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.
Microwave Oven Failure: Spontaneously turned on by its LED display (2024)
11–20 of 53 posts
Re: Microwave Oven Failure: Spontaneously turned on by its LED display (2024)
#12You 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 that situation one of the switches should short the mains voltage and blow the fuse when the door is opened.
Re: Microwave Oven Failure: Spontaneously turned on by its LED display (2024)
#13You 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.
Re: Microwave Oven Failure: Spontaneously turned on by its LED display (2024)
#14My 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.
Re: Microwave Oven Failure: Spontaneously turned on by its LED display (2024)
#15This 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.
Re: Microwave Oven Failure: Spontaneously turned on by its LED display (2024)
#16Very impressive engineering on the door switches. On the display, not so much.
sort by price strikes again
Re: Microwave Oven Failure: Spontaneously turned on by its LED display (2024)
#17You 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?
> 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.
Re: Microwave Oven Failure: Spontaneously turned on by its LED display (2024)
#18This 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.
what happens when that diode fails?
Re: Microwave Oven Failure: Spontaneously turned on by its LED display (2024)
#19This 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 "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.
Re: Microwave Oven Failure: Spontaneously turned on by its LED display (2024)
#20My 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.
Wouldn't it be more likely to be reverse-bias degradation of the LED junction causing permanently increased leakage current?