What happened to our dishwasher?

[leehljp]

Monday night we had a thunderstorm blow through, a nearby lightening flash and then the lights and everything went off for about 5 or 6 seconds and then back on. Everything except the DishWasher.

Our dishwasher (Maytag) is on its own circuit. Since we were out of town most of Tuesday, LOML did not notice that the dishwasher was not working. The DW worked Monday night before the thunderstorm.

Well, this morning LOML was all frustrated when she discovered it was dead. No buttons lit up when pushed. (It is a built in that I installed.) I disconnected it and pulled it out. I used an extension cord from another outlet. Nothing. Pressed all the buttons that I could. Then I closed the door, opened it and closed it, pushed a button and one button lit up on the wash cycle. NO other button would light up. I unplugged the DW, waited about 10 minutes and plugged it back in. The same light came on but then another light (LED) came on. The Start/Cancel button would not work.

I unplugged it and waited about 15 minutes this time. The two lights came on again. After opening and closing the door two or three times and pressing the buttons, suddenly ALL lit up. Another 15 minutes unplugged and replugged in and suddenly the Start/Cancel button lights up by itself.

At this time I unplugged the extension cord and plugged the DW back into its original and dedicated plug. The Start/Cancel light worked as normal. Hooked up the water and drain plugs and put it back under the counter. LOML set it to run through a regular cycle, and it did.

Then she placed the dishes back into the DW that she started with this morning and IT WORKED FINE.

Can DWs be resurrected like that? By all accounts, it should have been dead and I almost trashed it after the first couple of tests and trials!

Early this morning we were looking at new DWs briefly on online, and then the replacement circuit boards at $100.00+. I feel great that we didn't have to purchase a new DW and so is LOML. I just shake my head at how I almost trashed it. Got lucky I guess!

[mpc]

So many devices have electronic controllers - dedicated computers or microcontrollers - these days - that are either ON or in a STANDBY mode and are never really OFF. Any electronic device that can be turned ON via a remote control or a touchpad button is really in a low power STANDBY mode... waiting for the ON signal. VCRs, DVRs, almost all TVs today, etc. fall into this category - consuming a teeny bit of energy even when "off."

Like Windows Blue-screens-of-death, the software inside microcontrollers can get confused easily. A power line surge, static electricity, even a random cosmic ray (seriously!) can flip a transistor inside the computer, corrupting RAM memory, cache memory, registers, etc leading to nonsense operation. Electronic devices of course have power supplies: basically transformers to reduce power line voltages down to 6 to 12 volt ranges typically, 2 or 4 diodes to rectify that lower AC voltage into a low DC voltage, then a large electrolytic capacitor (like the ones in PC computers a few years ago that were failing regularly) to smoothen the "lumpy" rectified DC voltage into a smooth DC voltage. Those capacitors are basically electron sponges: they "fill up" at the peaks of the lumps, and discharge into the gaps - filling in the gaps. The capacitor has to be big enough to fill in the gaps while the device is ON and drawing whatever "maximum" power it uses. For dishwasher style electronics, that means powering the microcontroller, display LEDs/panels, and relays or other devices to switch the high-power stuff like motors, solenoids, etc. When the dishwasher is OFF, only the microcontroller is drawing power (in theory) and it's power needs are puny compared to the rest of the electronics.

When the device is unplugged, these capacitors can act like short-life batteries, keeping the microcontroller powered up. If the computer is "software confused" it'll stay confused of course - like your dishwasher. Since it's only powering the microcontroller, not the entire electronics of the dishwasher, that capacitor is now "way oversized" which is why it can power the puny amperage draw of the microcontroller for a long time.

Unplugged long enough though and the capacitor discharges enough that the microcontroller couldn't remain running and finally executed a "hard reset" when plugged back in. How long is long enough? Depends on the device... my DVR resets completely when unplugged for just a few seconds. A flaky computerized stereo/XM/Nav system in a high-end car I know about needs 20+ minutes with the battery unplugged to reset. Just like digital clocks - how many have you seen that blink "12:00" after just a few seconds of power failure while others survive a few minutes without power? Blame/thank capacitors.

mpc

[leehljp]

MPC,

Thanks for the explanation. I was about to throw it out but the "reset" by unplugging for the 15 minutes did wonders. I wonder how many electronics are junked when they could be re-set.