DIAGNOSIS F1 is a door switch failure code. One of the three door interlock switches is stuck open or closed, or has failed.
FIX Unplug the unit. Test the three door interlock switches for continuity with a multimeter while manually actuating the switch lever. The switch that does not click and change states correctly is faulty. Replace that specific interlock switch.
IF THAT DIDN'T WORK The wiring harness connecting the door switches to the main control board may have a broken wire or poor connection. Inspect the harness for damage.
HEADS UP Never bypass a door interlock switch. The microwave will emit radiation if the door is open. Always replace with the correct part.