Microwave shows F4 and will not start; sometimes occurs after a loud pop.

Safety Warning: Unplug the microwave before accessing door switches. Door interlock circuits are a critical safety system.

Checks:

• 1. Inspect door: Look for cracked or loose latch hooks on the door. If the door does not close firmly, the interlock switches may not engage.
• 2. Listen for clicks: Slowly open and close the door; you should hear multiple clicks from the switches. Missing clicks indicate a failed or misaligned switch.

Switch inspection (advanced DIY):

• 3. Access switch cluster: Unplug the unit, remove the outer cover or control panel, and locate the door switch assembly.
• 4. Test switches: Use a multimeter to test each switch for proper open/closed operation as the door is actuated. Replace any defective switch with an RCA-compatible interlock switch.

After replacement, reassemble carefully and test. If F4 persists, the wiring or control board door-sense circuit may be faulty and should be checked by a technician.