Full Analysis of Inspection and Testing Certification Standards for Microwave Oven Products: A Guide for Key Component Testing and Quality Control

April 7, 2026

I. Inspection Standards for Magnetron
The magnetron is the core component of a microwave oven. The inspectors need to conduct the following inspections using a multimeter:
Between the two electrodes of the filament: Measure with the R×1 setting. The normal resistance is very small (conducting). If it is infinity, it is judged as unqualified.
Filament to housing: Measured with the R×10k setting, the normal resistance value is ∞ (open circuit). If it is conducting or has a resistance value, it is judged as unqualified.
The connection between the transmitting head and the housing: Measure at position R×1. The normal resistance value is extremely small (conducting). If it is infinitely large, it is judged as unqualified.
Judgment: If any of the above items do not meet the standards, the magnetron should be deemed不合格 (unqualified) and the entire unit needs to be replaced.
II. Inspection Standards for High-Voltage Transformers
The transformer is a crucial component for voltage boosting in microwave ovens. The inspector should follow the following steps for inspection:
Primary winding resistance: Measured using the R×1 setting, the normal resistance value should be between 2Ω and 2.5Ω. If it is open circuit or less than 1.2Ω, it is considered不合格 (unqualified).
Secondary filament winding: The resistance is very low, and the voltage is approximately AC 3.4V.
Secondary high-voltage winding: The resistance should be normally between 100Ω and 150Ω, and the voltage is approximately AC 2100V. If the resistance is ∞ or less than 80Ω, it is judged as unqualified.
Judgment: If any item exceeds the permitted limit, the transformer is deemed不合格 (unqualified).
III. Inspection Standards for High-Voltage Diodes
High-voltage diodes are used for rectification and voltage boosting. The inspector should measure using the R×10k range:
Forward resistance: Normal range is 150kΩ to 300kΩ. Any value that is too high or too low is considered abnormal and is classified as non-compliant.
Reverse resistance: Normal value is ∞ (open circuit). If there is a resistance value or it is 0, it is judged as不合格 (unqualified).
Judgment: The forward and reverse resistances do not meet the standards. The diode is classified as unqualified.
IV. Inspection Standards for High Voltage Capacitors
High voltage capacitors are used for filtering and voltage boosting. The inspector should measure using the R×10k range:
Between the two electrodes: Both positive and negative directions should exhibit charging and discharging phenomena, and the resistance should be around 10MΩ. If there is no charging or discharging or the resistance is 0, it is judged as unqualified.
For the two poles, check the outer shell: normally, both should be ∞ (open circuit). If there is any resistance or it is 0, it is judged as unqualified.
Judgment: If the capacitor is leaking electricity or has malfunctioned, it is classified as unqualified.
V. Test Standards for Bidirectional Diodes (for some models)
Some microwave ovens (such as those made by Galesi) do not use this component. However, if it is present, the inspector should measure it with the R×10k range: both forward and reverse directions should show ∞. If there is a resistance value or it is 0, it is considered不合格 (unqualified).
VI. Motor Inspection Standards
Multiple motors in the microwave oven need to be inspected separately:
Timer motor: Measure at the R×1k setting. The normal resistance should be between 15kΩ and 20kΩ. Any value that is too high or too low is considered不合格 (unqualified).
Rotating disc motor: Measure with the R×1k setting. The normal resistance value should be between 7kΩ and 10kΩ. Anything too large or too small is considered不合格 (unqualified).
Fan motor: Measured at R×10 setting, the normal resistance value is 200Ω to 300Ω.
Judgment: The resistance value is outside the range. The motor is judged to be不合格 (unqualified).
VII. Common Fault Repair and Inspection Judgment (From the Perspective of Maintenance)
The following are typical faults that inspectors may encounter during inspections and the corresponding handling and judgment results. These can also serve as a reference for process improvements during supplier audits:
Timer (for mechanical furnaces)
Fault phenomenon: The contacts of the power distributor are burned out and no longer conduct → No heating.
Inspection determination: The burnt contact points are a major defect and should be classified as unqualified. The repair can be done by short-circuiting terminals 2 and 4 (for a four-terminal timer), but it is necessary to note that the fire intensity should be set to high at this time.
Timing motor malfunction: The timer fails to reset to zero. This issue was identified during inspection and is classified as non-compliant.
2. Capacitor
Fault phenomenon: One end plate is short-circuited to the housing → Does not heat up, and sometimes burns out the high-voltage fuse.
Inspection determination: Failure of capacitor insulation is a major defect. For emergency handling, it can be fixed by wrapping it with multiple layers of insulating paper and suspending it. However, for formal inspection, it should be judged as unqualified.
3. Bidirectional Diode
Fault phenomenon: Short circuit → Microwave oven does not heat up or 8A fuse blows.
Inspection determination: Short circuit is a major defect. If this component is absent, it does not affect the operation of the circuit (this component is not used in Gree models), but if it is designed to be present, it must be qualified.
4. Transformer
Fault phenomenon: One end of the secondary high-voltage winding is broken → No heating.
Inspection determination: Winding breakage is a fatal defect. Emergency repair can be done by connecting with wires, but it should be judged as不合格 (unqualified) in a formal inspection.
Core loosening: Produces a loud "sizzling" sound, but can still generate heat. This is a manufacturing defect and should be classified as non-compliant.
5. High-voltage fuse blowout
Inspection determination: If the high-voltage fuse blows out frequently, it indicates a circuit defect and should be judged as unqualified. Note: Some brands (such as Haier, Midea, LG, etc.) do not use this fuse; it should be judged according to the customer's specifications.
6. The magnetic control tube emission head was burned out.
Inspection determination: The damage to the emission head is a major defect. According to normal standards, it should be judged as unqualified. In an emergency, the outer cover can be removed, but this is not accepted in formal inspections.
7. The spring at the plastic door hook has broken.
Fault phenomenon: The door cannot be closed and the entire machine does not work.
Inspection determination: The fracture of the structural components is a major defect, and it is classified as unqualified.
8. Computer Board
The primary winding of the transformer is not connected: The computer has no display. This is usually caused by the internal temperature protection device burning out. During the inspection, it was determined to be unqualified.
The thermal stability of the 5V voltage stabilizing tube is poor: after working for a certain period of time, there is no display, but it returns after cooling. This is a latent defect. It can only be detected during the inspection process through aging tests and is classified as unqualified.
VIII. Linkage between Factory Audit and Certification
1. Supplier Capability Assessment (Key Point of Factory Audit)
During the factory audit, microwave oven suppliers need to focus on the following assessment:
Incoming inspection records for key components such as magnetrons and transformers, as well as supplier certifications.
The withstand voltage testing capabilities of safety components such as high-voltage capacitors and diodes.
Motor winding process and resistance testing equipment calibration.
Durability tests for structural components such as door hooks and timers during the assembly process.
Qualifications and training of inspectors.
2. Product Certification Requirements
Microwave ovens need to meet the corresponding certification standards when entering different markets:
Target market Certification requirements Inspection focus
Chinese market CCC certification, GB 4706.21 "Safety of household and similar electrical appliances - Special requirements for microwave ovens" Microwave leakage, high-voltage insulation, temperature rise
European market CE mark, EN 60335-2-25, RoHS Microwave radiation, harmful substances
American market UL certification, FDA 21 CFR 1030.10 Microwave leakage limit, electrical safety
During inspection, it is necessary to verify the consistency between the product label and the certification certificate, and confirm that the safety indicators such as microwave leakage meet the standards.
3. Continuous Improvement
Any quality issues identified during the inspection should be promptly reported to the supplier.
Repetitive issues need to be followed up and rectified through factory inspections.
Establish a quality traceability record to support product certification audits.
IX. Sampling and Decision Rules
Sampling Plan: Determine the sampling quantity and acceptance level based on the AQL standard. For critical safety items (microwave leakage, high-voltage insulation), it is recommended to have zero defects.
Defect Classification:
Critical defects: Excessive microwave leakage, high-voltage breakdown, and failure of the door interlock.
Main defects: The parameters of components such as the magnetron, transformer, and capacitor do not meet the standards. It does not heat up and the timer is malfunctioning.
Minor defects: Appearance scratches, packaging damage.
The inspection report should include the actual measured values of each component, the description of the fault phenomenon, the determination conclusion, and photos.