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Windshield Wiper Intermittent Voyager
RFI-EMI-GUY   12/12/2012 12:29:43 AM
A while back, my wife's 1999 Plymouth Voyager started to have a problem with the intermittent wipers. The were in fact "intermittent" in a bad way.

I started with the service manual and found that none of the resistor array voltages in the multifunction switch (used to control headlights, wipers etc.) matched the service manual. The body control unit (BCU) measures a voltage on one wire to detect the switch position, saving having 8 wires for the switch.

Great, I found the problem! After buying the $175 (non-refundable) part from the dealer I measured the replacement switch. Same resistance as the old one accross every section of the switch. Whoa, whats going on here? So Installed the new part anyway, figuring that luck would take over from this point. Nope, no such luck.

I proceeded to test the system again and again and noted that the wipers almost never parked themselves along the same location on the glass, sometimes being quite off the mark.

I then noticed that when the wipers landed near the very bottom of the glass in the normal position, the intermittent mode of the wiper system would start and run reliably. This was very perplexing. Concerned that I had a mechanical problem or that the motor had a parking switch that did not work, I looked further. But, the schematic did not show any parking switch, just sense connections back to the BCU. One thing did catch my eye, there were two relays, one for high/low speed and one to power on the motor.

The power relay was wired in a weird fashion. The motor lead was attached to the common pole of the relay and NO contact was wired to +12V as expected, the other NC to ground. A light came on in my head. I switched the two relays and the system worked fine! But why?

Think before looking below>






When the relay powers off, the grounded contact of the relay shorts the motor to ground causing a generator braking action. Because the generated current is brief, that relay contact tends to get a bit of corrosion and not clean itself as it would with normal current. Because the BCU does not see that terminal go low, it assumes a failure mode.

I contacted Haynes, the author of the service manual and they apologized for the misprint on the switch resistor values and actually sent me a corrected page.







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A Toaster Fix
rdrod   2/22/2012 2:04:11 PM
Any toaster or other incandescent nichrome wire/ribbon separation can easily be repaired. It entails making sure the parts are in contact at the break point. Then put a little borax on the break area and plug the appliance in. The borax will allow the break to fuse and produce a permanent weld, making the unit functional again. I have used this method to repair heaters and scientific instruments over the years.

Jon Titus
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Re: A Toaster Project
Jon Titus   2/21/2012 7:33:00 PM
Give an incandescent light bulb a whack with a soft-soled shoe and you'll increase the light output... at least briefly.  Probably easier to get a higher-wattage bulb, but hurry, they won't be available much longer if the US Congress has its way.

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Re: A Toaster Project
Walter   2/21/2012 7:22:40 PM
Did you know you can fix incandescdent light bulbs?  My mother told me her sister used to able to do that during the WWII rationing.  One day my little transformer-powered high intensity light (remember them?) burned out.  I could see the fat, little, broken filament through the clear class.  I turned on the power and tapped the unit so the two bits of filament vibrated past each other.  Then bingo! they touched and welded together.

It lasted about a week.  The second time I did this, it lasted about 15 minutes when an entire section dropped out of the middle.  End of story for that one.


Jon Titus
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A Toaster Project
Jon Titus   2/21/2012 5:40:47 PM
Hello, bdcst.  Your toaster fix reminded me of a story my grandfather told me years ago.  He was the principal at a New York City school years ago and many of the kids took vocational classes in which they built projects.  One fellow showed up with a toaster he built at home entirely on his own, but my grandfather would not let him plug it it.  He had made it of wood.

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Re: The No-Fix-It Mentality
ts4tomh   2/21/2012 5:11:19 PM
Jon Titus mentioned "DYI" projects. LOL! Are those the "Do Yourself Injury" ones? I've had a few of those over the last 50-odd years. Don't even ask me about the suggestion I get the dents out of a 1000 gallon oil tank by pumping 30psi of air into it... that woke up the entire neighborhood, and I live out in the country, (fortunately) hundreds of feet from any neighbor's stuff.

I do prefer the "DIY" projects, though, especially the ones that might not pencil out for time spent, but definitely help educate the kids.

And that oil tank? One half is a burn barrel now. I keep it as a reminder.

-- Tom in Oregon City

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Fixing appliances
techjohn   2/21/2012 5:00:36 PM
Well let's see last week I fixed an oven control board for an Engineering professor. Cleaned the contacts under one of the controls.  Today I fixed his portable CD player.  That only took a little super glue.  My brother emailed me yesterday wanting to know if I could look at some of the camera monitors for his church tha thave problems.  Not sure I can help there.

 Talking about getting kids interested in tinkering again, there is a great magazine called MAKE that is helping to fuel a new wave of tinkerers and DIY selfers. 

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Re: The No-Fix-It Mentality
bdcst   2/21/2012 4:41:39 PM
Yes, having kits for kids is a good thing but it's not essential.  My first major repair job while still a child was fixing my parents' Toastmaster pop up toaster which had served us since my infancy.  I was around 12 years old.  I could see a break in the heating element near the edge of the mica board that held it in place.  I knew that soldering wouldn't mend it as the nichrome wire got incandescent and would certainly melt the joint.  It hadn't occured to me, back then, that vaporized lead might also be rather toxic in a toaster!  Anyhow the lead free repair required that I enlarge the slot in the mica board so I could pull through sufficient nichrome wire to be able to crimp the ends together.  You wouldn't have expected that repair to last but it did until well into my college years!

They just don't make appliances as well as they used to!

As an aside, the cost of power tubes used in broadcast transmitters has skyrocketed of late making tubes less practical than transistors even though high power solid state RF amplifiers have traditionally been way more expensive to build.  The principle reason seems to be a global shortage of raw materials to fabricate power tubes, mostly a lack of quality tungsten wire for cathode filaments.

Rob Spiegel
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Re: A bit of a tangent
Rob Spiegel   2/16/2012 3:15:32 PM
Hey, Glenn, your story would make a good Sherlock Ohms posting. Could you give a little more detail (step-by-step on identifying the problem, step-by-step on solving the problem)?

If so, please send it to: rob.spiegel@ubm.com

Also, please include a short bio.

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Re: The No-Fix-It Mentality
BestFirmware   2/15/2012 8:34:04 PM
Perhaps many engineers share similar "philosophies" of life, and I find all these replies interesting, especially the note that fixing an appliance is better than replacing it (at least up to a point) and that this is, in fact, the ultimate in living green, not having to recycle because you're not yet "done" with the item in question, because you fixed it! 

I expect to fix as many household items as possible rather than pay to have them repaired or throw them away/recycle them and buy a replacement. It makes economic sense as well. But while I grew up in the era of building go-karts from old lawnmower engines, then fixing my own car when I got one, I have to say that many consumer items are simply not repairable, like digital cameras or cellphones. We are designing instruments these days with ball-grid-array ICs that have 1100 pins, on circuit boards that have buried traces and "blind vias" that almost defy imagination to troubleshoot and fix. 

On the other hand, it's not always the complexity of the technology that causes a disposable mentality; sometimes it is just the shabby components used, such as the motor winding wire that has thin or brittle insulation that fails. It only has to last to the end of the warrantee period... We didn't make stuff that way in decades gone by; it wasn't made to last 100 years, but it was made to last. The shabby parts make for a shabby product. Why should a refrigerator fail after only 2 or 3 years service? My parents had a Westinghouse refrigerator for 40 years or more that never needed more service than cleaning the condensor coils.

There are classes of product (smart phones?) that may never be repairable, and besides, evolving RF standards will obsolete them eventually. But that is no reason to make everything else in the cheapest, most shabby way, and maybe my best response is to buy a higher quality electric drill (or whatever) that WILL last, and support manufacturers that build them.

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