Why does my microwave start then cuts out after 4 seconds for no reason

Door Switch Start Your Repair Here
SEARCH Need Help Finding Your Model Number? MORE ABOUT THIS REPAIR - Customers rate this repair as Really Easy
- Takes less than 15 mins
We have 13 installation instructionsThere are many reasons your microwave won't turn on, one of which might be a faulty door switch. The door switch, also known as an interlock switch, signals other microwave components to begin powering when the door is closed, and to stop when the door opens. For this reason, everything else may appear in working order but the microwave will not begin heating. To access the door switch or interlock switch, unplug the microwave and dismantle the cabinet. The switches have terminals which are marked C for common and NO for normally open. Check each terminal with a multi-meter for continuity. If there is continuity while the actuator button is engaged, that means the switch is working. If there is no continuity, replace the switch. You can also take this opportunity to make sure the door hooks are working properly.
Ceramic Fuse Start Your Repair Here
SEARCH Need Help Finding Your Model Number? MORE ABOUT THIS REPAIR - Customers rate this repair as Really Easy
- Takes less than 15 mins
We have 1 installation instructionIf your microwave won't start and the display is blank and unresponsive, the issue may be with the ceramic fuse. This part protects other microwave components from power fluctuations, and causes a complete loss of power when it fails, meaning your microwave won't work. To access the ceramic fuse, located inside the cabinet near the power cord, first unplug your microwave. Use a multi-meter to test the continuity of the fuse. If you are aware of the cause of the fuse failure, such as opening or closing the microwave door, you can also test the door switch to see if that is working. If you are unaware of the reason for the fuse failure, you may want to test other microwave parts such as the magnetron, high voltage diode, capacitor, and transformer.
Thermal Fuse or Cut Out Start Your Repair Here
SEARCH Need Help Finding Your Model Number? MORE ABOUT THIS REPAIR - Customers rate this repair as Really Easy
- Takes less than 15 minsA problem with the thermal fuse or cut out could be the reason your microwave won't turn on. The thermal cut-outs, also known as thermal fuses, help keep the oven from overheating. When the thermal cut-outs fail, your microwave won't turn on as a safety precaution to keep it from getting too hot. To access the thermal cut-outs, first unplug your microwave and then remove the cabinet. Once you locate the thermal fuse, disconnect its wires from the terminals. Use a multi-meter to test for continuity, and replace the thermal cut-outs if there is no continuity. Take this opportunity to also check that the cooling fan is working and not causing the microwave to overheat by cutting off airflow.
Door Latch Assembly Start Your Repair Here
SEARCH Need Help Finding Your Model Number? MORE ABOUT THIS REPAIR - Customers rate this repair as Really Easy
- Takes less than 15 mins
We have 4 installation instructionsYour microwave may not start because of an issue with the door latch assembly. Most door latch assemblies are made of plastic hooks that stick out of the door and engage the door switch when the door is closed, signalling the rest of the controls to power the microwave. If the hooks are damaged or lacking tension due to worn-out springs, the switch will not latch properly meaning the microwave won't turn on. To access the door latch, first disconnect the microwave from its power source, and remove the inside door panel, which is held in place with plastic tangs. Inspect the door latch and replace it if it appears to be damaged.

You need to replace the diode. Scratch that. The voltage let alone the radiation could kill you. Call a technician. If it is a table top unit, buy a new one. It will be cheaper,

I guess your model number is GMV1540TW?

I think I answered this or a duplicate post already, but here goes:

The owner's manual covers that, but if for some reason you don't have yours, you can get it here.

To set child lock:

1. Press STOP/CLEAR.
2. Touch and hold START more than 4 seconds.
"LOCKED" will appear in the display window with two beeps.

To cancel child lock:

1. Touch and hold START more than 4 seconds.
"LOCKED" will disappear in the display window with two beeps.

its 13 years old it will probably be cheaper to replace it than have it repaired

MICROWAVE RUNS ABOUT 5 SECONDS AND SHUTS OFF AND SMOKE FROM UNDERNEATH CABINET

This is happening due to either the magnetron, or the Power Diode, or both, is breaking down, under load, then the unit detects the fault condition, & then, for safety reasons, to avoid a fire or explosion, shuts down the system. You need to take it in to be looked at please obtain a "Quote" before proceeding with any work. This way you can decide to repair or replace.

The Child Lock is on.

Your owner's manual covers it. If for some reason you don't have yours, you can download it free here.

CHILD LOCK
You may lock the control panel to prevent the microwave from being accidentally started or used by children.

Example: To set the child lock.
1. Touch STOP/CLEAR.
2. Touch and hold START more than 4 seconds. LOCKED will appear in the display window with two beeps.

Example: To cancel the child lock.
1. Touch and hold START more than 4 seconds. LOCKED will disappear and you hear two beeps. At this time the oven is ready.

We're happy to help you with free advice and we'd appreciate your thoughtful rating of our answer.

My panasonic microwave model # NN-S540BFW stops after 4 seconds after you hit the start button and cuts off on its own. What is wrong with my microwave?

The 22 seconds is the giveaway. In most cases, this is a problem with the inverter or a bad magnetron.

Due to the lethal voltages used and produced, I do not recommend that an inexperienced person work on these.

I would recommend that you contact your nearest Panasonic-authorized servicer. You can find one here.

We're happy to help and we appreciate your thoughtful rating of our answer.