SHARP R-770B Service Manual

DOUBLE GRILL

TURNOVER ADDSTAND

COVERSTIR DEFROST HELP

KG PCS

AUTO

COOK

AUTO COOK

PIZZA

AUTO GRILL

CRISPY SNACK

1

Grilled Chicken

2

Grilled Lobster

3

Grilled Fish

4

Steak

Fish Cake

Convenient Food

RICE COOK

REHEAT

STEAM MENU

HELP

SLOW COOK

POWER LEVEL

EASY DEFROST

GRILL

GRILL MIX

12345 6789O

STOP/CLEAR

INSTANT COOK/START

SER VICE MANU AL

DOUBLE GRILL

MICROWAVE OVEN

Potato Skin Garlic Bread

Chicken Wings



Salty Peanuts

MODEL

R-770B

S3811R770BPHR

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

TABLE OF CONTENTS

Page

CAUTION, MICROWAVE RADIATION.................................................................................................... 1

WARNING.................................................................................................................................................1

PRODUCT SPECIFICATIONS ................................................................................................................ 2

GENERAL INFORMATION.......................................................................................................................2

APPEARANCE VIEW .............................................................................................................................. 3

OPERATION SEQUENCE....................................................................................................................... 4

FUNCTION OF IMPORTANT COMPONENTS ....................................................................................... 7

SERVICING ..............................................................................................................................................8

TROUBLESHOOTING GUIDE .................................................................................................................9

TEST PROCEDURE.............................................................................................................................. 10

TOUCH CONTROL PANEL ASSEMBLY ..............................................................................................16

COMPONENT REPLACEMENT AND ADJUSTMENT PROCEDURE.................................................. 21

MICROWAVE MEASUREMENT ........................................................................................................... 26

WIRING DIAGRAM................................................................................................................................ 27

PICTORIAL DIAGRAM .......................................................................................................................... 30

POWER UNIT CIRCUIT .........................................................................................................................31

CONTROL PANEL CIRCUIT ..................................................................................................................32

PRINTED WIRING BOARD ....................................................................................................................33

PARTS LIST .......................................................................................................................................... 34

SHARP CORPORATION

R-770B

SERVICE MANUAL

MICROWAVE OVEN WITH TOP

AND BOTTOM HEATER

R-770B

GENERAL IMPORTANT INFORMATION

This Manual has been prepared to provide Sharp Corp. Service engineers with Operation and Service Information.

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

CAUTION

MICROWAVE RADIATION

PRODUCT SPECIFICATIONS

GENERAL INFORMATION

APPEARANCE VIEW

OPERATING SEQUENCE

FUNCTION OF IMPORTANT COMPONENTS

SERVICING AND TROUBLESHOOTING GUIDE

Service engineers should not be exposed to the microwave energy which may radiate from the magnetron or other microwave generating devices if it is improperly used or connected. All input and output microwave connections, waveguides, flanges and gaskets must be secured. Never operate the device without a microwave energy absorbing load attached. Never look into an open waveguide or antenna while the device is energized.

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 not any other visible damage with the oven.

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

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

Removal of the outer wrap gives access to potentials above 250V. All the parts marked "∆" on parts list may cause undue microwave

exposure, by themselves, or when they are damaged, loosened or removed.

Never operate the Top and/ or Bottom heater with the oven outer cabinet removed. (Because air flow is eliminated, and the excess heat generated on adjacent components). It can cause permanent damage or a fire.

TEST PROCEDURE

TOUCH CONTROL PANEL

COMPONENT REPLACEMENT AND ADJUSTMENT PROCEDURE

MICROWAVE MEASUREMENT

WIRING DIAGRAM

PARTS LIST

SHARP CORPORATION

OSAKA, JAPAN

R-770B

PRODUCT DESCRIPTION

SPECIFICATION

ITEM DESCRIPTION

Power Requirements 220 Volts

50 Hertz Single phase, 3 wire earthed

Power Consumption Microwave cooking 1.6 kW

Top Heater mode 1.3 kW

Grill cooking

Power Output

900 W nominal of RF microwave energy (measured by method of IEC 705) Operating frequency 2450 MHz

Grill heater Power Output (Top heater)

1200 W (600 W x 2) Bottom heater Power Output 800 W Case Dimensions Width 520 mm

Height 309 mm including foot

Depth 467 mm Cooking Cavity Dimensions Width 352 mm

Height 207 mm

Depth 368 mm Turntable diameter 325 mm Control Complement Touch Control System

Clock (1:00 - 12:59) / Timer (0 - 90 minutes)

Microwave Power for Variable Cooking

Repetition Rate;

100% ...................................................Full power throughout the cooking time

70%..................................................................... approx. 70% of FULL Power

50%..................................................................... approx. 50% of FULL Power

30%..................................................................... approx. 30% of FULL Power

10%..................................................................... approx. 10% of FULL Power

Mix cooking

Grill Mix High with Top Heater ............ Top heater with 50% microwave power

Grill Mix Low with Top Heater ............. Top heater with 10% microwave power

Grill Mix High with Bottom Heater ....... Bottom heater with 50% microwave power

Grill Mix Low with Bottom Heater........ Bottom heater with 10% microwave power

Bottom heater mode 0.9 kW Top and Bottom heater mode

2.1 kW

AUTO COOK pad, AUTO GRILL pad, PIZZA pad CRISPY SNACK pad, RICE COOK pad, REHEAT pad STEAM MENU pad, LESS (")/MORE (') pads HELP pad, SLOW COOK pad, POWER LEVEL pad EASY DEFROST pad, GRILL pad, GRILL MIX pad Number pads, STOP/CLEAR pad, CLOCK pad INSTANT COOK/START pad

Set Weight Approx. 19 kg

GENERAL INFORMATION

WARNING

THIS APPLIANCE MUST BE EARTHED

IMPORTANT

THE WIRES IN THIS MAINS LEAD ARE COLOURED IN ACCORDANCE WITH THE FOLLOWING CODE:

GREEN-AND-YELLOW : EARTH BLUE : NEUTRAL BROWN : LIVE

OVEN

1. Oven lamp

2. Top heaters (Grill heaters)

3. See through door

4. Door hinges

5. Door safety latches

6. Door seals and sealing surfaces

7. Bottom heater

8. Oven cavity

9. Turntable motor shaft

10.Ventilation openings

11.Waveguide cover

12.Door opening button

13.Control panel

14.Digital display

support

15.Power supply cord

16.Outer cabinet

Bottom  heater

APPEARANCE VIEW

Turntable Turntable

Turntable  motor shaft

High rack

Low rack

R-770B

NOTE:

1. Ensure that the bottom heater is in the lowest position as shown 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 on to the turntable support.

1. TOP HEATER SYMBOL The symbol will light when the top heater is in use.

2. BOTTOM HEATER SYMBOL The symbol will light when the bottom heater is in use.

3. MICROWAVE SYMBOL The symbol will light during microwave cooking.

A. AUTO COOK PAD

Press to select 4 popular menus.

B. AUTO GRILL PAD

Press to select 5 popular grill menus.

C. PIZZA PAD

Press to select 3 pizza menus.

D. CRISPY SNACK PAD

Press to select 5 popular snack menus.

E. RICE COOK PAD

Press to cook rice, congee or porridge.

F. REHEAT PAD

Press to reheat dish, soup, beverage or bread.

G. STEAM MENU PAD

Press to steam fish, meat or dumpling.

H. LESS (")/MORE (') pads

Press to adjust the doneness of food in one minute increments during cooking or to increase/ decrease the time whilst programming the automatic operations.

I. HELP PAD

Press to select auto start, child lock, language or demonstration modes. Press to get cooking information.

J. SLOW COOK PAD

Press to cook slowly and longer time.

K. POWER LEVEL PAD

Press to select microwave power setting. If not pressed, HIGH power is automatically selected.

L. EASY DEFROST PAD

Press to defrost meat by entering weight.

M. GRILL pad

Press to select GRILL mode.

N. GRILL MIX PAD

Press to select grill and microwave mix cooking mode.

O. NUMBER PADS

Press to enter cooking times, clock time, weight or quantity of food.

TOUCH CONTROL PANEL

TURNOVER ADD STAND

1 2

COVER STIR DEFROST HELP

KG PCS%AUTO

COOK

A B

1 2 3 4 5

RICE COOK

AUTO COOK

AUTO GRILL

Grilled Chicken Grilled Lobster

Grilled Fish

Steak

Fish Cake

REHEAT STEAM MENU

CRISPY SNACK

PIZZA

Potato Skin

Garlic Bread

Chicken

Salty Peanuts

Convenient Food

Wings



HELP

J K M

SLOW COOK

POWER LEVEL

GRILL GRILL MIX

EASY DEFROST

12345

6789O

P. STOP/CLEAR PAD

Press to clear during programming. Press once to stop operation of oven during cooking; Press twice to cancel cooking programme.

Q. CLOCK PAD

Press to set clock time.

R. INSTANT COOK/START PAD

Press once to cook for 1 minute at 100% (HIGH power) or increase by 1 minute multiples each time this pad is pressed during cooking. Press to start oven after setting programs.

STOP/CLEAR

INSTANT COOK/START

Indicator

C D

F G

I L

Q R

R-770B

OPERATION SEQUENCE

OFF CONDITION

Closing the door activates the 1st. latch switch, 2nd. interlock relay control switch.

IMPORTANT: When the oven door is closed, the contacts COM-NC of the monitor switch must be open. When the microwave oven is plugged in a wall outlet (220V 50Hz), the line voltage is supplied to the noise filter and the control unit.

Figure O-1 on page 27

1. The oven display will show " SHARP MICRO- WAVE OVEN " .

2. Press the STOP/CLEAR pad. The oven display will show " : ".

3. Set the clock as follows. 3-1. Press the CLOCK pad once. 3-2. Enter the time of day by perssing the number

pads.

3-3. Start the clock by pressing the CLOCK pad.

NOTE:

1. If you do not set the clock, " : " will appear on the display. When the operation of the oven is finished, " : " will appear on the display instead of the time of day.

2. The oven can be also used when the clock is not set.

3. When the oven door is opened, the oven lamp comes on at this time.

MICROWAVE COOKING CONDITION

100% (HIGH) COOKING

Enter a desired cooking time by pressing the number pads and start the oven by pressing START pad.

Function sequence Figure O-2 on page 27

CONNECTED COMPONENTS RELAY High voltage transformer RY2 Grill heater (Top) RY3 Bottom heater RY4 Fan motor, RY5 Oven lamp, Turntable motor RY6

1. The line voltage is supplied to the primary winding of the high voltage transformer. The voltage is converted to about 3.3 volts A.C. output on the filament winding and high voltage of approximately 2000 volts A.C. on the secondary winding.

2. The filament winding voltage (3.3 volts) heats the magnetron filament and the high voltage (2000 volts) is sent to the voltage doubling circuit, where it is doubled to negative voltage of approximately 4000 volts D.C..

3. The 2450 MHz microwave energy produced in the magnetron generates a wave length of 12.24 cm. This energy is channelled through the waveguide (transport channel) into the oven cavity, where the food is placed to be cooked.

4. When the cooking time is up, a signal tone is heard and the relays RY2 + RY5 + RY6 go back to their home position. The circuits to the oven lamp, high voltage transformer, fan motor and turntable motor are cut off.

5. When the oven door is opened during a cooking cycle, the switches come to the following condition.

Switch Contact Condition

1st. latch switch COM-NO Closed Opened 2nd. interlock relay

control switch Monitor Switch COM-NC Opened Closed

COM-NO Closed Opened

During Oven Door Cooking Open(No cooking)

The circuit to the high voltage transformer, fan motor and turntable motor are cut off when the 1st. latch switch, 2nd. interlock relay control switch are made open. The oven lamp remains on even if the oven door is opened after the cooking cycle has been interrupted, because the relay RY6 stay closed. Shown in the display is remaining time.

6. MONITOR SWITCH CIRCUIT The monitor switch is mechanically controlled by the oven door, and monitors the operation of the 1st. latch switch and the nd. interlock relay RY2.

6-1. When the oven door is opened during or after the

cycle of a cooking program, the 1st. latch switch and 2nd. interlock relay control switch must open their contacts first. After that the contacts (COM-NC) of the monitor switch can be closed.

6-2. When the oven door is closed, the contacts (COM-

NC) of the monitor switch must be opened. After that the contacts of the 1st. latch switch and the 2nd. interlock relay control switch are closed.

6-3. When the oven door is opened and the contacts of the

1st. latch switch and 2nd. interlock relay remain closed, the fuse M10A will blow, because the monitor switch is closed and a short circuit is caused.

70% (MEDIUM HIGH), 50% (MEDIUM), 30% (MEDIUM LOW), 10% (LOW COOKING)

When the microwave oven is preset for variable cooking power, the line voltage is supplied to the high voltage transformer intermittently within a 32-second time base through the relay contact which is coupled with the current-limiting relay RY2. The following levels of microwave power are given.

SETTING

32 sec. ON

100%

24 sec. ON 8 sec. OFF

70%

18 sec. ON 14 sec. OFF

50%

12 sec. ON 20 sec. OFF

30%

6 sec. ON 26 sec. OFF

10%

Approx. 100%

Approx. 70%

Approx. 50%

Approx. 30%

Approx. 10%

Note: The On/Off time ratio does not exactly correspond

to the percentage of microwave power, because approx. 2 seconds are needed for heating up the magnetron filament.

GRILL COOKING CONDITIONS

The oven has three grill cooking condition. They are the TOPHEATER mode, BOTTOM HEATER mode and TOP AND BOTTOM HEATER mode.

R-770B

TOP HEATER MODE In this mode, the food is cooked by the top heaters. Press

the GRILL pad once and then enter the cooking time by pressing the number pads. When the START pad is pressed, the following operations occur:

Figure O-3(a) on page 27

1. The relay RY3 + RY5 + 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 + 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.

BOTTOM HEATER MODE In this mode, the food is cooked by the bottom heater.

Press the GRILL pad twice and then enter the cooking time by pressing the number pads. When the START pad is pressed, the following operations occur:

Figure O-3(b) on page 28

1. The relay RY4 + RY5 + RY6 are energized.

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

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

4. Now, the food is grilled by the bottom heater.

5. Upon completion of the selected cooking time, audible signal sounds and the contacts of relays RY4 + RY6 are opened, then the bottom heating elements, 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.

TOP AND BOTTOM HEATER MODE In this mode, the food is cooked by both the top heaters

and bottom heater. Press the GRILL pad three times and then enter the cooking time by pressing the number pads. When the START pad is pressed, the following operations occur:

Figure O-3(c) on page 28

1. The relay RY3 + RY4 + RY5 + 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 + RY6 are opened, then the top heating elements, bottom heating element, 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 closed.

GRILL MIX COOKING CONDITION The oven will cook food by supplying grill heaters (top

heaters or Bottom heater) and microwave energy alternately within a 48 seconds time base. And the oven has four programmed cooking mode.

GRILL MIX HIGH WITH TOP HEATER MODE AND GRILL MIX LOW WITH TOP HEATER MODE

In these modes, the food is cooked by the top heaters and the microwave energy. Press the GRILL MIX pad once for GRILL MIX HIGH with TOP HEATER mode. Press the GRILL MIX pad twice for GRILL MIX LOW with TOP HEATER mode. And then enter the cooking time by pressing the number pads. When the START pad is pressed, the following operations occur:

Figure O-4(a) on page 29

1. The relay RY5 + RY6 are energized.

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

3. The turntable motor, oven lamp and fan motor are energized.

4. The relay RY2 + RY3 are energized alternately within a 48 seconds time base by the control unit.

5. The top heaters operate through the relay RY3 is energized. And the high voltage transformer operates through the relay RY2 is energized.

6. The relationship between the top heating elements and magnetron operations are as follows.

26 SEC. 22 SEC.

(MICRO.)

TOP  HEATERS

(MICRO.)

TOP HEATERS

OFF

GRILL MIX HIGH with TOP HEATER mode

OFF

GRILL MIX LOW with TOP HEATER mode

OFF

40 SEC.8 SEC.

MICROWAVE POWER

= APPROX. 50%

MICROWAVE POWER

= APPROX. 10%

Note: The On/Off time ratio does not exactly correspond

to the percentage of microwave power, because approx. 2 seconds are needed for heating up the magnetron filament.

7. Upon completion of the selected cooking time, audible signal sounds and the contacts of relays RY2 + RY3 + RY6 are opened, then the top heaters, high voltage transformer, 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 close.

GRILL MIX HIGH WITH BOTTOM HEATER MODE AND GRILL MIX LOW WITH BOTTOM HEATER MODE

IIn these modes, the food is cooked by the bottom heater and the microwave energy. Press the GRILL MIX pad three (3) times for GRILL MIX HIGH with BOTTOM HEATER mode. Press the GRILL MIX pad four (4) times for GRILL MIXLOW with BOTTOM HEATER mode. And then enter the cooking time by pressing the number pads.

R-770B

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

Figure O-4(b) on page 29

1. The relay RY5 + RY6 are energized.

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

3. The turntable motor, oven lamp and fan motor are energized.

4. The relay RY2 + RY4 are energized alternately within a 48 seconds time base by the control unit.

5. The bottom heater operate through the relay RY4 is energized. And the high voltage transformer operates through the relay RY2 is energized.

6. The relationship between the top heating elements and magnetron operations are as follows.

26 SEC. 22 SEC.

(MICRO.)

BOTTOM  HEATER

(MICRO.)

OFF

GRILL MIX HIGH with BOTTOM HEATER mode

OFF

40 SEC.8 SEC.

MICROWAVE POWER

= APPROX. 50%

MICROWAVE POWER

= APPROX. 10%

protect the oven door against temperature rising.

Cooking mode time (minutes) output (%) (seconds)

Microwave 100% Power

Top heaters 30 50 48 Bottom heater 15 50 48

Top browner and Bottom browner or Oven cooking

Specified cooking Limited power Time base

20 70 32

10 (Top) 50 48 10 (Bottom) 50 48

NOTE:

1. In case of Automatic operations, the limitations of power output are not carried out.

2. In case that the STOP/CLEAR pad is pressed or the oven door is opened during cooking, the limitations of power output are carried out after the total cooking time beyond the specified cooking time.

3. In case of the two or more same cooking modes are carried out, the limitations of power output are carried out after the total cooking time beyond the specified cooking time.

4. In case of the two or more different cooking modes are carried out, the specified cooking time is started to count from the point when the cooking mode is changed.

5. If the cooking mode has the power level display, the power level is also displayed when the limitations of power output are carried out.

BOTTOM HEATER

GRILL MIX LOW with BOTTOM HEATER mode

OFF

Note: The On/Off time ratio does not exactly correspond

to the percentage of microwave power, because approx. 2 seconds are needed for heating up the magnetron filament.

7. Upon completion of the selected cooking time, audible signal sounds and the contacts of relays RY2 + RY4 + RY6 are opened, then the bottom heater, high voltage transformer, 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 close.

AUTOMATIC OPERATIONS

This oven has the following automatic operations;

PIZZA CRISPY SNACK AUTO COOK AUTO GRILL REHEAT STEAM MENU RICE COOK

EASY DEFROST Thease will automatically compute the cooking mode and the cooking time. And the oven will cook or defrost the food according to the special cooking sequence.

LIMITATIONS OF POWER OUTPUT IN MANUAL OPERATION

After the same cooking mode is carried out for more than the specified cooking time, the power output is automatically reduced by turning the control relays on and off intermittently, as shown in the table below. This is to

FUNCTION OF IMPORTANT COMPONENTS

R-770B

DOOR OPEN MECHANISM

The door can be opened by pushing the open button on the control panel. When the open button is pushed, the switch lever is moved upward, operating the latch head. The latch head is moved upward and released from the latch hook. Now, the door can be opened.

Latch Heads

Latch Hook

2nd. Interlock Relay Control Switch

Door

Monitor Switch

1st. Latch Switch

Switch Lever

Figure D-1. Door Open Mechanism

1ST. LATCH SWITCH AND 2ND. INTERLOCK RELAY CONTROL SWITCH

1. When the oven door is closed, the contacts (COM-NO) of each switch must be closed.

2. When the oven door is opened, the contacts (COMNO) of each switch must be opened.

MONITOR SWITCH

1. When the door is closed, the contacts (COM-NC) must be opened.

2. When the door is opened, the contacts (COM-NC) must be closed.

3. If the oven door is opened and he contacts (COM-NO) of the 1st. latch switch and 2nd. interlock relay RY2 fail to open, the fuse M10A blows immediately after closing the contacts (COM-NC) of the monitor switch.

CAUTION: BEFORE REPLACING A BLOWN FUSE

M10A TEST THE 1ST. LATCH SWITCH, 2ND. INTERLOCK RELAY RY2, MONITOR SWITCH AND MONITOR RESISTOR FOR PROPER OPERATION. (REFER TO CHAPTER “TEST PROCEDURE”).

FUSE M10A 250V

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

2. This fuse blows when the 1st. latch switch and 2nd. interlock relay RY2 remain closed with the oven door open and when the contacts (COM-NC) of monitor switch closes.

HIGH VOLTAGE FUSE 0.75A

The high voltage fuse blows when the high voltage rectifier or the magnetron is shorted.

THERMAL CUT-OUT 125˚C (MG)

This thermal cut-out protects the magnetron against overheating. If the temperature goes up higher than 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 cut back in at 95˚C.

THERMAL CUT-OUT170˚C (OVEN)

The thermal cut-out located on the top of the oven cavity is designed to prevent damage to the oven if the foods 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 temperature are reached within the oven cavity, oven thermal cut-out will open at 170˚C causing the oven to shut down. The thermal cut-out will cut back in at 155˚C.

TURNTABLE MOTOR

The turntable motor drives the turntable roller assembly to rotate the turntable.

FAN MOTOR

The 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 vapours given off from heating food. It is then exhausted through the exhausting air vents of the oven cavity.

NOISE FILTER

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

TOP HEATERS

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

BOTTOM HEATER

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

FUSE 15A

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

R-770B

SERVICING

WARNING TO SERVICE PERSONNEL

Microwave ovens contain circuitry capable of producing very high voltage and current. Contact with following parts will result in electrocution. High voltage capacitor, High voltage transformer, Magnetron, High voltage rectifier assembly, High voltage harness.

REMEMBER TO CHECK 3D

1) Disconnect the supply.

2) Door opened, and wedged open.

3) Discharge high voltage capacitor. WARNING: AGAINST THE CHARGE OF THE

HIGH-VOLTAGE CAPACITOR.

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, of the connecting lead of the high-voltage rectifier) against the chassis with the use of an insulated screwdriver.

Sharp recommend that wherever possible fault-finding is carried out with the supply disconnected. It may in, some cases, be necessary to connect the supply after the outer case has been removed, in this event carry out 3D checks and then disconnect the leads to the primary of the high voltage transformer. Ensure that these leads remain isolated from other components and the oven chassis. (Use insulation tape if necessary.) When the testing is completed carry out 3D checks and reconnect the leads to the primary of the high voltage transformer.

REMEMBER TO CHECK 4R

1) Reconnect all leads removed from components during testing.

2) Replace the outer case (cabinet).

3) Reconnect the supply.

4) Run the oven. 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 level to HIGH (100%) and set the microwave timer for two (2) minutes. And push the start key. When the two minutes has elapsed (timer at zero) carefully check that the water is now hot. If the water remains cold carry out 3D checks and re-examine the connections to the component being tested.

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

TROUBLESHOOTING GUIDE

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 fuse M10A in the 1st. latch switch - 2nd. interlock relay(RY2)- monitor switch - monitor resistor circuit, check the 1st. latch switch, 2nd. interlock relay(RY2), monitor switch and monitor resistor before replacing the fuse M10A.

R-770B

CONDITION

OFF CONDITION

COOKING CONDITION (COMMON MODE)

MICROWAVE COOKING CONDITION

GRILL COOKING CONDITION

GRILL MIX COOKING CONDITION

TEST PROCEDURE

AND

POSSIBLE CAUSE

DEFECTIVE PARTS

PROBLEM

Fuse 15A blows when power cord is plugged into wall outlet.

Fuse M10A blows when the door is opened.

Oven lamp does not light when door is opened. (Display operates.)

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

"SHARP MICRO- OVEN PRESS STOP" does not appear in display when power cord is plugged into wall outlet.

Display does not operate properly when STOP/CLEAR pad is pressed.

Oven does not start when the INSTANT COOK/ START pad is pressed. (Display operates.)

Oven lamp does not light. (Turntable motor operates.)

Fan motor does not operate. (Oven lamp lights.)

Turntable motor does not operate. (Oven lamp lights.)

Oven or electrical parts does not stop when cooking time is 0 or STOP/ CLEAR pad is pressed.

Oven goes into cook cycle but shuts down before end of cooking cycle.

Oven seems to be operating but little or no heat is produced in oven load.

Oven does not operating properly during variable cooking condition except 100% cooking condition.

Top heaters do not operate. Bottom heater does not operate. Oven seems to be operating but lit-

tle or no heat is produced in oven load. (Microwave power does not seem to be generated properly.)

Top heaters do not operate. Bottom heater does not operate.

ABCDE EEFFGH I J J KKL MNOOOOOP

MAGNETRON

HIGH VOLTAGE TRANSFORMER

H.V. RECTIFIER ASSEMBLY

HIGH VOLTAGE CAPACITOR

1ST. LATCH SWITCH

MONITOR SWITCH

2ND. INTERLOCK RELAY CONTROL SWITCH

THERMAL CUT-OUT 125˚C

THERMAL CUT-OUT 170˚C

FUSE M10A

FUSE 15A

NOISE FILTER

FAN MOTOR

TURNTABLE MOTOR

TOP HEATIER S

BOTTOM HEAER

HIGH VOLTAGE FUSE

POWER SUPPLY CORD

OVEN LAMP

SHORTED WIRE HARNESS

OPENED WIRE HARNESS

MIS-ADJUSTMENT OF SWITCHES

TOUCH CONTROL PANEL

KEY UNIT

RELAY RY2

RELAY RY3

RELAY RY4

RELAY RY5

RELAY RY6

FOIL PATTERN ON P.W.B.

R-770B

TEST PROCEDURES

PROCEDURE

LETTER COMPONENT TEST

A MAGNETRON TEST

NEVER TOUCH ANY PART IN THE CIRCUIT WITH YOUR HAND OR AN INSULATED TOOL WHILE THE OVEN IS IN OPERATION.

CARRY OUT 3D CHECKS. Isolate the magnetron from high voltage circuit by removing all leads connected to filament terminal. To test for an open circuit filament use an ohmmeter to make a continuity test between the magnetron

filament terminals, the meter should show a reading of less than 1 ohm. To test for short filament to anode condition, connect ohmmeter between one of the filament terminals

and the case of the magnetron (ground). This test should be indicated an infinite resistance. If a low or zero resistance reading is obtained then the magnetron should be replaced.

MICROWAVE OUTPUT POWER (1 litre load)

The following test procedure should be carried out with the microwave oven in a fully assembled condition (outer case fitted). Microwave output power from the magnetron can be measured by way of IEC 705, i.e. it is measured by how much power the water load can absorb. To measure the microwave output power in the microwave oven, the relation of calorie and watt is used. When P(W) heating works for t(second), approximately P x t/4.187 calorie is generated. On the other hand, if the temperature of the water with V(ml) rises ∆T (°C) during this microwave heating period, the calorie of the water is V x ∆T.

The formula is as follows;

P x t / 4.187 = V x ∆ T P (W) = 4.187 x V x ∆T / t

Our condition for water load is as follows:

Room temperature ........... around 20°C Power supply Voltage.............. Rated voltage

Water load.................................. 1000 g Initial temperature.............................. 10±2°C

Heating time.............................. 47 sec.

P = 90 x ∆T

Measuring condition:

1. Container The water container must be a cylindrical borosilicate glass vessel having a maximum material thickness of 3 mm and an outside diameter of approximately 190 mm.

2. Temperature of the oven and vessel The oven and the empty vessel are at ambient temperature prior to the start the test.

3. Temperature of the water The initial temperature of the water is (10±2)°C.

4. Select the initial and final water temperature so that the maximum difference between the final water temperature and the ambient temperature is 5K.

5. Select stirring devices and measuring instruments in order to minimize addition or removal of heat.

6. The graduation of the thermometer must be scaled by 0.1°C at minimum and be an accurate thermometer.

7. The water load must be (1000±5) g.

8. “t” is measured while the microwave generator is operating at full power. Magnetron filament heatup time is not included.

NOTE:The operation time of the microwave oven is “t + 2” sec. (2 sec. is magnetron filament heat-up time.)

Measuring method:

1. Measure the initial temperature of the water before the water is added to the vessel. (Example: The initial temperature T1 = 11°C)

2. Add the 1 litre water to the vessel.

3. Place the load on the centre of the shelf.

4. Operate the microwave oven at HIGH for the temperature of the water rises by a value ∆ T of (10 ± 2) K.

5. Stir the water to equalize temperature throughout the vessel.

6. Measure the final water temperature. (Example: The final temperature T2 = 21°C)

7. Calculate the microwave power output P in watts from above formula.

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