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
The power line frequency is carefully monitored and adjusted to ensure that deviations from the ideal (60 Hz in OP's case) are smoothed out [0]. Even a single ppm deviation equates to 2.6 seconds per month, and your cheap 32.768 kHz crystal is going to be orders of magnitude worse than that.
My microwave seems to gain minutes per month, my assumption was that it's due to incompetency of Eskom, the essentially sole producer of South African electricity. With the government and parastatals here incompetency is very common.
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.
My $$$ < 5 year old convection oven recently malfunctioned: with the thermostat off, it still experiences heat cycles (even while clearly showing OFF).
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?!?
My guess is the LED's suffer reverse bias thermal runaway when they're hot from being in a steamy enclosure and then they get a reverse 5v across them and any leakage current turns into heat accelerating the process.
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?
Later sections of the article detail how there are multiple different safety features integrated to guard against various different failures triggering the magnetron with the door open.
I'm so glad that my ancient Moulinex microwave has no display at all and no keypad. Just a motorised dial to set the time and another dial that sets the duty cycle.
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.
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 "choice" made here was sorting by price when buying components for the cheap device.
I don't think it's so much an issue of designed to fail as trying to get it as cheap as possible.
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.
Capitalist profit motive strikes again. The invisible hand expands tech and the visible hand keeps making tech worse.
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.
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 domestic kitchen.
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.
> Even with triple redundant relays, how do you know the salt water didn't just wet them all?
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.
bell-cot|19 days ago
fellerts|18 days ago
[0] https://en.wikipedia.org/wiki/Utility_frequency#Stability
jonathanlydall|18 days ago
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.
djdnndne|18 days ago
[deleted]
kotaKat|19 days ago
ProllyInfamous|15 days ago
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?!?
londons_explore|19 days ago
colechristensen|19 days ago
CGMthrowaway|19 days ago
Fnoord|19 days ago
nickff|19 days ago
https://europa.eu/youreurope/citizens/consumers/shopping/gua...
rbanffy|19 days ago
PunchyHamster|19 days ago
jcarrano|18 days ago
Is it necessary to be so skimpy with a safety feature?
akpa1|18 days ago
seba_dos1|18 days ago
ninalanyon|18 days ago
unknown|19 days ago
[deleted]
1970-01-01|19 days ago
Telemakhos|19 days ago
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.
PunchyHamster|19 days ago
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.
wat10000|19 days ago
benj111|18 days ago
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.
cogman10|19 days ago
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.
HPsquared|19 days ago
evan_|19 days ago
Atlas667|19 days ago
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.
tonypapousek|19 days ago
https://news.ycombinator.com/item?id=41480038
snvzz|18 days ago
A public prosecutor should take this on.
londons_explore|19 days ago
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?
sitharus|19 days ago
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.
snarfy|19 days ago
Aurornis|19 days ago
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.
dezgeg|19 days ago