I have a Magic Chef over-the-range microwave (MCO160UB), and recently the turntable and internal light stopped working while it runs. Light and fan underneath both work, and the internal light works when you open the door. The turntable and light will work on occasion. Any ideas?

If it lights up, the fuse is fine. On all of the recent Magic Chef's I've repaired, the magnetron has been the cause of the problem you described. Another possible common culprit is the high voltage rectifier.

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sounds like a cross wire, and a short. I'd inspect the socket for the bulbs to ensure that there's no short circuit.

There's a fuse that has blown. look for it near the bulb socket or on the main board inside the unit.

it is an internal fan that is the problems, if this is a counter top MW just replace it. if Over The Range (OTR) and under warranty call for service. if out of warranty replace.

If you could get it to reset by unplugging it I would suspect a problem with the main timer board. A blown fuse or bad connection wont reset by unplugging it. You would need to find a parts dealer who carris Magic Chef parts and give them your model number and ask for price and availability on the main PCB the printed circuit board
( timer board)

If the microwave is above the stove, the heat sensors in the microwave
may turn on fans to cool it even though the microwave itself is not
running. It tries to save its life. It should turn off when the stove is not
heating it.

You can still use it, but must be aware that this is a relatively high power microwave, so food will burn if it isn't turned.

Right, that would be MCO10UW and the owner's manual is here.

The owner's manual does say this, of course,

"To prevent overheating from taking place, the exhaust
fan is designed to automatically turn on at a low speed if
excessive temperatures occur. Should this happen, the
fan cannot be manually turned off, but it will
automatically turn off when the internal parts have
cooled. The fan may stay on for up to an hour after the
range and microwave oven controls have been turned
off."

That;'s standard on microwaves.

But these models do have a separate internal cooling fan (which should run any time you microwave) plus the hood vent exhaust fan, which should only run when you select it, or if there is an excessive stovetop or under-hood temperature.

So if it comes on whenever you microwave, that is incorrect.

When that happens, it's usually a defective vent thermal switch (a.k.a. hood TCO).

But since it's brand new, I would certainly contact Magic Chef about this. If it's in need of repair, they will fix it free, assuming the oven wasn't physically damaged.

For more help from Magic Chef / Ewave see here or their contact page.

For Magic Chef in Canada call 866.587.2002

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I'm guessing that nothing is working...is that right? If so, first guess is the breaker or an internal fuse. Nearly all units have them. You don't say what fuse you checked. Unplug the unit, remove the bulb and see what is in the socket. Next, open the breaker and then turn it back on. This will reset it. Something caused this.

The turn table and fan are connected in series with the bulb,as you have mentioned that you have replaced bulb,so please check again for any loose contact on bulb holder or bulb continuity again.