H99

Panasonic Inverter Communication / Overcurrent Protection Fault

Microwave stops heating and displays H99, often immediately or within a few seconds of starting a cook cycle.

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.

Possible Causes

Inverter board internal fault, Control PCB to inverter communication failure, Shorted magnetron drawing excessive current

How to Fix / Troubleshooting

Safety Warning: Internal diagnosis of H99 involves live high-voltage measurements and should only be done by a trained technician.

Steps you can try safely:

Hard reset: Unplug the microwave for at least 10 minutes. This can clear a latched inverter protection state.
Check outlet and power: Plug the microwave directly into a wall outlet (no extension cord or power strip). Low or unstable voltage can contribute to inverter errors.
Test with light load: Place a single cup of water in the oven and run for 30–60 seconds. If H99 appears again, stop using the unit.

Next steps:

Persistent H99 usually indicates a failing inverter board or magnetron. These parts are not user-serviceable.
Arrange service with a Panasonic-authorized technician; provide the model and H99 code for faster diagnosis.

Repair Difficulty

Professional Required 5/5

Required Part

Inverter Board (Power Supply Module)

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