcurrent.Contactwithfollowingpartswill
result in electrocution.
High voltage capacitor, High voltage transformer, Magnetron, High voltage rectifier assembly, High voltage harness.
REMEMBER TO CHECK 4R
1) Reconnect all leads removed from components dur-
ing testing.
2) Replace the outer case (cabinet).
3) Reconnect the supply.
4) Run the oven. Check all functions.
Microwaveovensshouldnotberunempty.Totestforthe
presence of microwave energy within a cavity, place a
cup of cold water on the oven turntable, close the door
and set the power level to HIGH (100%) and set the
microwave timer for two (2) minutes. And push the start
key. When the two minutes has elapsed (timer at zero)
carefully check that the water is now hot. If the water
remains cold carry out 3D checks and re-examine the
connections to the component being tested.

R-870B
11
Fuse 15A blows when power cord is plugged into wall outlet. Fuse M10A blows when the door is opened. Home fuse blows when power cord is plugged into wall outlet. "SHARP MICRO- OVEN" does not appear in display when power cord is plugged into wall outlet. Display does not operate properly when STOP/CLEAR pad is pressed. Oven does not start when the INSTANT COOK/ START pad is pressed. (Display operates.) Oven lamp does not light. (Turntable motor operates.) Fan motor does not operate. (Oven lamp lights.) Turntable motor does not operate. (Oven lamp lights.) Oven or electrical parts does not stop when cooking time is 0 or STOP/CLEAR pad is pressed.  Oven goes into cook cycle but shuts down before end of cooking cycle. Oven seems to be operating but little or no heat is produced in oven load.  Oven does not operating properly during variable cooking condition except 100% cooking condition. Top heaters do not operate. Bottom heater does not operate. Oven seems to be operating but little or no heat is produced in oven load. (Microwave power does not seem to be generated properly.) Top heaters do not operate. Bottom heater does not operate. Temperature is lower or higher than preset. Convection motor does not operate. Oven stops after 4 minutes 15 sec.. Oven is in sensor cooking condition but AH sensor does not end 1st. stage or does not stop cooking cycle or the oven stops soon.
CONDITION PROBLEM

MAGNETRON
HIGH VOLTAGE TRANSFORMER
H.V. RECTIFIER ASSEMBLY
HIGH VOLTAGE CAPACITOR
1ST. LATCH SWITCH
MONITOR SWITCH
2ND. INTERLOCK RELAY CONTROL SWITCH
THERMAL CUT-OUT 125˚C 
THERMAL CUT-OUT 170˚C
FUSE M10A 
FUSE 15A 
NOISE FILTER
FAN MOTOR
TURNTABLE MOTOR
CONVECTION MOTOR
TOP HEATERS
BOTTOM HEATER
THERMISTOR
HIGH VOLTAGE FUSE
TOUCH CONTROL PANEL
KEY UNIT
RELAY RY1
RELAY RY2
RELAY RY3
RELAY RY4
RELAY RY5
RELAY RY6
FOIL PATTERN ON P.W.B.
AH SENSOR
POWER SUPPLY CORD
OVEN LAMP 
SHORTED WIRE HARNESS
OPENED WIRE HARNESS
MIS-ADJUSTMENT OF SWITCHES
A B C D E E E F F G H I J J J K K L M N O P P P P P P Q R 
MIX COOKING CONDITION
CONVECTION COOKING CONDITION
AH. SENSOR
OFF CONDITION
COOKING CONDITION
(COMMON MODE)
MICROWAVE  COOKING CONDITION GRILL  COOKING CONDITION 
POSSIBLE CASE 
AND 
DEFECTIVE PARTS


12
R-870B
A MAGNETRON TEST
TEST PROCEDURES
PROCEDURE
LETTER COMPONENT TEST
CARRY OUT 3D CHECKS.
Isolate the magnetron from high voltage circuit by removing all leads connected to filament terminal.
Totest for anopen circuit filamentuse an ohmmeterto makeacontinuity testbetween the magnetron
filament terminals, the meter should show a reading of less than 1 ohm.
Totestforshortfilamenttoanodecondition,connectohmmeterbetweenoneofthefilamentterminals
and the case of the magnetron (ground). This test should be indicated an infinite resistance. If a low
or zero resistance reading is obtained then the magnetron should be replaced.
MICROWAVE OUTPUT POWER (1 litre load)
The following test procedure should be carried out with the microwave oven in a fully assembled
condition (outer case fitted). Microwave output power from the magnetron can be measured by way
of IEC 705, i.e. it is measured by how much power the water load can absorb. To measure the
microwave output power in the microwave oven, the relation of calorie and watt is used. When P(W)
heating works for t(second), approximately P x t/4.187 calorie is generated. On the other hand, if the
temperature of the water with V(ml) rises ∆T (°C) during this microwave heating period, the calorie of
the water is V x ∆T.
Measuring condition:
1. Container
The water container must be a cylindrical borosilicate glass vessel having a maximum material
thickness of 3 mm and an outside diameter of approximately 190 mm.
2. Temperature of the oven and vessel
The oven and the empty vessel are at ambient temperature prior to the start the test.
3. Temperature of the water
The initial temperature of the water is (10±2)°C.
4. Selecttheinitialandfinalwatertemperaturesothatthemaximumdifferencebetweenthefinalwater
temperature and the ambient temperature is 5K.
5. Selectstirringdevicesandmeasuringinstrumentsinordertominimizeadditionorremovalofheat.
6. The graduation of the thermometer must be scaled by 0.1°C at minimum and be an accurate
thermometer.
7. The water load must be (1000±5) g.
8. “t”is measured while the microwavegenerator isoperating at fullpower. Magnetronfilament heat-
up time is not included.
NOTE:Theoperation time ofthemicrowaveoven is“t+2” sec. (2sec.ismagnetron filamentheat-uptime.)
Measuring method:
1. Measure the initial temperature of the water before the water is added to the vessel.
(Example: The initial temperature T1 = 11°C)
2. Add the 1 litre water to the vessel.
3. Place the load on the centre of the shelf.
4. Operate the microwave oven at HIGH for the temperature of the water rises by a value ∆T of
(10 ±2) K.
5. Stir the water to equalize temperature throughout the vessel.
6. Measure the final water temperature. (Example: The final temperature T2 = 21°C)
7. Calculate the microwave power output P in watts from above formula.
NEVER TOUCH ANY PART IN THE CIRCUIT WITH YOUR HAND OR AN INSULATED TOOL
WHILE THE OVEN IS IN OPERATION.
The formula is as follows;
P x t / 4.187 = V x ∆T P (W) = 4.187 x V x ∆T / t
Our condition for water load is as follows:
Room temperature ........... around 20°C Power supply Voltage.............. Rated voltage
Water load..................................1000 g Initial temperature.............................. 10±2°C
Heating time.............................. 47 sec.
P = 90 x ∆T

R-870B
13
Initial temperature .................................................................................................. T1 = 11°C
Temperature after (47 + 2) = 49 sec ...................................................................... T2 = 21°C
Temperature difference Cold-Warm....................................................................... ∆T1 = 10C
Measured output power
The equation is “P = 90 x ∆T” ...................................................... P = 90 x 10°C = 900 Watts
JUDGMENT: The measured output power should be at least ±15 % of the rated output power.
CAUTION: 1°C CORRESPONDS TO 90 WATTS. REPEAT MEASUREMENT IF THE POWER IS
INSUFFICIENT.
TEST PROCEDURES
PROCEDURE
LETTER COMPONENT TEST
1000g
1000g
1000g
T1˚C T2˚C
Heat up for 49 sec
B HIGH VOLTAGE TRANSFORMER TEST
WARNING: High voltage and large currents are present at the secondary winding and
filamentwindingofthehighvoltagetransformer.Itisverydangeroustowork
near this part when the oven is on. NEVER make any voltage measurements
of the high-voltage circuits, including the magnetron filament.
C HIGH VOLTAGE RECTIFIER ASSEMBLY TEST
HIGH VOLTAGE RECTIFIER TEST
CARRY OUT 3D CHECKS.
Isolate the high voltage rectifier assembly from the HV circuit. The high voltage rectifier can be tested
usinganohmmetersettoitshighestrange.ConnecttheohmmeteracrosstheterminalB+Cofthehigh
voltagerectifierandnotethe reading obtained. Reversethemeterleadsandnote this second reading.
The normal resistance is infinite in one direction and more than 100 kΩin the other direction.
CARRY OUT 4R CHECKS.
NOTE: FOR MEASUREMENT OF THE RESISTANCE OF THE RECTIFIER, THE BATTERIES OF
THEMEASURINGINSTRUMENTMUSTHAVEAVOLTAGEATLEAST6VOLTS,BECAUSE
OTHERWISE AN INFINITE RESISTANCE MIGHT BE SHOWN IN BOTH DIRECTIONS.
CARRY OUT 3D CHECKS.
Disconnect the leads to the primary winding of the high voltage transformer. Disconnect the filament
and secondary winding connections from the rest of the HV circuitry. Using an ohmmeter, set on a low
range, it is possible to check the continuity of all three windings. The following readings should be
obtained:- a. Primary winding ................................ approximately 1.5 Ω
b. Secondary winding .......................... approximately 117 Ω
c. Filament winding......................................... less than 1 Ω
If the readings obtained are not stated as above, then the high voltage transformer is probably faulty
and should be replaced.
CARRY OUT 4R CHECKS.
BC
HIGH VOLTAGE RECTIFIER
D HIGH VOLTAGE CAPACITOR TEST
CARRY OUT 3D CHECKS.
A. Isolate the high voltage capacitor from the circuit.

14
R-870B
TEST PROCEDURES
PROCEDURE
LETTER COMPONENT TEST
ESWITCH TEST
CARRY OUT 3D CHECKS.
Isolate the switch to be tested and using an ohmmeter check between the terminals as described in
the following table.
Table: Terminal Connection of Switch
Plunger Operation COM to NO COM to NC
Released Open circuit Short circuit
Depressed Short circuit Open circuit
COM; Common terminal,
NO; Normally open terminal
NC; Normally close terminal
If incorrect readings are obtained, make the necessary switch adjustment or replace the switch.
CARRY OUT 4R CHECKS.
F THERMAL CUT-OUT TEST
CARRY OUT 3D CHECKS.
Disconnectthe leads fromtheterminals of thethermalcut-out.Then usinganohmmeter,make a continuity
test across the two terminals as described in the below.
Table: Thermal Cut-out Test
Temperature of "ON" Temperature of "OFF" Indication of ohmmeter
Parts Name condition (closed circuit). condition (open circuit). (Whenroomtemperature
(˚C) (˚C) is approx. 20˚C.)
Thermal cut-out 125˚C This is not resetable type. Above 125˚C Closed circuit
Thermal cut-out 170˚C Cuts back in at 155˚C. Above 170˚C Closed circuit
If incorrect readings are obtained, replace the thermal cut-out.
An open circuit thermal cut-out (MG) indicates that the magnetron has overheated, this may be due
to resistricted ventilation, cooling fan failure or a fault condition within the magnetron or HV. circuit.
An open circuit thermal cut-out (OVEN) indicates that the food in the oven cavity may catch fire, this
may be due to over heating produced by improper setting of the cooking timer or failure of the control
panel.
CARRY OUT 4R CHECKS.
GBLOWN FUSE M10A
CARRY OUT 3D CHECKS.
If the fuse M10A is blown when the door is opened, check the 1st. latch switch, 2nd. interlock relay,
monitor switch and monitor resistor.
If the fuse M10A is blown, there could be a short or ground in electrical parts or wire harness. Check
them and replace the defective parts or repair the wire harness.
CARRY OUT 4R CHECKS.
CAUTION: Only replace fuse M10A with the correct value replacement.
B. Continuity check must be carried out with measuring instrument which is set to the highest
resistance range.
C. Anormalcapacitorshowscontinuityforashorttime(kick)andthenaresistanceofabout10MΩafter
it has been charged.
D. A short-circuited capacitor shows continuity all the time.
E. An open capacitor constantly shows a resistance about 10 MΩbecause of its internal 10MΩ
resistance.
F. When the internal wire is opened in the high voltage capacitor shows an infinite resistance.
G. The resistance across all the terminals and the chassis must be infinite when the capacitor is
normal.
If incorrect reading are obtained, the high voltage capacitor must be replaced.
CARRY OUT 4R CHECKS.

R-870B
15
CARRY OUT 3D CHECKS.
Disconnect the leads from the motor. Using an ohmmeter, check the resistance between the two
terminals as described in the table below.
Table: Resistance of Motor
Motors Resistance
Fan motor Approximately 290 Ω
Turntable motor Approximately 14 kΩ
Convection motor Approximately 293 kΩ
If incorrect readings are obtained, replace the motor.
CARRY OUT 4R CHECKS.
TEST PROCEDURES
PROCEDURE
LETTER COMPONENT TEST
HBLOWN FUSE 15A
JMOTOR WINDING TEST
CARRY OUT 3D CHECKS.
Disconnect the leads from the terminals of noise filter.
Using an ohmmeter, check between the terminals as
described in the following table.
MEASURING POINTS INDICATION OF OHMMETER
Between N and L Approx. 680 kΩ
Between terminal N and WHITE Short circuit
Between terminal L and RED Short circuit
If incorrect readings are absorbed, replace the noise filter unit.
CARRY OUT 4R CHECKS.
INOISE FILTER TEST
F8A
WHT
RED
N
L
CARRY OUT 3D CHECKS.
Ifthefuse15Aisblown,therecouldbeashortorgroundinelectricalpartsorwireharness.Checkthem
and replace the defective parts or repair the wire harness.
CARRY OUT 4R CHECKS.
CAUTION: Only replace fuse 15A with the correct value replacement.
K TOP HEATERS AND BOTTOM HEATER TEST
CARRY OUT 3D CHECKS.
Before carrying out the following tests make sure the heater is cool completely.
1. Resistance of heater.
Disconnect the wire leads to the heater to be tested. Using ohmmeter with low resistance range.
Check the resistance across the terminals of the heater as described in the following table.
Table: Resistance of heater
Parts name Resistance
Top heaters Approximately 20 Ωx 2 = 40 Ω
Bottom heater Approximately 61 Ω
2. Insulation resistance.
Disconnect the wire leads to the heater to be tested. Check the insulation resistance between the
heaterterminalandcavityusinga500V-100MΩinsulationtester. Theinsulationresistanceshould
be more than 10 MΩin the cold start.
If the results of above test 1 and/or 2 are out of above specifications, the heater is probably faulty and
should be replaced.
CARRY OUT 4R CHECKS.

16
R-870B
TEST PROCEDURES
PROCEDURE
LETTER COMPONENT TEST
L THERMISTOR TEST
1. CARRY OUT 3D CHECKS.
2. Disconnect connector-D from the control unit. Measure the resistance of the thermistor with an
ohmmeter. Connect the ohmmeter leads to Pin No’s D1 and D3.
Room Temperature Resistance
68˚F(20˚C) - 86˚F(30˚C) Approx. 293kΩ- 184KΩ
3. If the meter does not indicate above resistance, replace the thermistor
4. CARRY OUT 4R CHECKS.
ThetouchcontrolpanelconsistsofcircuitsincludingsemiconductorssuchasLSI,ICs,etc.Therefore,
unlikeconventionalmicrowaveovens,propermaintenancecannotbeperformedwithonlyavoltmeter
and ohmmeter.
Inthisservice manual,thetouchcontrolpanelassemblyisdividedintotwo units,ControlUnitandKey
Unit, and also the Control unit is divided into two units, CPU unit and Power 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.
2. Control Panel
The following symptoms indicate a defective control unit. Before replacing the control unit.
perform the key unit test (Procedure O) 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.
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.
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.
O KEY UNIT TEST
N CONTROL PANEL ASSEMBLY TEST
M HIGH VOLTAGE FUSE TST
CARRY OUT 3D CHECKS.
If the high voltage fuse is blown, there could be a short in the high voltage rectifier or the magnetron.
Check them and replace the defective parts and the high voltage fuse.
CARRY OUT 4R CHECKS.
CAUTION: Only replace high voltage fuse with the correct value replacement.
If the display fails to clear when the STOP/CLEAR pad is depressed, first verify the flat ribbon cable
ismarkinggoodcontact,verifythatthe door sensing switch(stopswitch)operatesproperly;thatisthe
contactsareclosedwhenthedoorisclosedandopenwhenthedoorisopen.Ifthedoorsensingswitch

R-870B
17
TEST PROCEDURES
PROCEDURE
LETTER COMPONENT TEST
(stopswitch) isgood, disconnectthe flatribbon cablethat 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
betweenthepins that correspondtotheSTOP/CLEAR pad markingmomentarycontact. If thecontrol
unitrespondsbyclearingwithabeepthekeyunitisfaultyandmustbereplaced.Ifthecontrolunitdoes
notrespond, it is a faulty and must be replaced. Ifa specificpad 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.
ARRY OUT 3D CHECKS.
Remove the outer case and check voltage between Pin No. 1 of the 3 pin connector (A) and the
common terminal of the relay RY6 on the control unit with an A.C. voltmeter.
The meter should indicate 220 volts, if not check oven circuit.
Relay Test
Check voltage at the relay coil with a D.C. voltmeter during the microwave cooking operation, grill
operation, convection operation or mix operation.
DC. voltage indicated.......... Defective relay.
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. Convection motor
RY2 Approx. 24.0V D.C. High voltage transformer
RY3 Approx. 24.0V D.C. Grill heaters (Top)
RY4 Approx. 24.0V D.C. Bottom heater
RY5 Approx. 24.0V D.C. Fan motor
RY6 Approx. 24.0V D.C. Oven lamp / Turntable motor
CARRY OUT 4R CHECKS.
P RELAY TEST
Q PROCEDURES TO BE TAKEN WHEN THE FOIL PATTERN ON THE PRINTED WIRING BOARD
(PWB) IS OPEN
Toprotecttheelectroniccircuits,thismodelisprovidedwithafinefoilpatternaddedtotheinputcircuit
on 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.
CARRY OUT 4R CHECKS.
54321
09876
G 8 G 7 G 6 G 5 G 4 G 3 G 2 G 1
G12 G11 G10 G 9
PIZZA
HELP
BAKE
ROAST
EASY
DEFROST
(AUTO COOK)
GRILL
INSTANT
COOK/
START
CONVEC
POWER
LEVEL STEAM MENU CRISPY SNACK
REHEAT
DISH SLOW COOK GRILL
REHEAT MIX
STOP/
CLEAR
RICE
COOK

18
R-870B
STEPS OCCURRENCE CAUSE OR CORRECTION
1The rated AC voltage is not present at Check supply voltage and oven power cord.
Power terminal of CPU connector (CN-A).
2The 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.)
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 pri-
mary coil resistance).
If any abnormal condition is detected,
replace the defective parts.
CARRY OUT 4R CHECKS.
TEST PROCEDURES
PROCEDURE
LETTER COMPONENT TEST
Checking the initial sensor cooking condition
(1) The oven should be plugged in at least two minutes before sensor cooking.
(2) Room temperature should not exceed 35˚C.
(3) The unit should not be installed in any area where heat and steam are generated. The unit should
not be installed, for example, next to a conventional surface unit. Refer to the "INSTALLATION
Instructions" .
(4) Exhaust vents are provided on the back of the unit for proper cooling and air flow in the cavity. To
permitadequateventilation, besuretoinstallsoasnottoblockthese vents.Thereshouldbesome
space for air circulation.
(5) Be sure the exterior of the cooking container and the interior of the oven are dry. Wipe off any
moisture with a dry cloth or paper towel.
(6) The Sensor works with food at normal storage temperature. For example, chicken pieces would
be at refrigerator temperature and canned soup at room temperature.
(7) Avoid using aerosol sprays or cleaning solvents near the oven while using Sensor settings. The
sensor will detect the vapor given of by the spray and turn off before food is properly cooked.
(8) After the oven is started on sensor cooking condition, if the sensor has not detected the vapor of
the food, ERROR will appear and the oven will shut off.
Water load cooking test
Makesurethe ovenhasbeen plugged inatleast fiveminutesbefore checking sensorcook operation.
The cabinet should be installed and screws tightened.
(1) Fill approximately 200 milliliters (7.2 oz) of tap water in a 1000 milliliter measuring cup.
(2) Place the container on the center of tray in the oven cavity.
(3) Close the door.
(4)TouchSENSORREHEATDISHpad.AndthentouchtheSTARTpad.Now,theovenisinthesensor
cooking condition and "SENSOR" will appear in the display.
(5) The oven will operate for the first 16 seconds, without generating microwave energy.
When the AH sensor is defective (open or short), ERROR will appear in the display immediately.
If ERROR appears check sensor wire connections and/or AH sensor.
NOTE: ERROR will appear if the door is opened or STOP/CLEAR pad is touched during first stage of
sensor cooking.
(6) After approximately 16 seconds, microwave energy is produced, and the display should start to
count down the remaining cooking time and oven should turn off after water is boiling (bubbling).
If the oven does not turn off, replace the AH sensor or check the control unit, refer to explanation
below.
RAH SENSOR TEST
CN - A
AC
a
bd
cVRS1
1FAN
(J1)
5