Microwave Oven Failure: Spontaneously turned on by its LED display (2024)(blog.stuffedcow.net) |
Microwave Oven Failure: Spontaneously turned on by its LED display (2024)(blog.stuffedcow.net) |
I’m surprised that they chose to add a bunch of components to feed the AC line frequency to the microcontroller instead of just using a 32.768 kHz crystal. A single crystal oscillator seems like both the cheaper and more accurate option
[0] https://en.wikipedia.org/wiki/Utility_frequency#Stability
However, out of interest I just pulled yesterday's stats from my inverter on Sunsynk's website. It has the frequency of the grid at 5-minute intervals and the average over the whole day was 49.975Hz which doesn't strike me as particularly bad, so I have to wonder if the Microwave itself has an issue. It's a Samsung which is now 13 years old.
A day, having 86_400 seconds in it, is equivalent to 4_320_000 pulses at 50 Hz. At 49.975 Hz, it's only 4_317_840 pulses which is 2_160 pulses too few. Which, at assumption of 50 Hz, translates into discrepancy of 43.2 seconds, in this one day.
So, no, it's a pretty big discrepancy actually, over here anything over 0.2 Hz is legally declared to be "degraded quality", and it's been debated for years that this is actually a way too wide margin but the electricity providers/grid operators managed to successfully argue that they can't afford upgrades.
Moral of the story: don't get cute when designing electronics, just use AC/DC power supply and put a damn crystal oscillator as every other reasonable person.
After cooking, I must turn the circuit breaker off (every single time) to avoid overheating an empty stove. Annoyingly, the system still detects that it is hot, because it is hot, while aware that it has technically been "OFF" for hours.
Can't my next new stove just have manual controls and last decades like the one it just replaced?!?
https://europa.eu/youreurope/citizens/consumers/shopping/gua...
In some countries a fridge is expected to have a lifetime of 10 years but a warranty of 2 years. So in theory if you could prove that the fridge cannot meet the expected average lifetime, the cooling ability decreases below the stated parameters much earlier, then it becomes the manufacturer’s responsibility.
But some countries have a more lax law (Germany, for example, not).
For example, here in The Netherlands you can have more than two years warranty. If you buy a premium smartphone (say: the latest iPhone or Google Pixel), and it stops functioning after twenty-five months (two years and one month), then your warranty isn't exhausted because a premium / flagship device like that (costing that much) is to be expected to work longer than twenty-five months. So, your warranty is still active. Now, if you bought a budget smartphone, you're probably out of luck. This is also why, yes, sometimes Google Pixel devices are cheaper in Germany. But you'll have less warranty if you buy it from there.
Then there's non-conformity. A device like a microwave isn't supposed to stop working because of a LED display suddenly turning on due to a hardware failure. Especially not if a blue LED display has this issue far more often than a green one. You can argue non-conformity with the seller (so the company who sold you the product; not the manufacturer), and they have to figure out how to handle it with the manufacturer; such isn't your issue as consumer. Only issue is you need a lawyer to write the letter for you (but there are nice examples available online which you can copy/paste, and there are also some very nice lawyers who do this either for free or low fee).
For businesses, different laws apply…
Is it necessary to be so skimpy with a safety feature?
A public prosecutor should take this on.
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 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 domestic kitchen.
The design typically includes a mix of normally open and normally closed switches. If everything failed in the same direction (closed) it wouldn't satisfy the failsafe.
If you're spilling conductive liquid on the board, it's going to blow fuses anyway. It's more likely to short to ground than to short only to the precise path needed to activate.
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.
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 "choice" made here was sorting by price when buying components for the cheap device.
As if I needed another reason to detest the eye-searing blue LEDs that have infested every device.
Theres further issues with everything coming out of china and a brand slapped on it. No one is left to take responsibility on the engineering front. This feedback I doubt will get to the correct people at best buy, let alone going back to the microwave manufacturer. And then there's the question of if they care, as they aren't a customer facing brand.
LEDs are diodes (Light emitting diode). Certainly this was a cost saving measure, but it's not a bad assumption that the LED wouldn't allow reverse current flow.
People usually respond to this by saying that it would be absurd to suggest the company did this for its own benefit, when anyone who engineers knows these are often caused by revising design to minimize costs... and increase profits.
You're right (by my maths too, which I only did now) about it being a discrepancy of 43.2 seconds per day, which as you say is quite high.
However, it is my understanding that most grid operators are actually very good about maintaining a 50Hz average over a day specifically for devices doing time keeping based their frequency, I've heard they intentionally run the generators faster or slower at certain points in the day in response to needing to get the average right over a day.
I used to have no issues with time drift on my microwave, only started in the last few years.
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.
Source? People take risk in their day to day life and should expect to take risk. Why would they expect their microwave to be completely free of risk?
Note that it becomes the _sellers_ responsibility - this might be the manufacturer if you bought it direct, but otherwise it’s the retailer