SHARP R-370EK, R-370ES Service Manual
R-370EK
R-370ES
SERVICE MANUAL
S4112R370EPS/
MICROWAVE OVEN
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MODELS
R-370EK
R-370ES
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.
WARNING TO SERVICE PERSONNEL: Microwave ovens contain circuitry capable of producing very high voltage and
current, contact with following parts may result in a severe,
possibly fatal, electrical shock. (High Voltage Capacitor, High
Voltage Power Transformer, Magnetron, High Voltage Rectifier Assembly, High Voltage Harness etc..)
TABLE OF CONTENTS
Page
PRECAUTIONS TO BE OBSERVED BEFORE AND DURING SERVICING TO
AVOID POSSIBLE EXPOSURE TO EXCESSIVE MICROWAVE ENERGY...................INSIDE FRONT COVER
BEFORE SERVICING ......................................................................................................INSIDE FRONT COVER
WARNING TO SERVICE PERSONNEL................................................................................................................1
MICROWAVE MEASUREMENT PROCEDURE ...................................................................................................2
FOREWORD AND WARNING...............................................................................................................................3
PRODUCT SPECIFICATIONS ..............................................................................................................................4
GENERAL INFORMATION...................................................................................................................................4
OPERATION..........................................................................................................................................................6
TROUBLESHOOTING GUIDE ............................................................................................................................10
TEST PROCEDURE............................................................................................................................................12
TOUCH CONTROL PANEL.................................................................................................................................21
COMPONENT REPLACEMENT AND ADJUSTMENT PROCEDURE................................................................26
PICTORIAL DIAGRAM ........................................................................................................................................33
POWER UNIT CIRCUIT ......................................................................................................................................34
CPU UNIT CIRCUIT ............................................................................................................................................35
PRINTED WIRING BOARD .................................................................................................................................36
PARTS LIST ........................................................................................................................................................37
PACKING AND ACCESSORIES .........................................................................................................................39
SHARP CORPORATION
This document has been published to be used for after
sales service only.
The contents are subject to change without notice.
R-370EK
R-370ES
PRECAUTIONS TO BE OBSER VED BEFORE AND
DURING SERVICING T O AVOID POSSIBLE
EXPOSURE TO EXCESSIVE MICROW A VE
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
compartments, 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
Measurement Procedure outlined in this service manual.
If microwave emissions level is in excess of the specified limit, contact SHARP ELECTRONICS
CORPORATION immediately @1-800-237-4277.
If the unit operates with the door open, service person should 1) tell the user not to operate the oven
and 2) contact SHARP ELECTRONICS CORPORATION and Food and Drug Administration's
Center for Devices and Radiological Health immediately.
Service personnel should inform SHARP ELECTRONICS CORPORATION 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.
W ARNING TO SER VICE PERSONNEL
Microwave ovens contain circuitry capable of producing very high voltage and current, contact with
following parts
fatal, electrical shock.
(Example)
High Voltage Capacitor, High Voltage Power Trans-
former, Magnetron, High Voltage Rectifier Assembly, High Voltage Harness etc..
Read the Service Manual carefully and follow all
instructions.
may result in a severe, possibly
Don't Touch !
Danger High Voltage
R-370EK
R-370ES
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 highvoltage capacitor (that is the connecting lead of the highvoltage 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 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 a microwave leakage test should be carried out.
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R-370EK
R-370ES
MICROWAVE MEASUREMENT PROCEDURE
A. Requirements:
1) Microwave leakage limit (Power density limit): The power density of microwave radiation emitted by a microwave oven
should not exceed 1mW/cm2 at 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/cm2 at any point 5cm or more from the external
surface of the oven.
2) Safety interlock switches
Primary interlock 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/cm
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±5˚C (68˚F) 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.
2
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.
NOTE: After servicing, record data on service invoice and microwave leakage report.
2
SERVICE MANUAL
R-370EK
R-370ES
MICROWAVE OVEN
R-370EK/ R-370ES
FOREWORD
This Manual has been prepared to provide Sharp Electronics Corp.
Service Personnel with Operation and Service Information for the
SHARP MICROWAVE OVEN, R-370EK, R-370ES.
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 - Do not contact the following parts while the
appliance is energized;
High Voltage Capacitor, Power Transformer, Magnetron, High
Voltage Rectifier Assembly, High Voltage Harness;
If provided, Vent Hood, Fan assembly, Cooling Fan Motor.
PRODUCT DESCRIPTION
GENERAL INFORMATION
OPERATION
TROUBLESHOOTING GUIDE AND
TEST PROCEDURE
TOUCH CONTROL PANEL
COMPONENT REPLACEMENT
AND ADJUSTMENT PROCEDURE
WIRING DIAGRAM
PARTS LIST
All the parts marked “*” on parts list are used at voltages more than
250V.
Removal of the outer wrap gives access to voltage above 250V.
All the parts marked “∆” on parts list may cause undue microwave
exposure, by themselves, or when they are damaged, loosened
or removed.
SHARP ELECTRONICS CORPORATION
SHARP PLAZA, MAHWAH,
NEW JERSEY 07430-2135
3
R-370EK
R-370ES
SPECIFICATION
ITEM DESCRIPTION
Power Requirements 120 Volts / 13.5 Amperes
60 Hertz
Single phase, 3 wire grounded
Power Output 1000 watts (IEC TEST PROCEDURE)
Operating frequency of 2450MHz
Case Dimensions Width 17-1/4"
Height 13-3/8"
Depth 18-3/8"
Cooking Cavity Dimensions Width 13-3/4"
Height 7-1/4"
1.4 Cubic Feet Depth 16-1/2"
Control Complement Touch Control System
Clock ( 1:00 - 12:59 )
Timer (0 - 99 min. 99 seconds)
Microwave Power for Variable Cooking
Repetition Rate;
HIGH................................................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
SENSOR COOKING pads , INSTANT ACTION pads
COMPU DEFROST pads, Number selection pads
CUSTOM HELP PAD, POWER LEVEL pad,
KITCHEN TIMER/CLOCK pad
STOP/CLEAR pad, MINUTE PLUS /START pad
Oven Cavity Light Yes
Safety Standard UL Listed FCC Authorized
DHHS Rules, CFR, Title 21, Chapter 1, Subchapter J
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 accordance with the National Electrical Code and local codes and ordinances.
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.
Electrical Requirements
The electrical requirements are a 120 volt 60 Hz, AC only,
15 or 20 amp. fused electrical supply. It is recommended that a separate 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
4
R-370EK
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12
7
5
3
2
1
9
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8
13
6
10
R-370ES
contact a qualified electrician and have it replaced with a properly
grounded three-pronged wall receptacle or have a grounding adapter
properly grounded and polarized. If the extension cord must be used, it
should be a 3-wire, 15 amp. or higher rated 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 RE-
MOVE THE ROUND GROUNDING PRONG FROM THIS
PLUG.
OVEN DIAGRAM
1. Door handle
Pull to open door.
2. Auto-Touch control panel
3. Display: 99 minutes, 99 seconds
4. Oven door with see-through window
5. Safety door latch
The oven will not operate unless the door is
securely closed.
6. Door hinges
7. Door seals and sealing surface
8. Turntable motor shaft
9. Removable turntable support
Carefully place the turntable support in the center
of the oven floor.
10.Removable turntable
Place the turntable on the turntable support
cecurely. The turntable will rotate clockwise or
counterclockwise. Only remove for cleaning.
11.Ventilation openings (Rear)
12.Oven light
It will light when oven is operating or door is
opened.
13.Wave guide cover: DO NOT REMOVE.
3-Pronged Plug
Grounding Pin
3-Pronged Receptacle
Grounded
Receptacle Box
TOUCH CONTROL PANEL
Baked
Popcorn
Reheat
Sensor
Potatoes
Ground
Meat
Fresh
Vegetables
Frozen
Vegetables
Rice
Chicken
Breast
Frozen
Entree
Fish
Seafood
Rolls &
Muffins
Beverage
Compu
Defrost
Kitchen Timer
Clock
COOK SENSOR LBS DEF HELP
12345
67890
Power
Level
STOP
Clear
Custom
Help
Minute Plus
START
NOTE:
The directed features are disabled after three minutes when the oven is not in use. These features are
automatically enabled when the door is opened and closed or the STOP/ CLEAR pad is pressed.
5
R-370EK
R-370ES
OPERATION
DESCRIPTION OF OPERATING SEQUENCE
The following is a description of component functions during
oven operation.
OFF CONDITION
Closing the door activates the door sensing switch and
primary interlock switch. (In this condition, the monitor
switch contacts are opened.)
When oven is plugged in, 120 volts A.C. is supplied to the
control unit. (Figure O-1).
1. The display will show "SHARP SIMPLY THE BEST
PRESS CLEAR AND PRESS CLOCK".To set any
program or set the clock, you must first touch the STOP/
CLEAR pad. The display will clear, and " : " will appear.
COOKING CONDITION
Program desired cooking time by touching the NUMBER
pads. Program the power level by touching 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 the relays are turned on as follows.
(For details, refer to Figure O-2)
RELAY CONNECTED COMPONENTS
RY-1 oven lamp/turntable motor/fan motor
RY-2 power transformer
2. 120 volts A.C. is supplied to the primary winding of the
power transformer and is converted to about 3.4 volts
A.C. output on the filament winding, and approximately
2300 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 feedbox, 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, the
monitor switch, door sensing switch, primary interlock
switch, relay (RY1) and secondary interlock relay (RY2)
are activated with the following results. The circuits to the
turntable motor, the cooling fan motors, 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 electrically monitors the operation of
the primary interlock switch and secondary interlock
relay (RY2) and is mechanically associated with the door
so that it will function in the following sequence.
(1) When the door opens from the closed position, the
secondary interlock relay (RY2) and primary interlock
switch open their contacts. And contacts of the relay
(RY1) remains closed. Then the monitor switch contacts
close.
(2) When the door is closed from the open position, the
monitor switch contacts open first. Then the contacts of
the primary interlock switch and door sensing switch
close. And contacts of the relay (RY1) open.
If the primary interlock switch and secondary interlock relay
(RY2) fail with the contacts closed when the door is opened,
the closing of the monitor switch contacts will form a short
circuit through the monitor fuse, primary interlock switch,
relay (RY1) and secondary interlock relay (RY2), causing
the monitor fuse to blow.
POWER LEVEL P-0 TO P-90 COOKING
When Variable Cooking Power is programmed, the 120
volts A.C. is supplied to the power transformer intermittently
through the contacts of relay (RY2) which is operated by the
control unit within a 32 second time base. Microwave power
operation is as follows:
VARI-MODE DISPLAY ON TIME OFF TIME
100% HIGH 32 sec. 0 sec.
approx. 90% power P-90 30 sec. 2 sec.
approx. 80% power P-80 26 sec. 6 sec.
approx. 70% power P-70 24 sec. 8 sec.
approx. 60% power P-60 22 sec. 10 sec.
approx. 50% power P-50 18 sec. 14 sec.
approx. 40% power P-40 16 sec. 16 sec.
approx. 30% power P-30 12 sec. 20 sec.
approx. 20% power P-20 8 sec. 24 sec.
approx. 10% power P-10 6 sec. 26 sec.
0% power P-0 0 sec. 32 sec.
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.
POWER OUTPUT REDUCTION
If the oven is set for more than 30 minutes at 80, 90 or 100%
power level, after the first 30 minutes the power level will
automatically adjust itself to 70% power to avoid overcooking.
SENSOR COOKING CONDITION
Using the SENSOR function, the food is cooked without
figuring time, power level or quantity. When the oven senses
enough steam from the food, it relays the information to its
microprocessor which will calculate the remaining cooking
time and power level needed for best results. When the food
6
R-370EK
R-370ES
is cooked, water vapor is developed. The sensor “senses”
the vapor 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: (POTATOES)
1. Potates at room temperature. Vapor is emitted very
slowly.
MICROWAVE
2. Heat Potates. Moisture and humidity is emitted rapidly.
You can smell the aroma as it cooks.
AH SENSOR
MICROWAVE
3. Sensor detects moisture and humidity and calculates
cooking time and variable power.
Cooking Sequence.
1. Operate the oven in sensor cooking mode by referring to
the operation manual.
NOTE: The oven should not be operated on SENSOR
immediately after plugging in the unit. Wait two
minutes before cooking on SENSOR.
2. The coil of shut-off relay (RY-1) is energized, the turntable
motor, oven lamp and cooling fan motors are turned on,
but the power transformer is not turned on.
3. 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.
4. 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, turn, or
season food.
5. 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.
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
R-370EK
R-370ES
SCHEMATIC
NOTE: CONDITION OF OVEN
1. DOOR CLOSED
2. CLOCK APPEARS ON DISPLAY
NOTE: " " indicates components with potential above 250V.
AH SENSOR
OVEN THERMAL
CUT-OUT
OVEN LAMP
RELAY
(RY1)
OL
COM.
MG. THERMAL CUT-OUT
CONTROL UNIT
OVEN
LAMP
TTM
PRIMARY
INTERLOCK
SWITCH
TURNTABLE
MOTOR
120V AC
60 Hz
GRN
MONITOR
FUSE 20A
N.O.
Figure O-1. Oven Schematic-Off Condition
SCHEMATIC
NOTE: CONDITION OF OVEN
1. DOOR CLOSED
2. COOKING TIME PROGRAMMED
3. VARIABLE COOKING CONTROL "P-HI" (100%)
4. "START" PAD TOUCHED
POWER
MONITOR
SWITCH
TRANSFORMER
CAPACITOR
0.94µF
AC 2200V
RECTIFIER
FM
FAN
MOTOR
N.O.
COM.
FM
FAN
MOTOR
F2
F3
SECONDARY
INTERLOCK
RELAY
B2 B1
DOOR
SENSING
SWITCH
F1
(RY2)
NOTE: " " indicates components with potential above 250V.
MAGNETRON
120V AC
60 Hz
GRN
MONITOR
FUSE 20A
N.O.
OVEN THERMAL
CUT-OUT
OVEN LAMP
RELAY
(RY1)
OL
COM.
AH SENSOR
MG. THERMAL CUT-OUT
CONTROL UNIT
OVEN
LAMP
PRIMARY
INTERLOCK
SWITCH
TTM
TURNTABLE
MOTOR
FM
FAN
MOTOR
N.O.
COM.
FM
FAN
MOTOR
F2
F3
SECONDARY
INTERLOCK
RELAY
B2 B1
DOOR
SENSING
SWITCH
F1
(RY2)
Figure O-2. Oven Schematic-Cooking Condition
MONITOR
SWITCH
POWER
TRANSFORMER
CAPACITOR
0.94µF
AC 2200V
RECTIFIER
MAGNETRON
8
DESCRIPTION AND FUNCTION OF COMPONENTS
R-370EK
R-370ES
DOOR OPEN MECHANISM
The door is opened by pulling the door. Refer to the Figure
D-1.
Door
Latch
Heads
Latch Hook
Door Sensing
Switch
Monitor Switch
Primary
Interlock Switch
Figure D-1. Door Open Mechanism
DOOR SENSING AND PRIMARY INTERLOCK
SWITCHES
The primary interlock switch is mounted in the lower position
of the latch hook and the door sensing switch in the
secondary interlock system is mounted in the upper position
of the latch hook. They are activated by the latch heads on
the door. When the door is opened, the switches interrupt
the power to all high voltage 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.
MONITOR SWITCH
The monitor switch is activated (the contacts opened) by the
latch head on the door 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 secondary interlock relay (RY2) 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 secondary interlock relay (RY2)
and primary interlock switch 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 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 secondary interlock relay
(RY2) and 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,
SECONDARY INTERLOCK RELAY (RY2),
RELAY (RY1), PRIMARY INTERLOCK
SWITCH AND MONITOR SWITCH FOR
PROPER OPERATION. (REFER TO CHAPTER "TEST PROCEDURE").
NOTE: MONITOR FUSE AND MONITOR SWITCH ARE
REPLACED AS AN ASSEMBLY.
TURNTABLE MOTOR
The turntable motor rotates the turntable located on the
bottom of the oven cavity, so that the foods on the turntable
cook evenly during cooking. The turntable may turn in either
direction.
COOLING FAN MOTOR
The cooling 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 vapors given off from the heating foods. It is then
exhausted through the exhausting air vents at the oven
cavity.
MONITOR FUSE
1. The monitor fuse blows when the contacts (COM-NO) of
the secondary interlock relay (RY2) and primary interlock
switch remain closed with the oven door open and when
the monitor switch closes.
2. If the wire harness or electrical components are shortcircuited, this monitor fuse blows to prevent an electric
shock or fire hazard.
OVEN THERMAL CUT-OUT
The thermal cut-out, located on the top of the oven cavity, is
designed to prevent damage to the oven by fire. If the food
load is overcooked, by either error in cook time or defect in
the control unit, the thermal cut-out will open.
Under normal operation, the oven thermal cut-out remains
closed. However, when abnormally high temperatures are
reached within the oven cavity, the oven thermal cut-out will
open at 257˚F(125˚C), causing the oven to shut down.
MAGNETRON THERMAL CUT-OUT
The thermal cut-out located near the magnetron is designed
to prevent damage to the magnetron if an over heated
condition develops in the tube 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
257˚F(125˚C) causing the oven to shut down.
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TROUBLESHOOTING GUIDE
Never touch any part in the circuit with your hand or an uninsulated tool while the power supply is connected.
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)
secondary interlock relay (RY2), door sensing switch and primary interlock switch before replacing the
monitor fuse. If the monitor fuse is replaced, the monitor switch must also be replaced. Use part FFSBA023WRK0 as an assembly.
IMPORTANT: Whenever troubleshooting is performed with the power supply cord disconnected. It may, in some cases,
be necessary to connect the power supply cord 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 all leads removed from components during testing.
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.
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CK = Check / RE = Replace
CONDITION
OFF
CONDITION
COOKING
CONDITION
SENSOR
COOKING
CONDITION
TEST PROCEDURE
AND
POSSIBLE CAUSE
DEFECTIVE PARTS
PROBLEM
Home fuse or circuit breaker blows
when power cord is plugged into wall
receptacle.
Monitor fuse blows when power cord
is plugged into wall receptacle.
Any letters or indicators do not appear in display when power cord is
first plugged into wall outlet.
Display does not operate properly
when STOP/CLEAR key is touched.
(Buzzer should sound and ":" or time
of day should appear in display.)
Oven lamp does not light when door is
opened.
Oven lamp does not go out when door
is closed.
Oven lamp lights but fan motor and
turntable motor do not operate.
Oven does not go into cook cycle
when START pad is touched
Oven seems to be operating but little
or no heat is produced in oven load.
(Food incompletely cooked or not
cooked at all at end of cook cycle.)
Oven goes into a cook cycle but extremely uneven heating is produced
in oven load (food).
Oven does not cook properly when
programmed for Cooking Power P-50
mode. (Operates properly on Cooking Power HIGH (100%) mode.)
Oven goes into COMPU DEFROST
but food is not defrosted well.
AH sensor does not end during sensor cooking condition. (Oven does
not shut off after a cup of water is
boiling by sensor cooking.)
Oven stops at 16 sec. after starting.
RE RE
ABCDEFFGH
SHORT IN POWER CORD
SHORT OR OPENED WIRING
MAGNETRON
POWER TRANSFORMER
H.V. RECTIFIER ASSEMBLY
RERE
HIGH VOLTAGE CAPACITOR
THERMAL CUT-OUT
SECONDARY INTERLOCK SYSTEM
PRIMARY INTERLOCK SWITCH
MONITOR SWITCH
MONITOR FUSE
OVEN LAMP
CKICK CKCK
COOLING FAN MOTOR
TURNTABLE MOTOR
CONTROL UNIT
WRONG OPERATION
LOW VOLTAGE
DIRTY OVEN CAVITY
JKLMN
KEY UNIT
RELAY (RY1)
COMPU DEFROST
FOIL PATTERN ON PWB.
AH SENSOR
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TEST PROCEDURES
PROCEDURE
LETTER
A MAGNETRON ASSEMBLY TEST
1. Disconnect the power supply cord, and then remove outer case.
2. Open the door and block it open.
3. Discharge the high voltage capacitor.
4. 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.
5. 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.
6. Reconnect all leads removed from components during testing.
7. Reinstall the outer case (cabinet).
8. Reconnect the power supply cord after the outer case is installed.
9. Run the oven and check all functions.
MICROWAVE OUTPUT POWER
The following test procedure should be carried out with the microwave oven in a fully assembled
condition (outer case fitted).
HIGH VOLTAGES ARE PRESENT DURING THE COOK CYCLE, SO EXTREME CAUTION SHOULD
BE OBSERVED.
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:
COMPONENT TEST
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 P-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 30.7
to 57.1˚F(17.1 to 31.7˚C) 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 120 volts and the oven cavity is clean.
B POWER TRANSFORMER TEST
1. Disconnect the power supply cord, and then remove outer case.
2. Open the door and block it open.
3. Discharge the high voltage capacitor.
4. 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 85 ohms; the resistance of the filament coil should be less than 1 ohm.
5. Reconnect all leads removed from components during testing.
6. Reinstall the outer case (cabinet).
7. Reconnect the power supply cord after the outer case is installed.
8. Run the oven and check all functions.
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