Arcing and then went dead. Can see arcing from top vent behind fan blade

Make sure no metal item (forks-spoons or oven rack) is touching the outer wall of the microwave. That will cause sparks. If all that is OK then there is usually a metal fan type blade in the microwave top called a stirrer blade that may be out of place and rubbing the cavity causing sparks. Try to pin point the spark area so you know where to look for the problem. Sparks usually mean metal is touching metal somewhere.

Could be arcing around HV transformer or even an HV wire, Sometimes an insulator on a capacitor will get old, dusty or breakdown and arc between the terminals. Have you ran this with the cover off to see if you can see any visual arcing??? If it cooks sure sounds like it is probably not the mag. Something supplying power to the mag arcing to ground I would expect.

There are no bulletins covering a recurring issue with the exhaust fan on this model, so I would suspect the failing motor, an obstruction in the blades, a loose blade assembly, or a damaged wire arcing to the frame.

It will take some visual inspection with the oven removed from the wall (see your installation instructions) and the cover removed.

The service manuals for the variants are here:

http://www.microwavedisplay.com/smh7185_smh9187w_xaa_sm.pdf

http://www.microwavedisplay.com/smh7185_smh9187w_xac_v1.pdf

http://www.microwavedisplay.com/smh7185_smh9187w_xac_v2.pdf

http://www.microwavedisplay.com/smh9187b_smh9187w_smh9187b_xaa_sm.pdf

You can order Samsung parts from the Pros here or from Encompass here.

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It is quite possible the magnetron has burned out, when it arcs it puts a tremendous strain and causes it to overheat very quickly. On top of that you found a burned mark behind the pad which is not good, so there are least two problems that must be addressed perhaps more. In any case it may be cheaper to replace the microwave oven at this point.

There are 3 possible openings that you could be alluding to. One is for the light, one is for the air vent, the 3rd is for the magnatron micro beam energy. The sparking can be from dirt buildup, from a loose connection, from a fan blade rotating or from the scatter blade rotating, or from the magnatron gun shorting, or from the mica cover plate if so equiped. Best to carry it in to a service place; it is usually worth fixing, adn only the magnatron failure would be the highest cost of the repairs. it is at least worth spending a diagnosis cost for someone to tell you the real reason and you'll know for sure if you made the right decision. Goodluck, Macgivor

Hard to say for sure without a model number but if it has a stirrer on top than the stirrer is not turning and the microwaves are arcing off the blade.
Eric

Arcing is often the result of the cover over the magnatron (The thing that produces the microwaves) being aged, burned or damaged. If you look inside the oven, you will see a cover (usually square or round and around 3-5 inches across depending on the machine)made from a flakey silver plastic/fibre material. If this is burned or has a hole, it needs replacing and this will probably cure your problem.

If your motor runs freely and normally, I would not worry about the charred or burn smell as that will be there for a while. You can however to lessen that smell is to power everthing off and unplug the ac cord and use isopropyl alcohol with a cleaning brush like they use to clean circuit boards and clean the area thoroughly where the hot spot was. In that way in the future if you have a problem in that same area that persists after your initial fix then you can pin point it to the particular spot if it is a component that for instance drive the motor or is part of that circuitry. However, I do not think you will have anymore problems once you change the belt.

If it is burning and arcing at the antenna, it is probably arcing in the wave guide area. Probably will have to replace unit. I have had some success by removing the antenna, sanding and repainting the burnt areas of the cavity and sanding off any burnt marks on the antenna. Need to look at top of mag to see if also arcing there too.

Quite often this is due to grease or food particles stuck to the inside of the oven or stuck on or behind the waveguide cover.

The waveguide cover is usually about the size of a playing card and often held in place by a plastic rivet.

In some models it is the plastic ceiling.

It can be fragile, and the metal edges of the oven behind it can be sharp, so be careful!

The cover and the metal behind it should be cleaned with a mild, non-ammonia cleaner.

If the cavity metal of the oven is chipped or charred, it will have to be sanded smooth and clean and dried thoroughly.

Then you can apply some high-temperature appliance paint, available from places like Wal-Mart, Lowe's or Builder's Square.

If your waveguide cover is burned, it will need to be replaced.

If you need more specific help, please reply back with your brand and full model number.

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William E. Miller, AS-EET
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