SHARP R-420LK, R-420LW Service Manual
R-420LW
SERVICE MANUAL
S6603R420LPW/
MICROWAVE OVEN
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..)
CONTENTS
PRECAUTIONS TO BE OBSERVED BEFORE AND
DURING SERVICING TO AVOID POSSIBLE EXPOSURE TO EXCESSIVE MICROWAVE ENERGY
CHAPTER 1. WARNING TO SERVICE PERSONNEL
CHAPTER 2. MICROWAVE MEASUREMENT PROCEDURE
CHAPTER 3. FOREWORD AND WARNING
MODELS
R-420LK
R-420LW
CHAPTER 8. TEST PROCEDURES
CHAPTER 9. TOUCH CONTROL PANEL ASSEMBLY
CHAPTER 10. PRECAUTIONS FOR USING LEADFREE SOLDER
CHAPTER 11. COMPONENT REPLACEMENT AND
ADJUSTMENT PROCEDURE
CHAPTER 4. PRODUCT DESCRIPTION
CHAPTER 5. GENERAL INFORMATION
CHAPTER 6. OPERATION
CHAPTER 7. TROUBLESHOOTING GUIDE
SHARP CORPORATION
CHAPTER 12. CIRCUIT DIAGRAMS
Parts List
This document has been published to be used
for after sales service only.
The contents are subject to change without notice.
CONTENTS
PRECAUTIONS TO BE OBSERVED BEFORE AND
DURING SERVICING TO AVOID POSSIBLE EXPOSURE TO EXCESSIVE MICROWAVE ENERGY
CHAPTER 1. WARNING TO SERVICE PERSONNEL
[1] Before Servicing .........................................1-1
[2] When the testing is completed, ..................1-1
[3] After repairing .............................................1-1
CHAPTER 2. MICROWAVE MEASUREMENT PROCEDURE
[1] Requirements: ............................................2-1
[2] Preparation for testing: ...............................2-1
[3] Leakage test: ..............................................2-1
CHAPTER 3. FOREWORD AND WARNING
[1] FOREWORD ..............................................3-1
[2] WARNING ..................................................3-1
[3] DANGER ....................................................3-1
CHAPTER 4. PRODUCT DESCRIPTION
[1] SPECIFICATIONS ......................................4-1
CHAPTER 5. GENERAL INFORMATION
[1] GROUNDING INSTRUCTIONS .................5-1
[2] OVEN DIAGRAM........................................5-1
CHAPTER 6. OPERATION
[1] DESCRIPTION OF OPERATING SE-
QUENCE ...................................................6-1
[2] OVEN SCHEMATIC ...................................6-2
[3] DESCRIPTION AND FUNCTION OF
COMPONENTS..........................................6-3
CHAPTER 7. TROUBLESHOOTING GUIDE
[1] TROUBLESHOOTING CHART .................7-1
CHAPTER 8. TEST PROCEDURES
[1] Procedure A: MAGNETRON ASSEMBLY
TEST ..........................................................8-1
[2] Procedure B: POWER TRANSFORMER
TEST ..........................................................8-1
[3] Procedure C: HIGH VOLTAGE RECTIFI-
ER TEST ....................................................8-1
[4] Procedure D: HIGH VOLTAGE CAPACI-
TOR TEST..................................................8-2
[5] Procedure E: TEMPERATURE FUSE OR
THERMAL CUT-OUT TEST .......................8-2
[6] Procedure F: PRIMARY INTERLOCK
SWITCH TEST ...........................................8-2
[7] Procedure F: SECONDARY INTERLOCK
SYSTEM TEST...........................................8-3
[8] Procedure G: MONITOR SWITCH TEST.....8-3
[9] Procedure H: BLOWN MONITOR FUSE
TEST ..........................................................8-3
[10] Procedure I: NOISE FILTER TEST.............8-4
[11] Procedure J: TOUCH CONTROL PANEL
ASSEMBLY TEST ......................................8-4
[12] Procedure K: KEY UNIT TEST...................8-5
[13] Procedure L: RELAY TEST ........................8-5
[14] Procedure M: DEFROST TEST.................. 8-6
[15] Procedure N: FOIL PATTERN ON THE
PRINTED WIRING BOARD TEST.............. 8-6
[16] Procedure O: AH SENSOR TEST .............. 8-7
CHAPTER 9. TOUCH CONTROL PANEL ASSEMBLY
[1] OUTLINE OF TOUCH CONTROL PANEL ..... 9-1
[2] ABSOLUTE HUMIDITY SENSOR CIR-
CUIT ........................................................... 9-1
[3] SERVICING FOR TOUCH CONTROL
PANEL ........................................................ 9-2
CHAPTER 10. PRECAUTIONS FOR USING LEADFREE SOLDER
[1] Employing lead-free solder ....................... 10-1
[2] Using lead-free wire solder ....................... 10-1
[3] Soldering................................................... 10-1
CHAPTER 11. COMPONENT REPLACEMENT AND
ADJUSTMENT PROCEDURE
[1] WARNINGS ...............................................11-1
[2] OUTER CASE REMOVAL .........................11-1
[3] POWER TRANSFORMER REMOVAL...... 11-2
[4] HIGH VOLTAGE RECTIFIER AND HIGH
VOLTAGE CAPACITOR REMOVAL ..........11-2
[5] MAGNETRON REMOVAL .........................11-2
[6] OVEN LAMP REMOVAL............................11-3
[7] POSITIVE LOCK CONNECTOR (NO-
CASE TYPE) REMOVAL ...........................11-3
[8] CONTROL PANEL ASSEMBLY REMOV-
AL ..............................................................11-3
[9] GRAPHIC SHEET AND MEMBRANE
SWITCH REPLACEMENT......................... 11-3
[10] TURNTABLE MOTOR REMOVAL .............11-4
[11] COOLING FAN MOTOR REMOVAL..........11-4
[12] DOOR SENSING SWITCH/PRIMARY IN-
TERLOCK SWITCH AND MONITOR
SWITCH REMOVAL ..................................11-4
[13] DOOR SENSING SWITCH/PRIMARY IN-
TERLOCK SWITCH AND MONITOR
SWITCH ADJUSTMENT ...........................11-5
[14] DOOR REPLACEMENT ............................11-5
CHAPTER 12. CIRCUIT DIAGRAMS
[1] Pictorial Diagram (Figure S-1) .................. 12-1
[2] Control Panel Circuit (Figure S-2)............. 12-2
[3] Printed Wiring Board (Figure S-3) ............ 12-3
Parts List
R420LW
R420LW
PRECAUTIONS TO BE OBSERVED BEFORE AND DURING SERVICING TO AVOID
Service Manual
POSSIBLE EXPOSURE TO EXCESSIVE MICROWAVE ENERGY
PRECAUTIONS TO BE OBSERVED BEFORE AND DURING 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
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.
BEFOR SERVICING
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/cm . The owner of the unit should be instructed not to use the unit
until the oven has been brought into compliance.
2
i
R420LW
R420LW
CHAPTER 1. 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.
(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.
Service Manual
Don't Touch !
Danger High Voltage
[1] 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) 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.
[2] 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.
[3] 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 microwave leakage test should be carried out.
1 – 1
R420LW
R420LW
CHAPTER 2. MICROWAVE MEASUREMENT PROCEDURE
Service Manual
[1] Requirements:
1. Microwave leakage limit (Power density limit): The power density of microwave radiation emitted by a microwave oven should not exceed 1mW/
2
cm
at any point 5cm or more from the external surface of the oven, measured prior to acquisition by a purchaser, and thereafter (through the use-
ful life of the oven), 5 mW/cm
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
the oven.
2
at any point 5cm or more from the external surface of the oven.
2
at any point 5cm or more from the external surface of
[2] 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±5 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.
[3] 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.
2
4. Measure carefully at the point of highest leakage and make sure that the highest leakage is no greater than 4mW/cm
interlock relay and the primary interlock switch do turn the oven OFF before any door movement.
NOTE: After servicing, record data on service invoice and microwave leakage report.
, and that the secondary
2 – 1
R420LW
R420LW
CHAPTER 3. FOREWORD AND WARNING
Service Manual
[1] FOREWORD
This Manual has been prepared to provide Sharp Electronics Corp. Service Personnel with Operation and Service Information for the SHARP
MICROWAVE OVEN, R-420LK and R-420LW.
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.
[2] 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.
[3] 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.
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.
3 – 1
R420LW
CHAPTER 4. PRODUCT DESCRIPTION
Service Manual
[1] SPECIFICATIONS
ITEM DESCRIPTION
Power Requirements
Power Consumption 1600W / Approx. 13.5 Amperes
Power Output
Outside Dimensions
Cooking Cavity Dimensions
(1.4 Cubic feet)
Control Complement
120 Volts
60 Hertz
Single phase, 3 wire grounded
1100 W nominal of RF microwave energy (IEC Test procedure)
Operating frequency 2450 MHz
Width 21-5/8" (550mm)
Height 12-3/8" (315mm)
Depth 17-1/2" (445mm)
Width 15-3/8" (392mm) NOTE: Internal capacity is calculated by measuring
Height 9-3/8" (236.7mm) maximum width, depth and height.
Depth 16-3/4" (427mm) Actual capacity for holding food is less.
Touch Control System
Clock (1:00 - 12:59)
Timer (0 - 99 minutes 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. 30% of FULL Power
P-30 -------------------- approx. 40% 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
R420LW
CUSTOM HELP pad
HOT WATER pad
SENSOR REHEAT pad
KEEP WARM PLUS pad
SENSOR COOK pads
Defrost pads
Reheat pads
Number selection pads
Power Level pad
Timer/Clock pad
Stop/Clear pad
START/MINUTE PLUS pad
Oven Cavity Light Yes
Safety Standard
UL listed FCC Authorized
DHHS Rules, CFR, Title 21, Chapter 1, Subchapter J
4 – 1
R420LW
3-Pronged
Plug
Grounded
Receptacle Box
Grounding Pin
3-Pronged Receptacle
R420LW
CHAPTER 5. GENERAL INFORMATION
Service Manual
[1] 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:
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 wallreceptacle is encountered, it is the personal responsibility and obligation of the customer to 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 REMOVE THE ROUND
Improper use of the grounding plug can result in a risk of electric shock.
GROUNDING PRONG FROM THIS PLUG.
[2] OVEN DIAGRAM
1. OVEN
1. One touch door open button.
Push to open door.
2. Door latches.
The oven will not operate unless the door is securely closed.
3. Removable turntable support
4. Removable turntable.
The turntable will rotate clockwise or counterclockwise.
5. Oven lamp.
It will light when oven is operating or door is opened.
6. Oven door with see-through window
7. Ventilation openings. (Rear)
8. Auto-Touch control panel.
9. Time display: Digital display, 99 minutes, 99 seconds.
10.Waveguide cover:
6
2
3
7
11
5
9
8
10
1
4
11.Power supply cord.
2. TOUCH CONTROL PANEL
NOTE: Some one-touch cooking features such as “MINUTE
PLUS” 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 – 1
R420LW
CHAPTER 6. OPERATION
[1] DESCRIPTION OF OPERATING SEQUENCE
The following is a description of component functions during oven operation.
R420LW
Service Manual
1. 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 “ENJOY YOUR OVEN 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.
2. COOKING CONDITION
Program desired cooking time by touching the NUMBER pads. Program the power level by touching the POWERLEVEL pad and then a
Number 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 3.3 volts A.C. output on the filament winding, and approximately 2370 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, the monitor witch,
door sensing switch, primary interlock switch, relay (RY1) and secondary interlock relay 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 electrically monitors the operation of the primary interlock switch and secondary interlock relay and is mechanically associated with the door so that it will function in the following
sequence.
a) 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.
b) 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.
3. 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 (RY-2) which is operated by the control unit within a 32 second
time base. Microwave power operation is as follows:
VARI-MODE ON TIME OFF TIME
P-HI (100% power) 32 sec. 0 sec.
P-90 (approx. 90% power) 30 sec. 2 sec.
P-80 (approx. 80% power) 26 sec. 6 sec.
P-70 (approx. 70% power) 24 sec. 8 sec.
P-60 (approx. 60% power) 22 sec. 10 sec.
P-50 (approx. 50% power) 18 sec. 14 sec.
P-40 (approx. 40% power) 16 sec. 16 sec.
P-30 (approx. 30% power) 12 sec. 20 sec.
P-20 (approx. 20% power) 8 sec. 24 sec.
P-10 (approx. 10% power) 6 sec. 26 sec.
P-0 (0% power) 0 sec. 32 sec.
NOTE: The ON/OFF time ratio does not correspond with the per-
centage of microwave power, because approx. 3 seconds
are needed for heating of the magnetron filament.
4. POWER OUTPUT REDUCTION
After 80%, 90% or 100% power cooking mode is carried out for more
than 30 minutes, the power out-put is automatically reduced to 70%.
5. SENSOR COOKING CONDITION
Using the SENSOR unction, 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 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. Potatoes at room temperature. Vapor is emitted very slowly.
MICROWAVE
2. Heat potatoes. Moisture and humidity is emitted rapidly. You can
smell the aroma as it cooks.;
6 – 1
R420LW
AH SENSOR
3. Sensor detects moisture and humidity and calculates cooking time
and variable power.
5.1. 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.
MICROWAVE
[2] OVEN SCHEMATIC
1. Off Condition
2. The coil of shut-off relay (RY-1) is energized, the turntable motor,
oven lamp and cooling fan motor 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 shutoff 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.
SCHEMATIC
NOTE: CONDITION OF OVEN
1. DOOR CLOSED
2. CLOCK APPEARS ON DISPLAY
120VAC
60Hz
N
OVE
THERMA
NOISE
FILTER
"TO LOAD"
C2
C3
"TO LOAD"
"TO SOURCE"
BLK
H
N
WHT
MONITOR
GRN
GND
C1: LINE CROSS CAPACITOR ------- 0.22uF/ AC250V
C2, C3: LINE BYPASS CAPACITOR ------ 0.033uF/ AC250V
FUSE (20A)
C1
"TO SOURCE"
L
CUT-O
UT
MAGNETRON
RAT
E
P
TEM
FUSE
(RY1)
OVEN LAMP
RELAY
RE
U
NOTE: " " indicates components with potentials above 250V
B2
B1
TTM
F-3
F-2
TURN
TAB LE
MOTOR
F-1
FAN
FM
MOTOR
(RY2)
SECONDARY
INTERLOCK
RELAY
CONTROL UNIT
OVEN
OL
LAMP
COM.
PRIMARY INTERLOCK
SWITCH
N.O.
Figure O-1. Oven Schematic-Off Condition
DOOR
SENSING
SWITCH
AH SENSOR
MONITOR
SWITCH
COM.
N.C.
POWER TRANSFORMER
HIGH
VOLTAGE
CAPACITOR
0.94uF/ AC2200V
HIGH
VOLTAGE
RECTIFIER
MAGNETRON
6 – 2
2. Cooking Condition
M
AGNET
RON
SCHEMATIC
NOTE: CONDITION OF OVEN
1. DOOR CLOSED.
2. COOKING TIME PROGRAMMED.
3. VARIABLE COOKING CONTROL "P-HI".
4. START PAD TOUCHED.
OV
THERMAL CUT
NOISE
FILTER
"TO LOAD"
C2
C3
"TO LOAD"
120VAC
60Hz
"TO SOURCE"
BLK
H
N
WHT
MONITOR
GRN
GND
C1: LINE CROSS CAPACITOR ------- 0.22uF/ AC250V
C2, C3: LINE BYPASS CAPACITOR ------ 0.033uF/ AC250V
FUSE (20A)
C1
"TO SOURCE"
R420LW
N
E
-OUT
RATURE
MPE
TE
USE
F
(RY1)
OVEN LAMP
RELAY
(RY2)
SECONDARY
INTERLOCK
RELAY
CONTROL UNIT
OVEN
OL
LAMP
COM.
PRIMARY INTERLOCK
SWITCH
N.O.
TTM
TURN
TAB LE
MOTOR
B2
DOOR
SENSING
SWITCH
B1
F-3
F-2
FAN
MOTOR
AH SENSOR
MONITOR
SWITCH
COM.
N.C.
F-1
FM
POWER TRANSFORMER
HIGH
VOLTAGE
CAPACITOR
0.94uF/ AC2200V
HIGH
VOLTAGE
RECTIFIER
MAGNETRON
Figure O-2. Oven Schematic-Cooking Condition
[3] DESCRIPTION AND FUNCTION OF COMPONENTS
1. DOOR OPEN MECHANISM
The door is opened by pushing the open button on the control panel,
refer to the Figure D-1. When the open button is pushed, the open button pushes up the switch lever, and then the switch lever pushes up
the latch head. The latch heads are moved upward and released from
latch hook. Now the door will open.
Latch Heads
Door Sensing
Switch
Monitor Switch
Door
Switch Lever
Primary Interlock
Switch
Figure D-1. Door Open Mechanism.
2. 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 there by activating both interlock switches.
The secondary interlock system consists of the door sensing switch
and secondary interlock relay located on the control circuit board.
3. 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 MONITORFUSE TEST
THE DOOR SENSING SWITCH, SECONDARY INTERLOCK RELAY (RY2), RE-LAY (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.
6 – 3
R420LW
4. 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.
5. 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 channeled 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.
6. 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 cutout 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
293°F(145°C), causing the oven to shut down.
7. MAGNETRON TEMPERATURE FUSE
The magnetron temperature fuse 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
magnetron temperature fuse remains closed. However, when abnormally high temperatures are reached within the magnetron, the magnetron temperature fuse will open at 302°F(150°C) causing the oven
to shut down.
NOTE: This is a fuse. It does not reset.
8. MONITOR FUSE
1) The monitor fuse blows when the contacts (COM-NO) of the primary interlock relay (RY2) and secondary interlock switch remain
closed with the oven door open and when the monitor switch
closes.
2) If the wire harness or electrical components are short-circuited, this
monitor fuse blows to prevent an electric shock or fire hazard.
9. NOISE FILER
The noise filter prevents the radio frequency interference that might
flow back in the power circuit.
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