Sharp R9h56 Service Manual

							R-9H56
SHARP CORPORATION
  SERVICE MANUAL
In interests of user-safety the oven should be restored to its original
condition and only parts identical to those specified should be used.
MODELR-9H56
S8409R9H56PJ/
COVECTION
MICROWAVE OVEN
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 ........................  7
SERVICING ....................................  10
TEST PROCEDURE ...............................  12
TOUCH CONTROL PANEL ................................. 21
COMPONENT REPLACEMENT AND ADJUSTMENT PROCEDURE ......................  27
MICROWAVE MEASUREMENT .....................................  32
WIRING DIAGRAM ..........................................  33
PICTORIAL DIAGRAM ..................................  35
CONTROL PANEL CIRCUIT ............................................. 36
PRINTED WIRING BOARD .............................................. 37
PARTS LIST ....................................................  38 
						

							R-9H56 
						

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1
SERVICE MANUAL
PRODUCT SPECIFICATIONS
SHARP CORPORATION
OSAKA, JAPAN
CAUTION
MICROWAVE RADIATION
DO NOT BECOME EXPOSED TO RADIATION FROM
THE MICROWAVE GENERATOR OR OTHER PARTS
CONDUCTING MICROWAVE ENERGY.
Service engineers should not be exposed to the microwave
energy which may radiate from the magnetron or other
microwave generating devices if it is improperly used or
connected. All input and output microwave connections,
waveguides, flanges and gaskets must be secured. Never
operate the device without 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.
All the parts marked * on parts list are used at voltages more
than 250V.
Removal of the outer wrap gives access to potentials above
250V.
All the parts marked D on parts list may cause undue
microwave exposure, by themselves, or when they are dam-
aged, loosened or removed.
CONVECTION
MICROWAVE OVEN
R-9H56
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.
TEST PROCEDURE SERVICING AND
TROUBLESHOOTING CHART FUNCTION OF IMPORTANT
COMPONENTS OPERATING SEQUENCE APPEARANCE VIEW
MICROWAVE MEASUREMENT
WIRING DIAGRAM
PARTS LISTTOUCH CONTROL PANEL
ASSEMBLY
COMPONENT REPLACEMENT
 AND ADJUSTMENT PROCEDURE 
						

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PRODUCT SPECIFICATIONS
ITEM DESCRIPTION
Power Requirements 240 Volts
50 Hertz
Single phase, 3 wire earthed
Power Consumption 1500 W (Microwave)
1600 W (Convection)
Power Output 750 watts nominal of RF microwave energy (AS 2895 1986)
850 watts (IEC-705-1988 )
Operating frequency of 2450MHz
Convection heater 1500 W
Case Dimensions Width 627mm
Height 378mm
Depth  483mm
Cooking Cavity Dimensions Width 410mm
Height 245mm
Depth  410mm
Control Complement Touch Control System
Clock ( 1:00 - 12:59)
Timer (0 - 99 min. 99 sec.)
Microwave Power for Variable Cooking
  Repetition Rate;
HIGH ................... Full power throughout the cooking time
MED HIGH .............. approx.  70% of Full Power
MED .................. approx. 50% of Full Power
MED LOW (DEFROST) ........... approx. 30% of Full Power
LOW ..................... approx. 10% of Full Power
Convection Temperature for Variable Cooking
CONVECTION ............... 40 to 250ûC Temp. control
LOW MIX(BAKE) ......... 180ûC with 10% of microwave power
HIGH MIX(ROAST) ............. 200ûC with 30% of microwave power
GRILL .............................. 250ûC (Preheat)
SENSOR INSTANT ACTION pads
MULTI COOK pad
REHEAT SENSOR pad
CONVECTION COOKING FUNCTION pads
EASY DEFROST pad
NUMBER and TEMPERATURE pads
POWER LEVEL pad
MORE. LESS pads
STOP/CLEAR pad
AUTO START/CLOCK pad
INSTANT COOK/START pad
Set Weight Approx. 29 kg 
						

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APPEARANCE VIEW
111
1415
111
123
459
10
213
467 8
1. Ventilation opening
2. Oven lamp
3. Door hinges
4. Door safety latches
5. See through door
6. Door open button
7. Touch control panel
8. Digital readout
9. Wave guide cover
10. Coupling
11. Access cover for oven lamp replacement
12. Menu label
13. Rating label
14. low rack
15. High rack
TOUCH CONTROL PANEL
SMART
& EASY
REHEART
SENSOR
LOW MIXHIGH MIX GRILL
CONVEC
LESS MORE
123 45
678 90
STOP
CLEARAUTO
START
CLOCKINSTANT COOK
START
40˚C 70˚C 130˚C 150˚C 160˚C
180˚C 200˚C 220˚C 230˚C 250˚ C
MULTI
COOK
Fresh
VegetablesReheat
PieJacket
Potato
Frozen
VegetablesCasseroles
Desserts
POWER
LEVELEASY
DEFROST 
CONV
GRILL
MIXREHEAT
TEMPCOOK
LOW M.LOW MED M.HIGH HIGHConvection
Fan Symbol
Micro/Defrost
Symbol
Indicator
DEFROST AUTO
Pcs kg
MULTI COOK PAD
Press to select Multi Cook mode.
REHEAT SENSOR PAD
Press to select 3 popular Reheat
menus.
SENSOR INSTANT ACTION PADS
Press once to cook or reheat 6 
popular menus.
CONVECTION COOKING
FUNCTION PADS
Press to cook for each function. 
MORE(     ), LESS(    ) PADS
Press to increase/decrease the time
in one minute increments during
cooking or to alter the doneness for
the Sensor Instant Action, Reheat 
Sensor, Multi Cook or Easy Defrost
mode.
INSTANT COOK/START PAD
Press once to cook for 1 minute at 
HIGH or increase by 1 minute 
multiples each time this pad is 
pressed Microwave, Convection,
Grill or Mix cooking. AUTO START/CLOCK PAD
Press to set clock or Auto Start time.
STOP/CLEAR PAD
Press to clear during programming.
Press once to stop operation of
oven during cooking; press twice
to cancel cooking programe.  NUMBER AND TEMPERATURE
PADS
Press to enter cookling times, clock
time, convection temperature or to
select the Multi Cook menus. EASY DEFROST PAD
Press to defrost meat by entering
weight only. POWER LEVEL PAD
Press to select microwave power
setting. If not pressed, HIGH is
automatically selected.
SENSOR 
						

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OPERATION SEQUENCE
The following is a description of component functions during
oven operation.
Relay and Components Connection
RELAY CONNECTED COMPONENT
RY1 Oven lamp/ Turntable motor
RY2 Power transformer
RY3 Convection heater
RY4 Damper motor
RY5 Convection motor
RY6 Fan motor
OFF CONDITION
Closing the door activates all door interlock switches: upper
latch switch, lower latch switch and stop switch. (In this
condition, the monitor switch contacts are closed.)
When oven is plugged in a wall outlet (240V 50Hz), 240volts
A.C. is supplied to the control unit. (Figure O-1):
1. The display flashes Ò88:88Ó.
To set any programmes or set the clock, you must first
touch the STOP/CLEAR pad.
Ò   :   Ò appears in the display and the time counts up every
minute.
NOTE: When the oven door is opened, the oven lamp
comes on at this time.
2. A signal is input to the control unit, energizing the coil of
shut-off relay (RY4).
RY4 contacts close, completing a circuit to the damper
motor. The damper motor mow operates moving the
damper to the open position, thereby closing the contacts
of damper switch inputs a signal to the control unit.
The coil of relay RY4 is de-energized, opening its contacts,
thereby turning off the damper motor.
MICROWAVE COOKING CONDITION
HIGH COOKING
Program desired cooking time and Variable Cooking Con-
trol with the touching NUMBER pads and the POWER
LEVEL pad. When the START pad is touched, the following
operations occur:
1. The contacts of relays are closed and components
connected to relays are turned on (RY1, RY2, RY6).
(Figure O-2)
2. 240 volts A.C. is supplied to the primary winding of the
power transformer. The voltage is converted to about
3.35 volts A.C. output on the filament winding and high
voltage of approximately 2120 volts A.C. on the high
voltage winding.
3. The filament winding voltage (3.35 volts) heats the
magnetron filament and the high voltage (2120 volts) is
sent to the voltage doubling circuit.
4 The 2450 MHz microwave energy produced in the
magnetron generates a wave length of 12.24 cm. This
energy is channelled through the waveguide (transport
channel) into the oven cavity, where the food is placed tobe cooked.
5. Upon completion of the cooking time, the power
transformer, oven lamp, etc. are turned off and the
generation of microwave energy is stopped. The oven
will revert to the OFF condition..
6 When the door is opened during a cook cycle, the
monitor switch, upper latch switch, lower latch switch
and stop switch are activated with the following results.
The circuits to the turntable motor, cooling fan motor and
high voltage components are de-energized, the oven
lamp remains on and the digital read-out displays the
time still remaining in the cook cycle when the door was
opened.
7. The monitor switch is electrically monitoring the operation
of the upper latch switch and lower latch switch and is
mechanically associated with the door so that it will
function in the following sequence.
1) When the door opens from a closed potion, the upper
latch switch and the lower latch switch open their contacts,
and then the monitor switch contacts close.
2) When the door is closed, from the open position, the
monitor switch contacts first open, and then the contacts
of the upper latch switch and lower latch switch must be
closed.
If the common and normal open contacts of upper latch
switch and the lower latch switch fail with their contacts
closed when the door is opened, the closing of the monitor
switch contacts will form a short circuit through the fuse,
upper latch switch and the lower latch switch, causing the
monitor fuse to blow.
MEDIUM HIGH, MEDIUM, MEDIUM LOW, LOW
COOKING
When variable cooking power is programmed, the 240 volts
A.C. is supplied to the power transformer intermittently
through the contacts of the relay (RY2) which is operated by
the control unit within a 32-second time base. Microwave
power operation is  follows:
VARI MODE ON TIME OFF TIME
HIGH (100% power) 32 sec. 0 sec.
MED HIGH (approx. 70% power) 24 sec. 8 sec.
MED (approx. 50% power) 18 sec. 14sec.
MED LOW (approx. 30% power) 12 sec. 20 sec.
LOW (approx. 10% power) 6 sec. 26 sec.
NOTE: The ON/OFF time ratio does not exactly correspond
to the percentage of microwave power, because
approx. 2 seconds are needed for heating up the
magnetron filament.
CONVECTION COOKING CONDITION
PREHEATING CONDITION
Program desired convection temperature by touching the
CONVECTION pad and the temp. pad. When the START
pad is touched, the following operations occur:
1. The coil of shut-off relays RY1+RY5+RY6 are energized,
the oven lamp, cooling fan motor, turntable motor and
convection motor are turned on. 
						

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2. The coil of relay (RY4) is energized by the CPU unit. The
damper is moved to the closed position, opening the
damper switch contacts. The opening of the damper
switch contacts sends a signal to the LSI on the CPU unit
de-energizing the relay (RY4) and opening the circuit to
the damper motor.
3. The coil of heater relay (RY3) is energized by the CPU
unit and the main supply voltage is added to the convection
heater.
4. When the oven temperature reaches the selected preheat
temperature, the following operations occur:
4-1. The heater relay (RY3) is de-energized by the CPU
unit temperature circuit and thermistor, opening the
circuit to the convection heater.
4-2. The oven will continue to function for 15 minutes,
turning the convection heater on and off, as needed to
maintain the selected preheat temperature. The oven
will shut-down completely after 15 minutes.
CONVECTION COOKING CONDITION
When the preheat temperature is reached, a beep signal will
sound indicating that the holding temperature has been
reached in the oven cavity. Open the door and place the
food to be cooked in the oven. Program desired cooking
time and convection temperature by touching the number
pad, CONVECTION pad and Temperature pad. When the
START pad is touched, the following operations occur:
1. The numbers of the digital read-out start the count down
to zero.
2. The oven lamp, turntable motor, cooling fan motor and
convection motor are energized.
3. Heater relay (RY3) is energized (if the cavity temperature
is lower than the selected temperature) and the main
supply voltage is applied to the convection heater to
return to the selected cooking temperature.
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-energized. At the
end of the convection cycle, if the cavity air temperature
is above 116ûC, the circuit to (RY6) will be maintained (by
the thermistor circuit) to continue operation of the cooling
fan motor until the temperature drops below 116ûC, at
which time the relay will be de-energized, turning off the
fan motor. Relay (RY5) will however, open as soon as
the convection cycle has ended, turning off the convection
fan motor. This will now cool and allow the damper door
to open.
5. At the end of the convection cook cycle, shut-off relay
(RY4) is energized turning on the damper motor. The
damper is returned to the open position, closing the
damper switch contacts which send a signal to the
control unit, de-energizing shut-off relay (RY4).
AUTOMATIC MIX COOKING CONDITION
Program desired cooking time and temperature by touching
the number pads and the LOW MI or HIGH MIX pad. When
the START pad is touched, the following operations occur:
1. The numbers of the digital read-out start the count down
to zero.2. The shut-off relay (RY1+RY5+RY6) energized, turning
on the oven lamp, turntable motor, cooling fan motor and
convection motor.
3. The shut-off relay (RY4) is energized.
The damper door is closed from the open position.
4. The heater relay (RY3) is energized, adding the mains
supply voltage to the convection heater.
5. Now, the oven is in the convection cooking condition.
6. When the oven temperature reaches the selected
temperature, the following operations occur:
6-1. The power supply voltage is added to the convection
heater and power transformer alternately.
6-2. The convection heater operates through the heater
relay (RY3) contacts and the power transformer operates
through the cook relay (RY2) contacts.
6-3. These are operated by the CPU unit to supply alternately
within a 32 second time base, convection heat and
microwave energy.
The relationship between the convection and microwave
power operations are as follows.
Note: The ON and OFF time ratio does not correspond
with the percentage of microwave power, because
approx. 2 seconds are needed for heating of the
magnetron filament.
12 SEC. 20 SEC.
32 SEC.
LOW MIX
BAKE
HIGH MIX
ROAST
MICROWAVE POWER
= APPROX. 30%
CONVECTION 
TEMPERATUE
= 300˚F MICROWAVE POWER
= APPROX. 10%
CONVECTION 
TEMPERATUE
= 350˚F (180˚C) 26 SEC. 6 SEC.
ON
ON
OFFOFF
OFF
ON (MICRO.)
(CONVEC.)(MICRO.)
(CONVEC.)
Note: During alternate Microwave/Convection operation,
the convection heater is energized only if the cavity
temperature drops below the set temperature.
ABSOLUTE HUMIDITY SENSOR (AH SENSOR)
COOKING CONDITION
In case where the AH sensor is used (REHEAT SENSOR or
SENSOR INSTANT ACTION), the foods are cooked in
microwave 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 developed. The
sensor ÒsensesÓ the vapour and its resistance increases
gradually. When the resistance reaches the value set ac-
cording to the menu, supplementary cooking is started.
The time of supplementary cooking is determined by experi- 
						

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AH SENSOR COOKING SEQUENCE
1. In case the AH sensor cooking condition is started, the
coil of shut-off relays (RY1+RY6) are energized, the
oven lamp and cooling fan motor are turned on, but the
power transformer is not turned on.
NOTE: The oven should not be operated on AH SENSOR
COOKING immediately after plugging in the unit.
Wait five minutes before cooking on AH SENSOR
COOKING CONDITION.
2. After about 16 seconds, the cook relay (RY2) is energized.
The power transformer is turned 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. The oven will go to the Mix Cooking Condition at the 2nd.
or 3rd. stage when Reheat pie, Casseroles or Desserts
has been chosen. (Figure O-4)
4. When the sensor detects the vapour emitted from the
food, the display switches over to the remaining cooking
time and the timer counts down to zero. At this time, the
door may be opened to stir food, turn it or season, etc.
NOTE: In case where a small quantity of food is cooked, the
oven will stop without displaying the remaining
cooking time.
5. When the timer reaches zero, an audible signal sounds.
The shut-off relay (RY1+RY6) and cook relay (RY2) are
de-energized and the power transformer, oven lamp,
etc. are turned off.
6. Opening the door or touching the STOP/CLEAR pad, the
time of day will reappear on the display and the oven will
revert to an OFF condition.
MULTI COOK
MULTI COOK will automatically compute the oven tem-
perature, microwave power and cooking time for baking and
roasting. Set the desired program by touching the MULTI
COOK pad, and number pad. Enter the weight by touching
the Number pads. When the START pad is touched, the
following operations occur:
1. The COOK indicator will light and the Microwave Symboland/or the Convection Fan Symbol will rotate.
2. The cooking time will appear on the display and start
counting down to zero. The cooking time is adjusted
automatically according to the weight of the food.
3. The shut-off relays (RY1, RY3, RY5 and RY6) are
energized, turning on the oven lamp, turntable motor,
cooling fan motor and convection motor. The power
supply voltage is added to the convection heater.
4. Now, the oven is in the convection cooking mode.
5. When the oven temperature has reached the programmed
convection temperature, the oven goes into the
programmed cooking mode.
6. At the end of the MULTI COOK cycle, the damper is
returned to the open position and the oven will go to the
off condition. The cooling fan will remain on until the oven
has cooled.
EASY DEFROST COOKING
The EASY DEFROST key is a special function key to defrost
meats and poultry faster and better.
EASY DEFROST key has 4 defrost stages.
EASY DEFROST automatically defrosts roast beef, etc.
When EASY DEFROST is selected and the food weight is
entered by using the number pads, the oven will cook
according to the special cooking sequence. (Figure O-2)
FIRE SENSING FEATURE (MICROWAVE MODE)
This model incorporates a sensing feature which will stop
the ovens 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 (ther-
mistor) during its 32-seconds time base comparing the
obtained voltage measurements. If the most recent  voltage
measured is 300mV grater than the previous voltage meas-
ured, the LSI judges it as a fire in the oven cavity and
switches off the relays to the power transformer, fan motor
and convection motor. The LSI also stops counting down
and closes the damper door so that no fresh air will enter the
oven cavity. Please refer to the following section for a more
detailed description.
Operation
Please refer to the timing diagrams below.
1. The thermistor operates within a 32-seconds time base
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
measurement circuit is sampled by the LSI and twenty
one (21) seconds after the thermistor is cut off the LSI
turns 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 300mV 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 motor and convection
motor. The LSI also stops counting down and closes the
damper door so that no fresh air will enter the oven
cavity. ment 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 rapidly. You
can smell the aroma as it cooks.
;
3. Sensor detects moisture and
humidity and calculates
cooking time and variable
power.
MICROWAVE
MICROWAVEAH SENSOR 
						

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7
3. Once the fire sensor feature has shut the unit down, the
programmed cooking cycle may be resumed by  pressing
the START pad or the unit may be reset by pressing the
CLEAR pad.
IMPORTANT:
During sensor cooking operation, the fire sensing op-
eration sequence will not begin until the AH sensor has
detected vapours and initiated a sensor cooking cycle.
This is because the operation of the convection fan
would interfere with the AH sensors vapour detection.
CONVECTION
MOTOR
THERMISTOR
Sensing 
VoltageON
OFF
ON
OFF
ON
OFF
0 2 24 30 64 (sec.)
3 sec.
Sensing the voltage across the temperature measurement circuit.
6 sec. 332 (sec.)
UPPER AND LOWER LATCH SWITCHES
Those latch switches are mounted in the latch hooks as
shown in figure. They are activated by the latch heads on the
door.
When the door is opened, the switches interrupt the circuit
to all components except CPU unit and relay unit and oven
lamp. A cook cycle cannot take place until the door is firmly
closed thereby activating both interlock switches.
LATCH HOOK
STOP SWITCH
MONITOR SWITCH
SWITCH LEVER
OPEN LEVER LATCH
HEADS
DOOR OPEN 
BUTTON
UPPER LATCH SWITCH
LOWER LATCH SWITCH
Figure D-1. Switches
MONITOR SWITCH
The monitor switch is mounted on the latch hook. It is
activated (the contacts opened) by the lower latch head
when the door is closed. The switch is intended to render the
oven inoperative by means of blowning the fuse when the
contacts of the common and normal open contacts of upper
latch switch and lower latch switch
fail to open when the door is opened.
Functions:
1. When the door is opened, the monitor switch contacts
close (to the ON condition) due to their being normally
closed. At this time the common and normal open
contacts of upper latch switch and lower latch switch are
in the OFF condition (contacts open) due to their being
normally open contacts switch.
2. As the door goes to a closed position, the monitor switch
contacts are first opened and then the common and
normal open contacts of upper latch switch close. (Onopening the door, each of these switches operate
inversely.)
3 If the door is opened during cooking, and the common
and normal open contacts of upper latch switch and
lower latch switch fail to open, the fuse blows
simultaneously with closing of the monitor switch contacts.
CAUTION: BEFORE REPLACING A BLOWN FUSE TEST
THE UPPER LATCH SWITCH, LOWER LATCH
SWITCH AND MONITOR SWITCH FOR
PROPER OPERATION. (REFER TO CHAP-
TER ÒTEST PROCEDUREÓ).
STOP SWITCH
The stop switch is activated by the latch head.
When the door is opened while the oven is in cook cycle, the
stop switch contacts open to de-energize the relay (RY-
1,RY-2,RY-3,RY-5,RY-6). Then the cook cycle is stopped.
THERMAL CUT-OUT 150ûC (OVEN)
The oven thermal cut-out located on the left side of the
thermal protection plate is designed to prevent damage to
the convection heater unit if an overheated condition devel-
ops in the tube due to cooling fan failure, obstructed air
ducts, dirty or blocked air intake, etc. Under normal opera-
tion, the oven thermal cut-out remains closed. However,
when abnormally high temperatures are reached within the
heater unit, the oven thermal cut-out will open, causing the
oven to shut down. When the oven has cooled temperature,
the oven thermal cut-out closes.
THERMAL CUT-OUT 95ûC  (FAN MOTOR)
The thermal cut-out protect the fan motor against overheat-
ing. If its temperature goes up higher than 95ûC because the
fan motor is locked or the ventilation operating are blocked,
the contacts of the thermal cut-out will open and switch off
the oven. When the thermal cut-out cools itself down to
75ûC, the contacts of the thermal cut-out will close again.
TEMPERATURE FUSE 150ûC  (MG)
This fuse protects the magnetron against overheating. If the
temperature goes up higher than 150ûC because the fan
motor is interrupted, the air inlet duct is blocked or the
ventilation openings are obstructed, the fuse blows and cuts
off the power supplying to the power transformer. The
defective fuse must be replaced with new rated one.
FUNCTION OF IMPORTANT COMPONENTS 
						

							R-9H56
8
FUSE M8A 250V
1. If the wire harness or electrical components are short-
circuited, this fuse blows to prevent an electric shock or
fire hazard.
2. The fuse also blows when upper latch switch and lower
latch switch remain closed with the oven door open and
when the monitor switch closes.
3. The fuse M8A also blows when asymmetric rectifier,
H.V. rectifier, H.V. wire harness, H.V. capacitor,
magnetron or secondary winding of power transformer is
shorted.
ASYMMETRIC RECTIFIER
The asymmetric rectifier is a solid state device that prevents
current flow ins both directions. And it prevents the tempera-
ture rise of the power transformer by blowing the fuse M8A
when the high voltage rectifier is shorted.
FAN MOTOR
The fan motor drives a blade which draws external cool air.
This cool air is directed through the air vanes surrounding
the magnetron and cools the magnetron. This air is chan-
nelled through the oven cavity to remove steam and va-
pours given off from the heating foods. It is then exhausted
through the exhausting air vents at the oven cavity.
CONVECTION HEATER
The convection heater is located at the rear of the oven
cavity. It is intended to heat air driven by the convection fan.
The heated air is kept in the oven and force-circulated and
reheated by the convection heater.
CONVECTION COOKING SYSTEM
This oven is designed with a hot air heating system where
food is not directly heated by the convection heater, but is
heated by forced circulation of the hot air produced by the
convection heater. The air heated by the convection heater
is circulated through the convection passage provided on
the outer casing of the oven cavity by means of the convec-
tion fan which is driven by the convection motor. It then
enters the inside of the oven through the vent holes provided
on the left side of the oven. Next, the hot air heats the food
on the turntable and leaves the oven cavity through the vent
in the oven cavity left side wall. Without leaving the oven,
this hot air is reheated by the convection heater, passes
through the convection 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 convection heater is
de-energized. When the temperature inside the oven cavity
drops below the selected temperature, the convection heater
is energized again. In this way, the inside of the oven cavity
is maintained at approximately the selected temperature.
When the convection time reaches 0, the convection heater
is de-energized and the convection fan stops operating and
the oven shuts off. Upon completion of the cooking time, the
audible signal will sound, and oven lamp, turntable motor,
cooling fan motor and convection motor are de-energized.
At the end of the convection cycle, if the cavity air tempera-
ture is above 116ûC, the circuit to RY6 will be maintained (by
the thermistor circuit) to continue operation of the cooling
fan motor until the temperature drops below 116ûC, at which
time the relay will be de-energized, turning off the fan motor.
Relay RY5 will however, open as soon as the convection
cycle has ended, turning off the convection fan motor. This
will now cool and allow the damper door to open.
DAMPER OPEN-CLOSE MECHANISM
Usually, the damper is in the open position except during
convection cooking.
Damper position is set automatically by damper motor,
damper switch, motor cam and damper shaft.
These components are operated by a signal that judges if
microwave cooking or convection cooking operation is
selected by the CPU unit. The rated peak reverse voltage of D1 of the asymmetric
rectifier is 6 KV The rated peak reverse voltage of D2 of the
asymmetric rectifier is 1.7 KV. D1 and D2 of the asymmetric
rectifier or high voltage rectifier are shorted when the each
peak reverse voltage goes beyond the each rated peak
reverse voltage. (The process of blowing the fuse M8A.) .
1. The high voltage rectifier is shorted by any causes when
microwave cooking.
2. The peak reverse voltage of D2 of the rectifier goes
beyond the rated peak reverse voltage 1.7 KV in the
voltagedoubler circuit.
3. D2 of the rectifier is shorted.
4. The large electric currents flow through the high voltage
winding of the power transformer.
5. The large electric currents beyond 8A flow through the
primary winding of the power transformer.
6. The fuse M8A blows by the large electric currents.
7. The power supply to the power transformer is cut off.
THERMISTOR
The thermistor is a negative temperature coefficient type.
The temperature in the oven cavity is detected through the
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 M8A 250V bursting
when the fuse M8A 250V blows due to the operation of the
monitor switch.
TURNTABLE MOTOR
The turntable motor drives the turntable supporting plate to
rotate the turntable.
CONVECTION MOTOR
The convection motor drives the convection fan and pro-
vides the heated air.
D2 D1
ASYMMETRIC
RECTIFIER
HIGH VOLTAGE RECTIFIERAB
C