My daughter put metal in oven it shut off. the oven turns buts shuts off after a few seconds. help

There might be a problem with door switch for your microwave to be turning off after 3 seconds and the door switch will need replacement on your microwave.

NOT FAMILIAR WITH Lincoln MICROWAVES BUT IF IT RUNS A FEW SECONDS THEN SHUTS OFF IT IS DOING WHAT UNITS WITH A BAD MAGNETRON AND OR INVERTER DO, HAVE THEM BOTH CHECKED OR REPLACE UNIT

When a Panasonic Inverter Microwave shuts off after a feew seconds, it is either a bad inverter which is the quite expensive circuit board that powers the magnetron that puts out the microwave energy, or a bad magnetron, Or BOTH typically this would be a costly repair, But since it is still under warranty. You need to find a Panasonic warranty service provider in your area. If it is a counter top unit, you may have to take it to them for repair.

Mark sounds like it is tripping a internal limit relay, weak power supply or door switch possibly. Below are links to help diagnose.
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Kenmore Microwave Model 401 80084700 40180084700 401 80084700 Parts

Kenmore Microwave Shuts Off After Few Seconds

Microwave Oven Shuts Off After 2 Or 3 Seconds How To Fix

If our Panasonic microwave shuts off after 2 seconds is it likely door...

The problem is the magnetron, or the inverter board, "if 7 years old or less" and possibily the keypad control board.

Your wave guide cover and magnitron need to be replaced.

See this FixYa solution.

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check your wave gaurd inside microwave... it should have no holes or burns........................

I am surprised that the GE seervice tech did not explain to you why the microwave will still cook. By saying that transformer is damaged or shot really means that the internal windings may be shorted together so the transformer no longer has as many good windings to produce the original power it did when it was new. That is pretty clear. It will still function a little but the protection circuits inside the microwave would start to shut it down when it overloads by trying to pull more current than the windings inside the transformer can handle. You can replace the transformer yourself if you are a do it yourselfer and are confident around unplugging the transformer with All Power Off and unscrewing a couple of screws that hold it in place. It is pretty straightforward you just need to find the correct transformer (maybe you can buy one from GE or go to www.mwoparts.com which carry all the parts in microwaves for all models especially name brands like yours. Taking the cover off is of course easy. Good luck. Let me know how you do or if I can help you in any other way.

We are all in the same boat. It is very annoying. I think it is a sensor tripping.