SHARP R-426HS, R-426HK, R-426HW Service Manual

SER VICE MANUAL

S13M203R426HE

MICROWAVE OVEN

R-426HS R-426HK R-426HW

MODELS

R-426HS R-426HK R-426HW

R-426HS

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 ............................................................................................................................................11

TOUCH CONTROL PANEL..................................................................................................................................22

COMPONENT REPLACEMENT AND ADJUSTMENT PROCEDURE ..................................................................28

PICTORIAL DIAGRAM ........................................................................................................................................35

CPU UNIT CIRCUIT.............................................................................................................................................36

PRINTED WIRING BOARD .................................................................................................................................37

PARTS LIST........................................................................................................................................................38

PACKING AND ACCESSORIES .........................................................................................................................42

SHARP ELECTRONCS CORPORATION

Service Headquarters: Sharp Plaza, Mahwah, New Jersey, 07430-2135

This document has been published to be used for after sales service only. The contents are subject to change without notice.

R-426HS R-426HK R-426HW

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.

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 SERVICE 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-426HS R-426HK R-426HW

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 operated 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.

R-426HS R-426HK R-426HW

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 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±5

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.

SERVICE MANUAL

R-426HS R-426HK R-426HW

MICROWAVE OVEN

R-426HS/R-426HK/R-426HW

FOREWORD

This Manual has been prepared to provide Sharp Electronics Corp. Service Personnel with Operation and Service Information for the SHARP MICROWAVE OVENS, R-426HS, R-426HK & R-426HW.

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.

PRODUCT DESCRIPTION

GENERAL INFORMATION

OPERATION

TROUBLESHOOTING GUIDE AND TEST PROCEDURE

TOUCH CONTROL PANEL

COMPONENT REPLACEMENT AND ADJUSTMENT PROCEDURE

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.

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.

WIRING DIAGRAM

PARTS LIST

SHARP ELECTRONICS CORPORATION

SHARP PLAZA, MAHWAH,

NEW JERSEY 07430-2135

R-426HS R-426HK R-426HW

SPECIFICATION

ITEM DESCRIPTION

Power Requirements 120 Volts

14.3 Amperes, 1700 watts 60 Hertz Single phase, 3 wire grounded

Power Output 1200 watts (IEC 705 TEST PROCEDURE)

Operating frequency of 2450MHz

Case Dimensions Width 21-21/32"

Height 12-3/8" Depth 18-7/16"

Cooking Cavity Dimensions Width 15-23/32"

Height 9-21/32"

1.6 Cubic Feet Depth 17-7/8" Control Complement Touch Control System

Clock ( 1:00 - 12:59 ) 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

Keep warm plus pad, Sensor cook pads, Reheat pads, Number selection pads, Power Level pad, Timer/Clock pad,Stop/Clear pad, Hot Water and Custom help.

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 contact

a qualified electrician and have it replaced with a properly grounded

3-Pronged Plug

Grounded Receptacle Box

Grounding Pin

3-Pronged Receptacle

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. 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.Wave guide cover.

11.Power supply cord

TOUCH CONTROL PANEL

R-426HS R-426HK R-426HW

NOTE: The directed features are disabled after one minute 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.

R-426HS/HK/HW

R-426HS R-426HK R-426HW

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 flashing:

"SHARP SIMPLY THE BEST....".

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 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)

the primary interlock switch and secondary interlock relay 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 C/T fuse, primary interlock switch, relay (RY1) and secondary interlock relay (RY2), causing the C/T 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 (RY-2) which is operated by the control unit within a 32 second time base. Microwave power operation is as follows:

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 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 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

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.

SENSOR COOKING CONDITION

Using the SENSOR function, 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 increase 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.

R-426HS R-426HK R-426HW

2. The coil of shut-off relay (RY-1) is energized, the turntable 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 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 the day will reappear on the display and the oven will revert to an OFF condition. When the timer reaches zero, an audible signal sounds.

MICR

OWAVE

2.Heat Potatoes. Moisture and humidity is emitted very 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. Touch one of the SENSOR pads. NOTE: The oven should not be operated on sensor

immediately after plugging in the unit. Wait two minutes before cooking on SENSOR.

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SCHEMATIC

NOTE: CONDITION OF OVEN

1. Door Closed

2. CLOCK APPEARS ON DISPLAY

RED

N.O.

C/T FUSE

(RY1)

OVEN LAMP RELAY

ORG ORG

N.O.

COM.

GRY

120VAC 60Hz

CAVITY TEMPERATURE FUSE

RED

GRN

GND

WHT

Note:* Indicates component

COM.

TURN TABLE MOTOR

ORG

RED

DOOR SENSING SWITCH

HUMIDITY

ORG

WHT

ORG

WHT

BRN

WHT

GRY

ORG

SECONDARY INTERLOCK RELAY

CONTROL UNIT

OVEN LAMP

COM.

PRIMARY INTERLOCK SWITCH

(RY2)

N.O.

WHT

BRN

TTM

WHT

SENSOR

FAN MOTOR

MONITOR SWITCH

WHT

N.C.

COM.

WHT

RED

WHT

POWER TRANSFORMER

HIGH VOLTAGE CAPACITOR

HIGH VOLTAGE RECTIFIER

MAGNETRON

Figure O-1 Oven Schematic - Off Condition

SCHEMATIC

NOTE: CONDITION OF OVEN

1. DOOR CLOSED

2. COOKING TIME PROGRAMMED

3. VARIABLE COOKING CONTROL "HIGH"

4. "START" PAD TOUCHED

RED

N.O.

C/T FUSE

(RY1)

OVEN LAMP RELAY

ORG ORG

BRN

ORG

N.O.

(RY2)

SECONDARY INTERLOCK RELAY

ORG

WHT

CONTROL UNIT

OVEN LAMP

COM.

GRY

PRIMARY INTERLOCK SWITCH

COM.

GRY

120VAC 60Hz

CAVITY TEMPERATURE FUSE

RED

GRN

GND

WHT

N.O.

WHT

TTM

BRN

WHT

COM.

TURN TABLE MOTOR

ORG

RED

ORG

WHT

DOOR SENSING SWITCH

HUMIDITY

SENSOR

FAN MOTOR

MONITOR SWITCH

WHT

COM.

WHT

N.C.

RED

WHT

POWER TRANSFORMER

HIGH VOLTAGE CAPACITOR

HIGH VOLTAGE RECTIFIER

MAGNETRON

Figure O-2 Oven Schematic - Cooking Condition

DESCRIPTION AND FUNCTION OF COMPONENTS

R-426HS R-426HK R-426HW

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

Switch Lever

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 C/T 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 C/T fuse blows simultaneously with closing of the monitor switch contacts.

CAUTION: BEFORE REPLACING A BLOWN C/T 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: C/T 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 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.

CAVITY TEMPERATURE FUSE

The cavity temperature fuse 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 cavity temperature fuse will open. Under normal operation, the cavity temperature fuse remains closed. However, when abnormally high temperatures are reached within the oven cavity, the cavity temperature fuse will open at 302OF(150OC) causing the oven to shut down. NOTE: This is fuse. It does not reset.

C/T TEMPERATURE FUSE

The C/T 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 C/T fuse remains closed. However, when abnormally high temperatures are reached within the magnetron, the C/T fuse will open at 302OF(150OC) causing the oven to shut down.

1. The C/T 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.

NOTE: This is fuse. It does not reset.

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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 C/T fuse, check the monitor switch, relay (RY1) secondary

interlock relay (RY2), door sensing switch and primary interlock switch before replacing the C/T fuse. If the C/T fuse is replaced, the monitor switch must also be replaced. Use part FFS-BA019/KIT 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 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.

CK = Check / RE = Replace

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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

C/T fuse blows when power cord is plugged into wall receptacle.

All letters and 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 P50 mode. (Operates properly on Cooking P-HI (HIGH) 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

ABCDEEF FG H

SHORT IN POWER CORD

SHORT OR OPENED WIRING

MAGNETRON

POWER TRANSFORMER

H.V. RECTIFIER ASSEMBLY

RE RE CKICK CK CK

HIGH VOLTAGE CAPACITOR

CAVITY TEMPERATURE FUSE

C/T FUSE

SECONDARY INTERLOCK SYSTEM

PRIMARY INTERLOCK SWITCH

MONITOR SWITCH

C/T FUSE

OVEN LAMP OR SOCKET

COOLING FAN MOTOR

TURNTABLE MOTOR

TOUCH CONTROL PANEL

WRONG OPERATION

LOW VOLTAGE

DIRTY OVEN CAVITY

J K L M N

KEY UNIT

RELAY (RY1)

COMPU DEFROST

FOIL PATTERN ON PWB.

AH SENSOR

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 high voltage capacitor.

TEST PROCEDURES

COMPONENT TEST

R-426HS R-426HK R-426HW

TEST PROCEDURES

PROCEDURE

LETTER

COMPONENT TEST

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:

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 10(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 38 to 78OF(21O to 42.6OC) 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 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 90 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.

(HIGH VOLTAGES ARE PRESENT AT THE HIGH VOLTAGE TERMINAL, SO DO NOT ATTEMPT TO MEASURE THE FILAMENT AND HIGH VOLTAGE.)

TEST PROCEDURES

R-426HS R-426HK R-426HW

PROCEDURE

LETTER

C HIGH VOLTAGE RECTIFIER TEST

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. 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.

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.

NOTE: Be sure to use an ohmmeter that will supply a forward bias voltage of more than 6.3 volts.

D HIGH VOLTAGE CAPACITOR TEST

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. 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 continuity for a short time and should indicate an open circuit once 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.

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.

COMPONENT TEST

E CAVITY TEMPERATURE FUSE TEST

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. A continuity check across the cavity temperature fuse terminals should indicate a closed circuit unless the temperature of the cavity temperature fuse reaches approximately 302OF(150OC). An open cavity temperature fuse indicates overheating of the oven, exchange the cavity temperature fuse and check inside of oven cavity and for improper setting of cooking time or operation of control unit. Check for restricted air flow through the vent holes of the oven cavity, especially the cooling fan and air guide.

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.

C/T FUSE TEST

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. A continuity check across the C/T fuse terminals should indicate a closed circuit unless the temperature of the C/T fuse reaches approximately 302OF(150OC). An open C/T fuse indicates overheating of the magnetron. Check for restricted air flow to the magnetron, especially the cooling fan air guide.

CAUTION: IF THE TEMPERATURE FUSE INDICATES AN OPEN CIRCUIT AT ROOM

TEMPERATURE, REPLACE TEMPERATURE FUSE.

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