SHARP R820BK Service Manual

R-820BK

R-820BW

SERVICE MANUAL

GRILL

COOK

HELP

Iinteractive

CUSTOM

HELP

PIZZA		GRILL
BAKE	COMPU ROAST
COOK		DEFROST

CONVEC		GRILL		ROAST
POPCORN		REHEAT		MINUTE
1					PLUS
	2	3	4			5
100˚ F	150˚ F	275˚ F
6	7	8	9			O
350˚ F	375˚ F	400˚ F
KITCHEN			425˚ F			450˚ F
		CLOCK		POWER
TIMER
				LEVEL
STOP			START
CLEAR
		TOUCH ON

2	CONVECTION

S5812R820BPW/

DOUBLE GRILL

CONVECTION

MICROWAVE OVEN

MODELS R-820BK R-820BW

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 ............................................................................................................................	13
TEST PROCEDURE ............................................................................................................................................	15
TOUCH CONTROL PANEL .................................................................................................................................	24
COMPONENT REPLACEMENT AND ADJUSTMENT PROCEDURE ................................................................	30
PICTORIAL DIAGRAM ........................................................................................................................................	37
POWER UNIT CIRCUIT ......................................................................................................................................	38
CPU UNIT CIRCUIT ............................................................................................................................................	39
PRINTED WIRING BOARD .................................................................................................................................	40
PARTS LIST ........................................................................................................................................................	41
PACKING AND ACCESSORIES .........................................................................................................................	43

SHARP CORPORATION

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

The contents are subject to change without notice.

R-820BK

R-820BW

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 releasing oven 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-820BK

R-820BW

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 Assem-

bly, 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 microwave leakage test should be carried out.

1

R-820BK

R-820BW

MICROWAVE MEASUREMENT PROCEDURE

A. Requirements:

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

2)Safety interlock switches Primary interlock relay 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/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, and that the secondary interlock switch does turn the oven OFF before any door movement.

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

2

SERVICE MANUAL

DOUBLE GRILL

CONVECTION

MICROWAVE OVEN

R-820BK / R-820BW

FOREWORD

This Manual has been prepared to provide Sharp Electronics Corp. Service Personnel with Operation and Service Information for the SHARP MICROWAVE OVEN, R-820BK, R-820BW.

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-820BK

R-820BW

PRODUCT DESCRIPTION

GENERAL INFORMATION

OPERATION

TROUBLESHOOTING GUIDE AND TEST PROCEDURE

TOUCH CONTROL PANEL

COMPONENT REPLACEMENT AND ADJUSTMENT PROCEDURE

WIRING DIAGRAM

PARTS LIST

R-820BK

R-820BW

	SPECIFICATION
ITEM			DESCRIPTION
Power Requirements	120 Volts
	12.5 Amperes (Microwave) / 13.0 Amperes (Grill/ Convection)
	60 Hertz / Single phase, 3 wire grounded
Power Output	900 watts (IEC 705 Test Procedure)
	Operating frequency of 2450MHz
Top Heater Power Output	1000 Watts
Top & Bottom Heater Power Output	1500 Watts
Case Dimensions	Width 20-1/2"		Height 12-1/8"	Depth	19-3/4"
Cooking Cavity Dimensions	Width 13-7/8"		Height 7-1/2"	Depth	14-1/2"
(0.9 Cubic Feet )
Control Complement	Touch Control System
	Timer (0 - 99 min. 99 seconds)
	Microwave Power for Variable Cooking
	Repetition Rate;
	P-HI...........................................		Full power throughout the cooking time
	P-90 .............................................................			approx. 90% of Full Power
	P-80 .............................................................			approx. 80% of Full Power
	P-70 .............................................................			approx. 70% of Full Power
	P-60 .............................................................			approx. 60% of Full Power
	P-50 .............................................................			approx. 50% of Full Power
	P-40 .............................................................			approx. 40% of Full Power
	P-30 .............................................................			approx. 30% of Full Power
	P-20 .............................................................			approx. 20% of Full Power
	P-10 .............................................................			approx. 10% of Full Power
	P-0 .............................................		No power throughout the cooking time
	Grill Cooking (GRILL) ........		Top and Bottom Grill Mode / Top Grill Mode only
	Convection Cooking (CONVEC) ..........................			100 - 450˚F Temp. control
	Roast Cooking (ROAST) ..........................			325˚F with 30% microwave power
	CUSTOM HELP pad, COMPU COOK/ BAKE/ PIZZA/ GRILL/ ROAST pads
	COMPU DEFROST pad, CONVEC pad, GRILL pad, ROAST pad
	POPCORN pad, REHEAT pad, MINUTE PLUS pad
	Number and temperature selection pads, KITCHEN TIMER pad, CLOCK pad
	STOP/CLEAR pad, POWER LEVEL pad, START / TOUCH ON 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 115 -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.

4

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

Where a two-pronged wall-receptacle is encountered, it is the personal responsibility and obligation of the customer to contact a qualified electrician and have it replaced with a properly grounded 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-820BK

R-820BW

3-Pronged Plug	Grounded
	Receptacle Box

Grounding Pin

3-Pronged Receptacle

1.Oven light

2.Top heaters (Grill heaters)

3.Oven door with see through window

4.Door hinges

5.Safety door latches

6.Door seals and sealing surfaces

7.Bottom heater

8.Oven cavity

9.Turntable motor shaft

10.Ventilation openings 11.Waveguide cover

12.One touch door opening button 13.Auto-Touch control panel

14.Time display	Turntable
15.Power supply cord	support
16.Outer cabinet
17.Menu label
	Bottom
	heater

OVEN DIAGRAM
4	2	u
				t	0
				r
5		1			0
				e
	8	q
		9
3					y
6		0 7 5	w	0
Turntable				TOUCH CONTROL PANEL
		Rack
Turntable					COOK
					HELP
motor shaft

NOTE:

1.Ensure that the bottom heater is in the lowest position as shown in the figure, as it is possible to move it up and down to help with cleaning.

2.Place the turntable support over the turntable motor shaft on the floor of the cavity.

3.Then place the turntable onto the turntable support.

Iinteractive

CUSTOM

HELP

PIZZA

GRILL

BAKE

COMPU

ROAST

COOK

DEFROST

CONVEC

GRILL

ROAST

POPCORN

REHEAT

MINUTE

PLUS

1

2

3

4

5

100˚ F

150˚ F

275˚ F

300˚ F

325˚ F

6

7

8

9

O

350˚ F

375˚ F

400˚ F

425˚ F

450˚ F

KITCHEN

CLOCK

POWER

TIMER

LEVEL

STOP

START

CLEAR

TOUCH ON

5

R-820BK

R-820BW

OPERATION

DESCRIPTION OF OPERATING SEQUENCE

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

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 the

control unit. (Figure O-1).

1. The display will show

,

,

,

,

,

,

, ,

and

.

To set any program or set the clock, you must first touch the STOP/CLEAR pad. The display will clear, and " : " will appear.

MICROWAVE COOKING CONDITION

Program desired cooking time by touching the NUMBER pads. Program the power level by touching the POWER LEVEL pad and then a Number pad. When the START pad is touched, the following operations occur:

1.The contacts of relays are closed and components connected to the relays are turned on as follows.

(For details, refer to Figure O-2)

RELAY	CONNECTED COMPONENTS
RY-2	Power transformer
RY-5	Fan motor
RY-6	Oven lamp/ Turntable motor

2.120 volts A.C. is supplied to the primary winding of the power transformer and is converted to about 3.1 volts A.C. output on the filament winding, and approximately 2260 volts A.C. on the high voltage winding.

3.The filament winding voltage heats the magnetron filament and the H.V. winding voltage is sent to a voltage doubler circuit.

4.The microwave energy produced by the magnetron is channelled through the waveguide into the cavity feedbox, and then into the cavity where the food is placed to be cooked.

5.Upon completion of the cooking time, the power transformer, oven lamp, etc. are turned off, and the generation of microwave energy is stopped. The oven will revert to the OFF condition.

6.When the door is opened during a cook cycle, monitor switch, door sensing switch, secondary interlock switch, relay (RY5), relay (RY6) and primary interlock relay(RY2) 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 secondary interlock switch and primary interlock relay and is mechanically associated with the door so that it will function in the following sequence.

(1)When the door opens from the closed position, the relay (RY5), primary interlock relay(RY2) and secondary interlock switch open their contacts. And contacts of the relay(RY6) 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 secondary interlock switch and door sensing switch close. And contacts of the relay(RY6) 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(RY6) and primary 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(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)	32 sec.	0 sec.
(100% power)
Power 9(P-90)	30 sec.	2 sec.
(approx. 90% power)
Power 8(P-80)	26 sec.	6 sec.
(approx. 80% power)
Power 7(P-70)	24 sec.	8 sec.
(approx. 70% power)
Power 6(P-60)	22 sec.	10 sec.
(approx. 60% power)
Power 5(P-50)	18 sec.	14 sec.
(approx. 50% power)
Power 4(P-40)	16 sec.	16 sec.
(approx. 40% power)
Power 3(P-30)	12 sec.	20 sec.
(approx. 30% power)
Power 2(P-20)	8 sec.	24 sec.
(approx. 20% power)
Power 1(P-10)	6 sec.	26 sec.
(approx. 10% power)
Power 0(P-0)	0 sec.	32 sec.
(0% power)

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

GRILL COOKING CONDITIONS

The oven has two grill cooking conditions. They are the TOP HEATER mode and TOP AND BOTTOM HEATER mode.

6

TOP AND BOTTOM HEATER MODE

In this mode, the food is cooked by both the top heaters and bottom heater. Press the GRILL pad and number "1" pad and then enter the cooking time by pressing the number pads. When the START pad is pressed, the following operations occur (Figure O-3a):

1.The relays(RY3, RY4, RY5 and RY6) are energized.

2.The numbers of the digital read-out start the count down to zero.

3.Then the top heaters, bottom heater, turntable motor, oven lamp and fan motor are energized.

4.Now, the food is grilled by the top heaters and the bottom heater.

5.Upon completion of the selected cooking time, audible signal sounds and the contacts of relays(RY3, RY4 and RY6) are opened, then the top heating elements, bottom heating element, turntable motor and oven lamp are deenergized. But the relay(RY5) stays closed and the fan motor operates for 5 minutes. But if the cooking time is less than 2 minutes the relay(RY5) will not stay closed.

NOTE: If the total grill cooking time is beyond 35 minutes, the relay(RY1) is energized and the convection motor is energized.

TOP HEATER MODE

In this mode, the food is cooked by the top heaters. Press the GRILL pad and number "2" pad and then enter the cooking time by pressing the number pads. When the START pad is pressed, the following operations occur (Figure O-3b):

1.The relays(RY3, RY5 and RY6) are energized.

2.The numbers of the digital read-out start the count down to zero.

3.Then the top heaters, turntable motor, oven lamp and fan motor are energized.

4.Now, the food is grilled by the top heaters.

5.Upon completion of the selected cooking time, audible signal sounds and the contacts of relays(RY3 and RY6) are opened, then the top heaters, turntable motor and oven lamp are de-energized. But the relay(RY5) stays closed and the fan motor operates for 5 minutes. But if the cooking time is less than 2 minutes the relay(RY5) will not stay close.

NOTE: If the total grill cooking time is beyond 35 minutes, the relay(RY1) is energized and the convection motor is energized.

CONVECTION COOKING CONDITION WITH PREHEAT

Touch the CONVEC pad and select the convection with preheat mode by touching the number "1" pad.

1.Program desired convection temperature by touching the Temperature pad. Enter the cooking time by touching the number pads. When the START pad is touched, the following operations occur:

PREHEATING CONDITION

2.The coil of shut-off relays (RY5 and RY6) are energized, the oven lamp, cooling fan motor and turntable motor are turned on.

3.The coil of relays(RY3 and RY4) are energized by the control unit, and the top heaters and the bottom heater

R-820BK

R-820BW

work with 100% power. The relay(RY1) and the convection motor are not energized at this preheating condition.

NOTE: If the cavity temperature is lower than 100˚F(38C) at 4 minutes and 15 seconds after the preheat is started, the control unit judges that the thermistor is opened. And the oven is stopped.

4.When the oven temperature reaches the selected preheat temperature, the following operations occur:

4-1 The relays(RY3 and RY4) are de-energized by the control unit temperature circuit and thermistor, opening the circuit to the heating element.

4-2. The oven will continue to function for 30 minutes, turning the top heaters and the bottom heater on and off, as needed to maintain the selected preheat temperature. The oven will shutdown completely after 30 minutes

CONVECTION TIME COOKING CONDITION

5.When the preheat temperature is reached, a beep signal will sound indicating that the holding temperature has been reached in the oven cavity. Open the door and place the food to be cooked in the oven. When the START pad is touched, the following operations occur:

6.The numbers on the digital read-out start to count down to zero.

7.The relays(RY1, RY5 and RY6) are energized and the oven lamp, turntable motor, cooling fan motor and convection motor are energized.

8.The relays(RY3 and RY4) are energized (if the cavity temperature is lower than the selected temperature) and the main supply voltage is applied to the heating element to return to the selected cooking temperature. The top heaters and the bottom heater work in accordance with the following table while the heaters are energized.

Selected Temp-	Top Heaters	Bottom Heaters
erature (˚F)	Power (%)	Power (%)
100	20	10(after 3min. 0%)
150	20	10
275	40	40
300	40	50
325	50	50
350	50	60
375	60	60
400	60	70
425	70	70
450	70	80

9.Upon completion of the cooking time, the audible signal will sound, and oven lamp, turntable motor, cooling fan motor and convection motor are de-energized. At the end of the convection cycle, if the cavity air temperature is above 250˚F(120˚C), the circuit to RY5 will be maintained (by the thermistor circuit) to continue operation of the cooling fan motor until the temperature drops below 220˚F(104˚C), at which time the relay will be deenergized, turning off the fan motor. Relay RY1 will however, open as soon as the convection cycle has ended, turning off the convection fan motor.

7

R-820BK

R-820BW

ROAST COOKING CONDITION

Touch the ROAST pad once. And then program desired cooking time by touching the number pads. The ROAST pad is preprogrammed for 325˚F with 30% microwave power.

NOTE: The microwave power can not be changed. To change the temperature, touch the ROAST pad twice. When the display says "SELECT TEMP", touch desired temperature pad.

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

1.The numbers on the digital read-out start to count down.

2.The shut-off relays(RY1, RY5 and RY6) are energized, turning on the oven lamp, turntable motor, cooling fan motor and convection motor.

3.The microwave relay(RY2) is energized for 16 seconds within a 48 second time base.

4.The heater relays(RY3 and RY4) are energized intermittently within a 48 second time base. The power output is set in accordance with the following table.

Selected Temp-	Top Heaters	Bottom Heaters
erature (˚F)	Power (%)	Power (%)
100	20	40
150	30	50
275	50	60
300	60	70
325	70	70
350	70	70
375	70	70
400	70	70
425	70	70
450	70	70

5.The microwave relay(RY2) and the heater relays(RY3 and RY4) are not energized simultaneously.

ON/OFF TIME RATIO

In grill cooking, convection cooking or roast cooking, the top heaters, bottom heater or magnetron operate whithin a 48 second time base. The following table is the ON / OFF time ratio at each power output of the top heaters, bottom heater or magnetron.

POWER OUTPUT	ON TIME	OFF TIME
100%	48 sec.	0 sec.
90%	44 sec.	4 sec.
80%	40 sec.	8 sec.
70%	36 sec.	12 sec.
60%	32 sec.	16 sec.
50%	26 sec.	22 sec.
40%	22 sec.	26 sec.
30%	16 sec.	32 sec.
20%	12 sec.	36 sec.
10%	8 sec.	40 sec.

FIRE SENSING FEATURE (MICROWAVE MODE)

This model incorporates a sensing feature which will stop the oven's operation if there is a fire in the oven cavity during microwave cooking.

This is accomplished by the LSI repeatedly measuring the voltage across the temperature measurement circuit (thermistor) during it's 32-seconds time base comparing the obtained voltage measurements. If the most recent voltage measured is 700mV greater than the previous voltage measured, the LSI judges it as a fire in the oven cavity and switches off the relays to the power transformer, fan motor, oven lamp and turntable motor. The LSI also stops counting down. Please refer to the following section for a more detailed description.

Operation

Please refer to the timing diagrams below.

1.The thermistor operates within a 32-seconds time base and it is energized for three (3) seconds and off for 29 seconds. Two (2) seconds after the thermistor is energized, the voltage across the temperature measurement circuit is sampled by the LSI and twenty one (21) seconds after the thermistor is cut off the LSI turns on the cooling fan for six (6) seconds.

2.The above procedure is repeated. If the difference between the first voltage measured (in step 1) and the voltage measured when the procedure is repeated (step

2)is greater than 700mV the LSI makes the judgment that there is a fire in the oven cavity and will switch off the relays to the power transformer, fan motor, oven lamp and turntable motor. The LSI also stops counting down.

3.Once the fire sensor feature has shut the unit down, the programmed cooking cycle may be resumed by pressing the "START" pad or the unit may be reset by pressing the "CLEAR" pad.

0 2

32

64 (sec.)

3 sec.

ON

THERMISTOR

OFF

SENSING ON

VOLTAGE OFF

Sensing the voltage across temperature measurement circuit.

8

R-820BK R-820BW

SCHEMATIC

NOTE: CONDITION OF OVEN

1.DOOR CLOSED.

2.: OR CLOCK APPEAR ON DISPLAY.

NOTE: Indicates components with potential above 250 V.

			20A	THERMAL CUT-OUT
~60Hz120V	BRN	LIVE		(OVEN)
			FUSE	A1	CONTROL UNIT
	BLU	G-Y	EARTH	B1	B2	D1	D3
		NEUTRAL		DOOR SENSING SWITCH		THERMISTOR	CONVECTION
			THERMAL
			CUT-OUT
			(MAG.)

MOTORRY1

CM

MOTORFAN

FM

COM.

INTERLOCK RELAY

N.O.

TURNTABLE MOTOR

COM. RY4

N.O. N.O.

HEATERBOTTOM

HEATERGRILL(TOP)

MONITORSWITCH

POWER TRANSFORMER

CAPACITOR 0.94

AC2200V

RECTIFIERH.V.

LAMPOVENRY6 OL RY2:

COM. TTM

RY5

RPIMARY

RY3

MAGNETRON

A5

A3

N.O.

COM.

F

SECONDARY

INTERLOCK SWITCH

Figure O-1 Oven Schematic-OFF Condition

SCHEMATIC

NOTE: CONDITION OF OVEN

1.DOOR CLOSED.

2.MICROWAVE POWER LEVEL PAD PRESSED ONCE(100%).

3.COOKING TIME PROGRAMMED.

4.START PAD TOUCHED.

			20A	THERMAL CUT-OUT
~60Hz120V	BRN	LIVE		(OVEN)
			FUSE	A1	CONTROL UNIT
	BLU	G-Y	EARTH	B1	B2	D1	D3
		NEUTRAL		DOOR SENSING SWITCH		THERMISTOR	CONVECTION
			THERMAL
			CUT-OUT
			(MAG.)

MOTORRY1

CM

MOTORFAN

FM

COM.

INTERLOCK RELAY

N.O.

TURNTABLE MOTOR

COM. RY4

N.O. N.O.

HEATERBOTTOM

HEATERGRILL(TOP)

MONITORSWITCH

POWER TRANSFORMER

CAPACITOR 0.94

AC2200V

RECTIFIERH.V.

LAMPOVENRY6 OL RY2:

COM. TTM

RY5

RPIMARY

RY3

MAGNETRON

A5

A3

N.O.

COM.

F

SECONDARY

INTERLOCK SWITCH

Figure O-2 Oven Schematic-Microwave cooking Condition

9

R-820BK

R-820BW

SCHEMATIC NOTE: CONDITION OF OVEN

1.DOOR CLOSED.

2.GRILL PAD TOUCHED.

3.NUMBER "1" PAD TOUCHED.

4.COOKING TIME PROGRAMMED.

5.START PAD TOUCHED.

NOTE: Indicates components with potential above 250 V.

			20A	THERMAL CUT-OUT
~60Hz120V	BRN	LIVE		(OVEN)
			FUSE	A1	CONTROL UNIT
	BLU	G-Y	EARTH	B1	B2	D1	D3
		NEUTRAL		DOOR SENSING SWITCH		THERMISTOR	CONVECTION
			THERMAL
			CUT-OUT
			(MAG.)

MOTORRY1

CM

MOTORFAN

FM

COM.

INTERLOCK RELAY

N.O.

TURNTABLE MOTOR

COM. RY4

N.O. N.O.

HEATERBOTTOM

HEATERGRILL(TOP)

MONITORSWITCH

POWER TRANSFORMER

CAPACITOR 0.94

AC2200V

RECTIFIERH.V.

LAMPOVENRY6 OL RY2:

COM. TTM

RY5

RPIMARY

RY3

MAGNETRON

A5

A3

N.O.

COM.

F

SECONDARY

INTERLOCK SWITCH

Figure O-3a Oven Schematic-Grill cooking Condition (TOP AND BOTTOM HEATER mode)

SCHEMATIC

NOTE: CONDITION OF OVEN

1.DOOR CLOSED.

2.GRILL PAD TOUCHED.

3.NUMBER "2" PAD TOUCHED.

4.COOKING TIME PROGRAMMED.

5.START PAD TOUCHED.

			20A	THERMAL CUT-OUT
~60Hz120V	BRN	LIVE		(OVEN)
			FUSE	A1	CONTROL UNIT
	BLU	G-Y	EARTH	B1	B2	D1	D3
		NEUTRAL		DOOR SENSING SWITCH		THERMISTOR	CONVECTION
			THERMAL
			CUT-OUT
			(MAG.)

MOTORRY1

CM

MOTORFAN

FM

COM.

INTERLOCK RELAY

N.O.

TURNTABLE MOTOR

COM. RY4

N.O. N.O.

HEATERBOTTOM

HEATERGRILL(TOP)

MONITORSWITCH

POWER TRANSFORMER

CAPACITOR 0.94

AC2200V

RECTIFIERH.V.

LAMPOVENRY6 OL RY2:

COM. TTM

RY5

RPIMARY

RY3

MAGNETRON

A5

A3

N.O.

COM.

F

SECONDARY

INTERLOCK SWITCH

Figure O-3b Oven Schematic-Grill cooking Condition (TOP HEATER mode)

10

R-820BK

R-820BW

SCHEMATIC

NOTE: CONDITION OF OVEN

1.DOOR CLOSED.

2.CONVECTION PAD TOUCHED.

3.NUMBER "1" PAD TOUCHED.

4.TEMPERATURE PAD TOUCHED.

5.COOKING TIME PROGRAMMED.

6.START PAD TOUCHED.

			20A	THERMAL CUT-OUT
~60Hz120V	BRN	LIVE		(OVEN)
			FUSE	A1	CONTROL UNIT
	BLU	G-Y	EARTH	B1	B2	D1	D3
		NEUTRAL		DOOR SENSING SWITCH		THERMISTOR	CONVECTION
			THERMAL
			CUT-OUT
			(MAG.)

MOTORRY1

CM

MOTORFAN

FM

COM.

INTERLOCK RELAY

N.O.

TURNTABLE MOTOR

COM. RY4

N.O. N.O.

HEATERBOTTOM

HEATERGRILL(TOP)

MONITORSWITCH

POWER TRANSFORMER

CAPACITOR 0.94

AC2200V

RECTIFIERH.V.

LAMPOVENRY6 OL RY2:

COM. TTM

RY5

RPIMARY

RY3

MAGNETRON

A5

A3

N.O.

COM.

F

SECONDARY

INTERLOCK SWITCH

Figure O-4 Oven Schematic-Convection cooking Condition (Convection with preheat mode)

SCHEMATIC NOTE: CONDITION OF OVEN

1.DOOR CLOSED.

2.ROAST PAD TOUCHED.

3.COOKING TIME PROGRAMMED.

4.START PAD TOUCHED.

NOTE: The microwave relay (RY2) and the heater relay (RY3 or RY4) are not energized simultaneously.

			20A	THERMAL CUT-OUT
~60Hz120V	BRN	LIVE		(OVEN)
			FUSE	A1	CONTROL UNIT
	BLU	G-Y	EARTH	B1	B2	D1	D3
		NEUTRAL		DOOR SENSING SWITCH		THERMISTOR	CONVECTION
			THERMAL
			CUT-OUT
			(MAG.)

MOTORRY1

CM

MOTORFAN

FM

COM.

INTERLOCK RELAY

N.O.

TURNTABLE MOTOR

COM. RY4

N.O. N.O.

HEATERBOTTOM

HEATERGRILL(TOP)

MONITORSWITCH

POWER TRANSFORMER

CAPACITOR 0.94

AC2200V

RECTIFIERH.V.

LAMPOVENRY6 OL RY2:

COM. TTM

RY5

RPIMARY

RY3

MAGNETRON

A5

A3

N.O.

COM.

F

SECONDARY

INTERLOCK SWITCH

Figure O-5 Oven Schematic-Roast cooking Condition

11

R-820BK

R-820BW

DESCRIPTION AND FUNCTION OF COMPONENTS

DOOR OPEN MECHANISM

The door is opened by pushing the open button on the control panel, refer to 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 Latch Hook

Door

Sensing

Switch

Door	Monitor
	Switch

Secondary

Interlock

Switch Switch

Lever

Figure D-1. Door Open Mechanism

DOOR SENSING AND SECONDARY INTERLOCK SWITCHES

The secondary interlock switch is mounted in the lower position of the latch hook and the door sensing switch in the primary 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 primary interlock system consists of the door sensing switch and primary 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 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.

CAUTION: BEFORE REPLACING A BLOWN MONITOR FUSE TEST THE DOOR SENSING SWITCH, PRIMARY INTERLOCK RELAY (RY2), RELAY (RY6), SECONDARY 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 food 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 food. 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 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.

THERMAL CUT-OUT 125˚C (MAGNETRON)

This thermal cut-out protects the magnetron against overheating. If the temperature goes up higher than 257˚F (125˚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 cut-out will not resume.

THERMAL CUT-OUT 170˚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 catch fire due to over heating produced by improper setting of the cooking time or failure of control unit. Under the 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 338˚F(170˚C) causing the oven to shut down. The thermal cut-out will close in at 311˚F(155˚C).

TOP HEATERS

The top heaters are located on the top of the oven cavity assembly. The top heaters send out heat to grill foods.

12

BOTTOM HEATER

The bottom heater is located on the floor of the oven cavity assembly. The bottom heater sends out heat to grill foods.

CONVECTION COOKING SYSTEM

This oven is designed with a hot air heating system where food is not directly heated by the top heaters and the bottom heater, but is heated by forced circulation of the hot air produced by the top heaters and the bottom heater.

The air heated by the top heaters and the bottom heater is circulated through the convection passage provided on the outer casing of the oven cavity by means of the convection fan which is driven by the convection motor. It then enters the inside of the oven through the vent holes provided on the left side of the oven. Next, the hot air heats the food on the turntable and leaves the oven cavity through the vent in the center of the oven cavity rear wall.

R-820BK

R-820BW

Most of this hot air is reheated by the top heaters and the bottom heater and passes through the convection passage and enters the inside of the oven cavity again, in a continuing cycle.

In this way, the hot air circulates inside the oven cavity to raise its temperature and, at the same time, comes into contact with the food being cooked.

When the temperature inside the oven cavity reaches the selected temperature, the top heaters and the bottom heater are de-energized. When the temperature inside the oven cavity drops below the selected temperature, the top heaters and the bottom heater are energized again. In this way, the inside of the oven cavity is maintained at approximately the selected temperature.

When the convection time reaches 0, the top heaters and the bottom heater are de-energized and the convection fan stops operating and the oven shuts off.

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 (RY6), 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 FFSBA021WRK0 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.

13