Panasonic NN-GD391S - User Manual

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Overview

Function Description
Important Technical Specifications
Usage Features
Maintenance Features

This document provides a service manual for the Panasonic NN-GD391S and NN-GD371M microwave ovens, designed for markets including UAE (KTE), Iran (PTE), and CIS Countries (ZPE). The manual details the device's functions, technical specifications, usage, and maintenance procedures, with a strong emphasis on safety due to the high voltage and current components.

Function Description

The Panasonic NN-GD391S and NN-GD371M are microwave ovens equipped with inverter technology, offering variable power cooking, grill, and combination cooking functions. The inverter power supply circuit is a key feature, providing 4,000V DC to the magnetron tube and replacing traditional high voltage transformers and capacitors. This allows for precise control over microwave output power through a Pulse Width Modulation (PWM) signal from the Digital Programmer Circuit (DPC).

The ovens support 3-stage cooking, microwave-only operation, grill-only operation, and combination cooking. Advanced features include Auto Weight and Auto Weight Turbo Defrost, which automatically determine power levels and cooking times based on food weight. A Delay/Stand function, Clock, Memory, and Child Safety Lock enhance user convenience and safety.

Grill cooking is performed by upper heaters, with a cycle of 33 seconds. Combination cooking integrates both microwave and grill functions synchronously within a 33-second cycle. The DPC controls the ON-OFF times of power relays (RY1 and RY3) for both grill and combination cooking to achieve desired power levels.

The ovens also incorporate an energy-saving function, reducing display brightness in stand-by mode and entering stand-by mode automatically after the last operation or when first plugged in. A thermistor attached to the magnetron monitors its temperature, stopping operation if overheating is detected.

Important Technical Specifications

Models: NN-GD391S ZPE, NN-GD371M ZPE, NN-GD371M KTE, NN-GD371M PTE

Power Source: 220V AC Single Phase, 50Hz

Power Consumption:

Microwave: 1150W
Heater: 1050W

Output:

Microwave: 950W
Heater: 1000W

Microwave Frequency: 2450MHz

Timer:

90 minutes 00 seconds (HIGH/MAX Power Level)
30 minutes 00 seconds (Other Power Level)

Outside Dimensions: 488mm (W) x 395mm (D) x 279mm (H)

Oven Cavity Dimensions: 315mm (W) x 353mm (D) x 178mm (H)

Weight: 10kg

PbF (Lead-free solder): This product is manufactured with lead-free solder.

Magnetron Output Power Measurement (1L-1min. test):

900W Rated Output: Minimum 8.0°C Temperature Rise
1000W Rated Output: Minimum 8.5°C Temperature Rise

DC Fan Motor: Rated Voltage DC 12V, Control Signal DC 0-6V, PWM frequency 18KHz to 30KHz.

Usage Features

The control panel features dedicated buttons for Auto Reheat, Micro Power, Inverter Turbo Defrost, Auto Cook, Combination, and Grill. A Time/Weight Selection dial allows for precise input. Recipe Store, Timer, and Clock buttons provide additional functionality.

The "Stop/Reset" button serves multiple purposes: clearing instructions before cooking, temporarily stopping a cooking program, or canceling all instructions and reverting to the time of day display. The "Start" button initiates cooking after program settings are entered. If the door is opened or "Stop/Reset" is pressed during operation, the "Start" button must be pressed again to resume.

A "Beep Sound" confirms correct button presses. The oven beeps twice between programmed stages and five times upon program completion. An automatic cancellation feature will cancel any set operation if the "Start" button is not pressed within 6 minutes, reverting the display to clock or colon mode.

The display window shows operating status, power levels, and cooking times. For troubleshooting, the oven can display thermistor levels and self-diagnostic failure codes (H95, H97, H98, H99) to indicate magnetron and inverter circuit problems.

Maintenance Features

The service manual provides detailed procedures for disassembly and replacement of various parts, including the magnetron, digital programmer circuit (DPC), low voltage transformer, power relays, DC fan motor, door assembly, turntable motor, quartz heater, and H.V. Inverter Power Supply.

Safety Precautions:

High Voltage Warning: The inverter power supply operates at extremely high voltage and current. Technicians must exercise extreme caution to avoid electrical shock or burns.
Capacitor Discharge: High voltage charge may remain in capacitors for about 30 seconds after the oven is turned off. Always unplug the power cord and discharge capacitors using an insulated handle screwdriver before servicing.
Grounding: Proper grounding is crucial. The appliance must be properly grounded before any repair work. The inverter grounding bracket must be connected to the chassis.
Part Replacement: Only manufacturer-specified parts marked with a "▲" symbol should be used for critical components to prevent microwave leakage, shock, fire, or other hazards.
Fuse Replacement: If the 10A fuse blows due to interlock monitor switch malfunction, all components of the interlock system (primary latch switch, secondary latch switch, short switch, and power relay RY1) must be replaced simultaneously.
Sharp Edges: Caution is advised during disassembly and reassembly due to potentially sharp internal edges.
Microwave Radiation Leakage: After any repair or part replacement, especially involving the magnetron or door hinges, a microwave energy leakage test must be performed to ensure it does not exceed 5mW/cm².
Soldering: When working on the DPC, a soldering iron of no more than 30 watts should be used for low voltage transformer and power relay terminals. Lead-free solder has a higher melting point (30-40°C higher than standard solder), requiring a high-temperature soldering iron (370 ± 10°C).

Troubleshooting: The manual includes a comprehensive troubleshooting guide for various issues, such as the oven not starting, not accepting key input, no microwave oscillation, low microwave output, and specific failure codes related to the inverter circuit and magnetron. A simple "3/23 seconds rule" is provided to quickly identify whether a problem lies with the magnetron, inverter, or other components. Procedures for checking semiconductors using an OHM meter are also detailed.