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Microwave Oven Failure: Spontaneously turned on by its LED display (2024)

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Re: Microwave Oven Failure: Spontaneously turned on by its LED display (2024)

#21

Post by londons_explore »

sitharus wrote: post #13
londons_explore wrote: post #10

You can do an awful lot to make a device like a microwave safe with loads of failsafes... But rarely do those failsafes protect reliably against 'the mainboard was splashed with salt water'. Even with triple redundant relays, how do you know the salt water didn't just wet them all?

In almost every system with failsafes there will be conditions that can bypass them. The goal is not to make it impossible for the unsafe condition to happen, but to make it so that in the expected uses the failure will not happen. In this case it's a domestic microwave and the mainboard is housed inside the electronics enclosure, so covering the whole mainboard in salt water is not an expected occurrence in a domest…

But there are ~1 billion microwaves in the world... I'm sure it has happened somewhere. As a designer of a billion-sold device, your job is to make sure that the expected number of people harmed by your device is substantially less than one, which gets really hard when all the risks are multiplied by 1e9.

Re: Microwave Oven Failure: Spontaneously turned on by its LED display (2024)

#23

Post by snarfy »

londons_explore wrote: post #10

You can do an awful lot to make a device like a microwave safe with loads of failsafes... But rarely do those failsafes protect reliably against 'the mainboard was splashed with salt water'. Even with triple redundant relays, how do you know the salt water didn't just wet them all?

I noticed when tearing down an old microwave for salvage that the light bulb was part of the power circuit. If the bulb burned out, so did the microwave.

Re: Microwave Oven Failure: Spontaneously turned on by its LED display (2024)

#24

Post by foresto »

snarfy wrote: post #23
londons_explore wrote: post #10

You can do an awful lot to make a device like a microwave safe with loads of failsafes... But rarely do those failsafes protect reliably against 'the mainboard was splashed with salt water'. Even with triple redundant relays, how do you know the salt water didn't just wet them all?

I noticed when tearing down an old microwave for salvage that the light bulb was part of the power circuit. If the bulb burned out, so did the microwave.

Reminds me of a comment from a previous time this story was posted here:

https://news.ycombinator.com/item?id=41509748

Re: Microwave Oven Failure: Spontaneously turned on by its LED display (2024)

#27

Post by sitharus »

londons_explore wrote: post #21
sitharus wrote: post #13

Earlier quoted context omitted.

In almost every system with failsafes there will be conditions that can bypass them. The goal is not to make it impossible for the unsafe condition to happen, but to make it so that in the expected uses the failure will not happen. In this case it's a domestic microwave and the mainboard is housed inside the electronics enclosure, so covering the whole mainboard in salt water is not an expected occurrence in a domest…

But there are ~1 billion microwaves in the world... I'm sure it has happened somewhere. As a designer of a billion-sold device, your job is to make sure that the expected number of people harmed by your device is substantially less than one, which gets really hard when all the risks are multiplied by 1e9.

Your job is to make sure the number of people harmed _while using the device as intended in a reasonable situation_ is as close to 0 as possible.

A domestic microwave is for use only on land, indoors, in a domestic kitchen, and in an unmodified form. In these conditions there is no conceivable way that salt water could saturate the main board, or bypass all the interlocks in another way.

Yes there are ways that all the safety systems can be bypassed, but not while a reasonable person is using the device as intended.

Re: Microwave Oven Failure: Spontaneously turned on by its LED display (2024)

#28

Post by nickff »

Fnoord wrote: post #22

Articles like these are great to argue nonconformity which can get you your money back in EU. Even past the warranty period.

From what I can find, the guarantee period seems to be two years, after which the burden seems to 'flip'. Given that this microwave is at least five years old, I am not sure what standard one might cite to demonstrate 'non-conformity'. Do you know of a standard which says that a consumer microwave oven must work for more than five years?

https://europa.eu/youreurope/citizens/consumers/shopping/gua...

Re: Microwave Oven Failure: Spontaneously turned on by its LED display (2024)

#29

Post by galangalalgol »

xp84 wrote: post #19
PunchyHamster wrote: post #15

Earlier quoted context omitted.

nah, this is just not something designer would expect to fail like that. The LED has datasheet, the datasheet have leakage current, it has no data on increased leakage over years, you plan for what you have. What would help is not randomly planning for some of the segments to fail (they are multiplexed with other things, you'd have to put more diodes), but to just get slightly better/less cheap LED display Only "choi…

Sounds like this is far more common a problem with blue LEDs than others, and that was certainly a choice. As if I needed another reason to detest the eye-searing blue LEDs that have infested every device.

I miss the red led of my youth. Modern red and green diodes are both too harsh in comparison.

Re: Microwave Oven Failure: Spontaneously turned on by its LED display (2024)

#30

Post by Telemakhos »

1970-01-01 wrote: post #4

This is literally evidence of stuff being designed to fail. An extra diode costs less than a cent at production scale. This was a manufacturing choice, not an error.

My microwave mainboard failed because I changed the range light bulb without unplugging the whole microwave first, which I would not have thought necessary. It seems that, without unplugging the whole microwave, the act of changing a light bulb will cause catastrophic voltage to delicate parts. Turns out to be a common thing with this brand.

I ended up replacing the mainboard with a part from no apparent manufacturer with new features (the blue LEDs dim after inactivity so as not to illuminate the whole room at night) and no connection for the thermistor. Works like a charm. It feels very much like the original manufacturer wanted the board to fail and be replaced, while some random Chinese circuit-board maker sold me a better quality board.

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