Microwave failure modes - and fuse types

[ARWadsworth]

Time to take the wife shopping for a new one:-)?

[Roger Mills]

Possibly. Problem is that it's a built-in combi microwave (which are ridiculously expensive compared with free-standing ones[1], it's not a current model (about 11 years old, at a guess) and there's a matching single oven - so a new one ain't quite going to match, even if it fits the space! It would be better to mend it if it doesn't cost the earth.

[1] A Neff built-in combi is of the order of £400, whereas Lidl have got a free-standing microwave with grill on offer at £40 on Thursday!

[BigWallop]

Start with a word of warning. Never operate a microwave oven while it is empty. Always have, at least, a half cup of water inside. Also, unless stated on the front of the oven, never put metal inside the oven. Not even crockery (plates, cups, saucers etc.) with metallic design features. Another very common microwave oven killer, is the frozen pack of Sunday Bacon, which often contains metal foil in the packaging and is thrown in the micro' to defrost.

Microwave Ovens don't really have a low, medium or high setting, they only have "ON" or "OFF" periods for set times, depending on which option you choose. Setting the oven on low, and only running it for a short time set, may not have been long enough to show a fault.

Example: High setting starts the oven immediately, and remains on until the set time expires.

Medium starts the oven immediately, but only runs for, let's say, 10 seconds, then it switches off for a few seconds, then back on again, until the set time runs down.

Low setting may not start the heating cycle for a few seconds, then it will cycle the on / off periods even more frequently, thus giving the food only short blasts of energy at a time, rather than constantly like the high setting would.

My advice would be. Unplug the oven from the mains. Look inside at the walls, roof and around the base for any small scorch marks left by arcing metal which may have inadvertently been placed in the oven. The marks could be as small as a group of black dots, like ink dawbs from a ball-point pen. If you do see marks like that, then get a new oven. The wave guide has probably been blackened and will, more than likely, not be repairable. Replacing the whole 'innards will be more expensive than a new oven.

If you don't see marks on the inside of the oven, and make sure you have checked it thoroughly, then a repair, to something simple like the timer or control circuit, may not be an expensive option. Choose a reputable engineer for these types of repair, as a bodge can seriously damage health and damage property.

Who knows, it could be something silly like beef fat dripped across the turntable motor. But I am not going advise that you take this type of appliance apart by yourself. They contain large amounts of stored energy, even when unplugged and lying dormant for years, and can kill very easily. So get the Yellow Pages out.

Good luck with it.

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[NT]

Sorry but most of this is not good advice. The HV capacitor certainly can kill though.

NT

[whisky-dave]

Seemed quite reasonable to me, although saying HV capacitors can kill is rather misleading. Cars can kill too, but it's the charge on the capacitor that can kill not the capacitor itself well unless swallowed or inserted somewhere it really shouldn't be ;-)

[NT]

Probaly the biggest shortcoming of this group is the tendency of people with no electronic expertise to give advice on the susject. Telling people never to operate an oven empty is a classic, it only ever applied to the very first microwave oven model many decades ago.

NT

[Andy Burns]

I think the point is they can kill someone who is unaware of the charge they (can) hold even when switched off

It's usually the momentum of a car that kills, not the car itself.

[<me9]

Can easily be lethal to the unaware!

Metal foil is often used in microwaves to shield areas where the food is thinner to avoid overcooking those parts. Generally metal isn't a problem as long as not resonant and close to other metal parts, resulting in sparking. I regularly leave the spoon in when making gravy without a problem.

The majority of microwaves do pulse for lower than full power, however, my last two have used inverters and have reduced the power to the magnetron in the same way yhat switched mode power supplies regulate.

The failure of the first of my inverter microwaves was due to my forgetting to add the milk/water to my porridge. It never recovered from the resultant fire.

It is important that some load that will absorb the microwaves is present in the oven cavity. This is almost without exception water in a liquid form (rather than as ice which doiesn't absorb microwaes), hence adding a teaspoon of water to frozen veg before cooking.

[Andrew Gabriel]

For a few weeks, I had no kitchen due to ripping out and fitting a new one. I moved one of the floor-standing cupboards into the dining room, and stood the microwave, kettle, and toaster on it, and that was my kitchen, plus the fridge-freezer.

I bought a frozen multi-pack of microwave chips, which I had a few of. However, a year or two later, I found the last one still in the freezer. Of course, it was well past its best-before date, but what can go wrong with chips? Popped them into the microwave, and switched on. Within a few seconds, they explode into flames. Manage to get them out of the microwave quickly, and only damage was an internal coating of soot, and a burning smell which took a couple of weeks to leave the house.

On closer inspection, they had completely freeze-dried, leaving basically a mixture of starch powder and oil. Hence the fire. I did wonder if "best-before" was perhaps understating things.