Help from Microwave tech please.

[Canadian_Rainbi]

2002 motorhome, presume the Sharp micro convection oven is the same age. There is 100,000 miles on the coach, we use the oven a lot.

Recently, when reheating tea, or melting cheese on toast, power on high, time set for 15 to 30 seconds. 4 times in the past three weeks there has been a loud BANG or CRACK like an arc and the oven proceeds to heat to the end of the timer, items are hot, no burning smell.

Not every time, just once in a while. Convection seems OK.

Ideas what is happening? I am in Mexico and not too sure if I want to take this into a local shop.

My CV as it were" ham radio operator (built first radio transmitter at the age of 11) worked for a year in Radio TV shop as apprentice, have very few tools: VOM, soldering iron etc

Physical disability--couldn't get it out by myself but probably could with help.

Recommendations: Wait and watch for smoke with fire extinguisher at hand/ (I was a Volunteer Firefighter for many years) :B

Or open it up if I can figure out how to get it out.

[bucky]

My Jayco MW failed but it vented to the back, not the top. $69 USD at Wal*Mart took care of the problem.

[DownTheAvenue]

Canadian Rainbirds wrote:

DownTheAvenue wrote:

sch911 wrote:
Bottom line here is that microwaves are throw away devices. Just replace it period....

14 year old microwave. Probably not repairable. Parts not available. But a new one for less than $100.

Thanks for those with helpful suggestions.

Why don't people read the original post before making blanket statements?

I'm speaking of a micro/CONVECTION oven here. Like this one.

About $780.00 Canadian. I don't throw that kind of money away, it's a significant portion of my monthly pension.

Good luck to you! IF you have a failed part, you will be forced to buy a new unit. By the way, with a little effort on your part, you should be able to find a replacement, maybe not the same brand, for less than $100 USD. Google is your friend. And yes, I know it is a convection microwave.

[red31]

clean (both sides) or replace the wave guide.

[winnietrey]

At the risk of telling you something you already know, house units vent to the back, RV units to the top. That sharp you had a link to appears to vent to the back. If little or no clearance against the back wall of the microwave cupboard that maybe an issue, as far as overheating. Only outfit I know, that makes microwave/convection units for RV's top vented is Dometic. CW carries them. Went through this a year or so ago Your setup maybe different, but it might be something to consider

[fluffo2]

I had kind of the same experience with a microwave while trying to heat a cup of cold coffee. I was waiting for it to heat, and all of a sudden there was a loud bang in the microwave. Luckily I was watching my cup heat, and noticed it jumped at the same time as the bang.. Turned out that the cup had a concave bottom, and as I rinsed it and put the coffee in without drying the outside, some drops of water were trapped under the cup. As the coffee was heating, the trapped drops flashed to steam causing the commotion. Don't know if this helps...but strange things do happen.

Bob

[SaltiDawg]

Canadian Rainbirds wrote:


I am well aware of that because 50 years ago got a burn hole in the tip of my little finger from the high voltage rectifier in a colour TV back when I was working in a Radio & TV service shop. Probably in the 30,000 volt range? Took 30 years for the scar to eventually disappear!

Art VE7FED

Warning: SEA STORY.

55 Years ago I had a Navy Electronics Technician (ET) as an Instructor at ET School, in Great Lakes, Illinois.

Pierce at one point showed us one f his elbows, which was hideously disfigured and showed clearly that he had been seriously injured earlier in his life.

He told us he got a cross the hot end or a shipboard Radar magnetron with his hand. What saved his life was that his arm was bent and the energy could not make the "turn" due to "the skin effect." (At very high frequencies, all of the energy travels on the outermost surface or skin of the conductor. (Indeed on shipboard radars in those days the conductors were called "wave guides" and looked like roof gutter downspouts - hollow inside because no energy conducted there. Turns had to be small bends - NOT like a bent elbow!

[larry_cad]

The microwave power circuit consists of four major components: The magnetron, a high voltage diode, a high voltage capacitor and a transformer. Any one of those four components could be the problem. If the diode is bad, there won't be any heat. Ditto for the capacitor and transformer. Magnetrons are generally reliable. I would take the above advice and examine the remaining components to see if there is any sign of dirt or arcing, particularly around electrical connections. Look closely at the capacitor as it has a metal case that is grounded.

[Canadian_Rainbi]

Yes, I knew that but for some reason was not co-relating the 1500 Watt microwave with the watts or milliwatts of a colour TV. :E

Thanks for pointing that out. I think a long plastic rod will be handy! Wish I had my nylon alignment tools with me!

[DrewE]

Microwaves are more dangerous electrically speaking because the power available in the high voltage circuit is much, much greater. The magnetron takes something like 3 kV at maybe a half an ampere or so. Electrocution is a very real possibility if one touches the wrong spots.

That is not to suggest that one can't safely diagnose and repair one, but it is important to understand the dangers and necessary precautions.

[Canadian_Rainbi]

wa8yxm wrote:
Sounds like dirt to me.

There are some serious high voltages inside a microwave.. now if there is some dirt build up on some of the components this can happen (Dust and such).

Now I Will caution SHARP EDGES ON METAL PARTS, HANDLE WITH CARE OF HEAVY GLOVES OR BOTH.

Now... Remove the unit from the RV to the picnic table,, Remove the outer cover... Inspect visually (Do not touch internal parts) see if you can find evidence of an arc (Chared anything)

If you see an accumulation of dust/ or whatever, blast with compressed air, don't have a compressor, buy a can of "Dry Air" from a photo department (used to clean camera lenses) and use it.... Then reassemble.

now.. i've worked on Microwaves, all the way down to working on the high voltage circuit.. But I'm not suggesting you do that.. The kind of voltages on that cap are... Impressive.

I am well aware of that because 50 years ago got a burn hole in the tip of my little finger from the high voltage rectifier in a colour TV back when I was working in a Radio & TV service shop. Probably in the 30,000 volt range? Took 30 years for the scar to eventually disappear!

Art VE7FED

[GordonThree]

Anything electric that old and it starts acting up time to toss it. Doesn't matter if it's high end or not.

Micro convection aren't that expensive unless you're set on buying one with a fancy name plate on it.

[MEXICOWANDERER]

MÉXICO

Cities of 100,000 or more have authorized multi-company repair centers that use original authorized parts. There will be a diagnostic charge. Possibly $200 pesos.

Most arcing is caused by salt air deposits across the magnetron. The repair center will clean it and test "la placa" the control board. Depending on on where you are cities like Queretaro, Morelia, Acapulco, Lazaro Cardenas, Puebla, Veracruz, et al. will have a repair center.

To find it, simply consult the staff of any ELEKTRA store or vendor de electrodomesticos (electric appliances). A gold mine as to how to go about finding the nearest repair center. Take your Skil and Black & Decker misfits with you and they'll repair those as well. I have yet to find a dishonest or incompetent repair center and the cost is unbelievably low - even for the genuine brand repair parts. Don't expect to find anything like this north of the border.

[wa8yxm]

Sounds like dirt to me.

There are some serious high voltages inside a microwave.. now if there is some dirt build up on some of the components this can happen (Dust and such).

Now I Will caution SHARP EDGES ON METAL PARTS, HANDLE WITH CARE OF HEAVY GLOVES OR BOTH.

Now... Remove the unit from the RV to the picnic table,, Remove the outer cover... Inspect visually (Do not touch internal parts) see if you can find evidence of an arc (Chared anything)

If you see an accumulation of dust/ or whatever, blast with compressed air, don't have a compressor, buy a can of "Dry Air" from a photo department (used to clean camera lenses) and use it.... Then reassemble.

now.. i've worked on Microwaves, all the way down to working on the high voltage circuit.. But I'm not suggesting you do that.. The kind of voltages on that cap are... Impressive.

[doxiemom11]

Ours is like yours in a 2000 motorhome. Use ours all the time too.

Are you using a new coffee cup or putting something new in? Something that could have a small exposed piece of metal?
Trim around the top or in a design on the cup? I assume it's doing this when using the microwave .... I feel your pain and dread when something on ours goes out. We use both features a lot.