Sharp R-9H55 User manual

SHARI= SERVICE MANUAL
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CONVECTION
MICROWAVE OVEN
-------------_. MODEL R-9H55
In interests of user-safety the oven should be restored to its original condi-
TABLE OF CONTENTS page
GENERAL IMPORTANT INFORMATION ...................................................................................................... 1
WARNING ...................................................................................................................................................... 1
RODUCT SPECIFICATIONS ......................................................................................................................... 2
APPEARANCE VIEW .................................................................................................................................... 3
OPERATING SEQUENCE ............................................................................................................................. 4
FUNCTION OF IMPORTANT COMPONENTS’ ............................................................................................. 8
TRABLESHOOTING CHART ....................................................................................................................... 11
TEST PROCEDURE .................................................................................................................................... 14
TOUCH CONTROL PANEL ......................................................................................................................... 24
COMPONENT REPLACEMENT AND ADJUSTMENT PROCEDURE ....................................................... .31
MICROWAVE MEASUREMENT .................................................................................................................. 38
WIRING DIAGRAM ...................................................................................................................................... 39
PICTORIAL DIAGRAM ................................................................................................................................ 41
CONTROL PANEL CIRCUIT ....................................................................................................................... 42
PRINTED WIRING BOAD ............................................................................................................................ 43
PARTS LIST ................................................................................................................................................ 44
SHARP CORPORATION

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SERVICE MANUAL
SHARP
MICROWAVE OVEN
R-9H55
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 en-
tire text of this manual, so that they will be qualified to render sat-
isfactory customer service.
CAUTION
MICROWAVE RADIATION
Service engineers should not be exposed to the microwave en-
ergy which may radiate from the magnetron or other microwave
generating devices if it is improperly used or connected. All in-
put and output microwave connections, waveguides, flanges
andgaskets must be secured. Never operate the device without
a microwave energy absorbing load attached. Never look into
an open waveguide.
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 25OV.
Removal of the outer wrap gives access to potentials above
25ov.
SHARP CORPORATION
OSAKA, JAPAN

PRODUCT SPECIFICATIONS
ITEM
Power Requirements 240 Volts
50 Hertz
DESCRIPTION
Power Consumption
Power Output
Convection heater
Case Dimensions
Single phase, 3 wire earthed
1500 W (Microwave)
1600 W (Convection)
750 watts nominal of RF microwave energy (AS 2895 1986)
850 watts (IEC-705-I 988 )
Operating frequency of 2450MHz
1500 w
Width 627mm
Height 378mm
Depth 481 mm
Cooking Cavity Dimensions
Control Complement
Width 41Omm
Height 245mm
Depth 41Omm
Touch Control System
Clock ( 1:OO- 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 250°C Temp. control
LOW MIX(BAKE) ................................180°C with 10% of microwave power
HIGH MIX(ROAST) ............................200°C with
GRILL 30% of microwave power ..................................................................................250°C (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 -s
INSTANT COOK/START pad
Set Weight Approx. 30 kg
2

APPEARANCE VIEW
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 re-
placement
12. Menu label
13. Rating label
14. low rack
15. High rack
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DISPLAY
Convection
Fan Symbol’
Micro/Defrost _
Symbol
Indicator
TOUCH CONTROL PANEL
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OPERATION SEQUENCE
The following is a description of component functions dur-
ing oven operation.
Relay and Components Connection
SRELAY CONNECTED COMPONENT
RYl 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: up-
per 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-l):
1. The display flashes “88:88”.
To set any programmes or set the clock, you must first
touch the STOP/CLEAR pad.
II . II
. 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 con-
tacts of damper switch inputs a signal to the control
unit.
The coil of relay RY4 is de-energized, opening its con-
tacts, 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 HIGH pad of
the Variable Cooking Control. When the START pad is
touched, the following operations occur:
1. The contacts of relays are closed and components con-
nected to relays are turned on (RYI, RY2, RY6). (Fig-
ure 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 AC. 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 channeled through the waveguide (transport
channel) into the oven cavity, where the food is placed
to be cooked.
4
5. Upon completion of the cooking time, the power trans-
former, oven lamp, etc. are turned off and the genera-
tion of microwave energy is stopped. The oven will re-
vert 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 activared with the following results.
The circuits to the turntable motor, cooling fan motor
and high voltage components are deenergized, the
oven lamp remains on and the digital readout displays
the time still remaoning in the cook cycle when the door
was opened.
7. The monitor switch is electrically monitoring the opera-
tion of the upper latch switch and is mechanically asso-
ciated with the door so that it will function in the follow-
ing sequence.
1) When the door opens from a closed potion, the
upper latch switch and lower latch switch open their
contacs, 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 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 and upper latch
switch,causing the monitor fuse to blow.
MEDIUM HIGH, MEDIUM, MEDIUM LOW, LOW
COOKING
When variable cooking power is programmed, the 240
volts AC. is supplied to the power transformer intermit-
tently through the contacs of the relay (RY2) which is oper-
ated by the control unit within a 32-second time base.
Microwave power operation is follows:
VARI MODE ON TIME OFF TIME
HIGH (100% power)
MED HIGH (approx. 70% power)
MED (approx. 50% power)
MED LOW (approx. 30% power)
32 sec.
24 sec.
18 sec.
12 sec.
0 sec.
8 sec.
4sec.
20 sec.
LOW (approx. 10% power) 6 sec.26 sec.
NOTE:The ON/OFF time ratio does not exactly corre-
spond to the percentage of microwave power, be-
cause 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 RYI +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 con-
vection heater.
4. When the oven temperature reaches the selected pre-
heat 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 cook-
ing time and convection temperature by touching the num-
ber pad, CONVECTION pad and Temperature pad. When
the START pad is touched, the following operations occur:
1.
2.
3.
4.
5.
The numbers of the digital readout start the count down
to zero.
The oven lamp, turntable motor, cooling fan motor and
convection motor are energized.
Heater relay (RY3) is energized (if the cavity tempera-
ture is lower than the selected temperature) and the
main supply voltage is applied to the convection heater
to return to the selected cooking temperature.
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 112”C, the circuit to (RY6) will be maintained
(by the thermistor circuit) to continue operation of the
cooling fan motor until the temperature drops below
112”C, 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, turn-
ing off the convection fan motor. This will now cool and
allow the damper door to open.
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 touch-
ing the number pads and the LOW Ml or HIGH MIX pad.
When the START pad is touched, the following operations
occur:
1. The numbers of the digital readout start the count down
to zero.
2. The shut-off relay (RYl+RYS+RYG) 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 tem-
perature, the following operations occur:
6-l. The power supply voltages 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 oper-
ates through the cook relay (RY2) contacts.
6-3. These are operated by the CPU unit to supply alter-
nately 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.
16SEC: 26 SEC
MICROWAVE POWER
I APPROX 10%
(CONVEC ) CONVECTION
TEMPERATLIE
-1BOC
LOW MIX
BAKE
, 1PSEC a 20 SEC
MICROWAVE POWER
.APPROX 30%
(CONVEC )
iON
CONVECTION
TEMPERATUE
-200C
HIGH MIX
Note: During alternate Microwmonvection 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 microproces-
sor which will calculate the remaining cooking time and
power level needed for best results.
When the food is cooked, water vapor is developed. The
sensor “senses” the vapor 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 ex-
periment with each food category and inputted into the LSI.
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An example of how sensor works:
1. Potatoes at room temperature. Vapor 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. In case the AH sensor cooking condition is started, the
coil of shut-off relays (RYl+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 ener-
gized. 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
vapor 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 vapor emitted from the
food, the display switches over to the remaining cook-
ing 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 (RYl+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 Sym-
bol and/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 (RYl , RY3, RY5 and RY6) are ener-
gized, turning on the oven lamp, turntable motor, cool-
ing 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 pro-
grammed 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 de-
frost 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 ac-
cording to the special cooking sequence. (Figure O-2)
SENSING FIRE OPERATION
The oven will stop its operation when there is a fire in the
oven cavity in microwave cooking condition.
LSI measures the voltage across the temperature meas-
urement circuit intermittently within a 32-second time base
after since the oven is started in microwave cooking condi-
tion. The oven will-stop its operation when the difference of
the voltages is more than 0.3 volts in microwave cooking
condition.
1. Within a 32-second base, first the thermistor is ener-
gized for 3 seconds. After 2 seconds since the thermis-
tor is energized, the voltage across the temperature
measurement circuit is measured. And after 21 sec-
onds since the thermistor is cut off, the convection
motor operates for IO seconds.
2. The oven carries out the procedure above again. If the
second voltage is 0.3V higher than the first voltage, LSI
judges it is a fire in the oven cavity and stops the oven.
3. When sensor cooking, the sensing fire operation is not
carried out until the oven senses the steam from food.

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Because food cannot be cooked well by rotating the
convection fan at that time. After sensing the steam, the
sensing fire operation is started.
4. When LSI judges it is fire in the oven cavity, LSI will
switch off the relays to the power transformer, fan mo-
tor and convection motor and LSI stops counting down.
And then the damper is closed so that the fresh air does
not come into the oven cavity.
02 20 3032
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Sensing the voltage across temperature measurement circuit.
7

R-9H55
FUNCTION OF IMPORTANT COMPONENTS
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
UPPER LATCH
SWITCH
STOP SWITCH
LATCH
HEADS MONITOR SWITCH
LOWER LATCH
SWITCH
SWITCH LEVER
OPEN LEVER
Figure D-l. Switches
MONITOR SWITCH
The monitor switch is mounted on the latch hook. It is acti-
vated (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 up-
per latch switch and lower latch switch
fail to open when the door is opened.
Functions:
1.
2.
3
When the door is opened, the monitor switch contacts
close (to the ON condition) due to their being normally
closed. At this time the 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.
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.
(On opening the door, each of these switches operate
inversely.)
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 simulta-
neously with closing of the monitor switch contacts.
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 150°C (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 de-
velops 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 tem-
perature, the oven thermal cut-out closes.
THERMAL CUT-OUT 90°C (FAN MOTOR)
The thermal cut-out protect the fan motor against over-
heating. If its temperature goes up higher than 90°C be-
cause 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. The defective thermal cut-out
must be replaced with new one.
TEMPERATURE FUSE 150°C (MG)
This fuse protects the magnetron against overheating. If
the temperature goes up higher than 150°C because the
fan motor is interrupted, the air inlet duct is blocked or the
ventilation operatings 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.
FUSE M8A 250V
1.
2.
3.
If the wire harness or electrical components are short-
circuited, this fuse blows to prevent an electric shock or
fire hazard.
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.
The fuse M8A-also blows when asymmetric rectifier,
H.V. rectifier, H.V. wire harness, H.V.capacitor, mag-
netron or secondary winding of power transformer is
shorted.
ASYMMETRIC RECTIFIER
The asymmetric rectifier is a solid state device that pre-
vents current flow ins both directions. And it prevents the
temperature rise of the power transformer by blowing the
fuse M8A when the high voltage rectifier is shorted.
CAUTION: BEFORE REPLACING A BLOWN FUSE
TEST THE UPPER LATCH SWITCH,
LOWER LATCH SWITCHAND MONITOR
SWITCH FOR PROPER OPERATION. (RE-
FER TO CHAPTER “TEST PROCEDURE”). / HiGH VOLTAGE RECTIFIER
8

The rated peak reverse voltage of Dl of the asymmetric
rectifier is 6 KV The rated peak reverse voltage of D2 of the
asymmetric rectifier is 1.7 KV. Dl and D2 of the asymmet-
ric 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 02 of the rectifier goes be-
yond the rated peak reverse voltage 1.7 KV in the volt-
agedoubler circuit.
3. D2 of the rectifier is shorted.
4. The large electric currents flow through the high volt-
agewinding 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 cur-
rent 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.
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-
neled through the oven cavity to remove steam and vapors
given off from the heating foods. It is then exhausted
through the exhausing 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 pro-
vided on the outer casing of the oven cavity by means of
the convection 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 pas-
sage 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-ener-
gized. 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 deenergzed and the convection fan stops operat-
ing and the oven shutts 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 temperature is
above 112X, the circuit to RY6 will be maintained (by the
thermistor circuit) to continue operation of the cooling fan
motor until the temperature drops below 112”C, at which
time the relay will be de-energized, turning off the fan mo-
tor. Relay RY5 will however, open as soon as the convec-
tion 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 se-
lected by the CPU unit.
Microwave Cooking:
Damper is in the open position, because a portion of cool-
ing air is channeled through the cavity to remove steam
and vapors given off from the heating foods.
It is then exhausted at the top of the oven cavity into a con-
densation compartment.
Convection Cooking:
Damper is in the closed position, so that no hot air will be
allowed to leak out the oven cavity.
Damper Operation
1. When power supply cord is plugged in:
1-l. When power supply cord is plugged in, a signal is
sensed in the control unit, and operates shut-off relay
(RY4).
1-2. Contacts of shut-off relay (RY4) close, the damper
motor is energized, opening the damper door.
l-3. When the damper is moved to the open position by
the damper cam, damper switch is closed (ON posi-
tion).
f
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9

l-4. The signal of damper switch is m-sensed in the con-
trol unit and shut-off relay (RY4) is turned off.
l-5. The 240 volts A.C. to the damper motor is stopped
and the motor turns off.
2. When oven is microwave cooking:
Damper is in the open position
3. When oven is convection cooking:
3-1
3-2.
3-3.
3-4.
Damper motor is energized by touching the convec-
tion, temperature and START pads.
When damper is in the closed position (damper
switch is OFF), its signal is sensed by the control unit,
and shut-off relay (RY4) is de-energized.
The damper is held in the closed position during the
convection cooking operation
At the end of the convection cooking, shut-off relay
(RY4) is energized, and the damper is returned to the
open position.
NOTE:If the damper door is not in the proper position,
closed durining convection or open durning micro-
wave, the control unit will stop oven operation after
1 minute.
Cooking Mode Operation of Damper
Microwave cooking OPEN
Convection cooking CLOSE
Sensor cooking OPEN
Automatic mix cooking CLOSE
Grill cooking CLOSE
Slow cooking CLOSE
DAMPER SHAF
MPER DUCT
DAMPER CAM
MPER SWITCH
DAMPER MOTOR
Figure D-2. Damper Mechanism
10

TROUBLESHOOTING CHART
WARNING TO SERVICE PERSONNEL
Microwave ovens contain circuitry capable of producing very high voltage and current, contact with any part of the
high voltage circuit will result in electrocution.
REMEMBER TO CHECK 3D REMEMBER TO CHECKa
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 connection of the high-voltage capaci-
tor (that is, of the connecting lead of the high-volt-
age rectifier) against the chassis with the use of
an insulated screwdriver.
1) Reconnect all leads removed from components during
testing.
2) Replace the outer case (cabinet).
3) Reconnect the supply.
4) Run the oven. Check all functions.
Microwave ovens should not be run empty. To test for the
presence of microwave energy within a cavity, place a
cup of cold water on the oven turntable, close the door
and set the microwave timer for two (2) minutes. Set the
power level to HIGH and push the START button. 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.
Sharp recommend that wherever possible fault-find-
ing is carried out with the supply disconnected. It
may in, some cases, be necessary to connect the
supply after the outer case has been removed, in
this event carry out 3D checks and then disconnect
the leads to the primary of the power 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 power transformer.
When all service work is completed, and the oven is fully assembled, the microwave power output should be
checked and microwave reakage test carried out
TROUBLESHOOTING GUIDE
When troubleshooting the microwave oven,it is helpful IMPORTANT:lf the oven becomes inoperative because of a
to follow the Sequence of Operation in performing the blown fuse M8A in the upper latch switch -
checks. Many of the possible causes of trouble will re- lower latch switch - monitor switch - monitor
quire that aspecific test be performed. These tests are resisitor circuit check the upper latch switch,
given a procedure letter which will be found in the “Test lower latch switch, monitor switch and moni-
Procedure”section. tor resistor before replacing the fuse M8A..
11

TEST PROCEDURE ABCDEEEFGGHIJJ J JKL
4
POSSIBLE CASE
DEFECTIVE PARTS
:ONDITION PROBLEM b
Home fuse blows when power cord is plugged into
wall outlet.
Fuse M8A blows when power cord is plugged into
wall outlet. 0
IFF 88:88 does not appear in display when power cord is
:ONDlTION .
first plugged into wall outlet.
Display does not operate properly when STOP/
CLEAR pad is touched. (The time of day should
appear on the display with beep sound during nor-
mal condition.) ---
Oven tamp does not light with door opened.
Oven lamp does not light at all
0
000
0 0
000 I -- -- 0
:OOKING Oven lamp light, but turntable motor does not 0 0 0
‘ONDITION operate.
Cooling fan motor does not operate. 0 0
The oven stops after1 minute 0 0
Oven does not go into a cook cycle, when START
pad is touched. 0 0
Low or no power is produced during microwave
IfCROWAVE) ;o,;Q;ga/I$e food is heated incompletely or not 0 0 () 0 0
Extremely uneven heating is produced in oven load
(food).
Function of variable cooking does not operate prop-
erly except HIGH power.
CONV indicator lights, but heating-element does not
heat.
Temperature in the oven cavity is lower or higher
than preset.
Convection cycle runs 1 minute then the oven shuts
3NVECTfON) down.
Convection cycle runs 3 minutes then the oven shuts
down.
Oven is in the sensor cooking condition but AH sen-
,HSENSOR)sor does not end 1St.stage or does not stop cooking
cycle or the oven stops soon.
d C
00 0
00 00 0
0 0 0
0
0
I
12

RE = REPLACE / CK = CHECK
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13

Y
TEST PROCEDURES
PROCEDURE
LETTER COMPONENT TEST
A MAGNETRON TEST
NEVER TOUCH ANY PART IN THE CIRCUIT WITH YOUR HAND OR AN INSULATED TOOL
WHILE THE OVEN IS IN OPERATION.
CARRY OUT 3D CHECKS
Isolate the magnetron from the high voltage circuit by removing all leads connected to the filament
terminal.
To test for an open circuit filament use an ohmmeter to make a continuity test between the magnetron
filament terminals, the meter should show a reading of less than 1 ohm.
To test for a short circuit filament to anode condition, connect ohmmeter between one of the filament
terminals 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 Liter water load)
The following test procedure should be carried out with the microwaveoven in a fully assembled condi-
tion (outer case fitted).Microwave output power from the magnetron can be measured by way oflEC
705, i.e. it can be measured by using water load how much it can be absorbed by the water load. 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 tI4.187calorie is generated. On the
other hand, if the temperature of the water with V(ml) rises AT (“C) during this microwave heating
period, the calorie of thewater is V x AT
The formula is as follows;
f’xt/4.187=VxAT P(W)=4.187xVxAT/t
Our condition for the water load is as follows:
Room temperature ..........................around 20°C Power supply Voltage ...............Rated voltage
Water load ..... 1000 g Initial temperature ...........1O-t-2°C Heating time .....................49 sec.
P=85xAT
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 of the test.
3. Temperature of the water
The initial temperature of the water is (10 + 2)“C.
4. Select the initial and final water temperature so that the maximum difference between the final
water temperature and the ambient temperature is 5°C.
5. Select stirring devices and measuring instruments in order to minimize addition or removal of heat.
6. The graduation of the thermometer must be scaled by 0.1“C at minimum and an accurate ther-
mometer.
7. The water load must be (1000 sf:5) g.
8. “t” is measured while the microwave generator is operating at full power. Magnetron filament heat-
up time is not included.
NOTE: The operation time of the microwave oven is “t + 2” sec. 2 sec. is magnetron filament heat-up
time.
Measuring method:
1. Measure the initial temperature of the water before the water is added to the vessel.
(Example: The initial temperature Tl = 11“C)
2. Add the 1 litre water to the vessel.
3 Place the load on the centre of the shelf.
14

TEST PROCEDURES
PROCEDURE
LETTER COMPONENT TEST
4. Operate the microwave oven at HIGH for the temperature of the water rises by a value A T of
(10 *2)X.
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.
Initial temperature ............................................................................................Tl = 11°C
Temperature after (49+2)= 51 sec. .................................................................T2 = 21“C
Temperature difference Cold-Warm ............................................................. AT1 = 10°C
Measured output power
The equation is “P= 85 x AT” ................................................P= 85 x 10°C = 850 Watts
JUDGMENT: The measured output power should be at least + 15 % of the rated output
power.
CAUTION: 1 C CORRESPONDS TO 85 WATTS. REPEAT MEASUREMENT IF THE POWER IS
INSUFFICIENT.
~
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-- - Hea d
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* -I-
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T2%
MICROWAVE OUTPUT POWER (2 Liter water load)
The following test procedure should be carried out with the microwave oven in a fully assembled
condition (with outer case fitted).
Microwave output power from the magnetron can be measured by way of substitution, i.e. it can be
measured by using a water load how much it can be absorbed by the water load. To measure the
microwave output power in the microwave oven, the relation of calorie and watt is used.
On the other hand, if the temperature of the water with V(ml) rises AT (“C) during this microwave
heating period, the calorie of the water is V x AT.
The formulae is as follows;
P =8330xVxAT/t
Our condition for the water load is as follows:
Room temperature .................23+ 2°C Power supply Voltage ..........................240 volts.
Water load .......2000 ml Initial temperature .......23 + 1“C Heating time ....1min. 51 sec.
P = 75 x AT
Measuring method:
A) The two water containers must be prepared.
The water container must be one (1j litre beaker made of Pyrex glass and its diameter approxi-
mately 12cm.
B) Put the one (1) litre water into each beaker (Each beaker has one litre water). The initial tempera-
ture of the water should be 23+2”C.
C) Mark Tl on the one beaker and mark T2 on the other one. And stir the water and measure the
temperature of water the thermometer and note them. The graduation of the thermometer must be
scaled by 0.1 “C at minimum and an accurate mercury thermometer is recommended.
D) Place the two (2) beakers as touching each other in the-centre of the oven cavity.
E) Set the timer to 1 minute and 51 seconds start the oven at HIGH.
15

A-9H55
TEST PROCEDURES
PROCEDURE
LETTER COMPONENT TEST
F) The time must be measured with stopwatch or wristwatch.
G) After 1 minute and 51 seconds, stop the oven by opening the door.
H) Put the two (2) beakers out of the oven cavity and measure the temperature of the water by stirring
the water with thermometer and note them.
Example
Initial temperature ............................*...................*.................................. Tl = 23°C T2 = 24°C
Temperature after 1 min. 51 set . ...........................................................Tl = 33°C T2 = 34°C
Temperature difference Cold-Warm ...................................................ATl=
10°C AT2=
10°C
Mean temperature rise AT ..............................
Measured output power AT = (AT1 + AT2)/2 = (1O’C+lO”C) / 2 = 10°C
The equation is P= 75 x AT ..............................................................P= 75 x 10°C = 750 Watts
NOTE: The measured output power should be at least + 15 % of the rated output power.
CAUTION: 1“C CORRESPONDS TO 75 WATTS.
REPEAT MEASUREMENT IF THE POWER IS INSUFFICIENT.
B
(Tl ‘C) (T2OC) (Tl OC) (T2OC)
Heat up for min. 5 set
POWER TRANSFORMER TEST
WARNING: High voltages and large currents are present at the secondary winding and fila-
ment winding of the power transformer. It is very dangerous to work near this
part when the oven is on. NEVER make any voltage measurements at the high-
voltage circuits, including the magnetron filament.
CARRY OUT 3D CHECKS.
Disconnect the leads to the primary winding of the power 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 : -4
a. Primary winding .................................. less than 1.3 ohms.
b. Secondary winding ....................... approximately 72 ohms.
c. Filament winding.. .................................... less than 1 ohm.
If the reading obtained are not as stated above, then the power transformer is probably faulty and
should be replaced.
CARRY OUT 4R CHECKS
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
using an ohmmeter set to its highest range.
16

I R-9H55
TEST PROCEDURES
PROCEDURE
LETTER COMPONENT TEST
Connect the ohmmeter across the terminal B+C of the high voltage rectifier and note the reading
obtained. Reverse the meter leads and note this second reading. The normal resistance is infinite in
one direction and mor than 100 kR in the other direction.
A D2 Dl B
CARRY OUT 4R CHECKS
ASYMMETRIC
ASYMMETRIC RECTIFIER TEST
-T@
RECTIFIER
CARRY OUT 3D CHECKS. C HIGH VOLTAGE RECTIFIER
Isolate the high voltage rectifier assembly from the HV circuit. The asymmetric rectifier can be tested
using an ohmmeter-set to its highest range. Connect the ohmmeter across the terminals A+B of the
asymmetric rectifier and note the reading obtained. Reverse the meter leads and note this second
reading. If an open circuit is indicated in both directions then the asymmetric rectifier is good. If an
asymmetric rectifier is shorted in either direction, then the the asymmetric rectifier is probably faultly
and must be replaced with the high voltage rectifier. When the asymmetric rectifier is defective, check
whether magnetron, high voltage rectifier, high voltage wire or filament winding of the power trans-
former is shorted.
CARRY OUT fi CHECKS
NOTE: For measurement of the resistance of the rectifier, the batteries of the measuring instrument
must have a volyage at least 6 volts, because otherwise an infinite resistance might be shown
in both directions.
D HIGH VOLTAGE CAPACITOR TEST
CARRY OUT 3D CHECKS.
A. Isolate the high voltage capacitor from the circuit.
B. Continuity check must be carried out with measuring instrument which is set to the highest resis-
tance range.
C. A normal capacitor shows continuity for a short time (kick) and then a resistance of about 10 MQ
after it has been charged.
D. A short-circuited capacitor shows continuity all the time.
E. An open capacitor constantly shows a resistance of about 10 MQ because of its internal 10 MR
resistance.
F. When the internal wire is opened in the high voltage capacitor, the capacitor shows an infinite
resistance.
G. The resistance across all the terminals and the chassis must be inifinte when the capacitor is nor-
mal.
If incorrect readings are obtained, the high voltage capacitor must be replaced.
CARRY OUT 4R CHECKS
E SWITCH TEST
CARRY OUT 3D CHECKS.
Isolate the switch to be tested and using an ohmmeter check
following table.
Table: Terminal Connection of Switch
Plunger Operation 1 COMtoNO 1 COM to NC
Released I O.C. I S.C.
I Deoressed I S.C. I O.C. I
between the terminals as described in the
COM; Common terminal
NO; Normally open terminal
NC; Normally closed terminal
S.C.; Short circuit
O.C.; Open circuit
If incorrect readings are obtained, make the necessary switch adjustment or replace the switch.
CARRY OUT fi CHECKS.
17

>
TEST PROCEDURES
PROCEDURE
LETTER COMPONENT TEST
F BLOWN FUSE F M8A
CARRY OUT 3D CHECKS
1. If the fuse M8A is blown, there could be shorts or grounds in electrical parts or wire harness. Check
them and replace the defective parts or repair the wire harness.
2. If the fuse M8A is blown when the door is opened, check the upper latch switch, lower latch switch,
monitor switch and monitor resistor.
If the fuse M8A is blown by incorrect door switching, replace the defective switch(s) and the fuse
M8A.
3. If the fuse M8A is blown, there could be short in the asymmetric rectifier or there is a ground in wire
harness. A short in the asymmetric rectifier may have occured due to short or ground in H.V. recti-
fier, magnetron, power transformer or H.V. wire. Check them and replace the defective parts or
repair the wire harness.
CARRY OUT 4R CHECKS
CAUTION: Only replace fuse with the correct value replacement.
G TEMPERATURE FUSE AND THERMAL CUT-OUT TEST
CARRY OUT 3D CHECKS
Disconnect the leads from the terminals of the temp. fuse or thermal cut-out. Then using an ohmme-
ter, make a continuity test across the two terminals as described in the table below.
CARRY OUT $FJCHECKS
Table: Temperature Fuse and Thermal cut-out Test
Parts Name
Temp. fuse 15O’C
Thermal cut-out 150X
Thermal cut-out 9O’C
Temperature of “ON” condition Temperature of “OFF” condition Indication ofohmmeter
(closed circuit) (‘C) (open circuit) (‘C) (When room temperature
is approx. 20-C)
Below -20-C Above 150 ‘C Closed circuit
Below 130% Above 15O’C Closed circuit.
Below -20-C Above 90X Closed circuit.
If incorrect readings are obtained, replace the temp. fuse or thermal cut-out.;
An open circuit temperature fuse 150°C (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 150°C (OVEN) indicates that--the convection motor has over heated,
this may be due to convection motor locked.
An open circuit thermal cut-out 90°C (FM) indicates that the fan motor winding has overheated, this
may be due to blocked ventilation or locked cooling fan.
H CONVECTION HEATER TEST
CARRY OUT 3D CHECKS
Before carring out the following tests make sure the heater is fully cool.
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.
The resistance of heater is approximately 37.5 ohms.
18