My downfall when it comes to Sherlock Ohms work (or at least, one of my many downfalls over the years) was my misdiagnosis of my Maytag clothes washer problem. Our washer was about 15 years old. I had done a few simple repairs to keep it chugging along. This time the complaint was that the washer would fill up with water, but then it wouldn't agitate.
I checked out the wiring diagram and decided there was a problem with the water-level pressure switch. The switch is a very sensitive air-pressure switch that is connected, via a tube, to the tube that fills the washer. Increasing the water level results in increased air pressure in the tube. At a certain water level it would activate the agitator. The switch was in series with the motor start, so nothing happened if the water level was too low -- or, if the switch failed.
So I ran a small load with no clothes -- just water. When it got some water in it, I shorted out the switch leads and everything started up and ran. Fine. I decided that meant I had a bad switch. I ordered one for $75 (ka-ching). When it arrived, I installed it.
I ran a test load at low water level. Everything worked great. I ran it again with a test load at full water level. The motor came on and then... grunt. No agitator action. The thermal breaker clicked off.
Turns out the problem was a failing bearing in the agitator. It had not completely failed; it was just dragging enough so the agitator would work at a low water level with no clothes, but it would not work with more water or with clothes. I had quick conversation with a repair person and realized a repair was way too expensive. Our solution -- buy a new washer.
Anyone need a water level switch? I've got two of them.
This entry was submitted by Bob Groh and edited by Rob Spiegel.
Tell us your experience in solving a knotty engineering problem. Send to Rob Spiegel for Sherlock Ohms.
Wet clothes would put additional stress on the agitator regardless of water level. It's not a weight issue per se, though it came across as that; rather, it's a loading (or drag) issue.
When my electric dryer wouldn't heat up I would have bet money it was because the heating element went bad. It took me about an hour to tear it all apart to get to where I could ohm out the element. It tested good. I took the inpection panel off from behind the controls in a matter of seconds to see the control had melted.
This is a good example of the pitfalls of trying to validate a design solution with a test which doesn't adequately represent real-world conditions. With a small amount of water and no clothes, replacing the pressure switch appeared to work. It only became apparent that the pressure switch wasn't the problem when you tried to use the washing machine to actually wash clothes! Let those who are tasked with developing test and validation programs beware.
Washers do see a lot of force and friction during the normal operation. It is probably one of the hardest working pieces of equipment in a house. That may be the main reason that there are so many articles in Sherlock Ohms about washer failures.
We used a Maytag for about 7 years before the unit would not work. It seems the wiring to one of the pc boards was very loose so I recconnected the wires but the washer would still not wash. I replaced all of the power transistors on the motor control board to no avail. I finally purchased a combination motor and motor control board from Ebay, installed it and it has been working fine ever since. I was glad that I did not have to "junk" the entire unit causing global waste instead of repairing the washing machine. The loose wires appeared to be some kind of tachometer feedback to the motor control board. The loose wires may have taken out the motor microcontroller but I was not sure.
Yes, Tim, there are plenty of washer stories in both the Sherlock and Monkey blogs, but most of the posts find difficulty with the control panels rather than the mechanical operation of the washer. Even with the wear and tear, washers are remarkably durable. It's the relatively new electronics that seem to create most of the problems.
I womder if tin whisker growth have anything to do with it. (See: http://www.eetimes.com/design/military-aerospace-design/4230652/Understanding-and-mitigating-tin-whiskers?cid=NL_MilAero&Ecosystem=military-aerospace-design )
From Dell / Intel® New Paradigms in Design Work Scott Hamilton, vertical market strategist for Dell Precision workstations, 5/2/2013 5
Early in my career, I worked as a draftsman and remember the days of drawing on vellum with numbered pencils and Mylar with plastic lead. This was a fun experience in the sense that I ...
I've been using workstations for more than 10 years and love finding ways to get more performance from my system. With demanding professional applications that require more power each ...
A lasting memory from my first job as an engineer in an auto assembly plant is standing on hard concrete at six in the morning, vending-machine coffee clutched in hand, listening to ...
For industrial control applications, or even a simple assembly line, that machine can go almost 24/7 without a break. But what happens when the task is a little more complex? That’s where the “smart” machine would come in. The smart machine is one that has some simple (or complex in some cases) processing capability to be able to adapt to changing conditions. Such machines are suited for a host of applications, including automotive, aerospace, defense, medical, computers and electronics, telecommunications, consumer goods, and so on. This radio show will show what’s possible with smart machines, and what tradeoffs need to be made to implement such a solution.
To save this item to your list of favorite Design News content so you can find it later in your Profile page, click the "Save It" button next to the item.
If you found this interesting or useful, please use the links to the services below to share it with other readers. You will need a free account with each service to share an item via that service.
Tweet This
12 
