SHARP R425LS Service Manual

R425LS

SERVICE MANUAL

MICROWAVE OVEN

MODEL R-425LS

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

CHAPTER 4. PRODUCT DESCRIPTION

CHAPTER 5. GENERAL INFORMATION

CHAPTER 6. OPERATION

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

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 PRO-
CEDURE
[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 ..........................................................	8-4
[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: 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 ........................	11-2
[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 .................................	11-5

[13]DOOR SENSING SWITCH/PRIMARY INTERLOCK 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

R425LS

PRECAUTIONS TO BE OBSERVED BEFORE AND DURING SERVICING TO AVOID 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.

BEFORE 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/cm2. The owner of the unit should be instructed not to use the unit until the oven has been brought into compliance.

i

R425LS

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.

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

R425LS

CHAPTER 2. MICROWAVE MEASUREMENT PROCEDURE

[1] Requirements:

1. Microwave leakage limit (Power density limit): The power density of microwave radiation emitted by a microwave oven should not exceed 1mW/ cm2 at any point 5cm or more from the external surface of the oven, measured prior to acquisition by a purchaser, and thereafter (through the useful life of the oven), 5 mW/cm2 at any point 5cm or more from the external surface of the oven.

2. Safety interlock switches:

Primary interlock switch shall prevent microwave radiation emission in excess of the requirement as above mentioned. Secondary interlock relay and door sensing switch shall prevent microwave radiation emission in excess of 5 mW/cm2 at any point 5cm or more from the external surface of the oven.

[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/cm2, and that the secondary 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.

2 – 1

R425LS

CHAPTER 3. FOREWORD AND WARNING

[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-425LS

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

R425LS

CHAPTER 4. PRODUCT DESCRIPTION

[1] SPECIFICATIONS

	ITEM			DESCRIPTION
		120 Volts
	Power Requirements	60 Hertz
		Single phase, 3 wire grounded
	Power Consumption	1600W / Approx. 13.5 Amperes
	Power Output	1100 W nominal of RF microwave energy (IEC Test procedure)
		Operating frequency 2450 MHz
		Width	21-5/8" (550mm)
	Outside Dimensions	Height 12-3/8" (315mm)
		Depth 17-5/8" (449mm)
	Cooking Cavity Dimensions	Width	15-3/8" (392mm)	NOTE: Internal capacity is calculated by measuring
		Height	9-3/8" (237mm)	maximum width, depth and height.
	(1.4 Cubic feet)
		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
	Control Complement	P-20 --------------------		approx. 20% of FULL Power
		P-10		approx. 10% of FULL Power
		P-0 ----------------------		No power throughout the cooking time
		SENSOR REHEAT pad
		NIGHT LIGHT pad
		KEEP WARM PLUS pad
		CUSTOM HELP pad
		START/MINUTE PLUS pad
		SENSOR COOK pads
		REHEAT pads
		DEFROST pads
		Number selection pads
		Power Level pad
		TIMER/CLOCK pad
		STOP/CLEAR pad
	Oven Cavity Light	Yes
	Safety Standard	UL listed FCC Authorized
		DHHS Rules, CFR, Title 21, Chapter 1, Subchapter J

4 – 1

R425LS

CHAPTER 5. GENERAL INFORMATION

[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 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 GROUNDING PRONG FROM THIS PLUG.

Grounded

Receptacle Box

3-Pronged Plug

Grounding Pin

3-Pronged Receptacle

[2] OVEN DIAGRAM

	1. OVEN	10.Waveguide cover:
		11.Power supply cord.
	6	5
		2. TOUCH CONTROL PANEL
		9
	2	8
		10
		1

4

3

7

11

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.

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

R425LS

CHAPTER 6. OPERATION

[1] DESCRIPTION OF OPERATING SEQUENCE

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

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 flashing “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 percentage of microwave power, because approx. 3 seconds are needed for heating of the magnetron filament.

4. POWER OUTPUT REDUCTION

After 100% power cooking mode is carried out for more than 40 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.

MIC R OW

AVE

2. Heat potatoes. Moisture and humidity is emitted rapidly. You can smell the aroma as it cooks.;

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R425LS

AH S E NS O R	MIC R
	O
	W
	AVE

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.

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.

[2] OVEN SCHEMATIC

1. Off Condition

SCHEMATIC

NOTE: CONDITION OF OVEN

1.DOOR CLOSED

2.CLOCK APPEARS ON DISPLAY

"TO SOURCE"

BLK	H	MONITOR FUSE(20A)
	GRN
120VAC	GND	C1
60Hz	N

WHT "TO SOURCE"

NOISE FILTER

OVEN	MAGNETRON		NOTE: "	" indicates components with potentials above 250V
THERMAL CUT-OUT	TEMPERATURE
	FUSE
LOAD"					B2
"TO						DOOR
						SENSING
						SWITCH	POWER TRANSFORMER
					B1		MAGNETRON
	(RY1)		(RY2)	F-3		SENSORAH
C2		CONTROL UNIT
		SECONDARY
		INTERLOCK
			RELAY
				F-2
C3
	OVEN LAMP			F-1			HIGH
							VOLTAGE
	RELAY
							CAPACITOR
LOAD"							0.94uF/ AC2200V
				TURN		MONITOR	HIGH
							N.C.
						SWITCH
"TO	OL	OVEN	TTM	TABLE	FM	FAN	VOLTAGE
		LAMP		MOTOR		MOTOR	RECTIFIER
						COM.

			COM.	N.O.
C2, C3: LINE BYPASS CAPACITOR ------ 0.033uF/ AC250V			PRIMARY INTERLOCK
			SWITCH
C1:	-------LINE CROSS CAPACITOR	0.22uF/ AC250V

Figure O-1. Oven Schematic-Off Condition

6 – 2

R425LS

2. Cooking Condition

SCHEMATIC

NOTE: CONDITION OF OVEN

1.DOOR CLOSED.

2.COOKING TIME PROGRAMMED.

3.VARIABLE COOKING CONTROL "P-HI".

4.START PAD TOUCHED.

BLK

H

GRN

120VAC GND C1

60Hz N

WHT

	OVEN	MAGNETRON
		TEMPERATURE
	THERMAL CUT-OUT
		FUSE
SOURCE"	LOAD"			B2
"TO	"TO			DOOR
MONITOR FUSE (20A)				SENSING
				SWITCH	POWER TRANSFORMER
		(RY1)	CONTROL UNIT	SENSORAH	MAGNETRON
				B1
			(RY2)	F-3
	C2		SECONDARY
			INTERLOCK
			RELAY
	C3			F-2
		OVEN LAMP			HIGH
				F-1	VOLTAGE
		RELAY
					CAPACITOR
					0.94uF/ AC2200V

	SOURCE"	LOAD""TO
		NOISE
		FILTER
	"TO
C1:	LINE CROSS CAPACITOR ------- 0.22uF/ AC250V
C2, C3: LINE BYPASS CAPACITOR ------			0.033uF/ AC250V

			MONITOR	N.C.
		TURN	SWITCH	HIGH
	OL OVEN		FAN
		TTM TABLE FM		VOLTAGE
	LAMP	MOTOR	MOTOR	RECTIFIER
			COM.
	COM.	N.O.
	PRIMARY INTERLOCK
	SWITCH

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

Door

Switch

Monitor Switch

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.

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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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CHAPTER 7. TROUBLESHOOTING GUIDE

Never touch any part in the circuit with your hand or an uninsulated tool while the power supply is connected.

When troubleshooting the microwave oven, it is helpful to follow the Sequence of Operation in performing the checks. Many of the possible causes of trouble will require that a specific test be performed. These tests are given a procedure letter which will be found in the "Test Procedure "section.

IMPORTANT:

If the oven becomes inoperative because of a blown monitor fuse, check the monitor switch, relay (RY1) secondary interlock relay (RY2), door sensing switch and primary interlock switch before replacing the monitor fuse. If the monitor fuse is replaced, the monitor switch must also be replaced. Use part FFS-BA033WRKZ or FFS-BA037WRKZ 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

TTEST PROCEDURE

POSSIBLE CASE

AND DEFECTIVE PARTS

CONDITION PROBLEM

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

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

OFF All letters and indicators do not appear in dis-

CONDITION play when power cord is first plugged into wall outlet.

Display does not operate properly when STOP/CLEAR pad 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 COOKING heat is produced in oven load. (Food incom- CONDITION pletely cooked or not cooked at all at end of

cook cycle.)

Oven goes into a cook cycle but extremely uneven heating is produced in oven load (food).

Oven does not cook properly when programmed for Cooking Power P-50 mode. (Operates properly on Cooking Power P-HI (HIGH) mode.)

Oven goes into DEFROST but food is not defrosted well.

AH sensor does not end during Sensor cook- SENSOR ing condition. (Oven does not shut off after a COOKING cup of water is boiling by sensor cooking.)

CONDITION Oven stops at 16 sec. after starting.

RE CK A B C D E E F F G H RE RE CK I J CK CK CK K L M N O

SHORT IN POWER CORD

SHORT OR OPENED WIRING

MAGNETRON

POWER TRANSFORMER

H.V. RECTIFIER ASSEMBLY

HIGH VOLTAGE CAPACITOR

OVEN THERMAL CUT-OUT

MAGNETRON TEMPERATURE FUSE

SECONDARY INTERLOCK SYSTEM

PRIMARY INTERLOCK SWITCH

MONITOR SWITCH

MONITOR FUSE

OVEN LAMP

COOLING FAN MOTOR

TURNTABLE MOTOR

NOISE FILTER

TOUCH CONTROL PANEL

WRONG OPERATION

LOW VOLTAGE

DIRTY OVEN CAVITY

KEY UNIT (MEMBRAINE SWITCH)

RELAY (RY1)

DEFROST

FOIL PATTERN ON PWB

AH SENSOR

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