This document describes the SHARP R-961(W) / R-961(K) Grill and Convection Microwave Oven.
Function Description
The R-961(W)/R-961(K) is a versatile kitchen appliance combining microwave, grill, and convection cooking functionalities. It is designed to offer a wide range of cooking options, from rapid microwave heating to browning and baking with grill and convection elements.
Microwave Cooking:
The oven operates at 2450 MHz, generating 1000 watts nominal RF microwave energy. It utilizes a high-voltage transformer to convert 230V A.C. to approximately 3.3V A.C. for the magnetron filament and 2000V A.C. for the secondary winding, which is then doubled to approximately 4000V D.C. for microwave generation. The microwave power can be varied through intermittent operation of the high-voltage transformer within a 32-second time base, offering power levels of HIGH (100%), MEDIUM HIGH (70%), MEDIUM (50%), MEDIUM LOW (30%), and LOW (10%). During microwave cooking, a portion of cooling air is channeled through the cavity to remove steam and vapors, which are then exhausted into a condensation compartment.
Convection Cooking:
The convection system uses a 1.3kW convection heating element located at the rear of the oven cavity. Air is heated by this element and circulated by a convection fan, driven by a convection motor, through a convection passage. This hot air enters the oven cavity through vent holes, heats the food, and then recirculates, maintaining a consistent internal temperature. The oven can be programmed for various convection temperatures ranging from 40°C to 250°C. During preheating, if the programmed temperature is above 180°C, the grill heating element may also be activated to heat the cavity faster. The damper is in a closed position during convection cooking to prevent hot air leakage.
Grill Cooking:
The grill function uses a 1.2kW (600W x 2) grill heating element located at the top of the oven cavity to brown food. During the first 15 minutes of grill operation, the element is continuously on; after 15 minutes, it cycles on and off in 25-second intervals with 7 seconds off. In grill cooking, the damper is initially closed but opens after the convection heating element back-up has stopped.
Dual Cooking:
The R-961(W)/R-961(K) offers two dual cooking modes:
- Microwave and Convection: Combines microwave energy with convection heating. The microwave power operates intermittently within a 48-second time base, with ON times varying from 36 seconds (70% power) to 8 seconds (10% power).
- Microwave and Grill: Combines microwave energy with grill heating. Similar to microwave and convection, microwave power operates intermittently within a 48-second time base.
Rotisserie Cooking:
The oven includes a rotisserie motor that rotates a skewer, allowing for even cooking and browning of food. In dual cooking (Microwave and Grill) with rotisserie, microwave power can be programmed at 10% or 30%, and the grill heating element operates intermittently (26 seconds on, 22 seconds off).
AH Sensor Cooking:
This feature allows for automatic cooking without manual time, power level, or quantity input. The absolute humidity (AH) sensor detects steam emitted from food, and its resistance increases gradually. This information is relayed to a microprocessor, which calculates the remaining cooking time and power level for optimal results. The oven will stop sensor cooking when the preset value for the menu is reached.
Safety Features:
The oven incorporates several safety mechanisms:
- Door Interlock Switches: All door interlock switches (monitored latch switch, monitor switch, and door switch) are activated when the door is closed, ensuring the oven does not operate with an open door. A critical safety feature involves the fuse F2 F8A blowing if the monitored latch switch SW1 fails to open when the door is opened, and the monitor switch SW2 contact (COM-NC) closes, preventing microwave exposure.
- Thermal Cut-Outs: Multiple thermal cut-outs protect against overheating:
- TC1 (170°C, Grill): Protects against overheating during grill, convection, or dual cooking.
- TC2 (145°C, MG): Protects the magnetron from overheating.
- TC3 (190°C, Conv.): Protects the convection motor from overheating.
- TC4 (95°C, Fan Motor): Protects the fan motor from overheating.
- Fuses: F1 (15A 250V) protects against short circuits in wire harness or electrical components. F3 (10A 250V) protects against short circuits in the asymmetric rectifier, H.V. rectifier, H.V. wire harness, H.V. capacitor, magnetron, or secondary winding of the high voltage transformer.
- Fire Sensing Feature: During microwave cooking, the LSI repeatedly measures voltage across the thermistor circuit. If a rapid increase (300mV greater than previous measurement) is detected, indicating a fire, the LSI shuts off relays to the high voltage transformer, fan motor, and convection motor, and closes the damper door to restrict airflow.
- Open Judge by Thermistor: If the thermistor temperature does not rise by more than 40°C within 4 minutes and 15 seconds during convection, grill, or dual cooking, the oven shuts off, indicating a potential issue with heating or the thermistor itself.
Important Technical Specifications
- Power Requirements: 230 Volts / 50 Hertz / Single phase, 3 wire earthed
- Microwave Power Output: 1000 watts nominal RF microwave energy (IEC 705 method)
- Operating Frequency: 2450 MHz
- Power Consumption:
- Microwave cooking: 1.6 kW Approx. 7A
- Dual cooking (Microwave and Grill): 2.8kW Approx. 12A
- Dual cooking (Microwave and Convection): 2.9kW Approx. 12.5A
- Convection cooking: Max. 1.35kW Approx. 5.5A
- Grill cooking: Max. 2.5kW Approx. 11A
- Convection Heating Element Power Output: 1.3kW
- Grill Heating Element Power Output: 1.2kW (600W x 2)
- Case Dimensions: Width 550 mm, Height 342 mm (including foot), Depth 524 mm
- Cooking Cavity Dimensions: Width 390 mm, Height 240 mm, Depth 395 mm
- Turntable Diameter / Capacity: 360mm (34 litres)
- Set Weight: Approx. 27 kg
- Microwave Cooking Control: Repetition Rate with power levels: HIGH (Full), MEDIUM HIGH (approx. 70%), MEDIUM (approx. 50%), MEDIUM LOW (approx. 30%), LOW (approx. 10%).
- Convection Temperature Control Range: 250°C, 230°C, 220°C, 200°C, 180°C, 160°C, 130°C, 100°C, 70°C and 40°C.
Usage Features
The R-961(W)/R-961(K) features a Touch Control System with a Sensor Cook function for automated cooking. It includes a timer (0-99 min) and various dedicated keys for ease of use:
- SENSOR key: Activates sensor cooking.
- POTATO keys: Pre-programmed settings for potatoes.
- INSTANT ACTION keys: Quick start functions.
- LESS(▼)/MORE(▲) keys: Adjusts cooking time or power.
- Time keys: For manual time input.
- MICROWAVE key: Selects microwave cooking.
- GRILL key: Selects grill cooking.
- CONVECTION key: Selects convection cooking.
- DUAL COOK key: Selects dual cooking modes (Microwave + Convection or Microwave + Grill).
- ROTISSERIE key: Activates rotisserie function.
- MINUTE TIMER/HOLD key: Sets a minute timer or holds a setting.
- CLOCK SETTING key: Sets the clock.
- STOP key: Stops current operation.
- MINUTE PLUS/START key: Adds a minute or starts cooking.
- LANGUAGE SELECT key: For language selection.
- INFORMATION key: Provides information.
The digital display shows cooking time, indicators for CONVECTION, GRILL, MICROWAVE, ROTISSERIE, SENSOR, MICROWAVE POWER LEVEL, LESS/MORE, CLOCK SET, COOKING-IN-PROGRESS, and INFORMATION.
Maintenance Features
The manual provides comprehensive servicing instructions for trained service engineers, emphasizing safety precautions due to high voltage and current circuitry.
General Servicing Warnings:
- Always disconnect power supply.
- Ensure the door is opened and wedged open.
- Discharge the high voltage capacitor (which remains charged for about 60 seconds after power-off) using an insulated screwdriver.
- Never operate the oven without an energy-absorbing load.
- Never look into an open waveguide or antenna while energized.
- Do not become exposed to microwave radiation.
- Only use identical parts specified in the parts list.
Component Testing and Replacement Procedures:
The manual details specific tests for various components:
- Magnetron Test (Procedure A): Checks for open circuit filament (less than 1 ohm) and short filament to anode (infinite resistance).
- Microwave Output Power Measurement (Procedure A): IEC-705-1988 method using a water load to calculate power output (P = 4.187 x V x ΔT / t). Requires specific container, water temperature, and heating time (45 sec total, including 3 sec magnetron heat-up). Output power should be ± 15% of rated output.
- High Voltage Transformer Test (Procedure B): Checks continuity of primary (approx. 1.3 ohms), secondary (approx. 85 ohms), and filament (less than 1 ohm) windings.
- High Voltage Rectifier Assembly Test (Procedure C): Checks resistance across terminals B+C (infinite in one direction, >100 kΩ in the other).
- High Voltage Capacitor Test (Procedure D): Checks for continuity (short kick, then approx. 10 MΩ resistance for normal capacitor; continuous continuity for short-circuited; constant 10 MΩ for open; infinite for internal wire open).
- Switch Test (Procedure E): Checks terminal connections (COM to NO, COM to NC) for released and depressed plunger states.
- Thermal Cut-Out Test (Procedure G): Checks continuity across terminals for various temperature conditions (TC1 170°C, TC2 145°C, TC3 190°C, TC4 95°C).
- Motor Winding Test (Procedure H): Measures resistance of fan motor (approx. 205 Ω), turntable motor (approx. 15.5 kΩ), convection fan motor (approx. 180 Ω), and damper motor (approx. 16 kΩ).
- Noise Filter Test (Procedure I): Checks continuity and resistance between terminals (N and L, N and WHITE, L and RED).
- Fuse Tests (Procedures J, K, L): Instructions for checking and replacing F1 (15A), F2 F8A (250V), and F3 F10A (250V) fuses, including checks for shorts/grounds.
- Convection/Grill Heating Element Test (Procedure M): Checks resistance (Convection: approx. 39 Ω; Grill: approx. 44 Ω) and insulation resistance (>10 MΩ).
- Thermostat Test (Procedure N): Measures thermistor resistance.
- Touch Control Panel Assembly Test (Procedure M): Troubleshooting for key unit and control panel defects, including display issues and non-responsive pads.
- Key Unit Test (Procedure N): Verifies flat ribbon cable contact and door sensing switch operation.
- Relay Test (Procedure O): Checks operational voltage (DC) at relay coils and continuity of associated diodes.
- Printed Wiring Board (PWB) Foil Pattern Repair (Procedure P): Instructions for repairing open foil patterns acting as fuses.
Component Removal and Adjustment Procedures:
Detailed steps are provided for removing and reinstalling major components:
- Outer Case
- High Voltage Components (Capacitor, Rectifier Assembly)
- High Voltage Transformer
- Control Panel
- Magnetron (with caution for RF gasket and mounting screws)
- Fan Motor (with caution for fan blade assembly)
- Oven Lamp Socket
- Positive Lock® Connectors
- Power Supply Cord
- Convection Heating Element and Convection Fan Motor
- Grill Heating Element Assembly
- Damper Motor
- Rotisserie Motor
- Turntable Motor (with instruction to apply grease to coupling/O-ring)
- Monitored Latch Switch, Door Switch, and Monitor Switch (with adjustment procedure for door play and switch operation)
- Door Assembly (with adjustment criteria for latch heads and alignment)
- Choke Cover
- Door Frame and Glass
- Latch Head
Microwave Leakage Measurement:
After any service to the door or switches, a microwave survey meter (NARDA 8100/8200, HOLADAY HI 1500, SIMPSON 380M) must be used to ensure radiation emission is less than 5mW/cm² at 5cm or more from the external surface. The procedure involves placing a specific water load in the oven and slowly moving the probe along the gaps.
Wiring Diagrams:
The manual includes schematic and pictorial wiring diagrams for different oven conditions (OFF, Microwave Cooking, Convection Cooking, Dual Cooking) to aid in troubleshooting and re-wiring. Wire colors (BRN: BROWN, BLU: BLUE, G-Y: GREEN AND YELLOW STRIPE) and sectional area (1.5mm²MIN) are specified.
Parts List:
A comprehensive parts list is provided, categorizing electric parts, cabinet parts, control panel parts, door parts, and miscellaneous items, with part numbers, descriptions, quantities, and codes. It also indicates parts that may cause undue microwave exposure ("A" mark), parts used in voltages over 250V ("*" mark), and spare parts delivery section ("§" mark).
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