H99
Magic Chef Inverter Communication or Control Error

Microwave shows H99 and will not start; may occur intermittently.

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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

Loose harness between control board and inverter, Failed inverter board logic, Faulty main control board, Power line noise or surge

How to Fix / Troubleshooting

Safety: Unplug the microwave before removing covers.

Basic reset:

  • Disconnect power for 10–15 minutes, then reconnect and test. If H99 returns, proceed with inspection.

Internal inspection (technician recommended):

  • Remove the outer cabinet and locate the inverter board and main control board.
  • Check the low-voltage communication harness between the boards for secure connections and no corrosion.
  • Inspect both boards for visible damage or burnt components.

Corrective actions:

  • Reseat or replace the communication harness if damaged.
  • If no wiring issues are found, replace the inverter board first (common failure point).
  • If H99 persists, replace the main control board.

Note: Because this involves both logic and high-voltage circuits, professional service is strongly advised.

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Repair Difficulty

Professional Required 5/5

Required Part

Inverter Communication Harness
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