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Unfortunately the issue you're experiencing means that one of the control board thinks 1 of the 3 door switches has failed. You'd need to uninstall the entire microwave and remove the top sheet metal panel and such to expose the door switches. Then test the door switches as you open and close the door to determine if one of them isn't opening and closing properly. Either replace the faulty door switch if you find one, or replace the main control board if all of them test good because it thinks one of the switches is bad.
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