This document is a service manual for the Sharp R-642 series of microwave ovens, covering models R-642(W)W, R-642(IN)W, R-642(BK)W, R-642(W)E, R-642(IN)E, and R-642(BK)E, operating at 800W and 230V 50Hz.
Function Description
The Sharp R-642 series microwave oven is designed for heating and cooking food using microwave energy. It operates on the principle of microwave radiation, where a magnetron generates high-frequency electromagnetic waves that interact with food molecules, causing them to heat up. The oven is equipped with various components to ensure safe and efficient operation, including interlock switches, a monitor switch, a high voltage transformer, and a magnetron.
Important Technical Specifications
- Power Output: 800W
- Voltage: 230V
- Frequency: 50Hz
- Microwave Frequency: 2450 MHz (typical)
- Magnetron: The core component for microwave generation.
- Safety Interlocks: Primary and secondary interlock switches prevent microwave generation when the door is open.
- Monitor Switch: Acts as a safety backup, shorting the primary interlock circuit if it fails.
- High Voltage Transformer: Steps up the voltage to power the magnetron.
- Capacitor and Diode: Part of the high voltage circuit to rectify and filter the power for the magnetron.
- Thermostat: Prevents overheating of the magnetron and oven cavity.
- Fan Motor: Circulates air for cooling the magnetron and other components, and directs air into the oven cavity.
- Turntable Motor: Rotates the glass tray to ensure even heating of food.
- Control Panel: Provides user interface for setting cooking time and power levels.
Usage Features
The R-642 series microwave ovens are designed for ease of use with a control panel that allows users to set various cooking parameters. The turntable ensures that food is heated uniformly by rotating it during the cooking cycle. The oven cavity is designed to contain microwave energy safely.
Installation:
Before use, the oven requires proper installation, including ensuring adequate ventilation and a stable, level surface. It must be connected to a properly earthed electrical outlet. The power cord has specific color codes for wiring (green-and-yellow for earth, blue for neutral, brown for live) to ensure correct earthing. The oven should not be installed in areas where heat and steam are generated, or where the temperature exceeds 104°F (40°C). A minimum clearance of 10cm (4 inches) is required on the wall side.
Operating Instructions (General):
- Place food in a suitable microwave-safe container on the glass tray.
- Close the oven door securely.
- Set the desired cooking time and power level using the control panel.
- The oven will begin cooking once started.
- The turntable rotates to ensure even cooking.
- The fan motor operates to cool the magnetron and circulate air.
- The oven stops operating when the door is opened or the cooking time expires.
Maintenance Features
Maintenance of the Sharp R-642 microwave oven primarily focuses on safety and ensuring continued proper operation. Servicing should only be performed by qualified service personnel due to the presence of high voltage components.
Safety Precautions for Servicing:
- High Voltage: Always discharge the high voltage capacitor before servicing. The magnetron, high voltage transformer, capacitor, and high voltage diode are dangerous components.
- Microwave Leakage: After any service involving microwave-generating components, a microwave leakage test must be performed. The leakage should not exceed 5 mW/cm² at the oven door and 1 mW/cm² at other points.
- Interlock Switches: Ensure all interlock switches (primary, secondary, and monitor) are functioning correctly. These switches prevent microwave generation when the door is open.
- Component Replacement: Use only specified replacement parts. Any defective or misadjusted components in the interlock, monitor, door seal, and microwave generation and transmission systems must be repaired, replaced, or adjusted by procedures described in this manual.
- Earthing: Verify proper earthing of the oven.
- Visual Inspection: Regularly check for damage to the door seal, oven cavity, and other components.
Troubleshooting Procedures:
The manual provides detailed troubleshooting steps for common issues, including:
- No heating: Check fuse, primary and secondary winding of the transformer, earthing, pilot switch, interlock switch, power plug, and magnetron.
- Lamp not on: Check lamp and plug.
- Turntable not rotating: Check turntable motor and connecting shaft.
- Fan not operating: Check fan motor and wiring.
- Oven not heating/heating intermittently: Check magnetron, high voltage diode, and cooling system.
- Large amount of microwave leakage: Check door deformed, door seal, door crack, screws, waveguide, and magnetron.
- Door not opening: Check door latch and hinge.
- Button falling off: Replace button.
- Electricity leaking: Check earthing insulation resistances.
Measurement and Testing:
- Microwave Leakage Test: Performed using a microwave leakage detector.
- Measurement of Microwave Power Output: Involves heating a specific amount of water and measuring the temperature rise over a set time.
- Component Testing: Includes checking resistance of fan and turntable motors with an ohmmeter.
- Voltage Checks: Verify voltages at various points in the circuit, especially around the magnetron filament.
Safety Checks and Tests After Servicing:
After any repair, the following checks are mandatory:
- Correct wiring and adequate mechanical decrements.
- Adequate grounding.
- Proper door closing, seal/choke surfaces, and hinges.
- No outer case damage.
- Proper interlock and monitor operations.
- Insulation Resistance Test: Measure the resistance between the primary (Line and Neutral) of the power plug and operator accessible metal parts. The resistance should be no less than 2 Mega Ohms.
This comprehensive service manual ensures that the Sharp R-642 series microwave ovens can be maintained and repaired safely and effectively, prolonging their operational life and ensuring user safety.
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