Sharp Carousel R-990KS User manual

CHAPTER 1. BEFORE SERVICING
CHAPTER 2. WARNING TO SERVICE PERSONNEL
CHAPTER 3. PRODUCT SPECIFICATIONS
CHAPTER 4. APPEARANCE VIEW
CHAPTER 5. OPERATION SEQUENCE
CHAPTER 6. FUNCTION OF IMPORTANT COMPO-
NENTS
CHAPTER 7. TROUBLESHOOTING GUIDE
CHAPTER 8. TEST PROCEDURES
CHAPTER 9. TOUCH CONTROL PANEL ASSEMBLY
CHAPTER 10. COMPONENT REPLACEMENT AND
ADJUSTMENT PROCEDURE
CHAPTER 11. MICROWAVE MEASUREMENT
CHAPTER 12. CIRCUIT DIAGRAMS
Parts List
SX517R990KPJW
CONVECTION
MICROWAVE OVEN
R-990K(S)
R-990K(W)
SERVICE MANUAL
R990K(W)
MODELS
CONTENTS
SHARP CORPORATION This document has been published to be used
for after sales service only.
The contents are subject to change without notice.
In the interest of user-safety the oven should be restored to its
original condition and only parts identical to those specified
should be used.

CONTENTS
CHAPTER 1. BEFORE SERVICING
[1] GENERAL IMPORTANT INFORMATION.....1-1
[2] CAUTION MICROWAVE RADIATION ........1-1
[3] WARNING ..................................................1-1
CHAPTER 2. WARNING TO SERVICE PERSONNEL
CHAPTER 3. PRODUCT SPECIFICATIONS
CHAPTER 4. APPEARANCE VIEW
[1] OVEN .........................................................4-1
[2] TOUCH CONTROL PANEL........................4-1
CHAPTER 5. OPERATION SEQUENCE
[1] OFF CONDITION .......................................5-1
[2] MICROWAVE COOKING CONDITION ......5-1
[3] CONVECTION COOKING CONDITION.....5-1
[4] AUTOMATIC MIX COOKING CONDITION.....5-2
[5] ABSOLUTEHUMIDITYSENSOR (AH
SENSOR)COOKING CONDITION .............5-2
[6] AH SENSOR COOKING SEQUENCE .......5-3
[7] MULTI COOK .............................................5-3
[8] EASY DEFROST COOKING......................5-3
[9] FIRE SENSING FEATURE (MICROWAVE
MODE)........................................................5-3
CHAPTER 6. FUNCTION OF IMPORTANT COMPO-
NENTS
[1] DOOR OPEN MECHANISM.......................6-1
[2] UPPER LATCH SWITCH, LOWER LATCH
SWITCHAND STOP SWITCH ....................6-1
[3] MONITOR SWITCH ...................................6-1
[4] THERMAL CUT-OUT 150C (CONV.) .........6-1
[5] THERMAL CUT-OUT 95C (FAN MOTOR).....6-1
[6] TEMPERATURE FUSE 150C (MG) ...........6-1
[7] FUSE F10A 250V .......................................6-1
[8] THERMISTOR............................................6-1
[9] TURNTABLE MOTOR ................................6-1
[10] CONVECTION MOTOR .............................6-1
[11] FAN MOTOR ..............................................6-1
[12] CONVECTION HEATER ............................6-1
[13] CONVECTION COOKING SYSTEM..........6-2
[14] DAMPER OPEN-CLOSE MECHANISM.....6-2
[15] HIGH VOLTAGE FUSE ..............................6-2
CHAPTER 7. TROUBLESHOOTING GUIDE
[1] FOREWORD ..............................................7-1
[2] CHART .......................................................7-1
CHAPTER 8. TEST PROCEDURES
[1] Procedure A: MAGNETRON (MG) TEST.....8-1
[2] Procedure B: POWER TRANSFORMER
TEST ..........................................................8-2
[3] Procedure C: HIGH VOLTAGE RECTIFI-
ER TEST ....................................................8-2
[4] Procedure D: HIGH VOLTAGE CAPACI-
TOR TEST..................................................8-2
[5] Procedure E: SWITCH TEST .....................8-3
[6] Procedure F: FUSE F10A...........................8-3
[7] Procedure G: TEMPERATURE FUSE
AND TERMAL CUT-OUT TEST ................. 8-3
[8] Procedure H: CONVECTION HEATER
TEST........................................................... 8-3
[9] Procedure I: THERMISTOR TEST ............. 8-3
[10] Procedure J: MOTOR WINDING TEST...... 8-4
[11] Procedure K: HIGH VOLTAGE FUSE
TEST........................................................... 8-4
[12] Procedure L: NOISE FILTER TEST.......
..... 8-4
[13] Procedure M: TOUCH CONTROL PANEL
ASSEMBLY TEST....................................... 8-4
[14] Procedure N: KEY UNIT (MEMBRANE
SWITCH) TEST .......................................... 8-5
[15] Procedure O: RELAY TEST........................ 8-5
[16] Procedure P: PROCEDURES TO BE TAK-
EN WHEN THE FOIL PATTERN ON THE
PRINTED WIRING BOARD (PWB) IS
OPEN.......................................................... 8-5
[17] Procedure Q: AH SENSOR TEST .............. 8-6
CHAPTER 9. TOUCH CONTROL PANEL ASSEM-
BLY
[1] OUTLINE OF TOUCH CONTROL PANEL..... 9-1
[2] DESCRIPTION OF LSI ............................... 9-1
[3] ABSOLUTE HUMIDITY SENSOR CIR-
CUIT ........................................................... 9-4
[4] SERVICING FOR TOUCH CONTROL
PANEL ........................................................ 9-5
[5] PRECAUTIONS FOR USING LEAD-
FREE SOLDER .......................................... 9-6
CHAPTER 10. COMPONENT REPLACEMENT AND
ADJUSTMENT PROCEDURE
[1] BEFORE OPERATING ............................. 10-1
[2] OUTER CASE REMOVAL ........................ 10-1
[3] POWER TRANSFORMER REMOVAL ..... 10-2
[4] MAGNETRON REMOVAL ........................ 10-2
[5] HIGH VOLTAGE RECTIFIER ASSEMBLY
REMOVAL ................................................ 10-2
[6] HIGH VOLTAGE CAPACITOR REMOVAL... 10-2
[7] OVEN LAMP SOCKET REMOVAL........... 10-2
[8] HEATER UNIT ASSEMBLY REMOVAL
(HEATING ELEMENT/THERMISTOR) ..... 10-2
[9] CONTROL PANEL ASSEMBLY AND
CONTROL UNIT REMOVAL..................... 10-3
[10] TURNTABLE MOTOR AND/OR COU-
PLING REMOVAL..................................... 10-3
[11] CONVECTION MOTOR REMOVAL ......... 10-3
[12] DAMPER ASSEMBLY REMOVAL ............ 10-3
[13] FAN MOTOR REPLACEMENT................. 10-3
[14] CORD HOLDER REMOVAL ..................... 10-4
[15] POWER SUPPLY CORD REPLACE-
MENT........................................................ 10-4
[16] STOP SWITCH, UPPER LATCH SWITCH,
LOWER LATCH SWITCH AND MONITOR
SWITCH REMOVAL ................................. 10-5
[17] STOP SWITCH, UPPER LATCH SWITCH,
LOWER LATCH SWITCH AND MONITOR
SWITCH ADJUSTMENT .......................... 10-5

R990K(W)
1 – 1
R990K(W) Service Manual
CHAPTER 1. BEFORE SERVICING
[1] 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 ser-
vice.
[2] CAUTION MICROWAVE RADIATION
DO NOT BECOME EXPOSED TO RADIATION FROM THE MICROWAVE GENERATOR OR OTHER PARTS CON-
DUCTING 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.
[3] 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 "*" on parts list may cause undue microwave exposure, by themselves, or when they are damaged,
loosened or removed.
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

R990K(W)
2 – 1
R990K(W) Service Manual
CHAPTER 2. 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. High voltage capacitor, Power transformer, Magnetron, High voltage rectifier assembly, High voltage harness and High voltage fuse.
REMEMBER TO CHECK 3D
1) Disconnect the supply.
2) Door opened, and wedged open.
3) Discharge the high voltage capacitor.
WARNING: AGAINST THE CHARGE OF THE HIGH-VOLTAGE
CAPACITOR
The high-voltage capacitor remains charged about 60 sec-
onds after the oven has been switched off. Wait for 60 sec-
onds and then short-circuit the connection of the high-
voltage capacitor (that is, of the connecting lead of the
high-voltage rectifier) against the chassis with the use of
an insulated screwdriver.
Sharp recommend that wherever possible fault-finding 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 pri-
mary of the power transformer. Ensure that these leads remain iso-
lated 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.
REMEMBER TO CHECK 4R
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
reexamine the connections to the component being tested.
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.

R990K(W)
3 – 1
R990K(W) Service Manual
CHAPTER 3. PRODUCT SPECIFICATIONS
TEM DESCRIPTION
Power Requirements
230 - 240 Volts
50 Hertz
Single phase, 3 wire earthed
Power Consumption 1600 W (Microwave)
1600 W (Convection)
Power Output 900 watts (IE60705C)
Operating frequency 2450 MHz
Case Dimensions
Width 627 mm
Height 378 mm
Depth 487 mm
Control Complement
Touch Control System
Clock (1:00 - 12:59)
Timer (0 - 99 minutes 99 seconds)
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
HELP pad
SENSOR INSTANT ACTION pads
MULTI COOK pad
REHEAT SENSOR pad
CONVECTION COOKING FUNCTION pads
EASY DEFROST pad
NUMBER and TEMPERATURE pads
POWER LEVEL pad
MEMORY padMORE. LESS pads
STOP/CLEAR pad
CLOCK pad
INSTANT COOK/START pad
Set Weight (Approx.) 29 kg

R990K(W)
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R990K(W) Service Manual
CHAPTER 4. APPEARANCE VIEW
[1] OVEN
1. Ventilation opening
2. Oven lamp
3. Door hinges
4. Door safety latches
5. See through door
6. Door seal and sealing surfaces
7. Door open button
8. Touch control panel
9. Digital readout
10.Wave guide cover
11.Coupling
12.Menu label
13.Rating label 14. low rack 15. High rack 16. Power supply cord 17. Turntable 18. Roller stay
[2] TOUCH CONTROL PANEL
NOTE: Some one-touch cooking features such as "INSTANT" Cook are disabled after one minute when the ovenis not in use. These fea-
tures are automatically enabled when the door is opened and closed or the STOP/CLEAR pad is pressed.
1
10
2
12
9
8
7
517
18
14 15
13
11 4
6
3
4
16
MULTI COOK PAD
Press to select Multi Cook mode.
MORE ( ), LESS ( ) PADS
Press to increase/decrease the time in
one minute increments during cooking or
to alter the doneness for the Sensor In-
stant Action, Reheat Sensor, Multi Cook
or Easy Defrost modes.
POWER LEVEL PAD
Press to select microwave power setting.
If not pressed, HIGH is automatically se-
lected.
EASY DEFROST PAD
Press to defrost meat by entering weight
only.
NUMBER AND TEMPERATURE PADS
Press to enter cooking times, clock time, con-
vection temperature or to select the Multi
Cook menus.
STOP/CLEAR PAD
Press to clear during programming.
Press once to stop operation of oven dur-
ing cooking; press twice to cancel cook-
ing program.
CLOCK PAD
Press to set Clock
HELP PAD
Press to select auto start, in-
formation guide on/off, child
lock, demonstration modes or
info on pad.
Press to get cooking informa-
tion.
REHEAT SENSOR PAD
Press to select 3 popular Reheat
menu.
SENSOR INSTANT ACTION
PADS
Press once to cook or reheat 6
popular menus. (See NOTE)
CONVECTION COOKING
FUNCTION PADS
Press to cook for each func-
tion.
MEMORY PAD
Press to enter the frequently
used cooking program.
Press to recall the memorized
program.
INSTANT COOK/START PAD
Press once to cook for 1 minute
at HIGH or increase by 1 mi-
nute multiples each time this
pad is pressed during Micro-
wave, Convection, Grill or Mix
cooking.
(See NOTE)
Indicator
MIX CONV
DEFROST
SENSOR
COOK KG HELP

R990K(W)
5 – 1
R990K(W) Service Manual
CHAPTER 5. 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
[1] OFF CONDITION
Closing the door activates all door interlock switches: upper latch
switch, lower latch switch and stop switch. (In this condition, the moni-
tor switch contacts are closed.) When oven is plugged in a wall outlet
(230 - 240V, 50Hz), rated voltage is supplied to the control unit.
Figure O-1 on page 12-1
1. The display flashes “SHARP”, “MICRO-”, “WAVE”,'OVEN”.
To set any programmes or set the clock, you must first touch the
STOP/CLEAR pad.
“ : “ 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 now operates moving the damper to the open posi-
tion, 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.
[2] MICROWAVE COOKING CONDITION
1. HIGH COOKING
Enter cooking time by pressing the NUMBER pads and then select
microwave cooking and power level by pressing 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)
Figure O-2 on page 12-1
2. Rated voltage is supplied to the primary winding of the power trans-
former. The voltage is converted to about3.3 volts A.C. output on
the filament winding and high voltage of approximately 2260 volts
A.C. on the high voltage winding.
3. The filament winding voltage (3.3 volts) heats the magnetron fila-
ment and the high voltage (2260 volts) is sent to the voltage dou-
bling circuit.
4. The 2450 MHz microwave energy produced in the magnetron gen-
erates 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 to be 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 asso-
ciated 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.
2. MEDIUM HIGH, MEDIUM, MEDIUM LOW, LOW
COOKING
When variable cooking power is programmed, the rated voltage is sup-
plied to the power transformer intermittently through the contacts of
the relay (RY2) which is operated by the control unit within a 32-sec-
ond time base. Micro-wave power operation is follows:
SETTING;
NOTE: The ON/OFF time ratio does not exactly correspond to the
percentage of microwave power, because approx. 3 seconds
are needed for heating up the magnetron filament.
[3] CONVECTION COOKING CONDITION
1. PREHEATING CONDITION
Press the PREHEAT pad and then select preheating temperature by
pressing the temperature 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.
2. he 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 dampers witch 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 temper-
ature, the following operations occur:
1) The heater relay (RY3) is de-energized by the CPU unit temper-
ature circuit and thermistor, opening the circuit to the convection
heater.
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.

R990K(W)
5 – 2
2) The oven will continue to function for 30 minutes, turning the
convection heater on and off, as needed to maintain the
selected preheat temperature. The oven will shut-down com-
pletely after 30 minutes.
2. 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.
Press the CONVEC-TION pad and then enter the cooking temperature
by pressing the temperature pad. And then enter the cooking time by
pressing the NUMBER pads. When the START pad is touched, the fol-
lowing operations occur:
1. The numbers of the digital read-out start the countdown 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 116°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 116°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, 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 ener-
gized 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).
[4] AUTOMATIC MIX COOKING CONDITION
Choose the LOW MIX or HIGH MIX by pressing the LOWMIX pad or
HIGH MIX pad. And then enter cooking time by pressing the NUMBER
pads. When the START pad is touched, the following operations occur:
1. The numbers of the digital read-out start the countdown 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 volt-
age 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:
1) The power supply voltage is added to the convection heater and
power transformer alternately.
2) The convection heater operates through the heater relay (RY3)
contacts and the power transformer operates through the cook
relay (RY2) contacts.
3) These are operated by the CPU unit to supply alternately within
a 48 second time base, convection heat and microwave energy.
The relationship between the convection and microwave power opera-
tions are as follows.
NOTE: The ON and OFF time ratio does not correspond with the per-
centage of microwave power, because approx. 2 seconds are
needed for heating of the magnetron filament.
NOTE: During alternate Microwave/Convection operation, the con-
vection heater is energized only if the cavity temperature
drops below the set temperature.
[5] ABSOLUTEHUMIDITYSENSOR (AH
SENSOR)COOKING CONDITION
n 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 micropro-
cessor 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 “senses” the vapour and its resistance
increases gradually. When the resistance reaches the value set
according to the menu, supplementary cooking is 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 rapidly.You can
smell the aroma as it cooks.;
16 S E C . 32 S E C .
48 S E C .
LOW MIX
HIGH MIX
MICR OWAVE POWE R
= APPROX. 30%
CONVECTION
TEMPERATURE
= 200ûC
MICR OWAVE POWE R
= APPROX. 10%
CONVECTION
TEMPERATURE
= 180ûC
40 S E C .8SEC.
ON
ON
OFF
OFF
OFF
ON
(MICR O.)
(C ONVE C .)
(MICR O.)
(C ONVE C .)
MICR OWAVE

R990K(W)
5 – 3
3. Sensor detects moisture and humidity and calculates cooking time
and variable power.
[6] 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 SENSORCOOKING
immediately after plugging in the unit.Wait two minutes before
coo
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 the2nd. or 3rd.
stage when Reheat pie, Casseroles or Desserts has been chosen.
(Figure O-3)
4. When the sensor detects the vapour emitted from the food, the dis-
play 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.
[7] MULTI COOK
MULTI COOK will automatically compute and set the oven tempera-
ture, 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 oven works on Mix cooking mode, Convection
cooking mode or Preheating mode according to the special cooking
sequence.
[8] 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)
[9] 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-sec-
onds time base comparing the obtained voltage measurements. If the
most recent volt-age measured is 300mV grater than the previous volt-
age measured, the LSI judges it as a fire in the oven cavity and
switches off the relays to the power transformer, fan motor and con-
vection 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 29seconds. Two (2) sec-
onds after the thermistor is energized, the voltage across the tem-
perature 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 con-
vection motor. The LSI also stops counting down and closes the
damper door so that no fresh air will enter the oven cavity.
3. Once the fire sensor feature has shut the unit down, the pro-
grammed 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 operation 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 sensor's vapour detection.
MIC R OWAVE
AH S E NS OR
CONVECTION
MOTOR
THERMISTOR
Sensing
Voltage
ON
OFF
ON
OFF
ON
OFF
0 23 24 30 32(sec.) 64(sec.)
3sec.
S ens ing the voltage acros s temperature measurement circuit.
6sec.

R990K(W)
6 – 1
R990K(W) Service Manual
CHAPTER 6. FUNCTION OF IMPORTANT COMPONENTS
[1] DOOR OPEN MECHANISM
The door is opened by pushing the open button on the control panel,
refer to the Figure D-1.When the open button is pushed, the open
lever pushes up the switch lever, and then the switch lever pushes up
the latch head. The latch heads are moved upward and released from
latch hook. Now the door will open.
Figure D-1. Door Open Mechanism
[2] UPPER LATCH SWITCH, LOWER LATCH
SWITCH AND STOP SWITCH
1. When the oven door is closed, the contacts (COM-NO) must be
closed.
2. When the oven door is opened, the contacts (COM-NO) must be
opened.
[3] 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 blown-
ing the fuse when the contacts of the common and normal open con-
tacts 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. WAs the door goes to a closed position, the monitors witch 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.)
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 FUSETEST THE
UPPER LATCH SWITCH, LOWERLATCH SWITCH AND
MONITOR SWITCHFOR PROPER OPERATION. (REFER
TOCHAPTER “TEST PROCEDURE”)
[4] THERMAL CUT-OUT 150C (CONV.)
The oven thermal cut-out located on the left side of the thermal protec-
tion plate is designed to prevent damage to the convection heater unit
if an overheated condition develops in the tube due to cooling fan fail-
ure, obstructed air ducts, dirty or blocked air intake, etc. Under normal
operation, the oven thermal cut-out remains closed. How-ever, 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.
[5] THERMAL CUT-OUT 95C (FAN MOTOR)
The thermal cut-out protect the fan motor against over-heating. If its
temperature goes up higher than 95°C 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 75°C, the contacts of the thermal cut-out
will close again.
[6] TEMPERATURE FUSE 150C (MG)
This fuse protects the magnetron against overheating. If the tempera-
ture goes up higher than 150°C 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 trans-
former. The defective fuse must be replaced with new rated one.
[7] FUSE F10A 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.
[8] THERMISTOR
The thermistor is a negative temperature coefficient type.The tempera-
ture in the oven cavity is detected through the resistance of the ther-
mistor, and then the control unit causes the heating element relay to
operate, thus the current to the heating element is turned ON/OFF.
[9] TURNTABLE MOTOR
The turntable motor drives the turntable supporting plate to rotate the
turntable.
[10] CONVECTION MOTOR
The convection motor drives the convection fan and provides the
heated air.
[11] 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 channelled through the oven cavity to
remove steam and vapours given off from the heating foods. It is then
exhausted through the exhausting air vents at the oven cavity.
[12] 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.
LATCH HOOK
LATCH
HEADS
STOP SWITCH
MONITOR S WITC H
LOWER LATCH SWITCH
SWITCH LEVER
OPEN LEVER
DOOR OPEN
BUTTON
UPPER LATCH SWITCH

R990K(W)
6 – 2
[13] 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 circu-
lation 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 con-
vection 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. With-
out 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 circu-
lates inside the oven cavity to raise its temperature and, at the same
time, comes into contact with the food being cooked. When the tem-
perature 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 con-
vection time reaches 0, the convection heater is de-energized and the
convection fan stops operating and the oven shuts off. Upon comple-
tion 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 air temperature
is above 116°C, the circuit to RY6will be maintained (by the thermistor
circuit) to continue operation of the cooling fan motor until the temper-
ature drops below 116°C, at which time the relay will be de-energized,
turning off the fan motor. Relay RY5 will how-ever, 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.
[14] 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.
1. Microwave Cooking:
Damper is in the open position, because a portion of cooling air is
channelled through the cavity to removes team and vapours given off
from the heating foods.It is then exhausted at the top of the oven cav-
ity into a condensation compartment.
2. Convection Cooking:
Damper is in the closed position, so that no hot air will be allowed to
leak out the oven cavity.
3. Damper Operation
1. When power supply cord is plugged in:
1) When power supply cord is plugged in, a signal is sensed in the
control unit, and operates shut-off relay(RY4).
2) Contacts of shut-off relay (RY4) close, the damper motor is
energized, opening the damper door.
3) When the damper is moved to the open position by the damper
cam, damper switch is closed (ON position).
4) The signal of damper switch is re-sensed in the control unit and
shut-off relay (RY4) is turned off.
5) The rated voltage 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:
1) Damper motor is energized by touching the convection, temper-
ature and START pads.
2) When damper is in the closed position (dampers witch is OFF),
its signal is sensed by the control unit, and shut-off relay (RY4)
is de-energized.
3) The damper is held in the closed position during the convection
cooking operation.
4) .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 during
convection or open during microwave, the control unit will stop
oven operation after 1 minute.
Figure D-2. Damper Mechanism
[15] HIGH VOLTAGE FUSE
The high voltage fuse blows when the high voltage rectifier or the mag-
netron is shorted.
Cooking Mode Operation of Damper
Microwave cooking OPEN
Convection cooking CLOSE
Sensor cooking OPEN
Automatic mix cooking CLOSE
Grill cooking CLOSE
Slow cooking CLOSE
DAMPE R DUC T
DAMPE R
DAMPE R CAM
DAMP E R MOTOR
DAMPE R S WITC H
DAMPE R S HAFT

R990K(W)
7 – 1
R990K(W) Service Manual
CHAPTER 7. TROUBLESHOOTING GUIDE
[1] FOREWORD
When troubleshooting the microwave oven, it is helpful to follow the
Sequence of Operation in performing the checks. Many of the possible
causes of trouble will require that a specific test be performed. These
tests are given a procedure letter which will be found in the “Test Pro-
cedure”section.
IMPORTANT:
If the oven becomes inoperative because of a blown fuse F10A in the
upper latch switch - lower latch switch - monitor switch circuit, check
the upper latch switch, lower latch switch and monitor switch before
replacing the fuse F10A.
[2] CHART
MAGNETRON POWER TRANSFORMER H.V. RECTIFIER ASSEMBLY
HIGH VOLTAGE CAPACITOR LATCH AND STOP SWITCHES MONITOR SWITCH DAMPER SWITCH MAIN FUSE TEMPERATURE FUSE 150C THERMAL CUT-OUT CONVECTION HEATER THERMISTOR FAN MOTOR TURNTABLE MOTOR CONVECTION MOTOR
DAMPER MOTOR HIGH VOLTAGE FUSE TOUCH CONTROL PANEL KEY UNIT RELAY (RY-1) RELAY (RY-2) RELAY (RY-3)
RELAY (RY-4) RELAY (RY-5) RELAY (RY-6) FOIL PATERN ON P.W.B. AH. SENSOR OVEN LAMP OR SOCKET
O
PENED OR SHORTED WIRE HARNESS
WALL OUTLET LOW POWER SUPPLY VOLTAGE
SHORTED POWER CORD NOISE FILTER
CK = Check / RE = Replace
OFF
CONDITION
ABC D E EEFGGH I J J J J K MNOOOOOOPQRE CKCK CK RE L
COOKING
CONDITION
(MICROWAVE)
PROBLEM
CONDITION
TEST PROCEDURE
POSSIBLE CAUSE
AND
DEFECTIVE PARTS
(AH. SENSOR)
(CONVECTION)
Home fuse blows when power
supply cord is plugged into wall
outlet.
Fuse M8A blows when power
cord is plugged into wall outlet.
Oven lamp does not light with
door opened.
Oven lamp does not light at all
Cooling fan motor does not operate.
The oven stops after1 minute.
Oven lamp light, but turntable
motor does not operate.
Oven does not go into a cook cycle,
when START pad is touched.
Function of variable cooking does
not operate properly except
HIGH power.
Oven is in the sensor cook-ing
condition but AH sensor does not
end 1st. stage or does not stop
cooking cycle or the oven stops
soon.
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 down.
Convection cycle runs 3 min-
utes then the oven shuts down.
Extremely uneven heating is
produced in oven load (food).
Display does not show anything
when power cord is 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 normal condition.)
Low or no power is produced
during microwave cooking (The
food is heated incom-pletely or
not heated at all)

R990K(W)
8 – 1
R990K(W) Service Manual
CHAPTER 8. TEST PROCEDURES
[1] Procedure A: MAGNETRON (MG) 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 litre water 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 IEC test procedure, 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 (sec-
ond), 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 of the test.
3) Temperature of the water
The initial temperature of the water is (10±1)°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 thermometer.
7) The water load must be (1000±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 + 3" sec. 3 sec. is magnetron filament heat-up time.
Measuring method:
1) 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 100% for the temperature of the water rises by a value T of 10°C.
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.
JUDGEMENT: 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.
The formula is as follows;
P x t / 4.187 = V x T+ 0.55 x mc (T2-T0)/4.187 P (W) = 4.187 x V x T / t + 0.55 x mc (T2-T0)/t
Our condition for water load is as follows:
Room temperature (T0) ......................... around 20°C Power supply ........................... VoltageRated voltage
Water load .........................................................1000 g Initial temperature (T1) .................................... 10±1°C
Heating time ..................................................... 47 sec. Mass of container (mc) ...................................... 330 g
T2 .................................................... Final Temperature T = T2 - T1 P = 90 x T + 0.55 x mc (T2-T0)/47
Room temperature ................................................................... To = 21°C
Initial temperature ..................................................................... T1 = 11°C
Temperature after (47 + 3) = 50 sec ...................................... T2 = 21°C
Temperature difference Cold-Warm ( T = T2 - T1) .......... T = 10°C
Measured output power
The equation is "P = 90 x T" .................... P = 90 x 10°C = 900 Watts

R990K(W)
8 – 2
[2] Procedure B: POWER TRANSFORMER TEST
1. CARRY OUT 3D CHECKS.
2. 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 winding. The following readings should be
obtained:
a.Primary winding -------------------- approx. 1.2Ω
b.Secondary winding ----------------- approx. 66Ω
c.Filament winding -------------------less than 1Ω
If the readings obtained are not stated as above, then the power transformer is probably faulty and should be replaced.
3. Also, the power transformer has the thermal cut-out in the primary coil. The thermal cut-out will open when the temperature of the thermal cut-out
in the primary coil reaches approximately 150°C. The thermal cut-out resets automatically at 130°C. If an ohmmeter indicates an open circuit
under normal condition, replace the power transformer because the primary coil (thermal cut-out) has opened. An open primary coil (thermal cut-
out) indicates overheating of the power transformer. Check for restricted air flow to the power transformer, especially the ventilation opening.
4. CARRY OUT 4R CHECKS.
[3] Procedure C: 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.
Connect the ohmmeter across the terminal 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 more than 100 kΩin the other direction.
CARRY OUT 4R CHECKS.
NOTE: FOR MEASUREMENT OF THE RESISTANCE OF THE RECTIFIER, THE BATTERIES OF THE MEASURING INSTRUMENT MUST HAVE
A VOLTAGE AT LEAST 6 VOLTS, BECAUSE OTHERWISE AN INFINITE RESISTANCE MIGHT BE SHOWN IN BOTH DIRECTION.
[4] Procedure D: HIGH VOLTAGE CAPACITOR TEST
CARRY OUT 3D CHECKS.
1. Isolate the high voltage capacitor from the circuit.
2. Continuity check must be carried out with measuring instrument which is set to the highest resistance range.
3. A normal capacitor shows continuity for a short time (kick) and then a resistance of about 10MΩafter it has been charged.
4. A short-circuited capacitor shows continuity all the time.
5. An open capacitor constantly shows a resistance about 10 MΩbecause of its internal 10MΩresistance.
6. When the internal wire is opened in the high voltage capacitor shows an infinite resistance.
7. 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.
WARNING: High voltages and large currents are present at the secondary winding and filament winding of the power transformer. It is
very dangerous to work near this part when the oven is on. NEVER make any voltage measurements of the high-voltage cir-
cuits, including the magnetron filament.
1000g
1000g
1000g
T1 C T2 C
Heat up for 50 sec.
BC
HIGH VOLTAGE RECTIFIER

R990K(W)
8 – 3
[5] Procedure E: SWITCH 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.
If incorrect readings are obtained, make the necessary switch adjustment or replace the switch.
CARRY OUT 4R CHECKS.
[6] Procedure F: FUSE F10A
CARRY OUT 3D CHECKS.
1. If the fuse F10A 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 F10A is blown when the door is opened, check the upper latch switch, lower latch switch and monitor switch.
If the fuse F10A is blown by incorrect door switching, replace the defective switch(es) and the fuse F10A.
CARRY OUT 4R CHECKS.
CAUTION: Only replace fuse with the correct value replacement.
[7] Procedure G: TEMPERATURE FUSE AND TERMAL CUT-OUT TEST
CARRY OUT 3D CHECKS.
Disconnect the leads from the terminals of the temp. fuse or thermal cut-out. Then using an ohmmeter, make a continuity test across the two termi-
nals as described in the table below.
If incorrect readings are obtained, replace the temp. fuse or thermal cut-out.;
An open circuit temperature fuse 150°C (MG)/ thermal cut-out 145°C (MG) indicates that the magnetron has overheated, this may be due to resis-
tricted ventilation, cooling fan failure or a fault condition within the magnetron or HV circuit.
An open circuit thermal cut-out 150°C (CONV.) indicates that the convection motor has over heated, this may be due to convection motor locked.
An open circuit thermal cut-out 95°C (FM) indicates that the fan motor winding has overheated, this may be due to blocked ventilation or locked cool-
ing fan.
CARRY OUT 4R CHECKS.
[8] Procedure H: CONVECTION HEATER TEST
CARRY OUT 3D CHECKS.
Before carrying 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.
2. Insulation resistance
Disconnect the wire leads to the heater to be tested. Check the insulation resistance between the element and cavity using a 500V - 100M ohms
insulation tester. The insulation resistance should be more than 10M ohms in 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.
[9] Procedure I: THERMISTOR TEST
CARRY OUT 3D CHECKS.
Disconnect connector-E from the CPU unit. Measure the resistance of the thermistor with an ohmmeter. Connect the ohmmeter leads to Pin No’s E-3
and E-4 of the thermistor harness.
Table: Terminal Connection of Switch
Plunger Operation Common terminal to Normally open terminal Common terminal to Normally close terminal
Released Open circuit Short circuit
Depressed Short circuit Open circuit.
Table: Temperature Fuse and Thermal cut-out Test
Parts Name Temperature of “ON” condition
(closed circuit).
Temperature of “OFF” condition
(open circuit).
Indication of ohmmeter (When room
temperature is approx. 20°C.)
Temperature fuse 150°C (MG) This is not resetable type. Above 150°C Closed circuit
Thermal cut-out 145°C (MG) This is not resetable type. Above 145°C Closed circuit
Thermal cut-out 150°C (CONV.) Below 130°C Above 150°C Closed circuit
Thermal cut-out 95°C (FAN) Below 75°C Above 95°C Closed circuit

R990K(W)
8 – 4
Room Temp...................20°C - 30°C
Resistance.....................Approx. 350kΩ- 155kΩ
If the meter does not indicate above resistance, replace the thermistor.
CARRY OUT 4R CHECKS.
[10] Procedure J: MOTOR WINDING TEST
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.
If incorrect readings are obtained, replace the motor.
CARRY OUT 4R CHECKS.
[11] Procedure K: HIGH VOLTAGE FUSE TEST
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.
[12] Procedure L: NOISE FILTER TEST
CARRY OUT 3D CHECKS.
Disconnect the leads from the terminals of the noise filter. Using an ohmmeter, check
between the terminals as described in the following table. If incorrect readings are
obtained, replace the noise filter unit.
CARRY OUT 4R CHECKS.
[13] Procedure M: TOUCH CONTROL PANEL ASSEMBLY
TEST
The touch control panel consists of circuits including semiconductors such as LSI, ICs, etc. Therefore, unlike conventional microwave ovens, proper
maintenance cannot be performed with only a voltmeter and ohmmeter. In this service manual, the touch control panel assembly is divided into two
units, Control Unit and Key Unit and troubleshooting by unit 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.
1) When touching the pads, a certain pad produces no signal at all.
2) When touching a number pad, two figures or more are displayed.
3) When touching the pads, sometimes a pad produces no signal.
2. Control Unit.
The following symptoms indicate a defective control unit. Replace the control unit. Before replacing the control unit, perform the Key unit test (Pro-
cedure N) to determine if control unit is faulty.
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) 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.
Table: Resistance of Motor
Motors Resistance
Fan motor Approximately 295 Ω
Turntable motor Approximately 19.2 kΩ
Convection fan motor Approximately 210 Ω
Damper motor Approximately 11 kΩ
MEASURING POINT INDICATION OF OHMMETER
Between N and L Open circuit
Between terminal N and WHITE Short circuit
Between terminal L and RED Short circuit
FUSE
F10A
L
N
LINE CROSS CAPACITOR 0.22μ / AC 250V
NOISE SUPPRESSION COIL
LINE BYPASS CAPACITOR
0.0022μ /AC 250V
LINE BYPASS CAPACITOR
0.0022μ /AC 250V
NOISE FILTER
WHT RED

R990K(W)
8 – 5
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.
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.
[14] Procedure N: KEY UNIT (MEMBRANE SWITCH) TEST
If the display fails to clear when the STOP/CLEAR pad is depressed, first verify the flat ribbon cable is making good contact, verify that the door sens-
ing switch (stop switch) operates properly; that is the contacts are closed when the door is closed and open when the door is open. If the door sensing
switch (stop switch) is good, disconnect the flat ribbon cable that connects the key unit to the control unit and make sure the door sensing switch is
closed (either close the door or short the door sensing switch connector). Use the key unit matrix indicated on the control panel schematic and place
a jumper wire between the pins that correspond to the STOP/CLEAR pad making momentary contact.If the control unit responds by clearing with a
beep the key unit is faulty and must be replaced. If the control unit does not respond, it is faulty and must be replaced. If a specific pad does not
respond, the above method may be used (after clearing the control unit) to determine if the control unit or keypad is at fault.
[15] Procedure O: RELAY TEST
CARRY OUT 3D CHECKS.
Remove the outer case and check voltage between Pin No 9 of the 5-pin connector (A) and the common terminal of the relay RY1 on the control unit
with an A.C. voltmeter. The meter should indicate230 - 240 volts, if not check oven circuit.
Shut-off, Cook and Heater Relay Test
These relays are operated by D.C. voltage
Check voltage at the relay coil with a D.C. voltmeter during the microwave cooking operation or convection cooking 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.
CARRY OUT 4R CHECKS.
[16] Procedure P: PROCEDURES TO BE TAKEN WHEN THE FOIL PATTERN ON THE
PRINTED WIRING BOARD (PWB) IS OPEN
To protect the electronic circuits, this model is provided with a fine foil pattern added to the primary 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.
RELAY SYMBOL OPERATIONAL VOLTAGE CONNECTED COMPONENTS
RY1 APPROX. 21.0V D.C. Oven lamp / Turntable motor
RY2(COOK) APPROX. 21.0V D.C. Power transformer
RY3(HEATER) APPROX. 20.0V D.C. Heating element
RY4 APPROX. 21.0V D.C. Damper motor
RY5 APPROX. 21.0V D.C. Convection motor
RY6 APPROX. 21.0V D.C. Cooling fan motor
STEPS OCCURRENCE CAUSE OR CORRECTION
1The rated voltage is not applied between Pin No. 9 of the 5-pin connector (A)
and the common terminal of the relay RY1. Check supply voltage and oven power cord.
12345
67 890
STOP
CLEAR
REHEAT
PIE
EASY
DEFROST
LESS
POWER
LEVEL
40°C 70°C 130°C 150°C 160°C
180°C 200°C 220°C 230°C 250°C
HIGH MIX
LOW MIX
CONVEC GRILL
MEMORY
PREHEAT
CLOCK
HELP
REHEAT
SENSOR
MULTI
COOK
FROZEN
VEGETABLES
FRESH
VEGETABLES
DESSERTS
JACKET
POTATO
INSTANT COOK
START
MORE
CASSEROLES
G1
G2
G3
G4
G5 G6 G7 G8 G9 G10 G11 G12

R990K(W)
8 – 6
NOTE: *At the time of making these repairs, make a visual inspection of the varis-
tor.check for burned damage and examine the transformer with an ohmmeter
for the presence of layer short-circuit (check primary coil resistance). If any
abnormal condition is detected, replace the defective parts.
CARRY OUT 4R CHECKS.
[17] Procedure Q: AH SENSOR 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 permit adequate ventilation, be sure to install so
as not to block these vents. There should be some 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
Make sure the oven has been plugged in at least two minutes before checking sensor cook 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) Touch REHEAT SENSOR pad twice and touch INSTANT COOK/START pad. Now, the oven is in the sensor cooking condition and “SOUP”, “SEN-
SOR” and “REHEAT” 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 after 16 seconds cleaning time
.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 explanationbe-
low.
1. TESTING METHOD FOR AH SENSOR AND/OR CONTROL UNIT
To determine if the sensor is defective, the simplest method is to replace it with a new replacement sensor.
1) Disconnect oven from power supply and remove outer case.
2) Discharge the high voltage capacitor.
3) Remove the AH sensor.
4) Install the new AH sensor.
5) Re-install the outer case.
6) Reconnect the oven to the power supply and check the sensor cook operation, proceed as follows:
a) Fill approximately 200 milliliters (7.2 oz.) of tap water in a 1000 milliliter measuring cup.
b) Place the container on the center of tray in the oven cavity.
c) Close the door.
d) Touch REHEAT SENSOR pad twice and touch the INSTANT COOK/START pad.
e) The control panel is in automatic Sensor operation.
2 The rated voltage is applied to primary side of power transformer. Power transformer or secondary circuit defective.
Check and repair.
3 Only pattern at “a” is broken. *Insert jumper wire J1 and solder.
4 Pattern at “a” and “b” are broken. *Insert the coil RCILF2003YAZZ between “c” and “d”.
357 9
3
26
CN - A
VRS1
CONV M FAN M POWER
(J1)
T1
P
a
c
d
b

R990K(W)
8 – 7
f) The display will start to count down the remaining cooking time, and the oven will turn off automatically after the water is boiling (babbling).
If new sensor dose not operate properly, the problem is with the control unit.
2. CHECKING CONTROL UNIT
1) Disconnect oven from power supply and remove outer case.
2) Discharge the high voltage capacitor.
3) Disconnect the wire leads from the cook relay.
4) Disconnect the sensor connector that is mounted to lower portion of control panel.
5) Then connect the dummy resistor circuit (see fig.) to the sensor connector of control panel.
6) Reconnect the oven to the power supply and check the sensor cook operation, proceed as follows:
a) Touch REHEAT SENSOR pad twice and touch the INSTANT COOK/START pad.
b) The control panel is in the sensor cooking operation.
c) After approximately 20 seconds, push plunger of select switch. This condition is same as judgement by AH sensor.
d) After approximately 3 seconds, the display shows “X X. X X “ which is the remaing cooking time, and the display counts down.
If the above is not the case, the control unit is probably defective.If the above is proper, the AH sensor is probably defective.
R1,R2:22Ω±1% 1/2W
R3:4.3kΩ±?5% 1/4W
R4:1MΩ±5% 1/4W
Sensor Dummy Resistor Circuit
Plunger
NC
NO
COM
COM NO
NC
R3 R4
R1
R2
1
2
3
F-1
F-2
F-3
To connector (F)
on Control Unit.
CONNECTOR

R990K(W)
9 – 1
R990K(W) Service Manual
CHAPTER 9. TOUCH CONTROL PANEL ASSEMBLY
[1] OUTLINE OF TOUCH CONTROL PANEL
The touch control section consists of the following units as shown in
the touch control panel circuit.
(1) Key Unit (2) Control Unit
The principal functions of these units and their related signals are
explained below.
1. Key Unit
The key unit is composed of a matrix, signals generated in the LSI are
sent to the key unit through P10-P17.When a key pad is touched, a
signal is completed through the key unit and passed back to the LSI
through R24-R27to perform the function that was requested.
2. Control Unit
Control unit consists of LSI, power source circuit, synchronizing signal
circuit, ACL circuit, buzzer circuit, temperature measurement circuit,
absolute humidity sensor circuit and indicator circuit.
1) LSI
This LSI controls the temperature measurement signal, AH sensor
signal, key strobe signal, relay driving signal for oven function and
indicator signal.
2) Power Source Circuit
This circuit generates the voltages necessary for the control unit
from the AC line voltage.
3) Synchronizing Signal Circuit
The power source synchronizing signal is available in order to com-
pose a basic standard time in the clock circuit. It incorporates a
very small error because it works on commercial frequency.
4) ACL Circuit
A circuit to generate a signals which resetting the LSI to the initial
state when power is applied.
5) Buzzer Circuit
The buzzer is responds to signals from the LSI to emit noticing
sounds (key touch sound and completion sound).
6) Temperature Measurement Circuit: (OVENTHERMISTOR)
The temperature in the oven cavity is sensed by the thermistor. The
variation of resistance according to sensed temperature is detected
by the temperature measurement circuit and the result applied to
LSI. The LSI uses this information to control the relay and display
units.
7) Absolute Humidity Sensor Circuit
This circuit detects the humidity of a food which is being cooked, to
control its automatic cooking.
8) Stop Switch
A switch to inform the LSI if the door is open or closed.
9) Relay Circuit
To drive the magnetron, heating element, fan motor, convection
motor, damper motor, turntable motor and light the oven lamp.
10)Indicator Circuit
Indicator element is a Fluorescent Display.Basically, a Fluorescent
Display is triode having a cathode, a grid and an anode. Usually,
the cathode of a Fluorescent Display is directly heated and the fila-
ment serves as cathode.The Fluorescent Display has 8-digits, 16-
segments are used for displaying figures.
[2] DESCRIPTION OF LSI
The I/O signal of the LSI (IZA840DR) are detailed in the following table.
Pin No. Signal I/O Description
1 VCC IN Connected to GND.
2 VEE IN Anode (segment) of Fluorescent Display light-up voltage: -30V.
Vp voltage of power source circuit input.
3 AVSS IN Power source voltage: -5V.
VC voltage of power source circuit input.
4VREFIN
Reference voltage input terminal.
A reference voltage applied to the A/D converter in the LSI. Connected to GND.(0V)
5AN7IN
Used for initial balancing of the bridge circuit (absolute humidity sensor). This input is an analog input terminal
from the AH sensor circuit, and connected to the A/D coverter built into the LSI.
6AN6IN
AH sensor input.
This input is an analog input terminal from the AH sensor circuit, and connected to the A/D converter built into
the LSI.
7-9 AN5-AN3 IN Heating constant compensation terminal.
10 AN2 IN
Input signal which communicates the door open/close information to LSI.
Door closed; "H" level signal(0V).
Door opened; "L" level signal(-5V).
11 AN1 IN
Input signal which communicates the damper open/close information to LSI.
Damper opened; "H" level signal(0V:GND).
Damper closed; "L" level signal(-5V).
12 AN0 IN
Temperature measurement input: OVEN THERMISTOR.
By inputting DC voltage corresponding to the temperature detected by the thermistor, this input is converted
into temperature by the A/D converter built into the LSI.