SHARP R-370EK, R-370ES Service Manual

R - 370EK

R - 3 70 E S

SERVICE MANUAL

	Popcorn	Baked	Fresh
		Potatoes	Vegetables	Rice
	Reheat	Ground	Frozen	Chicken
	Sensor
		Meat	Vegetables	Breast

	Frozen	Rolls &	Compu
	Entree	Muffins
			Defrost
	Fish	Veverage	Kitchen Timer
	Seafood
			Clock

1	2	3	4	5
6	7	8	9	0

Power	Custom
Level	Help
STOP	Minute Plus
Clear	START

S4112R370EPS/

MICROWAVE OVEN

MODELS R-370EK R-370ES

In the interest of user-safety the oven should be restored to its original condition and only parts identical to those specified should be used.

WARNING TO SERVICE PERSONNEL: Microwave ovens contain circuitry capable of producing very high voltage and current, contact with following parts may result in a severe, possibly fatal, electrical shock. (High Voltage Capacitor, High Voltage Power Transformer, Magnetron, High Voltage Rectifier Assembly, High Voltage Harness etc..)

TABLE OF CONTENTS
	Page
PRECAUTIONS TO BE OBSERVED BEFORE AND DURING SERVICING TO
AVOID POSSIBLE EXPOSURE TO EXCESSIVE MICROWAVE ENERGY ...................	INSIDE FRONT COVER
BEFORE SERVICING ......................................................................................................	INSIDE FRONT COVER
WARNING TO SERVICE PERSONNEL ................................................................................................................	1
MICROWAVE MEASUREMENT PROCEDURE ...................................................................................................	2
FOREWORD AND WARNING ...............................................................................................................................	3
PRODUCT SPECIFICATIONS ..............................................................................................................................	4
GENERAL INFORMATION ...................................................................................................................................	4
OPERATION ..........................................................................................................................................................	6
TROUBLESHOOTING GUIDE ............................................................................................................................	10
TEST PROCEDURE ............................................................................................................................................	12
TOUCH CONTROL PANEL .................................................................................................................................	21
COMPONENT REPLACEMENT AND ADJUSTMENT PROCEDURE ................................................................	26
PICTORIAL DIAGRAM ........................................................................................................................................	33
POWER UNIT CIRCUIT ......................................................................................................................................	34
CPU UNIT CIRCUIT ............................................................................................................................................	35
PRINTED WIRING BOARD .................................................................................................................................	36
PARTS LIST ........................................................................................................................................................	37
PACKING AND ACCESSORIES .........................................................................................................................	39

SHARP CORPORATION

This document has been published to be used for after sales service only.

The contents are subject to change without notice.

R-370EK

R- 370ES

PRECAUTIONS TO BE 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 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.

R-370EK

R-370ES

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

Before Servicing

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

2.Open the door and block it open.

3.Discharge high voltage capacitor.

WARNING:RISK OF ELECTRIC SHOCK. DISCHARGE THE HIGH-VOLTAGE CAPACITOR BEFORE SERVICING.

The high-voltage capacitor remains charged about 60 seconds after the oven has been switched off. Wait for 60 seconds and then short-circuit the connection of the highvoltage capacitor (that is the connecting lead of the highvoltage rectifier) against the chassis with the use of an insulated screwdriver.

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

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

2.Open the door and block it open.

3.Discharge high voltage capacitor.

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

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

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

When the testing is completed,

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

2.Open the door and block it open.

3.Discharge high voltage capacitor.

4.Reconnect the leads to the primary of the power transformer.

5.Reinstall the outer case (cabinet).

6.Reconnect the power supply cord after the outer case is installed.

7.Run the oven and check all functions.

After repairing

1.Reconnect all leads removed from components during testing.

2.Reinstall the outer case (cabinet).

3.Reconnect the power supply cord after the outer case is installed.

4.Run the oven and check all functions.

Microwave ovens should not be run empty. To test for the presence of microwave energy within a cavity, place a cup of cold water on the oven turntable, close the door and set the power to HIGH and set the microwave timer for two (2) minutes. When the two minutes has elapsed (timer at zero) carefully check that the water is now hot. If the water remains cold, carry out Before Servicing procedure and reexamine the connections to the component being tested.

When all service work is completed and the oven is fully assembled, the microwave power output should be checked and a microwave leakage test should be carried out.

1

R- 370EK

R - 37 0ES

MICROWAVE MEASUREMENT PROCEDURE

A. Requirements:

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

2)Safety interlock switches

Primary interlock switch shall prevent microwave radiation emission in excess of the requirement as above mentioned, secondary interlock relay and door sensing switch shall prevent microwave radiation emission in excess of 5 mW/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 (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.

C. Leakage test:

Closed-door leakage test (microwave measurement)

1)Grasp the probe of the survey instrument and hold it perpendicular to the gap between the door and the body of the oven.

2)Move the probe slowly, not faster than 1 in./sec. (2.5 cm/sec.) along the gap, watching for the maximum indication on the meter.

3)Check for leakage at the door screen, sheet metal seams and other accessible positions where the continuity of the metal has been breached (eg., around the switches, indicator, and vents).

While testing for leakage around the door pull the door away from the front of the oven as far as is permitted by the closed latch assembly.

4)Measure carefully at the point of highest leakage and make sure that the highest leakage is no greater than 4mW/cm2.

NOTE: After servicing, record data on service invoice and microwave leakage report.

2

SERVICE MANUAL

MICROWAVE OVEN

R-370EK/ R-370ES

FOREWORD

This Manual has been prepared to provide Sharp Electronics Corp. Service Personnel with Operation and Service Information for the SHARP MICROWAVE OVEN, R-370EK, R-370ES.

It is recommended that service personnel carefully study the entire text of this manual so that they will be qualified to render satisfactory customer service.

Check the interlock switches and the door seal carefully. Special attention should be given to avoid electrical shock and microwave radiation hazard.

WARNING

Never operate the oven until the following points are ensured.

(A)The door is tightly closed.

(B)The door brackets and hinges are not defective.

(C)The door packing is not damaged.

(D)The door is not deformed or warped.

(E)There is no other visible damage with the oven.

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

DANGER

Certain initial parts are intentionally not grounded and present a risk of electrical shock only during servicing. Service personnel - Do not contact the following parts while the appliance is energized;

High Voltage Capacitor, Power Transformer, Magnetron, High Voltage Rectifier Assembly, High Voltage Harness;

If provided, Vent Hood, Fan assembly, Cooling Fan Motor.

All the parts marked “*” on parts list are used at voltages more than 250V.

Removal of the outer wrap gives access to voltage above 250V.

All the parts marked “∆ ” on parts list may cause undue microwave exposure, by themselves, or when they are damaged, loosened or removed.

SHARP ELECTRONICS CORPORATION

SHARP PLAZA, MAHWAH,

NEW JERSEY 07430-2135

3

R-370EK

R-370ES

PRODUCT DESCRIPTION

GENERAL INFORMATION

OPERATION

TROUBLESHOOTING GUIDE AND TEST PROCEDURE

TOUCH CONTROL PANEL

COMPONENT REPLACEMENT AND ADJUSTMENT PROCEDURE

WIRING DIAGRAM

PARTS LIST

R- 370EK

R - 37 0ES

		SPECIFICATION
ITEM		DESCRIPTION
Power Requirements	120 Volts / 13.5 Amperes
	60 Hertz
	Single phase, 3 wire grounded
Power Output	1000 watts (IEC TEST PROCEDURE)
	Operating frequency of 2450MHz
Case Dimensions	Width 17-1/4"
	Height 13-3/8"
	Depth
Cooking Cavity Dimensions	Width 13-3/4"
	Height 7-1/4"
1.4 Cubic Feet	Depth
Control Complement	Touch Control System
	Clock ( 1:00 - 12:59 )
	Timer (0 - 99 min. 99 seconds)
	Microwave Power for Variable Cooking
	Repetition Rate;
	HIGH	Full power throughout the cooking time
	P-90 ....................................................................	approx. 90% of Full Power
	P-80 ....................................................................	approx. 80% of Full Power
	P-70 ....................................................................	approx. 70% of Full Power
	P-60 ....................................................................	approx. 60% of Full Power
	P-50 ....................................................................	approx. 50% of Full Power
	P-40 ....................................................................	approx. 40% of Full Power
	P-30 ....................................................................	approx. 30% of Full Power
	P-20 ....................................................................	approx. 20% of Full Power
	P-10 ....................................................................	approx. 10% of Full Power
	P-0 ....................................................	No power throughout the cooking time
	SENSOR COOKING pads , INSTANT ACTION pads
	COMPU DEFROST pads, Number selection pads
	CUSTOM HELP PAD, POWER LEVEL pad,
	KITCHEN TIMER/CLOCK pad
	STOP/CLEAR pad, MINUTE PLUS /START pad
Oven Cavity Light	Yes
Safety Standard	UL Listed	FCC Authorized
	DHHS Rules, CFR, Title 21, Chapter 1, Subchapter J

GENERAL INFORMATION

GROUNDING INSTRUCTIONS

This oven is equipped with a three prong grounding plug. It must be plugged into a wall receptacle that is properly installed and grounded in accordance with the National Electrical Code and local codes and ordinances.

In the event of an electrical short circuit, grounding reduces the risk of electric shock by providing an escape wire for the electric current.

WARNING: Improper use of the grounding plug can result in a risk of electric shock.

Electrical Requirements

The electrical requirements are a 120 volt 60 Hz, AC only,

15 or 20 amp. fused electrical supply. It is recommended that a separate circuit serving only this appliance be provided. When installing this appliance, observe all applicable codes and ordinances.

A short power-supply cord is provided to reduce risks of becoming entangled in or tripping over a longer cord.

Where a two-pronged wall-receptacle is encountered, it is the personal responsibility and obligation of the customer to

4

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.

R-370EK

R-370ES

3-Pronged Plug	Grounded
	Receptacle Box

Grounding Pin

3-Pronged Receptacle

OVEN DIAGRAM

1.	Door handle
	Pull to open door.				7
2.	Auto-Touch control panel
					11	12
3.	Display: 99 minutes, 99 seconds		3
4.	Oven door with see-through window
5.	Safety door latch
	The oven will not operate unless the door is				8	13
	securely closed.
6.	Door hinges
7.	Door seals and sealing surface	2
8.	Turntable motor shaft
9.	Removable turntable support			5 4	6
	Carefully place the turntable support in the center
			1		10
	of the oven floor.
10. Removable turntable				9
	Place the turntable on the turntable support
	cecurely. The turntable will rotate clockwise or
	counterclockwise. Only remove for cleaning.

11.Ventilation openings (Rear)

12.Oven light

It will light when oven is operating or door is opened.

13.Wave guide cover: DO NOT REMOVE.

TOUCH CONTROL PANEL

Popcorn

Baked

Fresh

Rice

Frozen

Rolls &

Compu

1

2

3

4

5

Power

Custom

Potatoes Vegetables

Entree

Muffins

Defrost

Level

Help

Reheat

Ground

Frozen

Chicken

Fish

Beverage

Kitchen Timer

COOK SENSOR LBS

DEF HELP

6

7

8

9

0

STOP

Minute Plus

Sensor

Meat

Vegetables

Breast

Seafood

Clock

Clear

START

NOTE:

The directed features are disabled after three minutes when the oven is not in use. These features are automatically enabled when the door is opened and closed or the STOP/ CLEAR pad is pressed.

5

R- 370EK

R - 37 0ES

OPERATION

DESCRIPTION OF OPERATING SEQUENCE

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

OFF CONDITION

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

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

1.The display will show "SHARP SIMPLY THE BEST PRESS CLEAR AND PRESS CLOCK".To set any program or set the clock, you must first touch the STOP/ CLEAR pad. The display will clear, and " : " will appear.

COOKING CONDITION

Program desired cooking time by touching the NUMBER pads. Program the power level by touching the POWER LEVEL pad.

When the START pad is touched, the following operations occur:

1.	The contacts of relays are closed and components
	connected to the relays are turned on as follows.
	(For details, refer to Figure O-2)
		RELAY	CONNECTED COMPONENTS
		RY-1	oven lamp/turntable motor/fan motor
		RY-2	power transformer
2.	120 volts A.C. is supplied to the primary winding of the
	power transformer and is converted to about 3.4 volts
	A.C. output on the filament winding, and approximately
	2300 volts A.C. on the high voltage winding.
3.	The filament winding voltage heats the magnetron
	filament and the H.V. winding voltage is sent to a voltage
	doubler circuit.
4.	The microwave energy produced by the magnetron is
	channelled through the waveguide into the cavity 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 switch, door sensing switch, primary interlock
	switch, relay (RY1) and secondary interlock relay (RY2)
	are activated with the following results. The circuits to the
	turntable motor, the cooling fan motors, and the high
	voltage components are de-energized, the oven lamp
	remains on, and the digital read-out displays the time still
	remaining in the cook cycle when the door was opened.
7.	The monitor switch electrically monitors the operation of
	the primary interlock switch and secondary interlock
	relay (RY2) and is mechanically associated with the door

so that it will function in the following sequence.

(1)When the door opens from the closed position, the secondary interlock relay (RY2) and primary interlock switch open their contacts. And contacts of the relay (RY1) remains closed. Then the monitor switch contacts close.

(2)When the door is closed from the open position, the monitor switch contacts open first. Then the contacts of the primary interlock switch and door sensing switch close. And contacts of the relay (RY1) open.

If the primary interlock switch and secondary interlock relay (RY2) fail with the contacts closed when the door is opened, the closing of the monitor switch contacts will form a short circuit through the monitor fuse, primary interlock switch, relay (RY1) and secondary interlock relay (RY2), causing the monitor fuse to blow.

POWER LEVEL P-0 TO P-90 COOKING

When Variable Cooking Power is programmed, the 120 volts A.C. is supplied to the power transformer intermittently through the contacts of relay (RY2) which is operated by the control unit within a 32 second time base. Microwave power operation is as follows:

VARI-MODE	DISPLAY	ON TIME	OFF TIME
100%	HIGH	32 sec.	0 sec.
approx. 90% power	P-90	30 sec.	2 sec.
approx. 80% power	P-80	26 sec.	6 sec.
approx. 70% power	P-70	24 sec.	8 sec.
approx. 60% power	P-60	22 sec.	10 sec.
approx. 50% power	P-50	18 sec.	14 sec.
approx. 40% power	P-40	16 sec.	16 sec.
approx. 30% power	P-30	12 sec.	20 sec.
approx. 20% power	P-20	8 sec.	24 sec.
approx. 10% power	P-10	6 sec.	26 sec.
0% power	P-0	0 sec.	32 sec.

Note: The ON/OFF time ratio does not correspond with the percentage of microwave power, because approx. 2 seconds are needed for heating of the magnetron filament.

POWER OUTPUT REDUCTION

If the oven is set for more than 30 minutes at 80, 90 or 100% power level, after the first 30 minutes the power level will automatically adjust itself to 70% power to avoid overcooking.

SENSOR COOKING CONDITION

Using the SENSOR function, the food is cooked without figuring time, power level or quantity. When the oven senses enough steam from the food, it relays the information to its microprocessor which will calculate the remaining cooking time and power level needed for best results. When the food

6

is cooked, water vapor is developed. The sensor “senses” the vapor and its resistance increases gradually. When the resistance reaches the value set according to the menu, supplementary cooking is started. The time of supplementary cooking is determined by experiment with each food category and inputted into the LSI.

An example of how sensor works: (POTATOES)

1. Potates at room temperature. Vapor is emitted very

slowly.	MICROWAVE

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

AH SENSOR	MICROWAVE

R-370EK

R-370ES

3.Sensor detects moisture and humidity and calculates cooking time and variable power.

Cooking Sequence.

1.Operate the oven in sensor cooking mode by referring to the operation manual.

NOTE: The oven should not be operated on SENSOR immediately after plugging in the unit. Wait two minutes before cooking on SENSOR.

2.The coil of shut-off relay (RY-1) is energized, the turntable motor, oven lamp and cooling fan motors are turned on, but the power transformer is not turned on.

3.After about 16 seconds, the cook relay (RY-2) is energized. The power transformer is turned on, microwave energy is produced and first stage is started. The 16 seconds is the cooling time required to remove any vapor from the oven cavity and sensor.

NOTE: During this first stage, do not open the door or touch STOP/CLEAR pad.

4.When the sensor detects the vapor emitted from the food, the display switches over to the remaining cooking time and the timer counts down to zero.

At this time, the door may be opened to stir, turn, or season food.

5.When the timer reaches zero, an audible signal sounds. The shut-off relay and cook relay are de-energized and the power transformer, oven lamp, etc. are turned off.

6.Opening the door or touching the STOP/CLEAR pad, the time of day will reappear on the display and the oven will revert to an OFF condition.

7

R- 370EK R - 37 0ES

SCHEMATIC

NOTE: CONDITION OF OVEN

1.DOOR CLOSED

2.CLOCK APPEARS ON DISPLAY

NOTE: " " indicates components with potential above 250V.

				AH SENSOR
MONITOR	OVEN THERMAL	MG. THERMAL CUT-OUT
FUSE 20A	CUT-OUT
		N.O.
			F3	F2	F1
				SECONDARY
				INTERLOCK
				RELAY (RY2)
		CONTROL UNIT
GRN		COM.	B2	B1

120V AC 60 Hz DOOR

SENSING

SWITCH

	OL	OVEN
		LAMP	TTM	FM	FM
	OVEN LAMP
	RELAY (RY1)	PRIMARY	TURN-	FAN	FAN
			TABLE
		INTERLOCK		MOTOR	MOTOR
			MOTOR
		SWITCH
N.O.	COM.

POWER

TRANSFORMER

CAPACITOR 0.94 F

AC 2200V

SWITCH

MONITOR

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 "P-HI" (100%)

4."START" PAD TOUCHED

NOTE: "" indicates components with potential above 250V.

				AH SENSOR
MONITOR	OVEN THERMAL	MG. THERMAL CUT-OUT
FUSE 20A	CUT-OUT
		N.O.
			F3	F2	F1
				SECONDARY
				INTERLOCK
				RELAY (RY2)
		CONTROL UNIT
GRN		COM.	B2	B1

120V AC 60 Hz DOOR

SENSING

SWITCH

OL	OVEN
	LAMP	TTM	FM	FM
OVEN LAMP
RELAY (RY1)	PRIMARY	TURN-	FAN	FAN
		TABLE
	INTERLOCK		MOTOR	MOTOR
		MOTOR
	SWITCH

POWER

TRANSFORMER

CAPACITOR 0.94 F

AC 2200V

MONITORSWITCH

RECTIFIER

MAGNETRON

N.O.	COM.

Figure O-2. Oven Schematic-Cooking Condition

8

R-370EK

R-370ES

DESCRIPTION AND FUNCTION OF COMPONENTS

DOOR OPEN MECHANISM

The door is opened by pulling the door. Refer to the Figure D-1.

Door	Latch Hook
Latch	Door Sensing
Heads	Switch
	Monitor Switch
	Primary
	Interlock Switch

Figure D-1. Door Open Mechanism

DOOR SENSING AND PRIMARY INTERLOCK SWITCHES

The primary interlock switch is mounted in the lower position of the latch hook and the door sensing switch in the secondary interlock system is mounted in the upper position of the latch hook. They are activated by the latch heads on the door. When the door is opened, the switches interrupt the power to all high voltage components. A cook cycle cannot take place until the door is firmly closed thereby activating both interlock switches. The secondary interlock system consists of the door sensing switch and secondary interlock relay located on the control circuit board.

MONITOR SWITCH

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

Functions:

1.When the door is opened, the monitor switch contact close (to the ON condition) due to their being normally closed. At this time the secondary interlock relay (RY2) and primary interlock switch are in the OFF condition (contacts open) due to their being normally open contact switches.

2.As the door goes to a closed position, the monitor switch contacts are first opened and then the door sensing switch and the primary interlock switch contacts close. (On opening the door, each of these switches operate inversely.)

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

CAUTION: BEFORE REPLACING A BLOWN MONITOR FUSE TEST THE DOOR SENSING SWITCH, SECONDARY INTERLOCK RELAY (RY2),

RELAY (RY1), PRIMARY INTERLOCK SWITCH AND MONITOR SWITCH FOR PROPER OPERATION. (REFER TO CHAPTER "TEST PROCEDURE").

NOTE: MONITOR FUSE AND MONITOR SWITCH ARE REPLACED AS AN ASSEMBLY.

TURNTABLE MOTOR

The turntable motor rotates the turntable located on the bottom of the oven cavity, so that the foods on the turntable cook evenly during cooking. The turntable may turn in either direction.

COOLING FAN MOTOR

The cooling fan motor drives a blade which draws external cool air. This cool air is directed through the air vanes surrounding the magnetron and cools the magnetron. This air is channelled through the oven cavity to remove steam and vapors given off from the heating foods. It is then exhausted through the exhausting air vents at the oven cavity.

MONITOR FUSE

1.The monitor fuse blows when the contacts (COM-NO) of the secondary interlock relay (RY2) and primary interlock switch remain closed with the oven door open and when the monitor switch closes.

2.If the wire harness or electrical components are shortcircuited, this monitor fuse blows to prevent an electric shock or fire hazard.

OVEN THERMAL CUT-OUT

The thermal cut-out, located on the top of the oven cavity, is designed to prevent damage to the oven by fire. If the food load is overcooked, by either error in cook time or defect in the control unit, the thermal cut-out will open.

Under normal operation, the oven thermal cut-out remains closed. However, when abnormally high temperatures are reached within the oven cavity, the oven thermal cut-out will open at 257˚F(125˚C), causing the oven to shut down.

MAGNETRON THERMAL CUT-OUT

The thermal cut-out located near the magnetron is designed to prevent damage to the magnetron if an over heated condition develops in the tube due to cooling fan failure, obstructed air guide, dirty or blocked air intake, etc.

Under normal operation, the thermal cut-out remains closed. However, when abnormally high temperatures are reached within the magnetron, the thermal cut-out will open at 257˚F(125˚C) causing the oven to shut down.

9

R- 370EK

R - 37 0ES

TROUBLESHOOTING GUIDE

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

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

IMPORTANT: If the oven becomes inoperative because of a blown monitor fuse, check the monitor switch, relay (RY1) secondary interlock relay (RY2), door sensing switch and primary interlock switch before replacing the monitor fuse. If the monitor fuse is replaced, the monitor switch must also be replaced. Use part FFSBA023WRK0 as an assembly.

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

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

2.Open the door and block it open.

3.Discharge high voltage capacitor.

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

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

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

When the testing is completed

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

2.Open the door and block it open.

3.Discharge high voltage capacitor.

4.Reconnect all leads removed from components during testing.

5.Reinstall the outer case (cabinet).

6.Reconnect the power supply cord after the outer case is installed.

7.Run the oven and check all functions.

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R-370EK

R-370ES

CK = Check / RE = Replace

		TEST PROCEDURE
		POSSIBLECAUSE AND DEFECTIVEPARTS
	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.
		Any letters or indicators do not ap-
	OFF	pear in display when power cord is
	CONDITION	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
	COOKING	cooked at all at end of cook cycle.)
	CONDITION	Oven goes into a cook cycle but ex-
		tremely uneven heating is produced
		in oven load (food).
		Oven does not cook properly when
		programmed for Cooking Power P-50
		mode. (Operates properly on Cook-
		ing Power HIGH (100%) mode.)
		Oven goes into COMPU DEFROST
		but food is not defrosted well.
		AH sensor does not end during sen-
	SENSOR	sor cooking condition. (Oven does
		not shut off after a cup of water is
	COOKING
	CONDITION	boiling by sensor cooking.)
		Oven stops at 16 sec. after starting.

RE

RE

A

B

C

D

E

F

F

G

H

RE

RE

CK

I

CK

CKCK

J

K

L

M

N

SHORTINPOWERCORD

SHORTOROPENED WIRING

MAGNETRON

POWERTRANSFORMER

H.V.RECTIFIERASSEMBLY

HIGHVOLTAGECAPACITOR

THERMALCUT-OUT

SECONDARYINTERLOCKSYSTEM

PRIMARYINTERLOCKSWITCH

MONITORSWITCH

MONITORFUSE

OVENLAMP

COOLINGFANMOTOR

TURNTABLEMOTOR

CONTROLUNIT

WRONGOPERATION

LOWVOLTAGE

DIRTYOVENCAVITY

KEYUNIT

RELAY(RY1)

COMPUDEFROST

FOILPATTERNONPWB.

AHSENSOR

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R- 370EK

R - 37 0ES

TEST PROCEDURES

PROCEDURE

COMPONENT TEST

LETTER

AMAGNETRON ASSEMBLY TEST

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

2.Open the door and block it open.

3.Discharge the high voltage capacitor.

4.To test for an open filament, isolate the magnetron from the high voltage circuit. A continuity check across the magnetron filament leads should indicate less than 1 ohm.

5.To test for a shorted magnetron, connect the ohmmeter leads between the magnetron filament leads and chassis ground. This test should indicate an infinite resistance. If there is little or no resistance the magnetron is grounded and must be replaced.

6.Reconnect all leads removed from components during testing.

7.Reinstall the outer case (cabinet).

8.Reconnect the power supply cord after the outer case is installed.

9.Run the oven and check all functions.

MICROWAVE OUTPUT POWER

The following test procedure should be carried out with the microwave oven in a fully assembled condition (outer case fitted).

HIGH VOLTAGES ARE PRESENT DURING THE COOK CYCLE, SO EXTREME CAUTION SHOULD BE OBSERVED.

Power output of the magnetron can be measured by performing a water temperature rise test. This test should only be used if above tests do not indicate a faulty magnetron and there is no defect in the following components or wiring: silicon rectifier, high voltage capacitor and power transformer. This test will require a 16 ounce (453cc) measuring cup and an accurate mercury thermometer or thermocouple type temperature tester. For accurate results, the following procedure must be followed carefully:

1.Fill the measuring cup with 16 oz. (453cc) of tap water and measure the temperature of the water with a thermometer or thermocouple temperature tester. Stir the thermometer or thermocouple through the water until the temperature stabilizes. Record the temperature of the water.

2.Place the cup of water in the oven. Operate oven at POWER P-HI(HIGH) selecting more than 60 seconds cook time. Allow the water to heat for 60 seconds, measuring with a stop watch, second hand of a watch or the digital read-out countdown.

3.Remove the cup from the oven and again measure the temperature, making sure to stir the thermometer or thermocouple through the water until the maximum temperature is recorded.

4.Subtract the cold water temperature from the hot water temperature. The normal result should be 30.7 to 57.1˚F(17.1 to 31.7˚C) rise in temperature. If the water temperatures are accurately measured and tested for the required time period the test results will indicate if the magnetron tube has low power output (low rise in water temperature) which would extend cooking time or high power output (high rise in water temperature) which would reduce cooking time. Because cooking time can be adjusted to compensate for power output, the magnetron tube assembly should be replaced only if the water temperature rise test indicates a power output well beyond the normal limits. The test is only accurate if the power supply line voltage is 120 volts and the oven cavity is clean.

BPOWER TRANSFORMER TEST

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

2.Open the door and block it open.

3.Discharge the high voltage capacitor.

4.Disconnect the primary input terminals and measure the resistance of the transformer with an ohmmeter. Check for continuity of the coils with an ohmmeter. On the R x 1 scale, the resistance of the primary coil should be less than 1 ohm and the resistance of the high voltage coil should be approximately 85 ohms; the resistance of the filament coil should be less than 1 ohm.

5.Reconnect all leads removed from components during testing.

6.Reinstall the outer case (cabinet).

7.Reconnect the power supply cord after the outer case is installed.

8.Run the oven and check all functions.

12