Wolf MC24 User manual

General Information 2
Controls & Operation 9
Troubleshooting Guide 15
Component Access & Removal 25
Wiring Diagrams 32
subzero.com 800.222.7820
MC24 Convection Microwave
Service Manual

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MC24
PRECAUTIONSTO BE OBSERVED BEFORE AND DUR-
ING SERVICING TO AVOID POSSIBLE EXPOSURE TO
EXCESSIVE MICROWAVE ENERGY
(a) Do not operate or allow the oven to be operated with the door open.
(b) Make the following safety checks on all ovens to be serviced before activating the magnetron or other microwave
source, and make repairs as necessary: (1) interlock operation, (2) proper door closing, (3) seal and sealing
surfaces (arcing, wear, and other damage), (4) damage to or loosening of hinges and latches, (5) evidence of
dropping or abuse.
(c) Before turning on microwave power for any service test or inspection within the microwave generating compart-
ments, check the magnetron, wave guide or transmission line, and cavity for proper alignment, integrity, and
connections.
(d) Any defective or misadjusted components in the interlock, monitor, door seal, and microwave generation and
transmission systems shall be repaired, replaced, or adjusted by procedures described in this manual before
the oven is released to the owner.
(e) A microwave leakage check to verify compliance with the Federal Performance Standard should be performed
on each oven prior to release to the owner.
BEFORE SERVICING
Before servicing an operative unit, perform a microwave emission check as per the Microwave Measure-
ment Procedure outlined in this service manual.
If microwave emissions level is in excess of the specified limit, contact WOLF immediately @
1-800-332-9513.
If the unit operates with the door open, service person should 1) tell the user not to operate the oven
and 2) contact WOLF and Food and Drug Administration's Center for Devices and Radiological Health
immediately.
Service personnel should informWOLF of any certified unit found with emissions in excess of 4mW/cm2.The
owner of the unit should be instructed not to use the unit until the oven has been brought into compliance.
DANGER CAUTION
HIGH VOLTAGE
Do not energize a microwave oven with the outer case cabinet removed, because a microwave oven gener-
ates High Voltage in the circuit.
If you intend to operate the oven employing the high frequency switching power converter circuit, you should
take special precautions to avoid an electrical shock hazard.
The high voltage transformer, high voltage capacitor and high voltage diode have energized high voltage
potential approx. 8 KV.
The aluminium heat sink is connected to the switching power transistor Collector pole, and has an energized
high voltage potential approx. 650V peak.
DO NOT ACCESS THE HIGH VOLTAGE TRANSFORMER, HIGH VOLTAGE CAPACITOR, HIGH VOLTAGE
DIODE AND HEAT SINK WHEN THE POWER SUPPLY IS CONNECTED TO AN ELECTRICAL OUTLET.

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MC24
WARNING TO SERVICE PERSONNEL
Microwave ovens contain circuitry capable of pro-
ducing very high voltage and current, contact with
following parts
may result in a severe, possibly
fatal, electrical shock.
(Example)
High Voltage Capacitor, High Voltage Power
Transformer, Magnetron, High Voltage Rectifier
Assembly, High Voltage Harness etc..
Read the Service Manual carefully and follow all
instructions.
Before Servicing
1. Disconnect the power supply cord , and then
remove outer case.
2. Open the door and block it open.
3. Discharge high voltage capacitor.
WARNING: RISK OF ELECTRIC SHOCK.
DISCHARGE THE HIGH-VOLTAGE
CAPACITOR BEFORE SERVICING.
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 capacitor (that is the connecting lead of the
high-voltage rectifier) against the chassis with the use of
an insulated screwdriver.
Whenever troubleshooting is performed the power supply
must be disconnected.It may in, some cases, be necessary
to connect the power supply after the outer case has been
removed, in this event,
1. Disconnect the power supply cord, and then remove
outer case.
2. Open the door and block it open.
3. Discharge high voltage capacitor.
4. Disconnect the leads to the primary of the power
transformer.
5. Ensure that the leads remain isolated from other
components and oven chassis by using insulation tape.
6. After that procedure, reconnect the power supply cord.
When the testing is completed,
1. Disconnect the power supply cord, and then remove
outer case.
2. Open the door and block it open.
3. Discharge high voltage capacitor.
4. Reconnect the leads to the primary of the power
transformer.
5. Reinstall the outer case (cabinet).
6. Reconnect the power supply cord after the outer case
is installed.
7. Run the oven and check all functions.
After repairing
1. Reconnect all leads removed from components during
testing.
2. Reinstall the outer case (cabinet).
3. Reconnect the power supply cord after the outer case
is installed.
4. Run the oven and 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 power to HIGH and set the microwave timer for two (2)
minutes. When the two minutes has elapsed (timer at zero)
carefully check that the water is now hot.If the water remains
cold carry out Before Servicing procedure and re-examine
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 a microwave leakage test should be carried out.
Don't Touch !
Danger High Voltage

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MC24
MICROWAVE MEASUREMENT PROCEDURE (CANADA)
After adjustment of the door switches are completed individually or collectively, switch test and microwave leakage test
must be performed with survey instrument and test result must be confirmed to meet the requirement of the performance
standard
for microwave ovens as undermentioned.
A. Requirements:
Every microwave oven shall function in such a manner that when the oven is fully assembled and operating with its service
controls and user controls adjusted to yield the maximum output, the leakage radiation, at all points at least 5 cm. from the
external surface of the oven, does not exceed:
1) 1.0mW/cm2 with the test load of 275 ± 15 ml of water at an initial temperature 20 ±5oC.
2) 5.0mW/cm2 when the outer enclosure is removed with a test load of 275 ± 15 ml of water at an initial temperature 20±5oC.
3) 5.0mW/cm2 without a test load.
B. Preparation for testing:
Before beginning the actual measurement of leakage, proceed as follows:
1) Make sure that the actual instrument is operating normally as specified in its instruction booklet.
Important:
Survey instruments that comply with the requirement for instrumentation as prescribed by CSA and NHW performance
standard for microwave ovens must be used for testing recommended instruments are , NARDA 8100 and NARDA 8200.
2) Place the oven tray in the oven cavity.
3) Place the load of 275±15 ml of tap water initially at 20±5oC in the center of the oven cavity.
The water container shall be a low form of 600 ml beaker with an inside diameter of approx. 8.5 cm (3-1/2 in.) and made
of an electrically nonconductive material such as glass or plastic.
The placing of this standard load in the oven is important not only to protect the oven, but also to insure that any leakage
is measured accurately.
4) Set the cooking control on Full Power Cooking Mode, Close the door and select a cook cycle of several minutes. If the
water begins to boil before the survey is completed, replace it with 275 ml of cool water.
C. Leakage test with enclosure installed :
1) Grasp the probe of the survey instrument and hold it perpendicular to the gap between the door and the body of the
oven.
2) Move the probe slowly, not faster than 2.5 cm/sec. along the gap, watching for the maximum indication on the meter.
3) Check for leakage at the door screen, sheet metal seams and other accessible positions where the continuity of the
metal has been breached (eg., around the switches, indicator, and vents).
While testing for leakage around the door pull the door away from the front of the oven as far as is permitted by the
closed latch assembly.
4) Measure carefully at the point of highest leakage and make sure that the highest leakage is no greater than 4mW/cm2,
and that the secondary interlock switch does turn the oven OFF before any door movement.
C. Leakage test without enclosure:
1) Remove the enclosure (cabinet).
2) Grasp the probe of the survey instrument and hold it perpendicular to all mechanical and electric parts of the oven that
is accessible to the user of the oven including, but not limited to, the waveguide, cavity seams, magnetron gap between
the door and the body of the oven.
3) Move the probe slowly, not faster than 2.5 cm/sec. along the gap, watching for the maximum indication on the meter.
4) Measure carefully at the point of highest leakage and make sure that the highest leakage is under 5mW/cm2.
CAUTION: Special attention should be given to avoid electrical shock because HIGHVOLTAGE is generated during this test
No Load test
1) Operate the oven without a load and measure the leakage by the same method as the above test procedure "
Leakage test with enclosure installed"
2. Make sure that the highest leakage should not exceed 5mW/cm2.
NOTE: After servicing, record data on service invoice and microwave leakage report.

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MC24
MICROWAVE MEASUREMENT PROCEDURE (USA)
A. Requirements:
1) Microwave leakage limit (Power density limit): The power density of microwave radiation emitted by a microwave
oven should not exceed 1mW/cm2at any point 5cm or more from the external surface of the oven, measured prior to
acquisition by a purchaser, and thereafter (through the useful life of the oven), 5 mW/cm2at any point 5cm or more
from the external surface of the oven.
2) Safety interlock switches:
Primary interlock relay switch shall prevent microwave radiation emission in excess of the requirement as above
mentioned. Secondary interlock relay and door sensing switch shall prevent microwave radiation emission in excess of
5 mW/cm2 at any point 5cm or more from the external surface of the oven.
B. Preparation for testing:
Before beginning the actual measurement of leakage, proceed as follows:
1) Make sure that the actual instrument is operating normally as specified in its instruction booklet.
Important:
Survey instruments that comply with the requirement for instrumentation as prescribed by the performance standard for
microwave ovens, 21 CFR 1030.10(c)(3)(i), must be used for testing.
2) Place the oven tray in the oven cavity.
3) Place the load of 275±15 ml (9.8 oz) of tap water initially at 20±5O C (68OF) in the center of the oven cavity.
The water container shall be a low form of 600 ml (20 oz) beaker with an inside diameter of approx. 8.5 cm (3-1/2 in.)
and made of an electrically nonconductive material such as glass or plastic.
The placing of this standard load in the oven is important not only to protect the oven, but also to insure that any leakage
is measured accurately.
4) Set the cooking control on Full Power Cooking Mode.
5) Close the door and select a cook cycle of several minutes. If the water begins to boil before the survey is completed,
replace it with 275 ml of cool water.
C. Leakage test:
Closed-door leakage test (microwave measurement):
1) Grasp the probe of the survey instrument and hold it perpendicular to the gap between the door and the body of the
oven.
2) Move the probe slowly, not faster than 1 in./sec. (2.5 cm/sec.) along the gap, watching for the maximum indication on
the meter.
3) Check for leakage at the door screen, sheet metal seams and other accessible positions where the continuity of the
metal has been breached (eg., around the switches, indicator, and vents).
While testing for leakage around the door, pull the door away from the front of the oven as far as is permitted by the
closed latch assembly.
4) Measure carefully at the point of highest leakage and make sure that the highest leakage is no greater than 4mW/cm2,
and that the primary interlock switch/secondary interlock relay does turn the oven OFF before any door movement.
NOTE: After servicing, record data on service invoice and microwave leakage report.

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MC24
SERVICE MANUAL
MICROWAVE OVEN
FOREWORD
This Manual has been prepared to provide Wolf Service Personnel with
Operation and Service Information for the Wolf Microwave Oven, MC24.
It is recommended that service personnel carefully study the entire text of
this manual so that they will be qualified to render satisfactory customer
service.
Check the interlock switches and the door seal carefully. Special attention
should be given to avoid electrical shock and microwave radiation hazard.
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 no other visible damage with the oven.
Servicing and repair work must be carried out only by trained service
personnel.
DANGER
Certain initial parts are intentionally not grounded and present a
risk of electrical shock only during servicing. Service personnel -
Donotcontactthefollowingpartswhiletheapplianceisenergized;
HighVoltage Capacitor,PowerTransformer,Magnetron,HighVolt-
age Rectifier Assembly, High Voltage Harness;
If provided,Vent Hood, Fan assembly, Cooling Fan Motor.
Allthepartsmarked“*”onpartslistareusedatvoltagesmorethan250V.
Removal of the outer wrap gives access to voltage above 250V.
Allthe parts marked “∆”onpartslistmaycauseunduemicrowaveexpo
-
sure,bythemselves,orwhentheyaredamaged,loosenedorremoved.
MC24
Wolf Appliance, Inc
P.O. Box 44988
Madison, WI 53744-4988
Customer Care: 800.332.9513
7

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MC24
SPECIFICATION
ITEM DESCRIPTION
Power Requirements 120 Volts (USA) / 117 Volts (Canadian)
13.0 Amperes (Microwave) / 13.0 Amperes (Convection)
60 Hertz / Single phase, 3 wire grounded
Power Output 900 watts (IEC 705 Test Procedure)
Operating frequency of 2450MHz
Convection Power Output 1450 Watts
Case Dimensions Width 24-5/8" Height 14-7/8" Depth 19-1/8"
Cooking Cavity Dimensions
(1.5 Cubic Feet ) Width 16-1/8" Height 9-5/8" Depth 16-1/8"
Control Complement Touch Control with Touch Glass
Timer (0 - 99 min. 99 seconds)
Microwave Power for Variable Cooking
Repetition Rate;
P-HI........................................... Full power throughout the cooking time
P-90.............................................................. approx. 90% of Full Power
P-80.............................................................. approx. 80% of Full Power
P-70.............................................................. approx. 70% of Full Power
P-60.............................................................. approx. 60% of Full Power
P-50.............................................................. approx. 50% of Full Power
P-40............................................................... approx. 40% of Full Power
P-30 .............................................................. approx. 30% of Full Power
P-20.............................................................. approx. 20% of Full Power
P-10............................................................... approx. 10% of Full Power
P-0.............................................. No power throughout the cooking time
Convection Temperature for Variable Cooking
CONVECTION ............................................... 100 - 450οF Temp. control
MICRO BAKE.................................... 350οF with 10% microwave power
MICRO ROAST ................................. 300οF with 30% microwave power
SLOW COOK ...............................................................300οF for 4 hours
Reheat, Add Minute, Popcorn, Auto Defrost, Convec, Micro Roast, Micro
Bake, Number and temperature selections, Timer, Clock, Stop/Clear,
Power Level, Start / Quick On, Settings, Keep warm, Wolf Gourmet
Oven Cavity Light Yes
Safety Standard UL Listed FCC Authorized
DHHS Rules, CFR, Title 21, Chapter 1, Subchapter J
Canadian Standards Association.
Health CANADA, Industry CANADA.
GENERAL INFORMATION
GROUNDING INSTRUCTIONS
This oven is equipped with a three prong grounding plug. It must be plugged into a wall receptacle that is properly installed
and grounded.
In the event of an electrical short circuit, grounding reduces the risk of electric shock by providing an escape wire for the
electric current.
WARNING: Improper use of the grounding plug can result in a risk of electric shock.

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MC24
Electrical Requirements
The electrical requirements are a 115 -120 volt 60 Hz, AC only,
15 or more amp. fused electrical supply. It is recommended that a sepa-
rate circuit serving only this appliance be provided. When installing this
appliance, observe all applicable codes and ordinances.
A short power-supply cord is provided to reduce risks of becoming
entangled in or tripping over a longer cord.
Where a two-pronged wall-receptacle is encountered, it is the personal
responsibility and obligation of the customer to contact a qualified electri-
cian and have it replaced with a properly grounded three-pronged wall
receptacle or have a grounding adapter properly grounded and polar-
ized. If an extension cord must be used, it should be a 3-wire, 15 amp.
or more cord. Do not drape over a countertop or table where it can be
pulled on by children or tripped over accidentally.
CAUTION: DO NOT UNDER ANY CIRCUMSTANCES CUT OR REMOVE THE ROUND GROUNDING PRONG FROM
THIS PLUG.
OVEN DIAGRAM
1. Ventilation openings. (Rear side)
2. Oven door with see-through window.
3. Oven lamp.
4. Turntable support.
5. Removable turntable.
The turntable will rotate clockwise or
counterclockwise.
6. Safety door latches.
The oven will not operate unless the door is
securely closed.
7. Wave guide cover.
TOUCH CONTROL PANEL
8. Door open button.
9. Glass-Touch control panel.
10. Lighted digital display.
11. Convection air openings.
12. Removable low rack.
13. Removable low rack. (Baking rack)
14. Turntable motor shaft.
15. Power supply cord.
3-Pronged Plug Grounded
Receptacle Box
Grounding Pin
3-Pronged Receptacle
173
10
9
8
2
5
4
12
13
14 15
11 6
6

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MC24
OPERATION
DESCRIPTION OF OPERATING SEQUENCE
The following is a description of component functions dur-
ing oven operation.
OFF CONDITION
Closing the door activates the door sensing switch and
secondary interlock switch. (In this condition, the monitor
switch contacts are opened.)
When oven is plugged in, 117 volts A.C. is supplied to the
control unit. (Figure O-1).
1. The display will show "WELCOMETOUCH CLEAR AND
TOUCH CLOCK TO SET TIME"
To set any program or set the clock, you must first touch
the STOP/CLEAR pad. The display will clear, and " : "
will appear.
NOTE: When the door is opened, the oven lamp comes on.
2. A signal is input to the control unit, energizing the coil
of shut-off relay (RY-4). RY4 contacts close, completing
a circuit to the damper motor. The damper motor now
operates moving the damper to the open position, thereby
closing the contacts of the damper switch inputs a signal
to the control unit. The coil of relay RY-4 is de-energized,
opening its contacts, thereby turning off the damper
motor.
COOKING CONDITION
For Microwave cooking, first program the power level by
touching the POWER LEVEL pad then a number pad. (Touch
POWER LEVEL pad twice to choose high.) Then you can
enter the cooking time by touching the number pads.
For Convection cooking,touch a number pad to choose
temperature for preheat and cooking.
For either cooking method, when START pad is touched,
the following operations occur:
1. The contacts of relays are closed and components
connected to the relays are turned on as follows.
(For details, refer to Figure O-2)
RELAY CONNECTED COMPONENTS
RY-1 Oven lamp/Turntable motor
RY-2 Power transformer
RY-3 Heating element
RY-4 Damper motor
RY-5 Convevtion motor
RY-6 Fan motor
2. 117 volts A.C. is supplied to the primary winding of the
power transformer and is converted to about 3 volts A.C.
output on the filament winding, and approximately 2360
volts A.C. on the high voltage winding.
3. The filament winding voltage heats the magnetron
filament and the H.V. winding voltage is sent to a voltage
doubler circuit.
4. The microwave energy produced by the magnetron is
channelled through the waveguide into the cavity feed-
box, and then into the 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, third
door switch, monitor switch, door sensing switch, the
secondary interlock relay and the primary interlock switch
are activated with the following results. The circuits to
the turntable motor, the cooling fan motor, and the 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 relay (RY1) and the primary interlock switch and
is mechanically associated with the door so that it will
function in the following sequence.
(1) When the door opens from a closed position, the door
sensing switch and the primary interlock switch open
their contacts, and then the monitor switch contacts
close and then the third door switch contacts open.
(2) When the door is closed from the open position, the
monitor switch contacts open and the third door switch
contacts close first, and then the contacts of the primary
interlock switch and the door sensing switch close.
If the relay (RY1) and the primary interlock 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 monitor fuse, the relay (RY1) and the primary interlock
switch, causing the monitor fuse to blow.
POWER LEVEL P-0 TO P-90 COOKING
When Variable Cooking Power is programmed, the 117
volts A.C. is supplied to the power transformer intermittently
through the contacts of relay (RY-2). RY-2 is operated by the
control unit within an varying time base. Microwave power
operation is as follows:
VARI-MODE ON TIME OFF TIME
Power 10(P-HI) 32 sec. 0 sec.
(100% power)
Power 9(P-90) 30 sec. 2 sec.
(approx. 90% power)
Power 8(P-80) 26 sec. 6 sec.
(approx. 80% power)
Power 7(P-70) 24 sec. 8 sec.
(approx. 70% power)
Power 6(P-60) 22 sec. 10 sec.
(approx. 60% power)
Power 5(P-50) 18 sec. 14 sec.
(approx. 50% power)
Power 4(P-40) 16 sec. 16 sec.
(approx. 40% power)
Power 3(P-30) 12 sec. 20 sec.
(approx. 30% power)
Power 2(P-20) 8 sec. 24 sec.
(approx. 20% power)
Power 1(P-10) 6 sec. 26 sec.
(approx. 10% power)
Power 0(P-0) 0 sec. 32 sec.
(0% power)
Note: The ON/OFF time ratio does not correspond with the
percentage of microwave power, because approx. 2
seconds are needed for heating of the magnetron
filament.

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MC24
CONVECTION COOKING CONDITION
PREHEATING CONDITION
Program desired convection temperature by touching the
CONVECTION pad and the Temperature pad.
When the START pad is touched, the following operations
occur:
1. The coil of shut-off relays (RY1, RY3,RY5 and RY6) are
energized, the oven lamp, cooling fan motor, turntable
motor and convection motor are turned on.
2. The coil of relay (RY4) is energized by the control 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 control
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 control
unit and the main supply voltage is applied to the heating
element.
4. When the oven temperature reaches the selected preheat
temperature, the following operations occur:
4-1 The heater relay is de-energized by the control unit
temperature circuit and thermistor, opening the circuit
to the heating element.
4-2. The oven will continue to function for 30 minutes,
turning the heater on and off, as needed to maintain
the selected preheat temperature. The oven will
shut-down completely after 30 minutes
CONVECTION COOKING CONDITION
When the preheat temperature is reached, a beep signal
will sound indicating that the holding temperature has been
reached in the oven cavity. Open the door and place the
food to be cooked in the oven. Program desired cooking
time by touching the number pads. When the START pad
is touched, the following operations occur:
1. The numbers on the digital read-out start to count down
to zero.
2. The oven lamp, turntable motor, cooling fan motor and
convection motor are energized.
3. Heater relay (RY3) is energized (if the cavity temperature
is lower than the selected temperature) and the main
supply voltage is applied to the heating element 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 275οF, the circuit to RY6 will be maintained (by
the thermistor circuit) to continue operation of the cooling
fan motor until the temperature drops below 245οF, 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.
5. At the end of the convection cook cycle, shut-off relay
(RY4) is energized turning on the damper motor. The
damper is returned to the open position, closing the
damper switch contacts which send a signal to the control
unit, de-energizing shut-off relay (RY4).
AUTOMATIC MIX COOKING CONDITION
The Micro Roast pad (aka HIGH MIX/ROAST) is prepro-
grammed for 325°F with 10% microwave power, while the
Micro Bake pad (aka LOW MIX/BAKE) is preprogrammed
for 300°F with 30% microwave power.
Touch the MICRO ROAST or MICRO BAKE then touch
START to preheat (Touch same pad twice to change default
convection temperature.) Oven reaches preheating condi-
tions.. Open the door and place the food to be cooked in
the oven. Program desired cooking time by touching the
number pads. When the START pad is touched, the follow-
ing operations occur:
1. The power supply voltage is alternated to the heating
element and power transformer.
2. The heating element operates through the heater
relay (RY3) contacts and the power transformer
operates through the primary interlock relay (RY2)
contacts.
3. These are operated by the control unit to supply
alternately within a 32 second time base, convection
heat and microwave energy.
The relationship between the convection and microwave
power operations are as follows.
Note: The ON and OFF time ratio does not correspond
with the percentage of microwave power, because
approx. 2 seconds are needed for heating of the
magnetron filament.
Note: During alternate Microwave/Convection operation,
the convection heater is energized only if the cavity
temperature drops below the set temperature.
12 SEC. 20 SEC.
32 SEC.
LOW MIX
BAKE
HIGH MIX
ROAST
MICROWAVE POWER
= APPROX. 30%
CONVECTION
TEMPERATUE
= 300°F
MICROWAVE POWER
= APPROX. 10%
CONVECTION
TEMPERATUE
= 350°F (180°C)
26 SEC.6 SEC.
ON
ON
OFF
OFF
OFF
ON
(MICRO.)
(CONVEC.)
(MICRO.)
(CONVEC.)

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MC24
SENSOR COOKING CONDITION
Using the SENSOR COOK function, the foods are cooked
without figuring time, power level or quantity.When the oven
senses enough steam from the food, it relays the informa-
tion to its microprocessor 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.
An example of how sensor works:
1. Potatoes at room temperature.
Vapor is emitted very slowly.
2. Heat potatoes. Moisture and
humidity is emitted rapidly.
You can smell the aroma as
it cooks.
3. Sensor detects moisture
and humidity and calculates
cooking time and variable
power.
Cooking Sequence.
1. Touch SENSOR COOK pad.
NOTE: The oven should not be operated on SENSOR
COOK immediately after plugging in the unit. Wait
two minutes before cooking on SENSOR COOK.
2. Select desired Sensor setting.
3. Touch START pad.
The coil of shut-off relay (RY1, RY6) is energized, the
oven lamp and cooling fan motor are turned on, but the
power transformer is not turned on.
4. After about 16 seconds, the cook relay (RY-2) 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 vapor from
the oven cavity and sensor.
NOTE: During this first stage, do not open the door or touch
STOP/CLEAR pad.
5. When the sensor detects the vapor emitted from the
food, the display switches over to the remaining cooking
time and the timer counts down to zero. At this time, the
door may be opened to stir food, turn it or season, etc.
6. When the timer reaches zero, an audible signal sounds.
The shut-off relay and cook relay are de-energized and
the power transformer, oven lamp, etc. are turned off.
7. 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.
AUTO DEFROST COOKING
The AUTO DEFROST key is a special function key to de-
frost meats and poultry faster and better. AUTO DEFROST
automatically defrosts roast beef, etc.. When the AUTO
DEFROST is selected and the food weight is entered by
using the AUTO DEFROST pad, the oven will cook accord-
ing to the special cooking sequence.
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 dur-
ing microwave cooking.
This is accomplished by the LSI repeatedly measuring
the voltage across the temperature measurement circuit
(thermistor) during it's 32-seconds time base comparing the
obtained voltage measurements. If the most recent volt-
age measured is 300mV greater than the previous voltage
measured, the LSI judges it as a fire in the oven cavity and
switches off the relays to the power transformer, fan motor
and convection motor. The LSI also stops counting down
and closes the damper door so that no fresh air will enter
the oven cavity. Please refer to the following section for a
more detailed description.
Operation
Please refer to the timing diagrams below.
1. The thermistor operates within a 32-seconds time
base and it is energized for three (3) seconds and off
for 29 seconds. Two (2) seconds after the thermistor
is energized, the voltage across the temperature
measurement circuit is sampled by the LSI and twenty
one (21) seconds after the thermistor is cut off the LSI
turns on the cooling fan for six (6) seconds.
2. The above procedure is repeated. If the difference
between the first voltage measured (in step 1) and the
voltage measured when the procedure is repeated (step
2) is greater than 300mV the LSI makes the judgment
that there is a fire in the oven cavity and will switch
off the relays to the power transformer, fan motor and
convection motor.The LSI also stops counting down and
closes the damper door so that no fresh air will enter the
oven cavity.
3. Once the fire sensor feature has shut the unit down, the
programmed cooking cycle may be resumed by pressing
the "START" pad or the unit may be reset by pressing
the "CLEAR" pad.
IMPORTANT:
During sensor cooking operation, the fire sensing op-
eration sequence will not begin until the AH sensor has
detected vapors and initiated a sensor cooking cycle.
This is because the operation of the convection fan
would interfere with the AH sensor's vapor detection.
MICROWAVE
AH SENSOR
MICROWAVE
CONVECTION
MOTOR
THERMISTOR
Sensing
Voltage
ON
OFF
ON
OFF
ON
OFF
0 2 3 24 30 32 (sec.) 64 (sec.)
3 sec.
Sensing the voltage across temperature measurement circuit.
6 sec.

Page 12
13
MC24
Figure O-2. Oven Schematic-Microwave Cooking Condition
SCHEMATIC
NOTE: CONDITION OF OVEN
1. DOOR CLOSED.
2. COOKING TIME PROGRAMMED.
3. “START” PAD TOUCHED.
SCHEMATIC
NOTE: CONDITION OF OVEN
1. DOOR CLOSED.
2. CLOCK APPEARS ON DISPLAY.
SCHEMATIC DIAGRAM
Figure O-1. Oven Schematic-OFF Condition
CONV.
THERMAL
CUT-OUT
NOISE FILTER
MONITOR SWITCH
PRIMARY INTERLOCK SWITCH
OVEN LAMP
FAN MOTOR
A5
A3
A1
E-6
CONTROL UNIT
DAMPER
SWITCH
THER-
MISTOR
DOOR
SENSING
SWITCH AH SENSOR
DAMPER MOTOR
CONVECTION MOTOR
TURNTABLE MOTOR
0.0033µ/AC125V
0.022µ/AC250V
0.0033µ/AC125V
NOISE SUPPRESSION COIL
HEATIMG ELEMENT
MAGNETRON
POWER
TRANSFORMER
H.V. RECTIFIER
CAPACITOR
0.94µ
RY4 RY5
RY6
RY1
THIRD DOOR
SWITCH
MAGNETRON
THERMAL
CUT-OUT
OVEN
THERMAL
CUT-OUT
117V
60Hz
FM
COM.
(RY1)
E-5E-4E-3E-2E-1 F-3 F-2 F-1
RY3
SECONDARY
INTERLOCK
RERAY
N.O.
(RY1)
COM.
(RY3)
COM.
(RY2)
N.O.
(RY2)
N.O.
(RY3)
A-9
A-7
CM
DM
OL
FUSE
RY2
TTM
CONV.
THERMAL
CUT-OUT
NOISE FILTER
MONITOR SWITCH
PRIMARY INTERLOCK SWITCH
OVEN LAMP
FAN MOTOR
A5
A3
A1
E-6
CONTROL UNIT
DAMPER
SWITCH
THER-
MISTOR
DOOR
SENSING
SWITCH AH SENSOR
DAMPER MOTOR
CONVECTION MOTOR
TURNTABLE MOTOR
0.0033µ/AC125V0.0033µ/AC125V
NOISE SUPPRESSION COIL
HEATIMG ELEMENT
MAGNETRON
POWER
TRANSFORMER
H.V. RECTIFIER
CAPACITOR
0.94µ
RY4 RY5
RY6
RY1
THIRD DOOR
SWITCH
MAGNETRON
THERMAL
CUT-OUT
OVEN
THERMAL
CUT-OUT
117V
60Hz
FM
COM.
(RY1)
E-5E-4E-3E-2E-1 F-3 F-2 F-1
RY3
SECONDARY
INTERLOCK
RERAY
N.O.
(RY1)
COM.
(RY3)
COM.
(RY2)
N.O.
(RY2)
N.O.
(RY3)
A-9
A-7
CM
DM
OL
FUSE
RY2
TTM
0.022µ/AC250V

Page 13
14
MC24
SCHEMATIC
NOTE: CONDITION OF OVEN
1. DOOR CLOSED.
2. CONVECTION PAD TOUCHED.
3. DESIRED TEMP. TOUCHED.
4. COOKING TIME PROGRAMMED.
5. “START” PAD TOUCHED.
SCHEMATIC
NOTE: CONDITION OF OVEN
1. DOOR CLOSED.
2. MIX COOKING PAD TOUCHED.
3. COOKING TIME PROGRAMMED.
4. “START” PAD TOUCHED.
5. RY2 AND RY3 WILL ALTERNATELY CLOSE.
DURING COOK CYCLE.
Figure O-4. Oven Schematic-Convection Cooking Condition
Figure O-3. Oven Schematic-Automatic Mix Cooking Condition
CONV.
THERMAL
CUT-OUT
NOISE FILTER
MONITOR SWITCH
PRIMARY INTERLOCK SWITCH
OVEN LAMP
FAN MOTOR
A5
A3
A1
E-6
CONTROL UNIT
DAMPER
SWITCH
THER-
MISTOR
DOOR
SENSING
SWITCH AH SENSOR
DAMPER MOTOR
CONVECTION MOTOR
TURNTABLE MOTOR
0.0033µ/AC125V0.0033µ/AC125V
NOISE SUPPRESSION COIL
HEATIMG ELEMENT
MAGNETRON
POWER
TRANSFORMER
H.V. RECTIFIER
CAPACITOR
0.94µ
RY4 RY5
RY6
RY1
THIRD DOOR
SWITCH
MAGNETRON
THERMAL
CUT-OUT
OVEN
THERMAL
CUT-OUT
117V
60Hz
FM
COM.
(RY1)
E-5E-4E-3E-2E-1 F-3 F-2 F-1
RY3
SECONDARY
INTERLOCK
RERAY
N.O.
(RY1)
COM.
(RY3)
COM.
(RY2)
N.O.
(RY2)
N.O.
(RY3)
A-9
A-7
CM
DM
OL
FUSE
RY2
TTM
0.022µ/AC250V
CONV.
THERMAL
CUT-OUT
NOISE FILTER
MONITOR SWITCH
PRIMARY INTERLOCK SWITCH
OVEN LAMP
FAN MOTOR
A5
A3
A1
E-6
CONTROL UNIT
DAMPER
SWITCH
THER-
MISTOR
DOOR
SENSING
SWITCH AH SENSOR
DAMPER MOTOR
CONVECTION MOTOR
TURNTABLE MOTOR
0.0033µ/AC125V0.0033µ/AC125V
NOISE SUPPRESSION COIL
HEATIMG ELEMENT
MAGNETRON
POWER
TRANSFORMER
H.V. RECTIFIER
CAPACITOR
0.94µ
RY4 RY5
RY6
RY1
THIRD DOOR
SWITCH
MAGNETRON
THERMAL
CUT-OUT
OVEN
THERMAL
CUT-OUT
117V
60Hz
FM
COM.
(RY1)
E-5E-4E-3E-2E-1 F-3 F-2 F-1
RY3
SECONDARY
INTERLOCK
RERAY
N.O.
(RY1)
COM.
(RY3)
COM.
(RY2)
N.O.
(RY2)
N.O.
(RY3)
A-9
A-7
CM
DM
OL
FUSE
RY2
TTM
0.022µ/AC250V

Page 14
15
MC24
THIRD DOOR SWITCH
The switch is activated by the latch heads, while the door
is closed.When the door is opened, the switch interrupt the
circuit to the power transformer.This switch prevents power
transformer engaging and microwave when the door opened.
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 heater relay to operate, thus the current to the heating
element is turned ON/OFF.
MAGNETRON THERMAL CUT-OUT
The thermal cut-out located on the waveguide is designed to
prevent damage to the magnetron if an over heated condi-
tion develops in the magnetron due to cooling fan failure,
obstructed air guide, dirty or blocked air intake, etc.
Under normal operation, the thermal cut-out remains closed.
However, when abnormally high temperatures are reached
within the magnetron, the thermal cut-out will open at 257οF
(125οC) causing the oven to shut down. magnetron thermal
cut-out is not reset at room temperature.
OVEN THERMAL CUT-OUT
The thermal cut-out located on the side of the steam duct
is designed to prevent damage to the unit if the foods in the
oven catch fire due to over heating produced by improper
setting of cooking time or failure of control unit.
Under normal operation, the thermal cut-out remains closed.
However, when abnormally high temperatures are reached
within the oven cavity, the thermal cut-out will open at 302οF
(150οC) causing the oven to shut down.
When the thermal cut-out has cooled, the thermal cut-out
closes at 266οF (130οC)
CONV. THERMAL CUT-OUT
The thermal cut-out located on the left side of the thermal
protection plate (left) is designed to prevent damage to
the heater unit if an over heated condition develops in the
tube due to cooling fan failure, obstructed air ducts, dirty or
blocked air intake, etc.
Under normal operation, the thermal cut-out remains closed.
However, when abnormally high temperatures are reached
within the heater unit, the thermal cut-out will open at 302οF
(150οC) causing the oven to shut down.
When the thermal cut-out has cooled, the thermal cut-out
closes at 266οF (130οC)
HEATING ELEMENT
The heating element is located at the left side 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 heating element.
CONVECTION COOKING SYSTEM
This oven is designed with a hot air heating system where
food is not directly heated by the heating element, but is
heated by forced circulation of the hot air produced by the
heating element.
The air heated by the heating element is circulated through
the convection passage provided on the outer casing of the
DOOR SENSING AND PRIMARY INTERLOCK
SWITCHES
The door sensing switch in the secondary interlock system
is mounted in the upper position on the latch hook, the pri-
mary interlock switch is mounted in the lower position on
the latch hook.They are activated by the latch heads on the
door. When the door is opened, the switches interrupt the
circuit to all components. A cook cycle cannot take place
until the door is firmly closed thereby activating both interlock
switches. The secondary interlock system consists of the
door sensing switch and secondary interlock relay located
on the control circuit board.
DESCRIPTION AND FUNCTION OF COMPONENTS
Figure D-1. Door sensing switch, monitor switch, third
door switch and primary interlock switch
MONITOR SWITCH
The monitor switch is mounted on the middle position of latch
hook. It is activated (the contacts opened) by the lower latch
head while the door is closed.The switch is intended to render
the oven inoperative by means of blowing the monitor fuse
when the contacts of the relay RY1 and primary interlock
switch fail to open when the door is opened.
Functions:
1. When the door is opened, the monitor switch contact close
(to the ON condition) due to their being normally closed.
At this time the door sensing and primary interlock and
third door switches are in the OFF condition (contacts
open) due to their being normally open contact switches.
2. As the door goes to a closed position, the monitor switch
contacts are first opened and then the door sensing
switch, third door switch and the primary interlock switch
contacts close. (On opening the door, each of these
switches operate inversely.)
3. If the door is opened, and the relay RY1 and the primary
interlock switch contacts fail to open, the monitor fuse
blows simultaneously with closing of the monitor switch
contacts.
CAUTION: BEFORE REPLACING A BLOWN MONITOR
FUSE TEST THE DOOR SENSING SWITCH,
PRIMARY INTERLOCK SWITCH, RELAY(RY1)
AND MONITOR SWITCH FOR PROPER
OPERATION. (REFER TO CHAPTER “TEST
PROCEDURE”).
NOTE: MONITOR FUSE AND MONITOR SWITCH ARE
REPLACED AS AN ASSEMBLY.
LATCH HOOK
LATCH
HEADS
DOOR SENSING
SWITCH
MONITOR SWITCH
PRIMARY
INTERLOCK SWITCH
SWITCH LEVER
OPEN LEVER
DOOR OPEN
BUTTON
THIRD DOOR SWITCH

Page 15
16
MC24
TROUBLESHOOTING GUIDE
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 Procedure”section.
IMPORTANT: If the oven becomes inoperative because of a blown monitor fuse, check the monitor switch, relay (RY1),
door sensing switch and primary interlock switch before replacing the monitor fuse.If monitor fuse is replaced,
the mintor switch must also be replaced at the same time. Use part FFS-BA012WRK0 as an assembly.
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 center of the
oven cavity left side wall.
Without leaving the oven, this hot air is reheated by the
heating element, passes through the convection passage
and enters the inside of the oven cavity again, in a continu-
ing 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 heating element is de-energized.
When the temperature inside the oven cavity drops below
the selected temperature, the heating element 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 heating element
is de-energized and the convection fan stops operating and
the oven shuts off.
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 opera-
tion is selected by the control unit.
Microwave Cooking:
Damper is in the open position, because a portion of cooling
air is channelled 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
condensation 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:
1-1. 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.
1-3. When the damper is moved to the open position by
the damper cam the damper switch is closed (ON
position).
1-4. The signal from damper switch is re-sensed in the
control unit and shut-off relay (RY4) is turned off.
1-5. The 120 volts A.C. to the damper motor is removed
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. Damper motor is energized by touching the
convection, temperature and START pads.
3-2. 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.
3-3. The damper is held in the closed position during the
convection cooking operation.
3-4. 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
DAMPER DUCT
DAMPER
DAMPER CAM
DAMPER MOTOR
DAMPER SWITCH
DAMPER SHAFT

Page 16
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MC24
A MAGNETRON
B POWER TRANSFORMER
C H.V. RECTIFIER ASSEMBLY
D HIGH VOLTAGE CAPACITOR
E PRIMARY INTERLOCK SWITCH
F SECONDARY INTERLOCK SYSTEM
G MONITOR SWITCH
H MONITOR FUSE
I OVEN THERMAL CUT-OUT
I CONVECTION CUT-OUT
J CONVECTION HEATER
K THERMISTOR
L DAMPER MOTOR
M DAMPER SWITCH
N TOUCH CONTROL PANEL
O NOISE FILTER
P RELAY RY-1
P RELAY RY-2
P RELAY RY-3
P RELAY RY-4
P RELAY RY-5
P RELAY RY-6
Q AUTO DEFROST
Replace OVEN LAMP OR SOCKET
Replace FAN MOTOR
Replace TURNTABLE MOTOR
Replace CONVECTION MOTOR
Check LOOSE WIRING
Check SHORTED IN POWER CORD
Check NO POWER AT OUTLET
Check LOW VOLTAGE
R AH SENSOR
TEST PROCEDURE
POSSIBLE CAUSE
AND
DEFECTIVE PARTS
Home fuse blows when power cord is plugged into wall receptacle. Monitor fuse blows when power cord is plugged into wall receptacle 88:88 does not appear in display when power cord is first plugged
into wall receptacle.
Display does not operate properly when STOP/CLEAR pad is touched.
(The time of day should appear on the display with beep sound.)
Oven lamp does not light with door opened. Oven lamp does not light in cook cycle. (It light when door is opened). Cooking cycle runs 1 minute then shuts down. Oven lamp light, but turntable motor does not operate. Turntable motor operates normally but cooling fan motor does not
operate.
Oven does not go into a cook cycle, when START pad is touched. Low or no power is produced during microwave cooking (The food is
heated incompletely or not heated at all)
Extremely uneven heating is produced in oven load (food). Function of variable cooking does not operate properly except HIGH
power.
Function of AUTO DEFROST does not operate properly. CONV indicator lights, but oven does not go into cook cycle when
START pad is touched.
CONV indicator lights, but heating element does not heat. Temperature in the oven cavity is lower or higher than preset. Cooling fan motor runs intermittently or all the time. Convection cycle runs 4 minutes and 15 seconds then shuts down. Oven in the sensor cooking condition but AH sensor does not end or
AH sensor turns off about max. 30 min. after start.
PROBLEM
CONDITION OFF CONDITION COOKING CONDITION (MICROWAVE) (CONVECTION)
(SENSOR
COOKING)

Page 17
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MC24
TEST PROCEDURES
PROCEDURE
LETTER COMPONENT TEST
HIGH VOLTAGES ARE PRESENT DURING THE COOK CYCLE, SO EXTREME CAUTION SHOULD
BE OBSERVED.
DISCHARGE THE HIGH VOLTAGE CAPACITOR BEFORE TOUCHING ANY OVEN COMPONENTS
OR WIRING.
To test for an open filament, isolate the magnetron from the high voltage circuit. A continuity check
across the magnetron filament leads should indicate less than 1 ohm.
To test for a shorted magnetron, connect the ohmmeter leads between the magnetron filament leads
and chassis ground. This test should indicate an infinite resistance. If there is little or no resistance the
magnetron is grounded and must be replaced.
Power output of the magnetron can be measured by performing a water temperature rise test. This
test should only be used if above tests do not indicate a faulty magnetron and there is no defect in the
following components or wiring: silicon rectifier, high voltage capacitor and power transformer. This test
will require a 16 ounce (453cc) measuring cup and an accurate mercury thermometer or thermocouple
type temperature tester. For accurate results, the following procedure must be followed carefully:
1. Fill the measuring cup with 16 oz. (453cc) of tap water and measure the temperature of the water
with a thermometer or thermocouple temperature tester. Stir the thermometer or thermocouple
through the water until the temperature stabilizes. Record the temperature of the water.
2. Place the cup of water in the oven. Operate oven at POWER HI(HIGH) selecting more than 60
seconds cook time. Allow the water to heat for 60 seconds, measuring with a stop watch, second
hand of a watch or the digital read-out countdown.
3. Remove the cup from the oven and again measure the temperature, making sure to stir the
thermometer or thermocouple through the water until the maximum temperature is recorded.
4. Subtract the cold water temperature from the hot water temperature. The normal result should be
22 to 43οF(12.2 to 23.8οC) rise in temperature. If the water temperatures are accurately measured
and tested for the required time period the test results will indicate if the magnetron tube has low
power output (low rise in water temperature) which would extend cooking time or high power output
(high rise in water temperature) which would reduce cooking time. Because cooking time can be
adjusted to compensate for power output, the magnetron tube assembly should be replaced only if
the water temperature rise test indicates a power output well beyond the normal limits. The test is
only accurate if the power supply line voltage is 117 volts and the oven cavity is clean.
A MAGNETRON ASSEMBLY TEST
B POWER TRANSFORMER TEST
DISCHARGE THE HIGH VOLTAGE CAPACITOR BEFORE TOUCHING ANY OVEN COMPONENTS
OR WIRING.
Disconnect the primary input terminals and measure the resistance of the transformer with an ohmmeter.
Check for continuity of the coils with an ohmmeter. On the R x 1 scale, the resistance of the primary
coil should be less than 1 ohm and the resistance of the high voltage coil should be approximately 84.4
ohms; the resistance of the filament coil should be less than 1 ohm.
(HIGH VOLTAGES ARE PRESENT AT THE HIGH VOLTAGE TERMINAL, SO DO NOT ATTEMPT TO
MEASURE THE FILAMENT AND HIGH VOLTAGE.)
C HIGH VOLTAGE RECTIFIER TEST
DISCHARGE THE HIGH VOLTAGE CAPACITOR BEFORE TOUCHING ANY OVEN COMPONENTS
OR WIRING.
Isolate the rectifier from the circuit. Using the highest ohm scale of the meter, read the resistance across
the terminals and observe, reverse the leads to the rectifier terminals and observe meter reading. If a
short is indicated in both directions, or if an infinite resistance is read in both directions, the rectifier is
probably defective and should be replaced.
D HIGH VOLTAGE CAPACITOR TEST
DISCHARGE THE HIGH VOLTAGE CAPACITOR BEFORE TOUCHING ANY OVEN COMPONENTS
OR WIRING.

Page 18
19
MC24
If the capacitor is open, no high voltage will be available to the magnetron. Disconnect input leads and
check for short or open between the terminals using an ohmmeter.
Checking with a high ohm scale, if the high voltage capacitor is normal, the meter will indicate conti-
nuity for a short time and should indicate approximately 10 MΩonce the capacitor is charged. If the
above is not the case, check the capacitor with an ohmmeter to see if it is shorted between either of
the terminals and case. If it is shorted, replace the capacitor.
E PRIMARY INTERLOCK SWITCH AND THIRD DOOR SWITCH TEST
Isolate the switch and connect the ohmmeter to the common (COM.) and normally open (NO) terminal
of the switch. The meter should indicated an open circuit with the door open and a closed circuit with
the door closed. If improper operation is indicated, replace the switch.
F SECONDARY INTERLOCK SYSTEM TEST
DOOR SENSING SWITCH
Isolate the switch and connect the ohmmeter to the common (COM.) and normally open (NO) terminal
of the switch. The meter should indicated an open circuit with the door open and a closed circuit with
the door closed. If improper operation is indicated, replace the door sensing switch.
SECONDARY INTERLOCK RELAY
Disconnect two (2) wire leads from the tab terminal of the secondary interlock relay (RY2). Check the
state of the relay contacts using a ohmmeter. The relay contacts should be open. If the relay contacts
are closed, replace the circuit board entirely or the relay itself.
G MONITOR SWITCH
Disconnect the oven from power supply.
Before performing this test, make sure that the primary interlock switch and the secondary interlock
relay are operating properly, according to the above Test Procedures. Disconnect the wire lead from the
monitor switch (NC) terminal. Check the monitor switch operation by using the ohmmeter as follows.
When the door is open, the meter should indicate a closed circuit. When the monitor switch actuator
is pushed by a screw driver through the lower latch hole on the front plate of the oven cavity with the
door opened (in this condition the plunger of the monitor switch is pushed in), the meter should indi-
cate an open circuit. If improper operation is indicated, the switch may be defective. After testing the
monitor switch, re-connect the wire lead to the monitor switch (NC) terminal and check for continuity
of monitor circuit.
H BLOWN MONITOR FUSE
If the monitor fuse is blown when the door is opened, check the primary interlock switch, door sensing
switch relay (RY1) and monitor switch according to the "TEST PROCEDURE" for those switches before
replacing the blown monitor fuse.
CAUTION: IF THE MONITOR FUSE IS BLOWN BY IMPROPER SWITCH OPERATION, THE MONI-
TOR FUSE AND SWITCH MUST BE REPLACED WITH "MONITOR FUSE AND SWITCH
ASSEMBLY" PART NUMBER FFS-BA012WRK0, EVEN IF THE MONITOR SWITCH OP-
ERATES NORMALLY.THE MONITOR FUSE AND SWITCH ASSEMBLY IS PACKED WITH
20 AMPERE FUSE AND SWITCH.
I OVEN THERMAL CUT-OUT (on the side of steam duct)
A continuity check across the thermal cut-out terminals should indicate a closed circuit unless the tem-
perature of the oven thermal cut-out reaches approximately 302οF (150οC). The thermal cut-out reset
automatically at approximately 266οF (130οC). If the thermal cut-out has operated under the normal
condition, replace the thermal cut-out. An open thermal cut-out indicates overheating of the oven cavity.
TEST PROCEDURES
PROCEDURE
LETTER COMPONENT TEST
SCREW DRIVER
MONITOR SWITCH
OHMMETER
PRIMARY
INTERLOCK
SWITCH
COM.
N.C.

Page 19
20
MC24
Disconnect connector-E from the control unit. Measure the resistance of the thermistor with an ohm-
meter. Connect the ohmmeter leads to Pin No’s E-3 and E-4.
K THERMISTOR TEST
L DAMPER MOTOR TEST
If the meter does not indicate above resistance, replace the thermistor
Room Temperature Resistance
68οF(20οC) - 86οF(30οC) Approx. 350kΩ- 155KΩ
When the power cord is plugged into the wall receptacle and 117 volts A.C. is supplied to the damper
motor, the motor operates until the damper is opened and the damper switch closes. Then the damper
motor stops operation.
If the damper motor does not operate, check for A.C. voltage with a voltmeter at the motor.
1. Disconnect the power cord from the wall receptacle.
2. Disconnect the wire leads of motor and connect the meter leads to the wire leads of main wire
harness.
3. Re-connect the power cord into the wall receptacle.
If 117 volts A.C. is indicated at the wire leads, replace the motor and if 117 volts A.C. is not indicated,
check the wire harness and control unit.
Disconnect the wire leads from the switch terminals and connect ohmmeter leads to the common
(COM.) and normally open (N.O.) terminals of the switch.
1. When switch actuator is pushed by the damper motor cam, the meter should be indicated a closed
circuit.
2. When power cord is plugged into the wall receptacle, the damper motor operates and damper cam
will start to rotate. When the switch actuator is released, the meter should be indicated an open
circuit. If improper operation is indicated, replace the damper switch.
M DAMPER SWITCH TEST
TEST PROCEDURES
PROCEDURE
LETTER COMPONENT TEST
MAGNETRON THERMAL CUT-OUT (on the waveguide)
A continuity check across the thermal cut-out terminals should indicate a closed circuit unless the
temperature of the thermal cut-out reaches approximately 257οF (125οC).
An open thermal cut-out indicates overheating of the magnetron. Check for restricted air flow to the
magnetron through the vent holes of the oven cavity, especially the cooling duct and cooling fan.
CAUTION: IF THE THERMAL CUT-OUT INDICATES OPEN CIRCUIT AT ROOM TEMPERATURE,
REPLACE THE THERMAL CUT-OUT.
CONVECTION CUT-OUT (on side of the heater duct)
A continuity check across the thermal cut-out terminals should indicate a closed circuit unless the
temperature of thermal cut-out reaches 302οF (150οC). The thermal cut-out resets automatically at
approximately 266οF (130οC). If the thermal cut-out has operated under the normal condition, re-
place the thermal cut-out. An open thermal cut-out indicates overheating of heater unit, check for
restricted air flow to the heater unit through the vent hole of the oven cavity, especially the heater
duct and convection fan.
J HEATING ELEMENT TEST
Make sure the heating element is fully cooled and test as follows;
a. Disconnect wire leads and measure the resistance with an ohmmeter. On the R x 1 scale, the
resistance between the heating element terminals should be approximately 10.2Ω.
b. Disconnect wire leads and measure the insulation resistance with 500V - 100MΩinsulation resistance
meter. The insulation resistance between heating element terminal and cavity should be more than
0.5MΩ.

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CHECKING TEMPERATURE IN THE CONVECTION MODE
N TOUCH CONTROL/TOUCH GLASS TEST
TEST PROCEDURES
PROCEDURE
LETTER COMPONENT TEST
It is difficult to measure the exact temperature in the convection oven. An accurate thermocouple type
temperature tester must be used. A low priced bi-metal type thermometer is not reliable or accurate.
The temperature should be checked with outer case cabinet installed, approx. 5 minutes after preheat
temperature is reached (audible signal sounds four times). The temperature experienced may be ap-
prox. 30οF more or less than indicated on the display, however, in most cases the food cooking results
will be satisfactory.
Difference in power supply voltage will also affect the oven temperature. The Household power supply
voltage may sometimes become lower than the rated voltage (117 V) and cause under-cooking. If the
power supply voltage is 10% lower than the rated voltage, longer cooking time is required by 10% to 20%.
1. Key Unit.
Please note that key unit is projected capacitive touch technology.Touching the keyglass surface
changes a key pad sensor's local electric field to activate a key action. The amount of finger
flesh's needed to trigger key activation is ~10mm diameter surface contact to the glass surface.
You should not press hard to active a key; only a light touch is needed to change the pad's local
electric field.
a) Run the oven and check all functions.
The following symptoms indicate a defective key unit.
b) When lightly touching a fingertip to any pad and one or more keys do not respond.
c) When lightly touching a fingertip to any pad and only nearby keys respond.
d) When any pad only responds when touch with excessive flesh like a large thumb (more than
20mm diameter of surface contact to the glass surface).
2. Control Unit
The following symptoms indicate a defective control unit.
2-1 In connection with pads.
a) when touch any keypad and there is no key response. Check if key cable is unplugged between
control unit and key unit. Check if key cable end is fully seating into the key unit's connector.
2-2 In connection with indicators
a) At a certain digit, all or some segments do not light up.
b) At a certain digit, brightness is low.
c) Only one indicator does not light.
d) The corresponding segments of all digits do not light up; or they continue to light up.
e) Wrong figure appears.
f) A certain group of indicators do not light up.
g) The figure of all digits flicker.
2-3 Other possible problems 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.
3. If the Key unit or the Control unit is defective.
1) Disconnect the power supply cord, and then remove outer case.
2) Open the door and block it open.
3) Discharge high voltage capacitor.
4) Replace the Control unit assembly.
5) Reconnect all leads removed from components during testing.
6) Re-install the outer case (cabinet).
7) Reconnect the power supply cord after the outer case is installed.
8) Run the oven and check all functions.