What is Causing Your Microwave to Spark?

Paradise Appliance
December 13, 2019
Microwave Repair

Your microwave is small but mighty. It is an appliance you probably use almost every day. Unfortunately, you didn’t realize that until you couldn’t use it. Sparking in a microwave is one of the most terrifying things it can do.  These sparks are hot and can be a fire hazard, plus they are a sign that something is wrong and you cannot ignore it. If your microwave has started sparking, here are all the likely suspects.

WARNING: Do not attempt any repair on a microwave without the proper appliance repair training. The voltage from a microwave can do great harm or kill.

Metal in the Microwave

We are all well educated at this point that forks, metal dishes, and tin foil have no place in the microwave. Even if we aren’t specifically taught, it is a mistake that is only made once anyway. However, “metal in the microwave” doesn’t always come in forms we expect.

One excessively common example of this is steel wool. Your microwave is prone to baking on food to the interior, which makes it really difficult to remove. However, steel wool possesses strong scrubbing power. Unfortunately, what you don’t see when scrubbing with steel wool is all the very small shards of metal that get scraped off and left behind. You will see them the next time you use your microwave, though.

If this is your problem, then it is actually pretty easy to solve. You simply need to give your microwave a good wipe down with a wet cloth. Unfortunately, some of the metal may have been scraped off inside the vents, which will require disassembling so you can wipe them down on the other side to fully remove the metal and put an end to this problem.

Faulty Wave Guide

The waveguide is a small and easily ignored part in your microwave that actually directs the heat waves created by the appliance. When working normally, it will direct the waves at the center of your food while the turntable rotates it around. This ensures even heating so your food gets heated all the way through. Unfortunately, when it is not working properly, it can cause sparks in your microwave.

Usually, if food gets on the wave guide cover, it can manifest as sparks as it burns up. Luckily all you need is a good cleaning to fix this issue quickly. However, if the waveguide is malfunctioning, it can direct overly intense waves to only one area of your microwave. Over time, this will cause sparking to occur from that area. Unfortunately, for this malfunction, you will need to repair the waveguide. This isn’t overly complex as far as microwave repairs go, but it does involve some disassembly that appliance owners may not be particularly comfortable with.

Damaged Interior

For an appliance that specifically has warnings against putting metal inside, the interior of your microwave sure is made of a lot of metal. What prevents this interior metal from sparking usually is the paint job that sits over it. Unfortunately, over time, this paint can wear or be scraped away. This means that one day your microwave could start sparking simply because the metal on the walls or some shelf support is missing and the metal is exposed. What usually happens is that food gets on an area, bakes on there, and one of two things happens. First, you might try to scrape it off, which damages the paints. Second, you may do nothing, which creates a hot spot and essentially burns off the paint.

When this happens, your appliance is typically old enough that you might just want to replace it. Of course, if you have a real workhorse and you want to save it, you can look into repainting the worn interior. Microwave safe appliance paint can be found in most appliance stores. Repaint your interior, let it dry, and then test to see if it still sparks. Make sure to add in a cup of water before testing as you should never run a microwave empty if you do not want to damage it.

You may want to look into getting some of this paint even if this isn’t the cause of sparking. If your microwave had some major sparks inside and has manifested burn marks, then this appliance paint can help cover it up so this doesn’t become a new issue of sparking later.

Finally, sometimes metal exposure can come in unexpected places. If you don’t see any patches of wear inside your microwave, you will also want to check items such as the turntable stirrer underneath the turntable plate. Usually, this part is plastic, but if it is worn, it can expose the metal rod that attaches it to the turntable motor. It is often these semi-hidden parts that can cause a frustrating session of troubleshooting for an already frustrating problem.

Faulty High Voltage Diode

If you have checked all the above, then there is only one potential cause of sparking left, and it is the most complex one. The high voltage diode works with the magnetron by providing it with power so it can produce heat. If there is sparking happening in your microwave, it could mean that that the high voltage diode is shorting out and needs replacement.

While technically you can replace the high voltage diode yourself, you will highly want to consider leaving this particular repair to a professional. One typically unknown fact about microwaves is that the capacitors will hold a potentially lethal charge even when the appliance is unplugged. For many repairs, this is a non-issue as long as you are careful not to touch those capacitors. Unfortunately, the high voltage diode is located right next to them. This means one accidental bump could mean a trip to the hospital.

You can discharge the capacitors in your microwave by running the tip of an insulated screwdriver from one terminal to the next. You will know the capacitor is discharged when you hear a very loud and potentially jarring pop. Once you are sure the capacitors are all discharged, the high voltage diode can be tested with a multimeter. If it has no continuity or has low resistance in both directions, you will want to replace it.


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