H99
Toshiba
Intermittent High Voltage / Overheat Protection
Microwave intermittently stops heating and shows H99; may work again after cooling.
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Overheating magnetron,Weak high-voltage transformer,Failing inverter module,Blocked cooling airflow
How to Fix / Troubleshooting
Safety first: Unplug the microwave before inspecting vents.
Steps to mitigate H99:
- 1. Improve ventilation: Ensure the microwave has the clearances specified in the Toshiba manual. Move it away from walls or cabinets if necessary.
- 2. Clean vents: Remove dust and grease from intake and exhaust vents using a soft brush or vacuum.
- 3. Avoid long continuous runs: Give the microwave rest periods between long cooking cycles to reduce thermal stress.
- 4. Power reset: After an H99 event, unplug for 20–30 minutes to allow internal components to cool fully, then test with a short cycle.
- 5. If H99 recurs frequently: Internal HV components are likely overheating or failing and must be inspected by a technician.
Note: Do not attempt to service the magnetron or inverter yourself.
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Repair Difficulty
Professional Required
5/5
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