Sharp R772M-003 Schematic

SERVICE MANUAL

MICROWAVE OVEN WITH TOP

AND BOTTOM GRILLS

SERVICING

PRODUCT SPECIFICATIONS

R-772(W)M/ R-772(G)M

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.

WARNING

MICROWAVE RADIATION

Personnel 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.

GENERAL INFORMATION

APPEARANCE VIEW

OPERATING SEQUENCE

FUNCTION OF IMPORTANT COMPONENTS

TROUBLESHOOTING GUIDE AND TEST PROCEDURE

TOUCH CONTROL PANEL

COMPONENT REPLACEMENT AND ADJUSTMENT PROCEDURE

MICROWAVE MEASUREMENT

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 Grill 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.

SHARP CORPORATION

OSAKA, JAPAN

WIRING DIAGRAM

PARTS LIST

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 highvoltage capacitor (that is, of the connecting lead of the highvoltage 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 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 checks and reconnect the leads to the primary of the High voltage transformer.

3D checks and

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 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 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.

3D checks and re-examine the connections to

PRODUCT DESCRIPTION

SPECIFICATION

ITEM DESCRIPTION

Power Requirements 230 - 240 Volts / 50 Hertz / Single phase, 3 wire earthed Power Consumption Microwave cooking 1.6 kW Approx. 7.2 A

Oven cooking 1.5 kW Approx. 6.5 A

Top Grill mode ...................... 1.05 kW Approx. 4.2 A

Grill cooking Bottom Grill mode................. 0.55 kW Approx. 2.2 A

Top and Bottom mode ......... 1.55 kW Approx. 6.5 A

Dual cooking

Power Output

Top Grill heating element Power Output Bottom heating element Power Output Case Dimensions Width 520 mm Height 309 mm (including foot) Depth 436 mm Cooking Cavity Dimensions Width 349 mm Height 207 mm Depth 357 mm Turntable diameter 325 mm Control Complement Touch Control System

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

1.0 kW

0.5 kW

Clock (1:00 - 12:59) / Timer (0 - 99 minutes 90 sec.) Microwave Power for Variable Cooking

Repetition Rate;

100 (HIGH) ....................... Full power throughout the cooking time

70 (MEDIUM HIGH) ......................... approx. 70% of FULL Power

50 (MEDIUM) ................................... approx. 50% of FULL Power

30 (MEDIUM LOW).......................... approx. 30% of FULL Power

10 (LOW) ......................................... approx. 10% of FULL Power

Oven temperature control range:

200˚C, 180˚C, 160˚C, 130˚C, 100˚C, 70˚C and 40˚C

Micro and Top Grill ............... 2.55 kW Approx. 11.2 A

Micro and Bottom Grill ............ 2.1 kW Approx. 9.2 A

TIME keys, BREAKFAST key, PIZZA key, AUTO COOK key, AUTO DEFROST key, WEIGHT keys LESS/MORE keys, DUAL /GRILL key, MICROWAVE POWER LEVEL key STOP/CLEAR key, START/AUTO MINUTE key, WEIGHT CONVERSION key, AUTO START/CLOCK key,

Set Weight Approx. 20 kg

GENERAL INFORMATION

THIS APPLIANCE MUST BE EARTHED

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

INSTANT COOK keys

OVEN (˚C) key, GRILL key

TIMER key

WARNING

IMPORTANT

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

APPEARANCE VIEW

OVEN

1. Control panel

2. Oven lamp

3. Grill heating element (Top Grill)

4. Door opening button

5. Waveguide cover

6. Oven cavity

7. Turntable motor shaft

COOK indicator showing oven in operation.

TOP GRILL indicator.

BOTTOM GRILL indicator

MICROWAVE indicator.

WEIGHT indicators.

8. Grill heating element (Bottom Grill)

9. Door seals and sealing surfaces

10.Ventilation openings

11.Outer cabinet

12.Power supply cord

13.Turntable

14.Rack

CONTROL PANEL

DEFROST indicator.

COOK

LBSKGOZ

DEFROST

AUTO

AUTO indicator, showing auto cooking on progress. DIGITAL DISPLAY.

LESS/MORE indicators. % percentage microwave power level indicator.

TIME keys. Use to select cooking time.

BREAKFAST key.

AUTO COOK key.

WEIGHT keys.

GRILL key. Press to select Grill.

OVEN (˚C) key.

MICROWAVE POWER LEVEL key. Press to select microwave power level.

STOP/CLEAR key. Press once to stop a programme, and/or twice to cancel a programme.

TIMER key

WEIGHT CONVERSION key

BREAKFAST

MIXED GRILL

OVEN CHIPS

1 Chilled Ready Meals 1 Frozen Ready Meals 3 Roast Beef / Lamb 3 4 Roast Pork 4 Minced Meat 5 Roast Poultry 5 Bread

R-772

BAKED POTATOES

PIZZA

CHICKEN PTNS

CRISPY CRUMB FOODS

FRESH VEG.

1 Meat Joint 2 Poultry

Chicken Ptn, Steak, Chops

PIZZA key. Press to cook pizza.

INSTANT COOK keys.

AUTO DEFROST key.

LESS/MORE keys. Press to shorten or lengthen heating time.

DUAL GRILL key. Press to select Dual Grill.

START/AUTO MINUTE key. Press to start a programme. Press to cook on (HIGH) for 1 minute or increase time during cooking in multiples of 1 minute.

AUTO START/CLOCK key. Use to set the clock.

OPERATION SEQUENCE

OFF CONDITION

Closing the door activates the monitored latch switch and the stop 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 (230 - 240V / 50Hz), the line voltage is supplied to the noise filter.

Figure O-1 on page 29

1. The control unit is not energized. The display shows nothing (Fig. O-1 (a)).

2. Open the door. The contacts (COM-NC) of the monitored latch switch are closed and the control unit is energized. Then contacts of relays RY1 and RY5 are closed, and the oven lamp will light and the display will show "ENERGY SAVE MODE" (Fig. O-1(b)).

3. Close the door. The contacts (COM-NC) of the monitored latch switch are opened and the contacts of relay RY1 are opened and the oven lamp will be turned off. The display will show " . 0". (Fig. O-1(c)).

NOTE: Energy save mode

1. If the oven has not been used for more than 2 minutes, the contacts of the relay RY5 will be opened and the control unit will be not energized. Open and close the door, the control unit will resume.

2. If the clock is set, this energy save mode does not work.

MICROWAVE COOKING CONDITION

HIGH COOKING

Enter a desired cooking time by touching the TIME keys and start the oven by touching START key.

Function sequence Figure O-2 on page 30

CONNECTED COMPONENTS RELAY Oven lamp, Turntable motor RY1 High voltage transformer RY2 Fan 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 wavelength 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 RY1 + RY2 + 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

Monitored latch switch

Stop switch

Monitor Switch

COM-NO Closed Opened COM-NC Opened Closed COM-NO Closed Opened COM-NO Closed Opened COM-NC Opened Closed

During Oven Door Cooking Open(No cooking)

The circuit to the high voltage transformer is cut off when the contacts of relay RY2, and the contacts (COM-NO) of the monitored latch switch and monitor switch are made open. The circuit to the fan motor is cut off when the relay RY6 is made open. The circuit to the turntable motor is cut off when the contacts (COM-NO) of the monitored latch switch are made open. The relay RY2 and RY6 are made open when the door is opened. The oven lamp remains on even if the oven door is opened after the cooking cycle has been interrupted, because the relay RY1 stays 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 monitored latch switch.

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

cycle of a cooking program, the monitored latch switch and stop switch must open their contacts (COM-NO) first.

And

the contacts (COM-NC) of the monitored latch switch SW1 are made closed. After that the contacts (COM-NC) of the monitor switch can be closed and the contacts (COM-NO) of monitor switch are made open.

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

NC) of the monitor switch must be opened and the contacts (COM-NO) of monitor switch must be closed. After that the contacts (COM-NO) of the monitored latch switch and the stop switch are made closed. the contacts (COM-NC) of the monitored latch switch are made open

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

(COM-NO) of the monitored latch switch remain closed, the fuse F8A will blow. Because the relay RY1 and monitor switch are closed and a short circuit is caused.

MEDIUM HIGH, MEDIUM, MEDIUM LOW, 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.

900W (HIGH)

MEDIUM

630W

450W (MEDIUM) Approx. 50%

MEDIUM

270W

90W (LOW) Approx. 10%

32 sec. ON

24 sec. ON 8 sec. OFF

HIGH

18 sec. ON

12 sec. ON

LOW

6 sec. ON

Approx. 70%

14 sec. OFF

20 sec. OFF

Approx. 30%

26 sec. OFF

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

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

GRILL COOKING CONDITION

TOP GRILL (Figure O-3a)

In this condition the food is cooked by the top grill heating element. Programme the desired cooking time by touch-

And

100%

OPERATION SEQUENCE

ing the TIME keys and touh the GRILL key once. When the STARTkey is touched, the following operations occur:

1. The numbers on the digital readout start the count down to zero.

2. The oven lamp, cooling fan motor and turntable motor are energized.

3. The relay RY3 is energized and the main supply voltage is applied to the top grill heating element.

4. Now, the food is cooked by the top grill heating element.

BOTTOM GRILL (Figure O-3b)

In this condition the food is cooked by bottom grill heating element energy. Programme the desired cooking time by touching the TIME keys and touh the GRILL key twice. When the STARTkey is touched, the following operations occur:

1. The numbers on the digital readout start the count down to zero.

2. The oven lamp, cooling fan motor and turntable motor are energized.

3. The relay RY4 is energized and the main supply voltage is applied to the bottom grill heating element.

4. Now, the food is cooked by the bottom grill heating element.

TOP AND BOTTOM GRILL (Figure O-3c)

In this condition the food is cooked by top and bottom grill heating elements energy. Programme the desired cooking time by touching the TIME keys and touh the GRILL key three times. When the STARTkey is touched, the following operations occur:

1. The numbers on the digital readout start the count down to zero.

2. The oven lamp, cooling fan motor and turntable motor are energized.

3. The relay RY4 is energized and the main supply voltage is applied to the bottom grill heating element.

4. The relay RY3 is energized and the main supply voltage is applied to the top grill heating element.

5. Now, the food is cooked by the top and bottom grill heating elements.

OVEN COOKING CONDITION

PRE-HEATING (Figure O-4)

Programme the desired oven temperature by touching OVEN (˚C) key. When the STARTkey is touched, the following operations occur:

1. The coil shut-off relays RY1 and RY6 are energized, the oven lamp, cooling fan motor and turntable motor are turned on.

2. The coil shut-off relays RY3 and RY4 are energized by control unit and the main supply voltage is added to the top and bottom heating elements.

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

3-1. The coil shut-off relays RY3 and RY4 are energized

by control unit temperature circuit and thermistor, opening the circuit to the top and bottom grill heating elements.

3-2. The oven will continue to function for 30 minutes,

turning the top and bottom heating elements on and off, as needed to maintain the selected pre-heat temperature. The ovenwill shut-down completely after 30 minutes.

NOTE: The fan motor will be turned on and off at

preheating. And the convection motor will be turned off at preheating. See "Power setting" on page 9.

OVEN COOKING (Figure O-4)

When the pre-heat temperature is reached, a beep signal will sound indicating that the holding the temperature has been reached in the oven cavity. Open the door and place the food to cooked in the oven. Program desired cooking time by touching the TIME keys and program oven temperature by touching the OVEN (˚C) key . When the START key is touched, the following operations occur:

1. The numbers on the digital readout start the count down to zero.

2. The oven lamp, cooling fan motor and turntable motor are energized.

3. The relays RY3 and RY4 are energized (if the cavity temperature is lower than selected temperature) and the main supply voltage is applied to the top and bottom heating elements to return to the selected cooking temperature.

Upon completion of the cooking time, the audible signal will sound, and the oven lamp, turntable motor, cooling fan motor, top and bottom heating elements are de-energized. At the end of cooking cycle, if the cavity air temperature rise above 120˚C, the circuit to the relay RY6 will be maintained (by the thermistor circuit) to continue operation of the cooling fan motor until temperature drops below 105˚C, at that time the relay RY6 will be de-energized, turning off the fan motor.

DUAL COOKING CONDITION

MICROWAVE AND TOP GRILL (Figure O-5a)

Programme the desired cooking time by touching the TIME keys. Touch the DUAL GRILLL key once. Select the microwave power level by touching the MICROWAVE POWER LEVEL key. When the STARTkey is touched, the following operations occur:

1. The numbers on the digital readout start the count down to zero.

2. The oven lamp, cooling fan motor and turntable motor are energized.

3. The relay RY3 is energized and the main supply voltage is applied to the top grill heating element.

4. The relay RY2 is energized and the microwave energy is generated by magnetron.

5. Now, the food is cooked by microwave and top grill simultaneously.

MICROWAVE AND BOTTOM GRILL (Figure O-5b)

Programme the desired cooking time by touching the TIME keys. Touch the DUAL GRILL three twice. Select the microwave power level by touching the MICROWAVE POWER LEVEL key. When the STARTkey is touched, the following operations occur:

1. The numbers on the digital readout start the count

OPERATION SEQUENCE

down to zero.

2. The oven lamp, cooling fan motor and turntable motor are energized.

3. The relay RY4 is energized and the main supply voltage is applied to the bottom grill heating element.

4. The relay RY2 is energized and the microwave energy is generated by magnetron.

5. Now, the food is cooked by microwave and bottom grill simultaneously.

POWER SETTING

The power setting of the top heating element, bottom heating element and fan motor in the Oven cooking mode and Oven preheating mode is 100%.

ON/OFF TIME RATIO

In grill cooking, oven cooking or dual cooking, the top heater, 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.

AUTOMATIC COOKING

PIZZA BREAKFAST INSTANT COOK AUTO COOK AUTO DEFROST Above functions are automatic cooking. They automatically work out the correct cooking mode and cooking time and/or cooking temperature. They will cook 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 protect the oven door against temperature rising.

Cooking mode time (minutes) output (%) (seconds) Microwave (100%) Top grill 30 50 48 Bottom grill 45 50 48 Top grill and 15 (Top) 50 48

Bottom grill 15(Bottom) 50 48

Micro. (100%) 20 (Micro.) 70 48

+ Top grill 15 (Grill) 50 48

U A

Micro. (100%) 20 (Micro.) 70 48

+ Bottom grill 15 (Heater) 50 48

NOTE:

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

2. In case that the stop key is touched or the oven door is opened during cooking, the limitations of power output are not 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 not 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.

Specified cooking Limited power Time base

20 70 32

FUNCTION OF IMPORTANT COMPONENTS

DOOR OPEN MECHANISM

The door can be opened by pushing the open button on the control panel. When the open button is pushed, the open lever is pushes lower latch head on the door upward. The upper latch head is linked with the lower latch head, so now, the door can be opened.

DOOR

LATCH HEADS

LATCH HOOK

(SW2) MONITOR SWITCH

(SW1) MONITORED LATCH SWITCH

(SW3) STOP SWITCH

OPEN LEVER

Figure D-1. Door Open Mechanism

MONITORED LATCH SWITCH

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

2. When the oven door is opened, the contacts (COMNO) of the switch must be opened. And the contacts (COM-NC) must be closed.

STOP SWITCH

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

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

MONITOR SWITCH

The monitor switch is activated (the contacts opened) by the upper latch head on the door while the door is closed. The switch is intended to render the oven inoperative by means of blowing the fuse F8A when the contacts of the monitored latch switch fail to open when the door is opened.

Function

1. When the door is opened, the contacts (COM-NC) of monitor switch close (to the ON condition) due to their being normally closed and contacts (COM-NO) open. At this time the contacts (COM-NO) of monitored latch switch is 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 (COM-NC) are opened and contacts (COM-NO) closed and then contacts (COM-NO) of monitored latch switch and stop switch are closed.(On opening the door, each of these switches operate inversely.)

3. If the door is opened and the monitored latch switch contacts (COM-NO) fail to open, the fuse F8A blows immediately after closing of the monitor switch (COMNC) contacts.

CAUTION: BEFORE REPLACING A BLOWN FUSE F8A,

TEST THE MONITORED LATCH SWITCH AND MONITOR SWITCH FOR PROPER OPERATION. (REFER TO CHAPTER “TEST PROCEDURE”).

FUSE 15A 250V

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

FUSE F8A 250V

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

2. The fuse also blows when the monitored latch switch remains closed with the oven door open and when the monitor switch contact (COM-NC) closes.

3. The fuse also blows when the asymmetric rectifier, H.V. rectifier,.H.V. wire harness, H.V. capacitor, magnetron or secondary winding of high voltage transformer is shorted.

TC TRANSFORMER

T/C transformer converts A.C. line voltage into low voltage to drive the control unit.

THERMAL CUT-OUT 125˚C (MG)

This thermal cut-out protects the magnetron against overheat. 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 voltage to the high voltage transformer will cut off and operation of the magnetron will be stopped. The defective thermal cut-out must be replaced with a new one.

THERMAL CUT-OUT 150˚C (OVEN)

This thermal cut-out protects the oven against the overheat during grill cooking, oven cooking or dual (combination) cooking. If the temperature rises above 150˚C because the fan motor is interrupted, the air inlet duct is blocked or the ventilation openings are obstructed, the thermal cut-out opens and switches off all the electrical parts. When the cools itself down to the operating temperature of 130˚C, the contacts of the thermal cut-out will close again.

ASYMMETRIC RECTIFIER

The asymmetric rectifier is solid state device that prevents current flow is both directions. And it prevents the temperature rise of the high voltage transformer by blowing the fuseF8A when the high voltage rectifier is shorted.

D2 D1

ASYMMETRIC RECTIFIER

The rated peak reverse voltage of D1 of the asymmetric rectifier is 6 KV. The rated peak reverse voltage of D2 of the asymmetric rectifier is 1.7 KV. D1 and D2 of the asymmetric rectifier or high voltage rectifier are shorted when the each peak reverse voltage goes beyond the each rated peak reverse voltage. (The process of the blowing the fuseF8A.)

1. The high voltage rectifier is shorted by some fault when microwave cooking or dual cooking.

2. The peak reverse voltage of D2 of the rectifier goes beyond the rated peak reverse voltage 1.7 KV in the

HIGH VOLTAGE RECTIFIER

FUNCTION OF IMPORTANT COMPONENTS

voltage doubler circuit.

3. D2 of the rectifier is shorted.

4. The large electric currents flow through the high voltage winding of the high voltage transformer.

5. The large electric currents beyond 8A flow through the primary winding of the high voltage transformer.

6. The fuse F8A blows by the large electric currents.

7. The power supplying to the high voltage transformer is cut off.

NOISE FILTER

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

TURNTABLE MOTOR

The turntable motor rotates 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.

TOP GRILL HEATING ELEMENT

The grill heating element is provided to brown the food and is located on the top of the oven cavity.

BOTTOM GRILL HEATING ELEMENT

The grill heating element is provided to brown the food and is located at the base of the oven cavity.

When the oven cooking time reaches “0”, the heating elements are de-energized and the oven shuts off. At that time if the cavity air temperature has rised above120˚C, the fan motor remains rotating. Automatically the fan motor will be shut down at low temperature (less than 105˚C).

FIRE SENSING FEATURE

The oven will stop its operation when there is a fire in the oven cavity in microwave cooking condition. LSI measures the voltage across the temperature measurement circuit intermittently within 32-seconds time base since the oven is started in microwave cooking condition. The oven will stop its operation when the difference of the voltage is more than 0.781 volts in microwave cooking condition.

1. Within a 32-seconds base, the thermistor is energized for 2 seconds. At that time, the voltage across the temperature measurement circuit is measured.

2. The oven carries out the procedure above again. If the second voltage is 0.781V higher than first voltage, LSI judges it is a fire in the oven cavity and stop the oven.

3. When LSI judges it is a fire in the oven cavity, LSI will switch off the relays to high voltage transformer and fan motor and LSI stops countring down.

THERMISTOR

Sensing

Voltage

OFF

Sensing the voltage across temperature measurement circuit.

30 32 (sec.)

OVEN COOKING SYSTEM

Food is cooked by the top and bottom heating elements. And the temperature of the oven cavity can be controlled by the thermistor circuit. When the temperature inside the oven cavity reaches the selected temperature, the heating elements are de-energized. When the temperature inside the oven cavity drops below the selected temperature, the heating elements are energized again. In this way, the inside of the oven cavity is maintained at approximately

OPEN JUDGE BY THERMISTOR

1. If the temperature of the thermistor does not rise to more than 40˚C after 4 minutes and 15 seconds from when the oven is started in oven cooking mode, dual cooking mode or grill (top and bottom) cooking mode, the oven is turned off.

2. When the thermistor or the wire harness to the thermistor is opened, the oven is turned off after 4 minutes and 15 seconds because this condition is same as above.

the selected temperature.

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 (F8A) in the monitored latch switch - monitor

switch circuit, check the monitored latch switch and monitor switch before replacing the fuse (F8A).

TROUBLESHOOTING GUIDE

CONDITION PROBLEM

Fuse F8A blows when the door is opened. Home fuse blows when power cord is plugged into wall outlet.

OFF

CONDITION

Fuse 15A blows when power cord is plugged into wall outlet. Nothing appears in display when power cord is plugged into wall outlet

and the door is opened and closed. Display does not operate properly when STOP/CLEAR key is touched. Oven lamp does not light when door is opened. (Display operates.)

Oven does not start when the START key is touched. (Display operates.) Oven lamp does not light and turntable motor does not operate. Fan motor does not operate. (Oven lamp lights.) Turntable motor does not operate. (Oven lamp lights.)

COOKING

CONDITION

(COMMON MODE)

Oven or any electrical parts (except fan motor) does not stop when cooking time is 0 or STOP/CLEAR key is touched.

Oven stops after 4 minutes and 15 seconds since START key is touched. (Except Microwave mode)

Display operates properly but all electrical parts do not do not operate. Oven goes into cook cycle but shuts down before end of cooking cycle. After cooking, the temperature of oven cavity is higher than 105ßC but

fan motor does not operate. Oven seems to be operating but little or no heat is produced in oven

MICROWAVE

COOKING

CONDITION

load. (Microwave power control is set at HIGH) Oven does not seem to be operating properly during variable cooking

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

OVEN COOKING

CONDITION

GRILL COOKING

CONDITION

Oven seems to be operating but the temperature in the oven cavity is lower or higher than preset one.

Grill heating element does not operate. Oven goes into cook cycle but shuts down before end of cooking cycle.

DUAL COOKING

CONDITION

Oven seems to be operating but little or no heat is produced in oven load. (Microwave power does not seem to be generated properly)

Top or Bottom Grill heating element does not heat.

TEST PROCEDURE

POSSIBLE CAUSE

AND

DEFECTIVE PARTS

ABC DEEE FGGHH I J K L L MNOOOOOOP

HIGH VOLTAGE TRANSFORMER

MAGNETRON

HIGH VOLTAGE CAPACITOR

H.V. HARNESS

H.V. RECTIFIER ASSEMBLY

MONITOR SWITCH SW3

STOP SWITCH SW2

MONITORED LATCH SWITCH SW1

THERMAL CUT-OUT 150ßC TC2

THERMAL CUT-OUT 125ßC TC1

THERMISTOR

NOISE FILTER

FAN MOTOR

TURNTABLE MOTOR

TOP GRILL HEATING ELEMENT

FUSE F8A

FUSE 15A

TOUCH CONTROL PANEL

TC TRANSFORMER

BOTTOM GRILL HEATING ELEMENT

RELAY RY2

RELAY RY1

KEY UNIT

RELAY RY5

RELAY RY4

RELAY RY3

RELAY RY6

MIS-ADJUSTMENT OF SWITCHES

BLOCKED VENTILATION OPENINGS

OPENED WIRE HARNESS

SHORTED WIRE HARNESS

OVEN LAMP OR SOCKET

POWER SUPPLY CORD

FOIL PATTERN ON P.W.B.

BLOCKED

NO POWER AT WALL OUTLET

HOME FUSE OR BREAKER

COOLING FAN

TEST PROCEDURES

PROCEDURE

LETTER

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

The power output of this oven is rated using the method specified by IEC 705. Full details of how to curry out this procedure can be found in the Sharp Technical Training notes which is available from Sharp Parts Centre (part number SERV-LITMW01).

The IEC-705 procedure must be carried out using laboratory-type procedures and equipment.

These requirements make the procedure unsuitable for routine performance checks.

NOTE: The following test method gives an indication of the output power only, it cannot be used to

establish the actual/rated output power. If the true output power is required, then the IEC705 test method must be used.

COMPONENT TEST

Alternative simplified method:

1. Place 2 litres of cold water (between 12°C and 20°C) in a suitable container.

2. Stir the water and measure the temperature in °C. Note temperature as T1.

3. Place the container in the microwave and heat the water for 2 minutes on full power.

4. When the 2 minutes is completed, remove the container and stir the water. Note temperature as T2.

5. Calculate the output power using the following formula: R.F. Power Output = (T2 - T1) x 70.

NOTE: The result from this test should be within the allowance of 2000cc alternative method.

(±10%).

MICROWAVE LEAKAGE TEST

This oven should be tested for microwave leakage on completion of any repair or adjustment, following the procedure described in the Sharp Technical Training notes (part number SERV-LITMW01). The maximum leakage permitted in BS EN 60335-2-25 is 50W/m2 (equivalent to 5W/m2), however it is not normal to detect any significant leakage, therefore, any leakage which is detected should be investigated.

It is essential that only leakage detectors with current calibration traceable to National Physical Laboratories are used.

Suitable leakage detectors: CELTEC A100

APOLLO X1

TEST PROCEDURES

PROCEDURE

LETTER

B HIGH VOLTAGE TRANSFORMER TEST

WARNING: High voltage and large currents are present at the secondary winding and

filament winding of the high voltage transformer. It is very dangerous to work near this part when the oven is on. NEVER make any voltage measurements of the high-voltage circuits, including the magnetron filament.

CARRY OUT 3D CHECKS. Disconnect the leads to the primary winding of the high voltage transformer. Disconnect the filament and secondary winding connections from the rest of the HV circuitry. Using an ohmmeter, set on a low range, it is possible to check the continuity of all three winding. The following readings should be obtained:-

a. Primary winding ................................... approximately 2 Ω

b. Secondary winding ............................ approximately 99 Ω

c. Filament winding......................................... less than 1 Ω

If the readings obtained are not stated as above, then the high voltage transformer is probably faulty and should be replaced. CARRY OUT 4R CHECKS.

C HIGH VOLTAGE RECTIFIER TEST

CARRY OUT 3D CHECKS. Isolate the high voltage rectifier assembly from the HV circuit. The high voltage rectifier can be tested using an ohmmeter set to its highest range. Connect the ohmmeter across the terminal B+C of the high voltage rectifier and note the reading obtained. Reverse the meter leads and note this second reading. The normal resistance is infinite in one direction and more than 100 kΩ in the other direction.

CARRY OUT 4R CHECKS.

COMPONENT TEST

D2 D1

ASYMMETRIC RECTIFIER TEST

CARRY OUT 3D CHECKS.

Isolate the high voltage rectifier assembly from the HV circuit. The asymmetric rectifier can be tested using an ohmmeter set to its highest range across the terminals A+B of the asymmetric rectifier and note the reading obtained. Reverse the meter leads and note this second reading. If an open circuit is indicated in both directions then the asymmetric rectifier is good. If the asymmetric rectifier is shorted in either direction, then the asymmetric rectifier is probably faulty and must be replaced with high voltage rectifier. When the asymmetric rectifier is defective, check whether magnetron, high voltage rectifier, high voltage wire or filament winding of the high voltage transformer is shorted.

CARRY OUT 4R CHECKS.

NOTE:

FOR MEASUREMENT OF THE RESISTANCE OF THE RECTIFIER, THE BATTERIES OF THE MEASURING INSTRUMENT MUST HAVE A VOLTAGE AT LEAST 6 VOLTS, BECAUSE OTHERWISE AN INFINITE RESISTANCE MIGHT BE SHOWN IN BOTH DIRECTIONS.

D HIGH VOLTAGE CAPACITOR TEST

CARRY OUT 3D CHECKS. A. Isolate the high voltage capacitor from the circuit.

B. Continuity check must be carried out with measuring instrument which is set to the highest

resistance range.

C. A normal capacitor shows continuity for a short time (kick) and then a resistance of about 10MΩ

after it has been charged. D. A short-circuited capacitor shows continuity all the time. E. An open capacitor constantly shows a resistance about 10 MΩ because of its internal 10MΩ

resistance. F. When the internal wire is opened in the high voltage capacitor shows an infinite resistance. G. The resistance across all the terminals and the chassis must be infinite when the capacitor is

normal. If incorrect reading are obtained, the high voltage capacitor must be replaced.

ASYMMETRIC RECTIFIER

HIGH VOLTAGE RECTIFIER

CARRY OUT 4R CHECKS.

TEST PROCEDURES

PROCEDURE

LETTER

E SWITCH TEST

CARRY OUT 3D CHECKS. Isolate the switch to be tested and using an ohmmeter check between the terminals as described in the following table.

Plunger Operation COM to NO COM to NC

Released Open circuit Short circuit Depressed Short circuit Open circuit

If incorrect readings are obtained, make the necessary switch adjustment or replace the switch. CARRY OUT 4R CHECKS.

F THERMISTOR TEST

CARRY OUT 3D CHECKS. Disconnect theconnector B from CPU unit. Measure the resistance of the thermistor with an ohmmeter. Connect the ohmmeter leads to Pin No's C1 and C3 of the thermistor harness.

If the meter does not indiicate above resistance, replace the thermistor. CARRY OUT 4R CHECKS.

COMPONENT TEST

Table: Terminal Connection of Switch

COM; Common terminal, NO; Normally open terminal NC; Normally close terminal

Room Temperature Resistance

20˚C - 30˚C Approximately 359.9 kΩ - 152 kΩ

G THERMAL CUT-OUT TEST

CARRY OUT 3D CHECKS.

Disconnect the leads from the terminals of the thermal cut-out. Then using an ohmmeter, make a continuity test across the two terminals as described below.

Temperature of "ON" Temperature of "OFF" Indication of ohmmeter

Parts Name condition (closed circuit). condition (open circuit). (When room temperature

(˚C) (˚C) is approx. 20˚C.) Thermal cut-out 125˚C Thermal cut-out 150˚C

If incorrect readings are obtained, replace the thermal cut-out. An open circuit thermal cut-out (MG) indicates that the magnetron has overheated, this may be due to

restricted ventilation, cooling fan failure. An open circuit thermal cut-out (OVEN) indicates that the oven cavity has overheated, this may be due

to no load operation.

CARRY OUT 4R CHECKS.

H MOTOR WINDING TEST

CARRY OUT 3D CHECKS.

Table: Thermal Cut-out Test

This is not resetable Above 125˚C Closed circuit Below 130˚C. Above 150˚C Closed circuit

Disconnect the leads from the motor. Using an ohmmeter, check the resistance between the two terminals as described in the table below.

Table: Resistance of Motor

Motors Resistance Fan motor Approximately 293 Ω Turntable motor Approximately 15 kΩ

If incorrect readings are obtained, replace the motor.

CARRY OUT 4R CHECKS.

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