Sharp R771M-006 Schematic

WARNING

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 using a screwdriver with an insulated handle.

Sharp recommend that wherever possible, fault-finding is carried out with the supply disconnected. In some cases, it may be necessary to connect the supply with the cover removed to carry out fault investigation in the control circuitry. In such cases, the high voltage circuit should be disabled as described below to reduce the hazards:-

• Carry out 3D checks (see above).

• Disconnect the supply leads from the high voltage transformer, making a note of the polarity. Insulate the connectors, ensuring they are positioned away from the transformer and fastened there.

• Connect any relevant test equipment e.g. voltmeter.

• Reconnect the oven to the supply, then close the door.

• Note the results of the test, taking care to keep clear of the operational oven.

• Carry out 3D checks (see above).

• Reconnect the leads to the transformer. Take care to observe correct polarity.

• Carry out 4R checks (see below).

Microwave ovens should not be used without a load. 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 microwave timer for one (1) minute, set the power level to HIGH (100%) and push the start key. When the one (1) minute has elapsed (timer at zero) carefully check that the water is now hot.

AFTER REPAIR 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.

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.

IMPORTANT: If the oven becomes inoperative because of a blown fuse F8A in the 1st latch switch monitor switch circuit, check the 1st latch switch and monitor switch before replacing the fuse F8A.

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CAUTION/WARNING

CAUTION

MICROWAVE RADIATION

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.

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.

WARNING

THIS APPLIANCE MUST BE EARTHED. THE WIRES IN THIS MAINS LEAD ARE COLOURED IN

ACCORDANCE WITH THE FOLLOWING CODE: GREEN-AND-YELLOW : EARTH BLUE : NEUTRAL BROWN : LIVE

If the mains lead is replaced, only part number QACCBA004URE1 should be used.

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 A

Top Grill mode 1.25 kW Approx. 5.2 A

Grill cooking Bottom Heater mode 0.85 kW Approx. 3.5 A

Top and Bottom mode 2.05 kW Approx. 8.5 A

Dual cooking

Power Output

Grill heating element Power Output (Top Grill) Bottom heating element Power Output Case Dimensions Width 520 mm

Cooking Cavity Dimensions Width 349 mm

Turntable diameter 325 mm Control Complement Jog Touch Control System

Set Weight Approx. 19 kg

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

1200 W (600 W x 2) 800W

Height 309 mm including foot Depth 436 mm

Height 207 mm Depth 357 mm

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

FUNCTION KEYS: LESS (

TIMER key, PIZZA key, BREAKFAST key, AUTO COOK key, AUTO DEFROST key, MICROWAVE POWER LEVEL key DUAL key, GRILL key, OVEN key, STOP / CLEAR key, AUTO MINUTE / START key, CLOCK key, TIME/WEIGHT knob

)/MORE ( ) keys, WEIGHT CONVERSION key

Micro and Top Grill 2.8 kW 12A Approx. Micro and Bottom Heater 2.3 kW 10A Approx.

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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

8. Grill heating element (Bottom Heater)

9. Door seals and sealing surfaces

10.Ventilation openings

11.Outer cabinet

12.Power supply cord

High rack

Turntable Turntable

support

Bottom heater

Turntable motor shaft

Low rack

SNACK

AUTO COOK

...

WATT

min

/KG

STOP

R-771

567

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.

WIRING / RE-WIRING

WARNING: Before carrying out any work carry out 3D checks

1) Disconnect the supply.

2) Door opened, and wedged open.

3) Discharge high voltage capacitor.

RE-WIRING

Ensure the following:

1. Wires must not touch: a) High voltage parts.

(Magnetron, high voltage transformer, high voltage capacitor and high voltage rectifier assembly)

b) Parts that become hot.

(Heating elements, oven lamp, oven cavity magnetron and high voltage transformer)

c) Sharp edges.

(Bottom plates, oven cavity, waveguide flange, chassis support and other metallic parts)

d) Movable parts.

(Fan blade, any motor, switch, switch lever and open button)

2. Positive lock connectors are fitted correctly. Ensure the locking pin is located correctly.

3. Wires are connected correctly as per pictorial diagram.

4. No wire leads are trapped by the outer wrap.

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OPERATION SEQUENCE

MICROWAVE COOKING CONDITION

100% (HIGH) COOKING

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

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%

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.

Approx. 100%

Approx. 70%

Approx. 50%

Approx. 30%

Approx. 10%

NOTE:

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

2. In case that the stop key 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.

DUAL COOKING CONDITION

Power level ON time OFF time

100% 48 sec. 0 sec.

70% 36 sec. 12 sec 50% 26 sec. 22 sec. 30% 16 sec. 32 sec 10% 8 sec. 40 sec

Power level 0% can not be programmed in Dual Cooking condition.

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 20 70 32 Top grill 30 50 48 Bottom heater 45 50 48

Top grill and Bottom heater or Oven cooking

Micro. + Top 20 (Micro.) 70 48

grill heater 15 (Grill) 50 48

U A

Microwave + 20 (Micro.) 70 48

bottom heater 15 (Heater) 50 48

Specified cooking Limited power Time base

15 (Top) 50 48 15 (Bottom) 50 48

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FUNCTION OF IMPORTANT COMPONENTS

DOOR OPEN MECHANISM

DOOR

LATCH HEADS

LATCH HOOK

OPEN LEVER

MONITOR SWITCH

MONITORED

LATCH SWITCH

STOP SWITCH

Figure D-1. Door Open Mechanism

FIRE SENSING FEATURE

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 accomplished by the LSI repeatedly measures 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 300mV grater than the previous voltage measured, the LSI judges it as a fire in the oven cavity and switches off the relays to the high voltage transformer and fan 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.

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 300mV the LSI makes the judgment that there is a fire in the oven cavity and will switch off the relays to the high voltage transformer and fan motor. The LSI also stops counting down.

CAUTION: BEFORE REPLACING A BLOWN FUSE

F8A TEST THE MONITORED LATCH SWITCH, MONITOR SWITCH AND MONITOR RESISTOR FOR PROPER OPERATION.

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 29 64 (sec.)

3 sec.

THERMISTOR

SENSING

VOLTAGE

OFF

Sensing the voltage across temperature mesure circuit.

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 convection, grill or dual cooking (Microwave and Convection) 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.

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.

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IMPORTANT: If the oven becomes inoperative because

of a blown fuse F8A in the primary latch switch - monitor switch circuit, check the primary latch switch, monitor switch and monitor resistor before replacing the fuse F8A.

OUTPUT POWER TEST PROCEDURE

MICROWAVE OUTPUT POWER (IEC-705)

The power output of this oven is rated using the method specified by IEC-705. Full details of how to carry 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 IEC-705 test method must be used.

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 the water temperature as T2.

5. Calculate the output power using the following formula: R.F. Power Output = (T2 - T1) x 80.

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/m

(equivalent to 5mW/cm2), 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 the National Physical Laboratories

are used.

Suitable leakage detectors : CELTEC A100

APOLLO X1

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TEST PROCEDURES

PROCEDURE

LETTER

A TOUCH CONTROL PANEL ASSEMBLY TEST

The touch control panel consists of circuits including semiconductors such as LSI, ICs, etc. Therefore, unlike conventional microwave ovens, proper maintenance can not be performed with only a voltmeter and ohmmeter. In this service manual, the touch control panel assembly is divided into two units, Control Unit and Key Unit, and troubleshooting by replacement is described according to the symptoms indicated.

1. Key Unit Note : Check key unit ribbon connection before replacement. The following symptoms indicate a defective key unit. Replace the key unit.

a) When touching the pads, a certain pad produces no signal at all. b) When touching a number pad, two figures or more are displayed. c) When touching the pads, sometimes a pad produces no signal.

2. Control Panel The following symptoms indicate a defective control unit. Before replacing the control unit. perform the key unit test (Procedure N) to determine if control unit is faulty.

2-1 In connection with pads

a) When touching the pads, a certain group of pads do not produce a signal. b) When touching the pads, no pads produce a signal.

2-2 In connection with indicators

a) At a certain digit, all or some segments do not light up. b) At a certain digit, brightness is low. c) Only one indicator does not light up. d) The corresponding segments of all digits do not light up; or they continue to light up. e) Wrong figure appears. f) A certain group of indicators do not light up. g) The figure of all digits flicker.

2-3 Other possible troubles caused by defective control unit.

a) Buzzer does not sound or continues to sound. b) Clock does not operate properly. c) Cooking is not possible. d) Proper temperature measurement is not obtainned.

COMPONENT TEST

B KEY UNIT TEST

If the display fails to clear when the STOP/CLEAR pad is depressed, first verify the flat ribbon cable is marking good contact, verify that the door sensing switch (stop switch) operates properly; that is the contacts are closed when the door is closed and open when the door is open. If the door sensing switch (stop switch) is good, disconnecct the flat ribbon cable that connects the key unit to the control unit and make sure the door sensing switch is closed (either close the door or short the door sensing switch connecter). Use the Key unit matrix indicated on the control panel schematic and place a jumper wire between the pins that correspond to the STOP/CLEAR pad marking momentary contact. If the control unit responds by clearing with a beep the key unit is faulty and must be replaced. If the control unit does not respond, it is a faulty and must be replaced. If a specific pad does not respond, the above method may be used (after clearing the control unit) to determine if the control unit or key pad is at fault.

G5,9

G11

G4,12

BREAKFAST

STOP/

AUTO

(C˚)

CLEAR

START/

AUTO

MINUTE

MICROW.

POWER

DEFROST

GRILL

OVEN

KEY UNIT

G10

LEVEL

AUTO

COOK

G3,8

PIZZA

DUAL

GRILL AUTO

START/

CLOCK

TIMER

Kg / Lb

CARRY OUT

4R CHECKS.

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TEST PROCEDURES

PROCEDURE

LETTER

C RELAY TEST

COMPONENT TEST

CARRY OUT

3D CHECKS.

Remove the outer case and check voltage between Pin Nos. 1 and 3 of the 4 pin connector (A) on the control unit with an A.C. voltmeter. The meter should indicate 230-240 volts, if not check oven circuit.

Relay Test Check voltage at the relay coil with a D.C. voltmeter during the microwave cooking operation. convection cooking operation or grill operation.

DC. voltage indicated .......... Defective relay.

DC. voltage not indicated .... Check diode which is connected to the relay coil. If diode is good,

control unit is defective.

RELAY SYMBOL OPERATIONAL VOLTAGE CONNECTED COMPONENTS

RY1 Approx. 24.0V D.C. Oven lamp / Turntable motor RY2 Approx. 18.0V D.C. High voltage transformer RY3 Approx. 18.0V D.C. Grill heating element (Top grill) RY4 Approx. 18.0V D.C. Bottom heating element

RY5 Approx. 24.0V D.C. Fan motor

CARRY OUT 4R CHECKS.

D PROCEDURES TO BE TAKEN WHEN THE FOIL PATTERN ON THE PRINTED WIRING

BOARD (PWB) IS OPEN.

To protect the electronic circuits, this model is provided with a fine foil pattern added to the input circuit on the PWB, this foil pattern acts as a fuse. If the foil pattern is open, follow the troubleshooting guide given below for repair. Problem: POWER ON, indicator does not light up.

CARRY OUT

STEPS OCCURANCE CAUSE OR CORRECTION

1 The rated AC voltage is not present at Check supply voltage and oven power cord.

2 The rated AC voltage is present at primary Low voltage transformer or secondary circuit defective.

3 Only pattern at "a" is broken. *Insert jumper wire J1 and solder.

4 Pattern at "a" and "b" are broken. *Insert the coil RCILF2003YAZZ between "c" and "d".

3D CHECKS.

Power terminal of CPU connector (CN-A).

side of low voltage transformer. Check and repair.

(CARRY OUT

3D CHECKS BEFORE REPAIR)

NOTE: *At the time of these repairs, make a

visual inspection of the varistor for burning damage and examine the transformer with tester for the presence of

RY1

D21

layer short circuit (check primary coil resistance). If any abnormal condition is detected, replace the defective parts.

CARRY OUT

4R CHECKS.

CN -A

(J1)

VRS1

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TOUCH CONTROL PANEL ASSEMBLY

OUTLINE OF TOUCH CONTROL PANEL

The touch control section consists of the following units as shown in the touch control panel circuit.

(1) Key Unit (2) Control Unit

The principal functions of these units and signals communicated among them are explained below.

Key Unit

The key unit is composed of a matrix, signals generated in the LSI are sent to the key unit through P23 - P27. When a key pad is touched, a signal is completed through the key unit and passed back to the LSI through P74 - P77 to perform the function that was requested.

Control Unit

Control unit consists of LSI, power source circuit, synchronizing signal circuit, ACL circuit, buzzer circuit, temperature measurement circuit, indicator circuit, encoder circuit, and back light circuit.

1) LSI

This LSI controls the temperature measurement signal, the key strobe signal, relay driving signal for oven function and indicator signal.

2) Power Source Circuit

This circuit generates voltage necessary in the control unit.

Symbol Voltage Application

VC -5.2V LSI(IC1)

3) Synchronizing Signal Circuit

The power source synchronizing signal is available in order to compose a basic standard time in the clock circuit. It accompanies a very small error because it works on commercial frequency.

4) ACL

A circuit to generate a signals which resets the LSI to the initial state when power is supplied.

5) Buzzer Circuit

The buzzer is responsive to signals from the LSI to emit audible sounds (key touch sound and completion sound).

6) Door Sensing Switch (Stop Switch)

A switch to "tell" the LSI if the door is open or closed.

7) Relay Circuit

To drive the magnetron, heating element, fan motor, turntable motor and light the oven lamp.

8) Encoder

The encoder converts the signal generated by LSI into the pulse signal, and the pulse signal is returned to the LSI.

9) Back Light Circuit

A circuit to drive the back light (Light emitting diodes LD1 - LD5).

10) Indicator Circuit

This circuit consists of 4-digits, 30-segments and 3common electrodes using a Liquid Crystal Display.

11) Temperature Measurement Circuit

The temperature in the oven cavity is sensed by the thermistor. The variation of resistance according to sensed temperature is detected by the temperature measurement circuit and the result applied to LSI. The result of detecting is given to LSI controlling the relay and display.

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