Microwave spontaneously turned on by its LED display

https://blog.stuffedcow.net/2024/06/microwave-failure-spontaneously-turns-on/

by forgotthepasswd • 2 years ago

168 116 2 years ago

blog.stuffedcow.net

ThePowerOfFuet• 2 years ago

Unreadable on mobile. :(

hulitu• 2 years ago

Microwave Oven Failure: Spontaneously turned on by its LED display

It is an engineering failure. The oven is not to blame. /s

hex4def6• 2 years ago

Link seems dead. wayback version: https://web.archive.org/web/20240910031602/https://blog.stuf...

MisterTea• 2 years ago

Notice that door switch middle is a crowbar[1] which is there to prevent the magnetron from powering on when all else fails (and there is a lot of interlocking). My friends parents had a microwave that kept dying so I opened it up and realized one of the three switches was a crowbar and it blew the fuse. I changed the fuse and it powered on again and ran for a few more days until it blew again. They decided it was unsafe and canned it.

1. https://en.wikipedia.org/wiki/Crowbar_(circuit)

MarkusWandel2• 2 years ago

Ironically the switches are cheap (from Ali Express anyway) and easy to replace and TMK virtually all microwaves use the same type. But yes, when you open the door, they do the following, in order:

- open to send a "stop microwaving" signal to the controller

- open to physically open the power circuit to the magnetron transformer

- close to short out the power after the above relay (the crowbar part)

The bottom two relays (in the list, not necessarily physical order) are independent of what the control board does. If due to mechanical slop, the bottom one switches before the middle one, boom goes the fuse. Even if you're just opening the door of an idle microwave. That's why, at least in mine, it says on a label inside, if the fuse is blown, replace the door switches along with the fuse.

The sequencing is very tight. You have to push the button veeerrry slooowly to actually observe the switches clicking in sequence.

arghandugh3• 2 years ago

We recently got rid of a four year old microwave where the magnetron turned on spontaneously and silently when the door was closed, runaway heating the box. Control panel, lights, turntable, fan, everything is idle.

Manufacturer didn't consider this an interesting defect and refused to swap out-of-warranty. The lack of give-a-shit in appliances is becoming apparent.

quesera• 2 years ago

That sounds dangerous, and deserving of a name & shame.

Or a YouTube video with a pack of microwave popcorn that spontaneously pops and burns and smokes.

ak2172• 2 years ago

What was the model? I recently encountered something similar with a GE over-the-counter microwave. One day it stayed on after opening the door. I replaced the control module and the board in it looks exactly like the one in the OP photo (Midea with all of the same components), which leads me to think the fault is the same as the one described in the post.

arghandugh3• 2 years ago

Yep, the GE over-the-range model PNM9196SF3SS. GE is just a Haier badge since 2016. I'm not surprised by a Chinese company not giving a shit, but for a microwave magnetron to fire on its own feels like a sign of deep engineering rot.

The only fix was to unplug it then swap the logic board. Once it happened again with the new board we threw it out.

netdevnet• 2 years ago

One day it stayed on after opening the door.

So you basically got exposed to microwave radiation. That's dangerous. Have you checked in with a doctor?

lozenge• 2 years ago

The CPSC would be interested.

neilv• 2 years ago

Maybe not. I recently did the lengthy CPSC form, to report a defective new name-brand microwave oven unit, which was manufactured with a 1/8" mis-seating of parts, where I measured with a professional meter to be leaking much more than anywhere else.

A week later, I heard back:

[...] The product or particular concern that you describe does not fall within CPSC’s jurisdiction. You may wish to contact the agencies listed below, which we believe can best handle your concern.
U.S. Food and Drug Administration Center for Devices and Radiological Health Document Control Center – WO66-G609 10903 New Hampshire Avenue Silver Spring, MD 20993-0002
https://www.fda.gov/radiation-emitting-products/getting-radi... [...]

(BTW, I suspect the process apparently not forwarding a report between two agencies will result in some problems falling through the cracks. And it did, in this case, since I stopped holding the defective unit (I'd asked in my report that they let me know if they wanted to examine it), returned it to the store, and never looked into starting over the reporting process with a different agency.)

Prickle• 2 years ago

A defect like that would make it illegal to sell in my country. One big splash on a major network and they will probably go scrambling.

Have you contacted anyone other than the manufacturer?

arghandugh3• 2 years ago

No. I bitched about it on an old social media platform called Twitter but it never got any traction.

treve• 2 years ago

If your country has decent consumer rights there's probably another way to follow-up!

Rinzler892• 2 years ago

The lack of give-a-shit in appliances is becoming apparent.

Because most budget name brand kitchen appliances are just rebadged Haier/Midea OEM designs. I know HN has a hate boner for Samsung and LG appliances but for me they seem to be the most trustworthy budget appliances since at least they have their own designs instead of rebadging Chinese OEM ones like the rest.

Sure, if you have money you can go with a reputable brand like Bosch & Siemens, and if you have even more money you can go with Miele, but for one, not everyone has money, and two, I've even noticed even Bosch appliances made in Germany still have some issues due to poor design.

rdtsc2• 2 years ago

I have a lower end Samsung that “started” after I opened the door. I hope it was just the fan and lights like the article mentioned. But it scared the heck out of me.

jaeckel• 2 years ago

Sure, if you have money you can go with a reputable brand like Bosch & Siemens

Just FTR they're exactly the same -- "BSH Hausgeräte GmbH" -- with just a different label on it. ... And I didn't have a single good experience in the last years, IMO they're designed for planned obsolescence.

E.g. my premium Bosch Hand mixer broke after 2.5 years. Afterwards I bought a >35 years old used RG28e for half the price and it's still going stronger than the Bosch ever was, 5 years later.

if you have even more money you can go with Miele

If you buy cheap (or uninformed) you most likely buy at least twice.

WorldMaker• 2 years ago

With Haier, specifically, I certainly it were a lot easier to tell what they build in Kentucky versus what they ship from China. For now you can still seem to count on the GE Profile series, if you are rich enough, but the mid-grade stuff is slippery, GE badge or not. (Some of the non-GE badges are coming from Kentucky, too, but like I said, I, at least, don't know how to figure it out without begging any friends that work at Haier to give me specific model numbers to look for in stores.)

EricE• 2 years ago

I dunno about the fawning over Bosch. My Bosch induction cooktop performs far worse than the half price GE Profile cooktop I had at my previous house. The Bosch does not heat evenly at all - almost all energy is focused in the center of the pan. I'm hating it so much I'm about to rip it out and replace it either with another GE or an LG. My mom got an LG induction range and I took my largest pan over to her house, put in a few inches of water and turned it on high - it produced even heating/bubbles across the entire pan, something the Bosch just doesn't do. Feh. I wish I would have done that test before buying the overpriced and underperforming Bosch. Talk about coasting on your brand name.

HPsquared4• 2 years ago

Sounds like relay contacts stuck closed.

BizarroLand• 2 years ago

Sounds like some of the limit switches went bad. They're cheap and easy to replace if it's an expensive microwave worth the $30 or so and the time to install them.

r00fus3• 2 years ago

I migrated our house to a "commercial" variant of the microwave oven [1] as I was tired of all the over-engineering and annoying patterns in modern microwaves.

This microwave has exactly UI element other than the door - a digital dial that goes from 10s-6m. No start/cancel, no power level, no defrost, no program mode. I don't "cook" using the oven, only reheat or very rarely heat/boil small quantities of water.

The microwave beeps only once after complete and it's not incredibly loud.

Despite my kids literally abusing this device, it's been rock solid for 7+ years. Amusingly my company started putting these same exact models in our office break/kitchen areas a couple years after I bought mine.

[1] https://www.amazon.com/gp/product/B00BDF5ZNS

sonofhans2• 2 years ago

Great minds think alike. That is exactly the microwave I have, and for the same reasons. Such a brilliant tool.

goda90• 2 years ago

The thing is, the superior way to reheat something would usually be a lower power level. But not the standard "turn on - turn off" cycle that most microwaves do. Actual lower intensity microwaves. You need an inverter for that. The food would heat more evenly, which is especially useful for things like butter that are prone to splattering.

apricot• 2 years ago

The commercial microwaves we have at work have both a large dial to set the time, and four large buttons under it for 25%, 50%, 75% and 100% power. No other controls. They are great.

extraduder_ire• 2 years ago

I bought a microwave a couple of months ago, and found it impossible to determine which if any of the cheaper ones were inverter microwaves, or if they just used duty cycle power control. I assume that distinction is only made with higher-end microwaves.

In the end I went with the model that looked to have the simplest design and least things to break.

barbegal• 2 years ago

Pulse width modulation works just as well if the pulse width is short compared to the overall cooking time. And not having an inverter makes it more efficient. Unfortunately lots of cheap microwaves have a pulse width which is more than 10 seconds, presumably to help lifetime reliability, but means that for cooking times less than a couple of minutes it doesn't work well.

liminalsunset• 2 years ago

Interestingly enough, this particular question has been tested by Rtings [1] They found that during their tests, inverters which continuously varied the power did not necessarily lead to more even heating, but they do note that small quantities of food (like the butter you mentioned) that need to be heated for very short periods show some differences between inverter and non-inverter models.

Overall, they found that the improvement was much smaller than I'd originally anticipated.

[1] https://www.rtings.com/microwave/learn/research/microwave-in...

stronglikedan• 2 years ago

It's so limited without a power level feature. It needs to be able to cycle power to heat food evenly.

r00fus3• 2 years ago

It does heat food as evenly (possibly more evenly) than my other microwaves.

anitil• 2 years ago

I have this experience with so much equipment in the kitchen. The retail variant has features and knobs etc but is otherwise somehow flimsy, but the commercial variant is rock solid and only does one job.

An example is the atrocious slow cooker that I somehow ended up with that has so many settings on its terrible display I can never remember how to run it. Oh and it maxes out at 6 hours, when my work day is typically 8+ hrs. The old one had two settings with a physical switch - high (for saute) and low (for slow cooking). Perfection.

brokenmachine• 2 years ago

I opened my microwave and cut the piezo buzzer out with wire cutters.

I have never regretted doing my "silent microwave mod".

emchammer• 2 years ago

Why do manufacturers still release products like it's 1980. I can hear when it's done, because the unit has turned off about when I expected it to.

My combo microwave/air fryer beeps if you take food out and close the door before the timer is finished, like it doesn't know what to do now.

cenamus2• 2 years ago

"Dumb" microwaves (knob for modes, big knob with mechanical winding spring for the time) in general easily last over 20 years, we had to dispose of ours only because the plastic became disgusting from standing in a sunny spot for all its life

exitb• 2 years ago

I've bought a dumb microwave and it stopped working after a bit over two years (conveniently). I replaced it with a fancier model, with an inverter, and it's been working for about four years now. It probably won't work for 20 years, but maybe it will survive long enough to justify its higher price (3x).

HPsquared4• 2 years ago

A good example of "pay more, get less" being actually nice.

Porsche does this with special stripped-out models that cost more (less unnecessary stuff, less weight).

Similar thing here, "simplify and add lightness".

jajko• 2 years ago

Well, they use also tons of carbon instead of iron/aluminum to lower weight, so that price may be justifiable. Maybe.

kwhitefoot2• 2 years ago

I inherited my Moulinex microwave from my mother thirty years ago. Apart from the internal lamp failing it is in perfect order. No electronic controls just a power dial, clockwork timer.

ssl-33• 2 years ago

There was a time in the 1990s when a product was sold that was intended to cure that problem: A microwave light bulb.

And by "microwave light bulb" I don't mean the 25-Watt appliance bulb that is buried inside of your Moulinex, but a light bulb that was meant to be placed in the corner of the microwave oven.

Microwave on? Light bulb turns some of that RF energy into light energy, and illuminates the interior. Microwave off? Light goes dark.

I couldn't find any reference to them having existed when I last looked a few years ago, and I don't have time to look again right now, but it was a thing that was advertised on TV and sold on J-hooks in big grocery stores. It definitely existed. (It may have even been something that my mother bought once, but that concept is less clear in the ol' memory hole.)

leokennis• 2 years ago

Maybe a dumb question, but why do consumer microwaves have all these power settings (600W, 800W, 1000W) if apparently they are useless? I don't really know how microwaving works on a physical level - do I achieve the same effect by microwaving something for 30 seconds at 1000W or 1 minute at 500W?

cryptonym• 2 years ago

The waves are only heating specific parts of the product. By reducing power you let heat propagate more evenly. You can avoid explosion, for instance if the middle of a butter is melted and boiling while the outside is still cold. Or better defrost without cooking.

You can achieve the same by heating full power and doing regular pauses (which is often how this is implemented anyway).

beAbU2• 2 years ago

Who said theyre useless?

Lower power levels are great when heating things that are prone to boil over. The pause between heating cycles gives time for the heat to "soak" into the interior of the food, avoiding excessive heating on the outside.

viraptor• 2 years ago

The difference is amazing. 1kW uninterrupted is the "dry my food" setting. Reheating chicken like that basically dries and cooks it again. At half the power and twice the time you can have an actual warm, soft chicken again.

Try heating something you cooked yourself recently and you'll see the difference clearly.

ssl-33• 2 years ago

This is like asking "Why does a kitchen stove have a range of settings on a dial when simply having the burner be on or off would also be able to cook food?"

And the answer is simple: Because they can be useful settings.

The food being warmed does conduct heat, but it is not an ideal conductor of heat.

And microwave ovens (just as any other kind of oven I can think of) heat from the outside. And they're supposed to make things easier and simpler.

So let's make an example: Leftover refried beans, still cold from the fridge.

I can put them in a bowl at 100% power for three minutes, and they'll probably explode and make a mess and still have parts that are cold. This "works" but it's obviously not very good. (I can mitigate some of the mess by using a cover of some kind, but that's also kind of shit.)

Or: I can put them in for a minute or two at 100%, and then stir them, and then run them for a another minute, and then stir them again, and maybe then do another minute. This "works" but it's enough work that perhaps I would be better off to skip the bowl and warm them up in a pan on the stove instead.

Or: I can set the microwave to (say) 40% duty cycle, and put them in for whatever I think is a reasonable time for the volume of beans at that duty cycle. Let's say 5 or 6 minutes.

It's slower, which prevents layers from getting stupid-hot and explodey, and gives the beans more time to reach thermal equilibrium. It's completely hands-off once the buttons are pushed. I'll probably still give them a stir before serving, but they'll be fine.

(I'm a fan of simplicity, but I'm not a fan of lack of control like OP's microwave offers as a primary selling point.

The microwave oven that we had when I was growing up was simple and functional: It had mechanical timer switch with a mechanical bell to set the cook time and announce the end of a run, which is about as simple as it can get while retaining any aspect of automation. It also had an analog dial with which the duty cycle could be continuously set, from somewhere between ~5% to 100%, and this duty cycle could even be changed while the machine was running. No computers, and nothing particularly electronic at all. Just a timer and [what was probably] a heated bimetallic switch (just like a common, cheap electric range uses).)

GJim• 2 years ago

the over-engineering and annoying patterns in modern microwaves

I walked into our office tea room one morning and saw three engineers standing around trying to work out how to use the new microwave.

No joke.

Quite why a microwave needs anything more than cooking time and power level knob is beyond me. (This thing probably has options to ping my phone if my jacket spuds go soggy).

vanchor3• 2 years ago

We had a microwave in the office that auto started based on whatever number you pressed. If you wanted to type in 45 seconds, you would press 4 and it would instantly start running with 4 minutes on the timer. Everyone just pressed the "+30 seconds button" until it was close to the time they wanted and then stopped it manually to get it more precise.

If I remember right the solution was to press "Cook Power" then type in the number of seconds. There was nothing on the microwave to explain this, I had to look it up online.

sonofhans2• 2 years ago

Partially off-topic, but I’ve seen complaints in the thread about microwaves in general. Here’s the trick — buy a commercial microwave. They’re reliable, powerful, and have only a few features. They come in all sizes.

You’ll put less duty on one in a month than a commercial kitchen does in one day, so it will last forever. Time is money in a kitchen so they’re powerful and fast. They tend to have very simple, direct controls, rather than a myriad of popcorn/pizza/whatever buttons. Commercial microwaves often have an integrated diffuser, so they don’t need the stupid rotating glass plate in the bottom.

ToucanLoucan• 2 years ago

Can confirm. We got a commercial-grade Panasonic microwave I believe, that survived near daily use for almost 9 years before the magnetron finally gave out. We replaced it with an identical model, and it must be a pretty good one since a cursory comparison inside between the old and new revealed virtually no changes since our old one was made. If it ain't broke...

MarkusWandel2• 2 years ago

Can confirm because at my work, they initially put ordinary consumer microwaves in at the coffee/lunch stations. They failed quickly. The commercial ones last. However the latest ones have a very flimsy feeling control wheel, I somehow imagine a 25 cent rotary encoder behind that which, if it fails, may still cause the otherwise solid machine to be discarded.

ssl-33• 2 years ago

I cooked for a family in part with a consumer-grade, Walmart-sourced Panasonic inverter microwave oven for a dozen years until circumstances made me get rid of (donate) it.

No issues ever. It was reliable, had some useful programming options (that nobody ever used but me, but it had them), and it did a good job of microwaving food in a consistent and predictable manner.

(But that's not an indication that inverters are reliable, or that consumer is the same as professional, or that Panasonic is good, or of anything else really other than that anecdotes are anecdotes.)

bzzzt2• 2 years ago

That seems to be the issue with all kitchen appliances. I've had the same issue with kitchen scales. I like a digital display for small amounts, but had a few of those 'pretty design' scales fail after a year or 2 (no, it was not the battery ;). Bought one ugly thing from a company that also makes shop scales which is working for years now...

yborg• 2 years ago

My microwave is a 1993 Panasonic. It sat in a basement for about 10 of the intervening years, but has been a daily driver for the last 6-7. Comparing it to current retail units, it's remarkable how little has changed in that time.

Retr0id• 2 years ago

I have a Samsung microwave with a really weird bug. If the door is just a few millimetres ajar, it turns on by itself. It's not just mine either, a lot of reviewers point out the same. It seems to be a design flaw. It's not a huge issue, since I'm not exactly in the habit of positioning the door in a half-open state.

My guess is that they have some broken/inverted logic related to the "turn off if the door is open" feature.

solid_fuel• 2 years ago

I remember this flaw in a Samsung microwave from ~2007-2008. It freaked me out when I triggered it while trying to quietly close the door.

djmips2• 2 years ago

The article describes such an issue but the assures that the oven magnetron doesn't run. Maybe it's a similar problem where the turntable and light come on in that situation.

ctrlGsysop2• 2 years ago

Fascinating in that our GE microwave (still actively sold) has an undisclosed feature that if you lift the door, when fully closed, by no more than a few mm, the microwave will start. I noticed this when cleaning the enclosure with a rag and my hand ever so slightly lifted up the door from the bottom. I can see how a consumer could wedge a kitchen utensil or plate accidentally under the microwave causing it to start and continue to run. Zero logic protection.

djmips2• 2 years ago

They mention that in the article but assure that the magneton does not run.

ctrlGsysop2• 2 years ago

Indeed, nothing is heating in this state.

BlueGh0st• 2 years ago

A few weeks ago I noticed my cheap Toshiba microwave does the same when the door button is partially pressed. Scary! I stood there holding it just right for a very long time to make sure it wouldn't heat a cup of water.

farkanoid• 2 years ago

Doesn't seem limited to GE Microwaves! My wife uses a cheap Kmart house-brand microwave for waxwork that does the exact same thing.

I have another in the kitchen (Panasonic NNCD997) that has an interlock system which blows the primary fuse if a) The door is open and b) The magnetron is currently active.

Unfortunately, with this model, the incandescent bulb dying kills the inverter PCB.

Edit: The service/repair manual[1] for the Panasonic is an interesting read, if anyone is interested

[1] http://up.orificeworks.com/nn-cd997s_cd987w.pdf

xattt3• 2 years ago

The magnetron is on an interlock that blows a fuse if the door microswitch is on.

omoikane• 2 years ago

One of the comments linked to an article about keyboard problems caused by a LED, which was previously discussed here:

https://news.ycombinator.com/item?id=36581204 - Repair adventure: A single white LED causing stuck keys on a RN988 keyboard (2023-07-05)

I wasn't thinking about the color of the LED at the time, but after reading this article, I wonder if we should prefer products with green LEDs in general, like green LEDs are just more reliable than blue/white LEDs for some reason?

Also, I can't seem to find microwave ovens with red LEDs.

userbinator• 2 years ago

The title is a bit clickbaity, since the actual "oven" part (the magnetron) stayed off. As it should, since the safeties for it are much more robust than the other parts:

I’m quite impressed by how many independent mechanisms there are to prevent the magnetron from accidentally turning on. Not only are there three door switches to ensure the door is closed, there’s also a mechanism to guard against a faulty microcontroller or software.

Personally, I think the ones with mechnical controls, no microcontroller, are the most reliable and also easiest to repair.

rdtsc2• 2 years ago

I scared myself with my microwave, a cheaper Samsung. Somehow it turned “itself” on when I opened the door once. I quickly slammed it shot and jumped back. Hopefully it’s this exact failure and the magnetron didn’t actually start.

dusted• 2 years ago

There exists only one correct design of microwave ovens. It has zero ICs. It has exactly two direct user-inputs and one indirect.

The two dials select on-time and duty-cycle (cooking time and "power"). The third input is the safety switch which deactivates the cycle when the door opens.

This design is the most userfriendly, the most economic and the most reliable.

This is the hill I will die on.

bschwindHN• 2 years ago

You are exactly correct, and I'll die on that hill alongside you.

kwhitefoot2• 2 years ago

But the properly made microwave of that kind will probably carry on living after you. Mine (Moulinex) outlived my mother and has been working for me for the last thirty years.

martin_a• 2 years ago

I'd be interested in such a simple device, but does anybody even produce tech _that simple_?

TimeBearingDown• 2 years ago

Don’t forget a physical handle to pull open the door.

I’d take a steam sensor as well.

Thanks to Technology Connections, great channel. Convinced me to read all the fine print until I found a Breville that had it. https://youtu.be/UiS27feX8o0

pphysch• 2 years ago

Simple is good but another approach to simplicity would be more sensors (weight, thermal, steam, optical?) and a single "cook" button (or a menu/dial with few different cook options, defrost, warm, hot).

For casual use the UX is superior as it requires less micromanagement. Also lot more difficult to engineer well, though.

pajko• 2 years ago

Once had to repair my washing machine. It was easy to identify the problem after removing the control board: a single $1 chip integrating nothing more than 4 motor driver FETs cooked itself due to the lack of a heatsink. Unfortunately could not fix it because the board had a thick layer of some glue-like stuff which I could not remove, and so had to replace the whole board, doubling its lifetime to more than 10 years. It still rocks but got out of balance and is quite noisy sometimes.

reconvene1290• 2 years ago

Must be one sexy LED display.

ajb• 2 years ago

Nice investigation!

My 25 year old microwave is really solid, except for the lamp, which has blown. It's an old bulb so it should be replaceable - except that physically there's no way to do it without unscrewing the magnetron, which is well into scary territory - you need to basically re-qualify it after reassembly by scanning for leaks with a professional instrument. I don't want to throw it away because it still works, but fixing the lamp would cost more than buying a new one.

pantulis• 2 years ago

"I’m quite impressed by how many independent mechanisms there are to prevent the magnetron from accidentally turning on. "

Ok, I've never been really fond of microwave ovens so I don't use mine that much. After reading this I am starting to fear my microwave, definitely.

mark-r• 2 years ago

Interesting that he thinks the clock would be better with a 32kHz crystal than with monitoring the 60Hz power frequency. The power line frequency is very tightly regulated over the long term, and should have an overall better accuracy.

cesarb• 2 years ago

The power line frequency is very tightly regulated over the long term, and should have an overall better accuracy.

It depends on your country. I've heard of this being the case in Europe, but here in Brazil, as far as I could find there's no "long term regulation" of the power line frequency. Which makes sense to me; it means the power network operator doesn't have to artificially deviate from the correct power line frequency in an attempt to "compensate" for a past deviation.

Microwave spontaneously turned on by its LED display

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