On New Year's Eve, I was cooking fillet steak for a party with some friends. I first put it in the pan to sear it and then in a hot oven for a few minutes to finish it. As I was pulling it out, a beeper in the oven control panel started screeching. As the steaks were done and there was nothing obviously wrong with the oven, I simply turned it off at the fuse box and went on to eat the steak and ring in the New Year. I switched the oven on again prior to going to bed, but about two hours later it started beeping. I crawled out of bed and switched it off.
In the morning light, I switched the oven on again. Sure enough, a couple of hours later, it started beeping and none of the buttons would quiet it. I deduced that if the beep started with a cold oven after a couple of hours then it was unlikely to be an over temperature alarm and was most probably a time out -- i.e., the timer had counted down to zero. I switched it on again to observe pre-beep performance.
This time I noticed that the clock button, which was a plastic sheet over contacts on the faceplate, did not set the clock mode but did activate the timer in the same manner as the timer button. Then I perceived a slight bump in the plastic over the clock button icon. At this point I could deduce that something, possibly to do with the bump, had somehow jammed the clock button and set the timer counting down.
I then removed the front panel of the control unit. The plastic sheet covering the front panel had a transparent area over a slot behind it, which was where the clock display was mounted. And the slot was just over the row of push buttons. Just at the edge, where the plastic covered the slot, I saw the dessicated cadavers of some tiny insects.
I shook those out, inverted the faceplate, banged it on the table, and for good measure, ran a piece of paper between the plastic and the faceplate. Several bits of exoskeleton showered out.
After reassembly, the oven worked perfectly, and I now know what debugging means!
This entry was submitted by Phil Hughes and edited by Lauren Muskett.
Phil Hughes is CEO of Clustered Systems Company Inc.
Tell us your experience in solving a knotty engineering problem. Send stories to Jennifer Campbell for Sherlock Ohms.
Having once worked repairing computers in the back woods of Papua New Guinea, I can attest to the fact that "Raid Kills Computers Dead!". A client had a colony of ants take up residence in his computer, entering and exiting through the ventilation holes. He gave them a shot of Raid through the vent holes and left it to air out. The next time he powered up, all the magic smoke escaped from the computer. In due course I received the remains (of both the computer and the ants). At least this particular variety of Raid was both conductive and corrosive and did a real number on the PCB.
Most people would have just turned off the electronics of the stove to never use them again. Glad your went above and beyond. That isn't an obvious reason for failure either...
I recall the issue of the fire ants, notarboca. Some time in the last 20 years, a linear accelerator was planned for Texas (I believe it was eventually built there), but it ended up getting bogged down in debate about fire ants. Apparently, some engineers believed that the accelerator's large magnets would attract ants.
A friend of mine was visiting another guy one saturday morning and his friend remarked that his power bill was about zero the month before. My friend (a EE) said they should check to see if the meter was turning. Sure enough a moth had expired and was stuck in the meter works. My friend banged his hand on the meter and the bug fell out as the home owner screemed "OH No".
Buttons and options can be difficult. On our GE front loader, a certain button combination will lock the control panel. Unfortunately, this option is not shown in the manual and required a service call by a technician to show me how to reset the lock.
I don't understand why the industry can't realize that the american consumer just wants something that is easy to run. I really don't need 17 different cycles to wash my clothes in. I do want to be able to lock it out so my child doesn't accidently run the cat through the wash, but I don't have a PHD in unlocking my washing machine. Is it really that tough.
I agree with jmiller. And doesn't anyone who designs user interfaces on appliances ever use them? If they did, how could these interfaces (aka buttons, touchpads, knobs, etc) be so bad?
Ann, when I was designing appliances I would sit down with the marketing guys and have them press buttons on a sheet of paper. I would have them step through the keystrokes needed to implement what they had specified, and often times their fingers were doing a dance that looked like a version of "Twister" made for hands. If the feature they wanted proved too complicated they would sometimes add a special button or knob just for that feature. From their standpoint, now the nifty new feature was advertised because the consumer would see that feature button right on the front panel.
I had a similar experience when I lived in the Dallas TX area. My house had a LV lighting system (12VAC) around the exterior and walkways. There was a 300VA or so transformer that fed the system, with 2 separate outputs (dual secondaries on the xfmr). I started having intermittent outages on some lights, but the bulbs were OK. There wasn't much voltage at any of the fixtures on one of the outputs. I traced the apparent short down to a specific point (all wiring as buried so I really wanted to only have to excavate where the problem was likely to be) by locating the first fixture that had minimum VAC at it. I started to dig, and was quickly attacked by a bunch of fire ants! After I did away with them (took a full day for all to die), I dug down and found their nest had been located surrounding a splice insulated with some badly chewed away electrical tape. Thus a short between the conductors was created. Unfortunately, the long-term overload had weakened the one secondary; a couple of weeks after the wires were re-taped (very heavily!), that secondary winding opened up. I sent it back to the manufacturer, who was amazed that the primary protection hadn't tripped, and so the fusible link inside the winding had opened. The resistance of the wiring to the short location was apparently just enough to let the winding overheat without tripping the circuit breaker in the transformer primary. They sent me a brand-new transformer at no charge! When a similar outage occurred some time later, I concluded that the ants really loved the AC field (maybe got high on it!), and made future repairs with even more protection on the splices.
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