Sharp R-772WM - User Manual

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SERVICE MANUAL

MICROWAVE OVEN WITH TOP

AND BOTTOM GRILLS

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.

(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 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

SERVICING

PRODUCT SPECIFICATIONS

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

WIRING DIAGRAM

PARTS LIST

Main Page

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This document describes the SHARP R-772(W)M/ R-772(G)M microwave oven, outlining its functions, technical specifications, usage, and maintenance.

Function Description

The SHARP R-772(W)M/ R-772(G)M is a microwave oven designed for various cooking tasks, including microwave, grill, oven, and dual (combination) cooking. It features a control panel for selecting cooking modes, setting times, and adjusting power levels. The oven is equipped with a turntable motor for even cooking, a fan motor for ventilation, and heating elements for grill and oven functions. Safety features include door interlock switches, thermal cut-outs, and a fuse to prevent electrical hazards.

Door Open Mechanism: The door is opened by pushing a button on the control panel, which activates an open lever to release the latch heads.

Monitored Latch Switch: This switch ensures that the oven is inoperative if the door is open. Its contacts (COM-NO) close when the door is closed and open when the door is open.

Stop Switch: Similar to the monitored latch switch, this switch also has contacts (COM-NO) that close when the door is closed and open when the door is open.

Monitor Switch: This switch is activated by the upper latch head when the door is closed. It's designed to blow fuse F8A if the monitored latch switch fails to open when the door is opened, preventing oven operation.

Fuses (15A 250V and F8A 250V): These fuses protect against short circuits and electrical hazards. F8A specifically blows if the monitored latch switch remains closed with the door open, or if components like the asymmetric rectifier, H.V. rectifier, H.V. wire harness, H.V. capacitor, magnetron, or secondary winding of the high voltage transformer are shorted.

T/C Transformer: Converts AC line voltage to low voltage to power the control unit.

Thermal Cut-Out 125°C (MG): Protects the magnetron from overheating. It opens if the temperature exceeds 125°C due to fan motor interruption or blocked ventilation, stopping magnetron operation.

Thermal Cut-Out 150°C (OVEN): Protects the oven from overheating during grill, oven, or dual cooking. It opens if the temperature exceeds 150°C due to fan motor interruption, blocked air inlet, or obstructed ventilation, switching off all electrical parts. It closes again when the temperature cools to 130°C.

Asymmetric Rectifier: A solid-state device that prevents current flow in both directions and protects the high voltage transformer by blowing fuse F8A if the high voltage rectifier shorts. It has two diodes, D1 (rated peak reverse voltage 6 KV) and D2 (rated peak reverse voltage 1.7 KV).

Noise Filter: Prevents radio frequency interference from flowing back into the power circuit.

Turntable Motor: Rotates the turntable for even cooking.

Fan Motor: A blade-driven motor that circulates cool air, cools the magnetron, and exhausts steam and vapors from the oven.

Top Grill Heating Element: Provides heat for the top grill function.

Bottom Grill Heating Element: Provides heat for the bottom grill function.

Oven Cooking System: Food is cooked by top and bottom heating elements. The temperature is controlled by the control unit. Heating elements are de-energized when the target temperature is reached and re-energized when the temperature drops below the target.

Fire Sensing Feature: Stops oven operation if a fire is detected. A thermistor measures the temperature across the measurement circuit. If the temperature rises rapidly, the oven stops.

Important Technical Specifications

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) Grill Cooking:
Top Grill mode: 1.05 KW (Approx. 4.2 A)
Bottom Grill mode: 0.55 KW (Approx. 2.2 A)
Top and Bottom mode: 1.55 KW (Approx. 6.5 A) Dual Cooking:
Micro and Top Grill: 2.05 KW (Approx. 11.2 A)
Micro and Bottom Grill: 1.55 KW (Approx. 7.2 A) Power Output: 900 W nominal of RF microwave energy (measured by method of IEC 705). Operating Frequency: 2450 MHz. Top Grill heating element Power Output: 1.0 KW. Bottom heating element Power Output: 0.5 KW. 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. Clock: (0:00 - 12:59) / Timer (0 - 99 minutes 90 sec.). Microwave Power for Variable Cooking Repetition Rate:
100 (HIGH): Full power throughout the cooking time.
90 (MEDIUM HIGH): Approx. 70% of FULL Power.
50 (MEDIUM): Approx. 40% 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. Time Keys: BREAKFAST key, PIZZA key, INSTANT COOK keys. Auto Cook Key: AUTO DEFROST key, WEIGHT keys. Oven/Microwave (OVEN °C) key: GRILL key. Dual/Grill key: MICROWAVE POWER LEVEL key. Stop/Clear key: START/AUTO MINUTE key, TIMER key. Weight Conversion key: AUTO START/CLOCK key. Set Weight: Approx. 20 kg.

Usage Features

The oven offers a variety of cooking modes and controls:

Control Panel: Features a display, oven lamp, grill heating element (top grill), door opening button, waveguide cover, oven cavity, turntable, and turntable motor shaft. Indicators: COOK indicator (showing oven in operation), TOP GRILL indicator, BOTTOM GRILL indicator, MICROWAVE indicator, WEIGHT indicators, and DEFROST indicator. Digital Display: Shows cooking progress, time, and power level. Time Keys: Used to select cooking time (10min, 1min, 10sec). Breakfast Key: For cooking breakfast items. Pizza Key: For cooking pizza. Auto Cook Key: For automatic cooking functions. Weight Keys: For weight-based cooking. Oven (°C) Key: To select oven temperature. Microwave Power Level Key: To select microwave power level. Stop/Clear Key: To stop a program, cancel a program, or turn off the oven. Start/Auto Minute Key: To start a program or add cooking time in multiples of 1 minute. Timer Key: To set the timer. Weight Conversion Key: For weight conversion.

Operation Sequence: The oven operates through various sequences depending on the selected cooking mode. For example, in microwave cooking, the magnetron generates microwave energy, while in grill cooking, the top and/or bottom heating elements are activated. Dual cooking combines microwave and grill functions. The control unit manages the relays (RY1-RY6) to activate the appropriate components (magnetron, heating elements, fan motor, turntable motor) based on the selected program.

Power Setting: The power setting for top heating, bottom heating, and fan motor in Oven cooking and preheating modes is 100%.

ON/OFF Time Ratio: In grill, oven, or dual cooking, components operate within a 48-second time base. The ON/OFF time ratio varies with the power output. For example, 100% power means 48 seconds ON and 0 seconds OFF, while 10% power means 8 seconds ON and 40 seconds OFF.

Limitations of Power Output in Manual Operation: After a specified cooking time, the power output is automatically reduced to protect the oven door from overheating. This limitation is not applied in automatic operations, or if the stop key is touched or the door is opened during cooking.

Automatic Cooking: Functions like PIZZA, BREAKFAST, INSTANT COOK, AUTO COOK, and AUTO DEFROST automatically determine the correct cooking mode, time, and temperature.

Maintenance Features

General Information: The appliance must be earthed. Wiring colors are green-and-yellow (earth), blue (neutral), and brown (live).

Servicing Precautions:

High Voltage: Microwave ovens contain high voltage and current. Always discharge the high voltage capacitor before servicing.
Microwave Energy: Never operate the oven with the door open or if the door seals are damaged.
Component Checks: Before replacing a blown fuse F8A, test the monitored latch switch and monitor switch for proper operation.
Earthing: Ensure the appliance is properly earthed.
Capacitor Discharge: Always discharge the high voltage capacitor before handling components.
Leakage Test: Perform a microwave leakage test after any repair that involves microwave-generating components.

Troubleshooting Guide: A table is provided to diagnose problems based on symptoms and possible causes, linking them to specific components.

Test Procedures: Detailed procedures are outlined for testing various components:

Magnetron Test: Check continuity and resistance.
Microwave Output Power: Measure output power using a water load test (IEC 705 procedure).
Microwave Leakage Test: Use a microwave leakage detector to ensure safety.
High Voltage Transformer Test: Disconnect leads and measure winding resistance.
High Voltage Rectifier Test: Measure resistance across terminals.
Asymmetric Rectifier Test: Measure resistance across terminals.
High Voltage Capacitor Test: Isolate and check capacitance, resistance, and continuity.
Switch Test: Check continuity of door switches (monitored latch, stop, monitor).
Thermistor Test: Disconnect and measure resistance.
Thermal Cut-Out Test: Disconnect and measure continuity.
Motor Winding Test: Disconnect and measure resistance of fan and turntable motors.
Noise Filter Test: Disconnect and measure resistance and capacitance.
Blown Fuse 15A/F8A: Check for shorts or grounds in electrical parts.
Grill Heating Element (Top) and Bottom Heating Elements Test: Measure resistance.
Touch Control Panel Assembly Test: Check key unit ribbon connection and functionality of individual keys.
Relay Test: Check voltage at relay coil and continuity of connected components.
Procedures to be Taken When the Foil Pattern on the Printed Wiring Board (PWB) is Open: Inspect for burned patterns and repair.

Component Replacement and Adjustment Procedure:

Oven Lamp Socket Removal: Disconnect power, remove wire leads, and lift up the lamp.
Power Supply Cord Replacement: Disconnect power, remove wire leads, and replace the cord.
Top Heating Element Removal: Remove screws and wire leads.
Bottom Heating Element Removal: Disconnect wire leads.
Monitored Latch Switch, Stop Switch and Monitor Switch Removal: Disconnect power, remove screws, and remove switches. Adjust latch hook position after replacement.
Door Replacement: Remove screws, lift door upwards, and replace.
High Voltage Components Removal: Disconnect power, discharge capacitor, and remove high voltage transformer, magnetron, and rectifier.
Fan Motor Replacement: Disconnect power, remove screws, and replace the motor.
Turntable Motor Replacement: Disconnect power, remove screws, and replace the motor.
Positive Lock® Connector Removal: Push down on the positive lock® connector.

Printed Wiring Board (PWB) and CPU Unit Circuit: Detailed diagrams are provided for the power unit circuit and CPU unit circuit, showing connections and components.

Parts List: Comprehensive lists of electric parts, cabinet parts, control panel parts, oven parts, door parts, miscellaneous/packing and accessories, and screws/nuts/washers are provided with part numbers, descriptions, and quantities.