I used to work at Nordson Corp., and it was there that I ran into two Sherlock-worthy problems:
First, the company had hot-melt glue applicators ranging from units with small tanks (that glue was added to as small pellets or chips), up to a 55-gallon drum in heated-platen units. One of the 55-gallon drum units had an overheating problem.
When the line started, the LED indicators flashed, showing the heating cycle. The temperature display showed the temperature was rising. As the temperature neared the set point, the PID (proportional integral derivative) compensation was supposed to reduce the heat, and the LED flash rate slowed to mimic the change. But the temperature kept increasing until the over-heat tripped.
When this happened, the unit had to be allowed to cool before any testing could be done. The heating was controlled by a triac (triode for alternating current). When the unit cooled, I monitored the triac control voltage and output voltage. Even when the triac control was not on, it was heating, so the triac was shorted.
When I explained to the manager that I would need to replace the triac, he said that there wasn’t a replacement in stock. I checked stock myself, and found a replacement that would work. The triac for the 55-gallon unit was the same triac as was used on the tank-style unit. The two had different Nordson part numbers, but they were the same triac. After I replaced the triac, the over-heat problem was fixed.
Next, I experienced another line snafu. Our company had sealant dispensing units at the General Motors Oshawa Car Plant. There were two units on one line, and one wasn’t working properly. The plant was still in start-up, so the problem was not urgent. Another technician had been working on the unit, but had not been able to fix the problem. I was asked to look into the situation. I asked the technician for the details of all the testing he had done.
He narrowed the problem to a ribbon cable, but when he replaced the cable, it didn’t fix the problem. When I got to the plant, I asked if it would be a problem to shut down the other, working unit. We shut the working unit down, pulled the ribbon cable, and installed it on the non-working unit. That unit powered-up and worked. We then installed the suspect cable in the first unit. That proved the cable was the problem. The replacement cable also happened to be faulty. When available, swap-tronics can be a big help.
This entry was submitted by Glenn Aitchison and edited by Rob Spiegel.
Glenn Aitchison’s first field service job was in 1987. Since then he has worked in robotics, automotive, as well as industrial automation and machinery. He received his Certificates of Qualification as an Industrial Electrician and as an Industrial Mechanic (Millwright).
Tell us your experience in solving a knotty engineering problem. Send stories to Rob Spiegel for Sherlock Ohms.
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.
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.
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.
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!
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.
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.
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!
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."
Rob, I think that philosophy falls under what in ethics is called utilitarianism. In their minds it brings about a desired result (employment for a large number of people) therefore it is good - the means are not as important as the end. It's especially hard to fight in this case because it is part of their worldview...
In the early 1980s, a fellow engineer (of Chinese descent) told me quite emphatically that he AVOIDED doing ANY business with anything connected to the Chinese (as a nation) because of their unethical behavior. Since this was at a time in history which was less than 10 years removed from Pres. Nixon's historic trip to mainland China, I immediately dismissed his comments as being very biased & bigoted. At that time the world was not so deeply engaged with Chinese manufacturing & trade.
Now, however, as I reflect on those comments from decades ago, and become more aware of the devious business practices that are undertaken AND sanctioned by the "higher-ups", it is becoming more apparent that his comments bore a great deal of validity, SORRY to say!
I'm SURE that with every other endeavor in human relations, one can find the "bad apple" which seems to rise to the fore, make the news, etc. whereas the rest of the barrel of apples goes completely unnoticed and/or unrecognized!
p.s. During his diatribe against the Chinese, he mentioned one startling fact...... he'd MUCH rather engage in business deals with a Japanese company or entity since they ARE so ethical.
Yes, Rob - and when it is an ingrained mindset it is really hard to change. There are so many ethical systems and when doing business with folks who don't subscribe to the same ethical standards - people call foul on one side while the other side is scratching their heads thinking, but we aren't doing anything wrong...
Oh, I agree Rob. You have to draw a line at some point. There is even an ethical system called ethical egoism which says that selfishness should not be feared but rather embraced as the highest principle of morality. But just because someone subscribes to a certain ethical system, it doesn't mean that it is an acceptable system. Counterfeiting is such a gross violation of standard business practice - and if they expect to participate in the global economy, they should recognize standard business practices...but another issue that is part of our global economy is that we are all coming from different worldviews. It is a challenge to be sure!
Nancy, I think part of the problem with counterfeiting is that we tend to do what we get rewarded for. If those doing the counterfeiting are not facing any negative impact, they'll keep doing it.
You are so right Rob - I face that with my teenagers everyday! We always follow through with consequences because if we don't, they think that they can still get what they want even though they knowingly broke the rules. It's just easier to apply that to your kids than to a whole country!
I have teenagers, too, Nancy, so I know what you mean. One of the problems with counterfeiting in China is there doesn't seem to be any negative consequences. The government in China seems to be a buffer between the counterfeiters and their victims.
In the late 80's during a business trip to Russia I was given a tour of a fabrication facility. Standing on the mezzanine with my interpreter and 2 managers we overlooked a floor with probably 70 lathes and at least 50 milling machines, all being operated. Sitting right in the middle of the floor was a very modern multi-axis CNC machine surrounded by yellow lines on the floor and sitting idle. Upon seeing the CNC machine I asked why it was idle? The manager smiled and said that machine could replace 5 skilled machinists and produce 3-4x the volume, but "you understand in Russia, we can have no unemployment". The only time the CNC machine was operated was when dignitaries from the central Government came to visit. From stories I gather China has smiliar problems.
Your story reminds me of a recent trip to China where I went to a KFC for dinner. At the completion of my meal, I picked up my tray to discard my trash, and a KFC employee agressively approached me telling me something that I did not understand. My interpreter explained to me that the employee was telling me that I was trying to take her job, and clearing tables was only her responsibility. It is a different culture.
That's an interesting story, Bob. And it certainly illustrates a culture that is far different from the business culture in the U.S. We would replace all of the workers if we could.
Glenn Atchison wrote "When this happened, the unit had to be allowed to cool before any testing could be done. The heating was controlled by a triac (triode for alternating current). When the unit cooled, I monitored the triac control voltage and output voltage. Even when the triac control was not on, it was heating, so the triac was shorted."
"Latchup" is the most common failure mode of triacs. They remain in the "off" (non-conducting) state when power is applied until the trigger voltage is first applied to the gate. Then they turn "on" (conducting) as they should. The problem occurs when the trigger voltage is removed from the gate. The triac should turn off at the first AC voltage zero-crossing but it does not. The device "latches up" and remains conducting until voltage is completely removed from device terminals. In other words, the triac won't reset until the product is completely powered off.
I had the same failure and related symptoms in my 1984 washing machine in about 2007. A new controller board would have cost $350, but they were no longer available. I isolated the problem to the triac, as Glenn did. Also similar to Glenn's experience, I could not get an identically-labelled replacement--no longer made. But triacs are not critical components. Any one with comparable or greater ratings and a similar package will do. Fortunately replacements were available for 37 cents.
Trouble shooting a problem in any complex product isn't always straight forward.
I have had hundreds of product returned because it didn't work like the prior production build lot... Only to find out what was assumed to be the "same"... wasn't. In this case, the customer incorrectly documented the cables required - and fooled themselves during the course of swapping things around, into thinking the only item changing was the interface board we shipped to them. The problem was the cables they built.. and had their end users build (incorrectly) in hundreds of airports across the world!
Simply put.. they thought the only thing they were swapping out was the interface card we were providing. They were certain this was the only thing being done.
It required a third party to discover the real cause (we didn't have examples of "their" bad cables).
Any single level failure is generally easy to fix with swapping out components with known good components.
But if that is your only skill set during trouble shooting, YOU are in trouble.
Your trouble shooting skills are really "put to the test"? ... when fixing a system with 2 or more different failures at the same time. No one component swap out will "fix" the system.
And a variation of this scenario .. swapping components from questionable stock (never assume "new" = good/working)
This issue is not directly related to Nationality or even counterfeit components. I have seen bad "new" components from nearly all countries / companies on occasion. Counterfeit parts (aircraft industry) happen in the USA all the time. And corrupt business leaders happen everywhere. Little value in making sweeping generalizations on the subject.
Having the skill to not to depend on assumptions.. is the real lesson being presented.
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