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Sherlock Ohms

Glue & Sealant Gunk Up the Line

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Rob Spiegel
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They can't both be bad
Rob Spiegel   10/24/2012 5:56:05 AM
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Good detective work, Glenn. When the replacement cable was also bad, it would have been easy to determine that the cable wasn't the problem.

naperlou
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Re: They can't both be bad
naperlou   10/24/2012 10:35:01 AM
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Glenn, that was good work.  I always found that there are often several different failure modes and it is important to isolate them.  The problem with the second cable is a difficult one.  I wonder if that cable was considered "new" or if it was a spare from another unit.

Rob Spiegel
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Re: They can't both be bad
Rob Spiegel   10/24/2012 11:00:11 AM
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Good point Naperlou. Glenn will likely weigh in on this. If the cable was new but defective, you would get a powerful bias that the cable wasn't the problem.

Nancy Golden
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Re: They can't both be bad
Nancy Golden   10/24/2012 12:32:00 PM
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I agree, Rob - since part swapping is usually a quick way to verify if a part is operating correctly. I would also have been tempted to call the cable good and look further for a different problem. I have done it in the past (just grabbing another part out of a parts bin) and after wasting time verifying everything else was okay, I would return to the part I had called "good" and finally figure out that while it was not the obvious answer, the replacement was also bad. Glenn did a great job going to a KNOWN good cable to make his call - a great tip for anyone involved in troubleshooting!

Rob Spiegel
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Re: They can't both be bad
Rob Spiegel   10/24/2012 12:35:53 PM
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I agree, Nancy. Glenn had a great solution. He knew the cable on the second machine was good. So he was able to double check the cable.

GlennA
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Re: They can't both be bad
GlennA   10/24/2012 12:55:35 PM
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naperlou;  The cable was new from stock.  It had never been installed into a machine before.  Fortunately I had a known-good cable in the working unit to use for troubleshooting.  But 'swap-tronics' only works when you have multiple identical units to swap parts between.

Nancy Golden
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Re: They can't both be bad
Nancy Golden   10/24/2012 1:08:53 PM
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It is tempting to assume that because something is "new" that it is good...we forget that manufacturing processes can shift and sometimes entire lots of "new" stuff with a defect escape QC before it is detected and wind up for sale. Kind of the same idea - I remember one time I bought several red LEDS for a project I was building, from the same place I usually bought my parts from. My project was a wind rose being controlled by an 8751 and different color LEDs would light in response to changes in wind strength and direction.  After I soldered in the LEDS into my homemade PC board, I was amazed that my "red" LEDS were both "orange" red and "red" red. I just couldn't understand how I could buy something new and have that much variance in the same product. I went back to the electronics store I had bought the LEDs at and because I wanted my LEDs to match in color, I powered them up before I bought them (with the store manager's permission) so that I could get matching colors. That went a long way in teaching me not to assume that what I purchased would meet my expectations, regardless of how well prior purchases had worked in the past.

Rob Spiegel
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Re: They can't both be bad
Rob Spiegel   10/24/2012 6:14:38 PM
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That's a good story, Nancy. With counterfeit parts, it can be really bad. The parts often come back to the distributor or supplier in its own packaging. They look and act right -- the first layer or the first part of the roll. After that, it's garbage. In the independent distributor market, their association offers classes and certification on how to identify counterfeit parts.

Nancy Golden
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Re: They can't both be bad
Nancy Golden   10/24/2012 6:55:40 PM
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That reminds me of what Mitt Romney said during one of the debates, Rob. The topic was about trade with China and Romney was talking about some type of valve that came back to the manufacturer as defective, so the company replaced it. But the company noticed something was wrong when they got several additional defective valves returned - all sporting the same serial number!

Rob Spiegel
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Re: They can't both be bad
Rob Spiegel   10/25/2012 5:32:03 AM
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Yes, I remember that comment during the debate. And that's how a lot of it works. I remember a story about a plant in a small town in China that was producing counterfeit components. Officials were apparently well aware of what the plant was doing. When an Chinese official was asked why the government didn't shut down the plant, he replied, "This plant employees 2,000 people. It's the biggest employer in town by far."

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