SHARP KWK Service Manual

R21LTF

SERVICE MANUAL

S7606R21LTFP/

LIGHT DUTY COMMERCIAL

MICROWAVE OVEN

1000W

-21L T

MODELS

R-21LTF

MME

MICR

VEN

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

BEFORE SERVICING

CHAPTER 1. WARNING TO SERVICE PERSONNEL

CHAPTER 2. MICROWAVE MEASUREMENT PROCEDURE

CHAPTER 3. FOREWORD AND WARNING

CHAPTER 4. PRODUCT DESCRIPTION

CHAPTER 5. GENERAL INFORMATION

R-21LVF

CHAPTER 7. TROUBLESHOOTING GUIDE

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 12. CIRCUIT DIAGRAMS

Parts List

CHAPTER 6. OPERATION

SHARP CORPORATION

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 SCHENATIC....................................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: THERMAL CUT OUT TEST.....8-2

[6] Procedure F: SECONDARY INTERLOCK

SWITCH TEST ...........................................8-2

[7] Procedure F: PRIMARY INTERLOCK

SYSTEM TEST...........................................8-3

[8] Procedure G: MONITOR SWITCH TEST.....8-3

[9] Procedure H: BLOWN MINITOR 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 ........................8-6

[14] Procedure M: FOIL PATTERN ON THE

PRINTED WIRING BOARD TEST.............. 8-6

CHAPTER 9. TOUCH CONTROL PANEL ASSEMBLY

[1] OUTLINE OF TOUCH CONTROL PANEL ..... 9-1

[2] SERVICING FOR TOUCH CONTROL

PANEL ........................................................ 9-1

[3] PROCEDURE FOR CHECKING/CLEAR-

ING SERVICE COUNTS OF MICRO-

WAVE OVEN .............................................. 9-2

[4] OTHER SETTING AND CHECKING PRO-

CEDURE..................................................... 9-3

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] WARNING..................................................11-1

[2] OUTER CASE REMOVAL .........................11-1

[3] POWER TRANSFORMER REMOVAL......11-2

[4] HIGH VOLTAGE RECTIFIER ASSEMBLY

AND HIGH VOLTAGE CAPACITOR RE-

MOVAL ......................................................11-2

[5] MAGNETRON REMOVAL .........................11-2

[6] CONTROL PANEL ASSEMBLY REMOV-

AL ..............................................................11-2

[7] OVEN LAMP AND LAMP SOCKET RE-

MOVAL ......................................................11-3

[8] POSITIVE LOCK CONNECTOR (NO-

CASE TYPE) REMOVAL .......................

[9] ANTENNA MOTOR REMOVAL .................11-3

[10] COOLING FAN MOTOR REMOVAL..........11-3

[11] POWER SUPPLY CORD REPLACE-

MENT.........................................................11-4

[12] DOOR SENSING SWITCH/SECONDARY

INTERLOCK SWITCH AND MONITOR

SWITCH REMOVAL ..................................11-4

[13] DOOR SENSING SWITCH/SECONDARY

INTERLOCK SWITCH AND MONITOR

SWITCH ADJUSTMENT ...........................11-5

[14] DOOR PARTS REMOVAL .........................11-5

[15] ANTENNA MOTOR SHAFT REPLACE-

MENT.........................................................11-6

[16] INSTALLATION OF CERAMIC SHELF......11-8

CHAPTER 12. CIRCUIT DIAGRAMS

[1] Pictorial Diagram (Figure S-1) .................. 12-1

[2] Control Panel Circuit (Figure S-2a and S-

2b)............................................................. 12-2

[3] Printed Wiring Board (Figure S-3) ............ 12-4

Parts List

....11-3

R21LTF

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.

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.

R21LTF

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 shortcircuit the connection of the high-voltage capacitor (that is the connecting lead of the high-voltage rectifier) against the chassis with the use of an insulated screwdriver.

Whenever troubleshooting is performed the power supply must be disconnected. It may, in some cases, be necessary to connect the power supply after the outer case has been removed, in this event,

1) Disconnect the power supply cord, and then remove outer case.

2) Open the door and block it open.

3) Discharge high voltage capacitor.

4) Disconnect the leads to the primary of the power transformer.

5) Ensure that the leads remain isolated from other components and oven chassis by using insulation tape.

6) After that procedure, reconnect the power supply cord.

[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

R21LTF

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/ cm

2 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 relay and door sensing switch shall prevent microwave radiation emission in excess of the requirement as above mentioned, secondary interlock switch shall prevent microwave radiation emission in excess of 5 mW/cm the external surface of the oven.

at any point 5cm or more from the external surface of the oven.

at any point 5cm or more from

[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.

4. Measure carefully at the point of highest leakage and make sure that the highest leakage is no greater than 4mW/cm interlock switch and the primary interlock relay 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

R21LTF

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-21LTF and R-21LVF.

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.

(D) The door is not deformed or warped.

(E) There is not any other visible damage with the oven.

Servicing and repair work must be carried out only by trained service 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

R21LTF

CHAPTER 4. PRODUCT DESCRIPTION

[1] SPECIFICATIONS

ITEM DESCRIPTION

120 Volts

Power Requirements

Power Output

Outer Case Dimensions

Cooking Cavity Dimensions

Control Complement

Oven Cavity Light Yes

Safety Standard

14 Amperes 60 Hertz Single phase, 3 wire grounded 1000 watts (IEC Test procedure) Operating frequency 2450 MHz Width 20-1/2" (520mm) Height 12-1/8" (309mm) Depth 16" (406mm)

Width 13-7/8" (353mm) NOTE: Internal capacity is calculated by measuring Height 8-1/ 8" (207mm) maximum width, depth and height. Depth 14-5/8" (370mm) Actual capacity for holding food is less.

Touch Control System 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 DOUBLE QUANTITY pad EXPRESS DEFROST pad Ten number pads SELECTATIME pad STOP/CLEAR pad SELECTAPOWER pad (R-21LTF only) START pad SET pad CHECK pad SIGNAL pad

UL Listed. FCC Authorized DHHS Rules, CFR, Title 21, Chapter 1, Subchapter J, NSF certified

R21LTF

Service Manual

4 – 1

R21LTF

3-Pronged Plug

Grounded Receptacle Box

Grounding Pin

3-Pronged Receptacle

R21LTF

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: 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 amp. or more protected 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 twopronged 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 threepronged 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

GROUNDING PRONG FROM THIS PLUG.

[2] OVEN DIAGRAM

1. OVEN

1. Back splash cover

2. Side splash cover

3. Oven light

4. Ceramic shelf

5. Control panel

6. Cavity face plate

7. Door latch openings

8. Door latches

9. Door hinges

10.Door seals and sealing surfaces

11.Door handle

12.Oven door with see-through window

13.Air ventilation cover and openings

14.Power supply cord

15.Air intake openings

16.Outer case cabinet

2. TOUCH CONTROL PANEL

912

3 2

DEFONNO.X2CHECK

6 8

9 10

6 8 11

R-21LTF R-21LVF

1. Digital Readout

2. DOUBLE QUANTITY pad

3. EXPRESS DEFROST pad

4. Ten number pads for time and memory programming

5. SELECTATIME pad

6. STOP/CLEAR pad; touch to stop operation of oven and clear remaining heating time

7. SELECTAPOWER pad for setting variable power level (R-21LTF only)

8. START pad; touch to operate oven after door is closed and time is set

9. SET pad for setting memory

10.CHECK pad for checking memory

11.SIGNAL pad for setting signal sound

5 – 1

R21LTF

CHAPTER 6. OPERATION

[1] DESCRIPTION OF OPERATING SEQUENCE

The following is a description of component functions during oven operation.

R21LTF

Service Manual

1. OFF CONDITION

Closing the door activates door sensing switch and secondary interlock switch. (In this condition, the monitor switch contacts are opened.)

When oven is plugged in, 120 volts A.C. is supplied to noise filter of the control unit (Figure O-1).

1) The display will show " . ".

2. COOKING CONDITION

Program desired cooking time by touching SELECTATIME pad and the NUMBER pads. When the START pad is touched, the following operations occur:

1) The contacts of the 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-2 power transformer RY-3 oven lamp/antenna motor/fan motor

2) 120 volts A.C. is supplied to the primary winding of the power transformer and is converted to about 3.2 volts A.C. output on the filament winding, and approximately 2150 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, monitor switch, door sensing switch, secondary interlock switch, relay (RY3) and primary interlock relay (RY2) are activated with the following results. The circuits to the antenna 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 secondary interlock switch and control relay (RY3) 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 primary

interlock relay (RY2) and secondary interlock switch open their contacts. And contacts of the relay (RY3) 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 secondary interlock switch and door sensing switch close and contacts of the relay (RY3) open.

If the secondary interlock switch and primary 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, secondary interlock switch, relay (RY3) and primary interlock relay (RY2), causing the monitor fuse to blow.

3. POWER LEVEL P-0 TO P-90 COOKING (R-21LTF only)

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 Power 10 (P-HI) (100% power) 32 sec. 0 sec. Power 9 (P-90) (approx. 90% power) 30 sec. 2 sec. Power 8 (P-80) (approx. 80% power) 26 sec. 6 sec. Power 7 (P-70) (approx. 70% power) 24 sec. 8 sec. Power 6 (P-60) (approx. 60% power) 22 sec. 10 sec. Power 5 (P-50) (approx. 50% power) 18 sec. 14 sec. Power 4 (P-40) (approx. 40% power) 16 sec. 16 sec. Power 3 (P-30) (approx. 30% power) 12 sec. 20 sec. Power 2 (P-20) (approx. 20% power) 8 sec. 24 sec. Power 1 (P-10) (approx. 10% power) 6 sec. 26 sec. Power 0 (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. 2 seconds are needed for heating of the magnetron filament.

6 – 1

R21LTF

[2] OVEN SCHENATIC

1. Off Condition

SCHEMATIC

NOTE: CONDITION OF OVEN

1. DOOR CLOSED

2. “ . “ APPEARSED

AC120V 60 Hz

THERMAL

CAPACITOR

0.0033μF / AC 250V

CAPACITOR

0.0033μF / AC 250V

CUT-OUT 125ºC (OVEN)

NOISE FILTER

FUSE

20A

LINE BYPASS

NOISE SUPPRESSION COIL

LINE CROSS CAPACITOR 0.22μF AC250V

LINE BYPASS

THERMAL CUT-OUT 145ºC (MAG.)

B1 B2

DOOR SENSING SWITCH

RY3

CONTROL

RELAY

CONTROL UNIT

OL FM AM

OVEN LAMP

SECONDARY INTERLOCK SWITCH

Figure O-1. Oven Schematic-Off Condition

2. Cooking Condition

SCHEMATIC

NOTE: CONDITION OF OVEN

1. DOOR CLOSED.

2. SELECTATIME PAD TOUCHED.

3. COOKING TIME ENTERED.

4. START PAD TOUCHED.

RY2

PRIMARY

FAN MOTOR

INTERLOCK

RELAY

ANTENNA MOTOR

POWER TRANSFORMER

MONITOR SWITCH

CAPACITOR

1.00 μF 2300V

MAGNETRON

RECTIFIER

AC120V 60 Hz

THERMAL

CAPACITOR

0.0033μF / AC 250V

CAPACITOR

0.0033μF / AC 250V

CUT-OUT 125ºC (OVEN)

NOISE FILTER

FUSE

20A

LINE BYPASS

NOISE SUPPRESSION COIL

LINE CROSS CAPACITOR 0.22μF AC250V

LINE BYPASS

THERMAL CUT-OUT 145ºC (MAG.)

B1 B2

DOOR SENSING SWITCH

RY3

CONTROL UNIT

CONTROL

RELAY

RY2

OL FM AM

OVEN LAMP

FAN MOTOR

SECONDARY INTERLOCK SWITCH

Figure O-2. Oven Schematic-Cooking Condition

PRIMARY

INTERLOCK

RELAY

ANTENNA MOTOR

POWER TRANSFORMER

MONITOR SWITCH

CAPACITOR

1.00 μF 2300V

MAGNETRON

RECTIFIER

6 – 2

[3] DESCRIPTION AND FUNCTION OF COMPONENTS

R21LTF

1. DOOR OPEN MECHANISM

The door is opened by grasping the door handle, refer to Figure D-1.

When the door handle is grasped, the handle lever is pulled. And then the upper and lower latch heads are moved upward by the handle lever, and they are released from the latch hook. Now the door will open.

Handle Lever

Door Handle

Latch Lever

Latch Head

Latch Switch Lever C

Latch Head

Latch Hook

Latch Switch Lever A

Secondary Interlock Switch

Latch Switch Lever B

Monitor Switch

Door Sensing Switch

CAUTION: BEFORE REPLACING A BLOWN MONITOR FUSE TEST

THE DOOR SENSING SWITCH, PRIMARY INTERLOCK RELAY (RY2), RELAY (RY3) SECONDARY INTERLOCK SWITCH AND MONITOR SWITCH FOR PROPER OPERATION. (REFER TO CHAPTER "TEST PROC

NOTE: MONITOR FUSE AND MONITOR SWITCH ARE REPLACED

AS AN ASSEMBLY.

4. ANTENNA MOTOR

The antenna motor rotates the stirrer antenna located on the bottom of the oven cavity, so that the food on the ceramic shelf is cooked evenly during cooking. The antenna motor 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 channelled through the oven cavity to remove steam and vapors given off from the heating food. It is then exhausted through the exhausting air vents at the oven cavity.

6. 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 shortcircuited, this monitor fuse blows to prevent an electric shock or fire hazard.

Figure D-1. Door Open Mechanism.

2. DOOR SENSING AND SECONDARY INTERLOCK SWITCHES

The secondary interlock switch is mounted in the upper position of the latch hook and the door sensing switch in the primary interlock system is mounted in the lower position of the latch hook. The secondary interlock switch is activated by the latch switch lever A. The latch switch lever A is activated by the upper latch head. The door sensing switch is activated by the latch switch lever C. The latch switch lever C is activated by the lower latch head. 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 primary interlock system consists of the door sensing switch and primary interlock relay located on the control circuit board.

3. MONITOR SWITCH

The monitor switch is activated (the contacts opened) by the latch switch lever B on the latch hook while the door is closed. The latch switch lever B is activated by the lower latch head. The switch is intended to render the oven inoperative, by means of blowing the monitor fuse, when the contacts of the primary interlock relay (RY2) and secondary interlock switch fail to open when the door is opened.

Functions:

1) When the door is opened, the monitor switch contacts close (to the ON condition) due to their being normally closed. At this time the primary interlock relay (RY2) and secondary 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 secondary interlock switch contacts close. (On opening the door, each of these switches operate inversely.)

3) If the door is opened, and the primary interlock relay (RY2) and secondary interlock switch contacts fail to open, the monitor fuse blows simultaneously with closing of the monitor switch contacts.

7. THERMAL CUT-OUT 145°C (MAGNETRON)

This thermal cut-out protects the magnetron against overheating. If the temperature goes up higher than 293°F (145°C) because the fan motor is interrupted or the ventilation openings are blocked, the thermal cut-out will open and line voltages to the high voltage transformer will be cut off and the operation of the magnetron will be stopped. The thermal cutout will not resume.

8. THERMAL CUT-OUT 125°C (OVEN)

The thermal cut-out located on the top of the oven cavity is designed to prevent damage to the oven if the food in the oven catches fire due to over heating produced by improper setting of the cooking time or failure of control unit. Under normal operation, the oven thermal cutout 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. The thermal cut-out will not resume.

9. NOISE FILER

The noise filter prevents the radio frequency interference that might flow back in the power circuit.

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CHAPTER 7. TROUBLESHOOTING GUIDE

Service Manual

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 (RY3), primary interlock relay (RY2), door sensing switch and secondary interlock switch before replacing the monitor fuse. If monitor fuse is replaced, the monitor switch must also be replaced. Use part FFS-BA033WRKZ 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.

[1] TROUBLESHOOTING CHART

CONDITION

OFF CONDITION

COOKING CONDITION

ERROR MODE

TEST PROCEDURE

POSSIBLE CASE

AND

DEFECTIVE PARTS

PROBLEM

Home fuse or circuit breaker blows when power cord is plugged into wall outlet.

Monitor fuse blows when power cord is plugged into wall receptacle.

. does not appear in display when

power cord is first plugged into wall outlet.

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 antenna 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 5 mode. (Operates properly on Cooking Power 10 (HIGH) mode.)

"EE9" Maximum time is exceeded.

ABC DEF FGH JK L M

MAGNETRON

POWER TRANSFORMER

H.V. RECTIFIER ASSEMBLY

HIGH VOLTAGE CAPACITOR

THERMAL CUT-OUT

SECONDARY INTERLOCK SWITCH

PRIMARY INTERLOCK SYSTEM

MONITOR SWITCH

MONITOR FUSE

TOUCH CONTROL PANEL

KEY UNIT

RELAY (RY3)

RE RE RE RE RE CK CK CK I

EXCEED MAX. HEATING TIME

FOIL PATTERN ON P.W.B.

OVEN LAMP OR SOCKET

COOLING FAN MOTOR

ANTENNA MOTOR

SHORTED IN POWER CORD

SHORT OR OPENED WIRING

LOW VOLTAGE

WRONG OPERATION

DIRTY OVEN CAVITY

NOISE FILTER

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CHAPTER 8. TEST PROCEDURES

Service Manual

[1] Procedure 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.

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.

1. 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 34.7 to 64.6°F(19.3 to 35.9°C) rise in tempera- ture. 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.

[2] Procedure 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 83.7 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.)

[3] Procedure 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.

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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.

[4] Procedure 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.

[5] Procedure E: THERMAL CUT OUT TEST

1. THERMAL CUT OUT 125°C (OVEN)

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 thermal cut-out terminals should indicate a closed circuit unless the temperature of the thermal cut-out reaches approximately 257°F(125°C). An open thermal cut-out indicates overheating of the oven, exchange the thermal cut-out 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.

2. THERMAL CUT OUT 145°C (MAGNETRON)

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 thermal cut-out terminals should indicate a closed circuit. If the temperature of the magnetron reaches approximately 293°F(145°C), the thermal cut-out opens. An open thermal cutout indicates overheating of the magnetron. Check for restricted air flow to the magnetron, especially the cooling fan 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.

CAUTION: IF THE THERMAL CUT-OUT INDICATES AN OPEN CIRCUIT AT ROOM TEMPERATURE,

REPLACE THERMAL CUT-OUT.

[6] Procedure F: SECONDARY INTERLOCK SWITCH 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 switch and connect the ohmmeter to the common (COM.) and normally open (NO) terminal of the switch. The meter should indicate an open circuit with the door open and a closed circuit with the door closed. If improper operation is indicated, replace the secondary interlock switch.

5. Reconnect all leads removed from components during testing.

6. Reinstall the outer case (cabinet).

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