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Emphasizes the importance of proper grounding for microwave oven safety.
Highlights dangers associated with high voltage and temperature in the inverter circuit.
Guidelines for safely replacing internal components of the microwave.
Troubleshooting steps when the 20A fuse blows due to interlock switch issues.
Warning against inserting foreign objects into the oven cavity to prevent leakage.
Checks required after component replacement to ensure safety and function.
Procedure for testing continuity of interlock switches and power relay.
Procedure for testing the continuity of the monitor switch.
Guide for diagnosing issues with the inverter circuit and magnetron using failure codes.
A simplified method for troubleshooting H.V. inverter and magnetron issues.
Emphasizes the importance of proper grounding for microwave oven safety.
Highlights dangers associated with high voltage and temperature in the inverter circuit.
Guidelines for safely replacing internal components of the microwave.
Troubleshooting steps when the 20A fuse blows due to interlock switch issues.
Warning against inserting foreign objects into the oven cavity to prevent leakage.
Checks required after component replacement to ensure safety and function.
Procedure for testing continuity of interlock switches and power relay.
Procedure for testing the continuity of the monitor switch.
Guide for diagnosing issues with the inverter circuit and magnetron using failure codes.
A simplified method for troubleshooting H.V. inverter and magnetron issues.
This document is a service manual for the Panasonic NN-SD291S and NN-SD291W Microwave Ovens, identified by order number PHAMOS1106067AE. It provides comprehensive information for servicing, troubleshooting, and maintaining these models.
The microwave ovens operate on a 120V AC single-phase, 60Hz power source, with a power requirement of 1440W and an output of 1100W. They utilize a microwave frequency of 2450MHz. The external dimensions are 29 7/8" (W) x 15 1/2" (D) x 16 7/16" (H) or 759mm (W) x 393mm (D) x 418mm (H). The oven cavity dimensions are 23 1/4" (W) x 14 7/16" (D) x 9 1/2" (H) or 591mm (W) x 367mm (D) x 242mm (H). The approximate weight is 55 lbs (25.0 Kg). These models are PbF (lead-free) compliant.
The microwave ovens feature variable power cooking control, managed by a Digital Programmer Circuit (DPC) that sends a Pulse Width Modulation (PWM) signal to the High Voltage Inverter Power Supply (U). This inverter circuit, unlike traditional microwave transformers, capacitors, and diodes, directly supplies 4,000V DC to the magnetron tube. The output power of the magnetron is continuously monitored by a current transformer within the inverter circuit, providing feedback to the DPC for precise power control.
The ovens offer various cooking settings:
A key feature is the "Inverter Turbo Defrost," which automatically determines cooking time based on selected weight (e.g., 1.0 LB defrosts in 5 min. 28 sec.).
The models incorporate "Auto Sensor Cooking" and "Sensor Reheat" functions. These features allow the oven to automatically determine the correct power level and cooking time without manual input. A humidity sensor element detects steam escaping from food, and the microprocessor calculates the remaining cooking time (T2 time) based on an initial T1 time and a K factor. The K factor varies with "More" or "Less" button selections. For example, in Oatmeal mode, if T1 is 2 minutes 40 seconds, T2 would be 16 seconds (160 sec * 0.1). Sensor Reheat is a quick and easy way to reheat refrigerated and room temperature foods, requiring only a button press.
The manual emphasizes safety precautions during servicing, particularly regarding the high voltage and high current circuits of the Inverter Power Supply (U). Servicing should only be performed by trained, qualified personnel.
The oven includes a self-diagnostics failure code system (H95, H97, H98, H99) to indicate magnetron and inverter circuit problems. The manual provides a flowchart for troubleshooting these codes, including checks for magnetron filament continuity, inverter input AC voltages, and inverter control signals.
The manual explicitly states: "DO NOT try to REPAIR H.V. Inverter power supply (U). Replace complete H.V. Inverter(U) Unit." This is due to the extreme danger associated with repairing these high voltage, high current circuits without proper test equipment. Defective inverter boards must be replaced with new ones.
Procedures are outlined for testing:
The manual also includes exploded views, parts lists (including lead-free solder PCBs indicated by "PbF" stamp), and schematic diagrams for the digital programmer circuit and wiring materials. It notes that PbF solder has a higher melting point (30-40°C higher than standard solder) and requires a high-temperature soldering iron (370 ± 10°C), with eye protection recommended due to splashing.
General| Type | Countertop Microwave Oven |
|---|---|
| Power Output | 800 watts |
| Control Type | Electronic |
| Turntable | Yes |
| Weight | 26 lbs |
| Color | White |
| Voltage | 120V |
| Frequency | 60Hz |
| Sensor Cooking | Yes |
| Pre-Programmed Settings | Yes |
| Child Safety Lock | Yes |
| Dimensions (W x H x D) | 489 x 275 x 382 mm |
| Exterior Dimensions | 489 x 275 x 382 mm |
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