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.
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.
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.
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.
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.
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.
All LEDs are photodiodes too, certain degredations of parts or poor circuit design could lead to the display turning into a switch.
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 domestic kitchen.
In that situation one of the switches should short the mains voltage and blow the fuse when the door is opened.
168 points and 116 comments at the time: https://news.ycombinator.com/item?id=41480038
More proof blue LEDs are the devil and should have never been put into all of our electronics to be the shining beacon of "OW MY EYES" at 2 AM.
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.
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.
Eh, I don't agree.
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.
Don't underestimate the appeal of saving one cent per unit. So long as the costs are externalised, anyway...
It’s not exactly designed to fail, they just don’t care. If they could add a one-cent part that made it fail sooner, they wouldn’t do that either.
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.
Very impressive engineering on the door switches. On the display, not so much.