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Sherlock Ohms

Case of the Failing 'C' Batteries

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GlennA
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Check and Double Check ?
GlennA   5/4/2012 8:51:11 AM
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It is interesting that none of your predecessors seemed to have taken the time to check to see if the rejected batteries were actually rejects.  There is an old saw about 'assuming'.  The problem is not 'assuming'.  The problem is not recognizing what assumptions you are making, and then not reviewing those assumptions to see if they are valid.

naperlou
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Re: Check and Double Check ?
naperlou   5/4/2012 10:26:03 AM
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John, as Gelnn said, this is a good example of not making assumptions.  Your predecessors all assumed that the test harness was fine.  That is often where there is a problem.  Again, check the whole chain starting from where the failure occured.

naperlou
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Re: Check and Double Check ?
naperlou   5/4/2012 10:26:03 AM
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John, as Gelnn said, this is a good example of not making assumptions.  Your predecessors all assumed that the test harness was fine.  That is often where there is a problem.  Again, check the whole chain starting from where the failure occured.

naperlou
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Re: Check and Double Check ?
naperlou   5/4/2012 10:41:16 AM
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John, as Gelnn said, this is a good example of not making assumptions.  Your predecessors all assumed that the test harness was fine.  That is often where there is a problem.  Again, check the whole chain starting from where the failure occured.

Nancy Golden
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Re: Check and Double Check ?
Nancy Golden   5/5/2012 5:34:36 PM
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The author did a good job isolating the problem. I think perhaps the other folks were not so experienced in troubleshooting. I'll never forget as a young tech making an assumption that wound up delaying a resolution to a problem we were having. I don't remember what the problem was but I sure remember my angry boss pulling me into his office and writing       ASS U ME in large letters on his white board. He then asked me if I knew what happens when I assume - If you look closely, I  am sure you can figure out the rest of the story...

That happened in 1990 but is a lesson I carry with me to this day!

GlennA
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Assumptions
GlennA   5/7/2012 8:38:00 AM
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The 'When you assume...' phrase is common, but useless.  Everybody makes assumptions.  Assuming the rejected parts are actually bad, or assuming the rejected parts are really good is a beginning of troubleshooting.  The real trick is to know and realize what your assumptions are, and be prepared to revisit them when troubleshooting doesn't agree.  During a light-hearted conversation I was asked of I knew what happens when you assume.  I replied 'Did you assume that I was listening to you ?.  Of course you can't say that to your manager.

OLD_CURMUDGEON
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Re: Check and Double Check ?
OLD_CURMUDGEON   5/7/2012 10:01:36 AM
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In one of the more famous (TV) episodes of the ODD COUPLE, Felix Unger told the judge a simple fact .......  When you ASSUME something, you make an ASS of U and ME!  Very sage words, indeed!!!!

Nancy Golden
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Re: Check and Double Check ?
Nancy Golden   5/7/2012 10:12:57 AM
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The Odd Couple - Felix and Oscar - haven't thought about them in years! I probably saw that episode, I can certainly picture Felix doing exactly that, LOL! Thanks for the memories, OLD_CURMUDGEON!

ScotCan
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Re: Check and Double Check ?
ScotCan   5/4/2012 4:15:54 PM
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To be fair to the previous investigators, none of them were trouble shooters...they were parachuted into a situation which was sporadic in nature because of the two sets of tooling which could be installed in a random fashion. In Liaison Engineering, when something goes wrong you have to come up with a fix "toute suite"...management expects fast answers even 'though they look down their noses at the "Quick Fix" crowd (Liaison Engineers).

3drob
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Re: Check and Double Check ?
3drob   5/8/2012 8:22:07 AM
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I appreciate that you want to be fair, but step # 1 in ANY endeavor (Engineering or other) is to identify the task or requirement.  In this case, to identify what kind of failure you are investigating (luckily there was a quar. set of failed batteries to test).

If you manually test your failed bin of parts and the failure rate matches the expected (hopefully low) failure rate, then NDF (no defect found).  Of course, you want to cut a few "good" ones apart to make sure there are no latent or intermittent problems before you announce to your boss NDF.  Task identified:  find out why good batteries tested bad.

Which is what the author did, which is what makes this one a good story.  Kudo's.

ScotCan
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Re: Check and Double Check ?
ScotCan   5/4/2012 4:27:42 PM
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The rate at which the cells were produced provided very little time to troubleshoot, and policy was to make up the shortfall where suspect cells were concerned, quarantine the defects and pick up on their disposition later. For some reason management left me to my own devices and I could work at a rate that suited me instead of being under pressure.

GlennA
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Re: Check and Double Check ?
GlennA   5/4/2012 5:27:18 PM
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Another variable may have been your testing the rejected parts during the operators' break time.  If you had instead tried to take 'production' time to do the testing you may not have been allowed the time you needed.

ScotCan
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Re: Check and Double Check ?
ScotCan   5/4/2012 5:34:43 PM
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That is very true. There is no way that time would have been allocated for troubleshooting during production. In fact several of the gizmos I designed for in process trouble shooting had to be carefully designed such that if production supervision called for their removal they could be removed on the fly without interruption to the line flow. 

tekochip
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Common Assumption
tekochip   5/4/2012 11:31:43 AM
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It's a common assumption; people tend to believe that components are bad. Even when you have evidence to the contrary, it's easier to blame a component than a process or a tool. This issue is magnified when you have a marginal design, one that only works when a component is at its nominal rather than one end of the tolerance. I had an issue with a board that would not come out of Reset because the supervisory chip was holding the part in Reset. Technicians, the Production Manager, even Purchasing all believed that the supervisory chip was at fault because they could replace the chip and the circuit would come to life. A quick look at the spec. sheet showed that the pull-up resistor used for the supervisory chip was far too weak. Even after demonstrating that components once removed as failed were now operating properly, they refused to believe that the problem was not a faulty component, after all, the circuit had worked through two years of production without issue. I guess the cure would have been telling them that the pull-up resistor was a faulty component and needed to be replaced.


ScotCan
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Re: Common Assumption
ScotCan   5/4/2012 4:21:03 PM
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Yes, that happens often. Another example... quite common...was the disgruntled consumer who complained that a brand new set of batteries for his flashlight were no good. We changed a blown bulb for him and hel calmed down.

Nancy Golden
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Re: Common Assumption
Nancy Golden   5/5/2012 5:33:18 PM
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That's funny tekochip - I had the opposite problem. When I was a test engineer and parts started failing, everyone always wanted to point to the test set. I always kept calibrated "golden" units around so that I could verify tester operation. I made sure my golden units included passing units at both ends and the middle of the spec as well as rejects. Most of the time that would satisfy all involved that we needed to look at the parts themselves...

jhankwitz
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Gage R&R
jhankwitz   5/7/2012 10:51:45 AM
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Most any Quality Manager worth their salt will run Gage R&R (gauge repeatability and reproducibility) on their test and verification people and equipment on a regular basis.  When you don't do this, you haven't a clue as to what you're producing.  You need to understand or get get full control of all variables in your inspection processes.

Our people are amazed when we report the source of variables and variation in our most basic inspections (like using a mic or caliper).  It's a real eye-opener for most people outside the Quality field.  Managing Type I and Type II inspection errors is a fundamental problem in most every company.

roddalitz
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Precise failure mechanism?
roddalitz   5/7/2012 11:35:28 AM
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I read that the position which failed held the batteries in a "canted" position, but what was the precise reason for the test failing? Did the canted batteries fail to make contact at all? Was there poor contact resistance, or what? The observation and deduction is smart, but I feel I am left hanging.

ScotCan
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Re: Precise failure mechanism?
ScotCan   5/8/2012 9:57:11 AM
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Apologies for keeping you hanging...the canted condition caused bad or high resistance contact and the test registered as a failure. The observation that the test position was canted jogged my memory about other tests I had done varying the terminal contact which led to a wide variance in test results.

JimT@Future-Product-Innovations
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Fix the Process and not the Part
JimT@Future-Product-Innovations   5/8/2012 1:09:48 PM
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When part & component designers experience fit problems with their designed parts, they often point a finger at the tooling & mold engineers; "must be out of spec ; making bad parts".

When industrial automation engineers experience testing and analysis problems, they often point a finger at the component engineers; "must be a design flaw; back to the drawing board".

Then tooling & mold engineers experience trouble getting mold cavities to spec, they often point a finger at faulty heavy equipment manufacturers; "the CNC has slop in the indexing plate".

Truth be told to all, problems and anomalies can exist in every aspect, and looking at yourself first can save a lot of time and embarrassment. 

We used to have a mission statement: "Fix the Process and not the Part".  It tought a lot out looking at issues from a system level

Ann R. Thryft
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Re: Fix the Process and not the Part
Ann R. Thryft   5/8/2012 7:19:38 PM
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This Sherlock reminds me of some things I heard when reporting on machine vision and inspection equipment. Mainly, how do you tell when the test/inspection equipment is the cause of a failure, and not the part? The big automated production and assembly systems have the ability to gather data, via software, which can be aided by the use of machine vision, to allow just that. But it all has to be configured correctly, and that takes a lot of time and energy. I heard from MV vendors that often that doesn't get done.


William K.
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Case of the failing c cells.
William K.   5/17/2012 9:27:32 PM
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I have designed a lot of industrial testing machines and one common feature on many of them was code to detect three-in-a-row failures at any test position. That would either set a warning flag or stop the machine, since the processes were stable enough to make 3 in a row faults be a warning about some kind of process deviation problem. Of course if the tester did not record which fixture position the faults were in then it would never have spotted the problem. 

But it was certainly good detective work to locate the cause.

tekochip
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Re: Case of the failing c cells.
tekochip   5/18/2012 10:17:29 AM
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Collecting stats on which position failed is a great idea William.

William K.
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Re: Case of the failing c cells.
William K.   5/18/2012 3:02:45 PM
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Monitoring failures for each test position is usually mandatory for quite a few organizations. Others just monitor for three in a row on the whole machine. The reason is that in an automated line there could be a test fixture failure and it could result in a shift's worth of rejects when there was nothing wrong with the parts. So it is very good economics.

Cadman-LT
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Seems Obvious
Cadman-LT   5/20/2012 8:30:06 PM
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Your solution seems so obvious, yet if there is no one there to explore the problem people just believe the machine they are told to I suppose.

Cadman-LT
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Platinum
Charger
Cadman-LT   5/20/2012 8:32:04 PM
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I have a battery charger that sometimes says my batteries are fried and sometimes they get the green light. I'd like to know why that happens.

Cadman-LT
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Platinum
Re: Charger
Cadman-LT   5/20/2012 8:53:43 PM
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Actually I have 2 chargers. One will say yes and no depending on the day, and the other always says yes(green light). It's very annoying and I wish I had an answer as to why this happens. Either way, the batteries work...I just never am sure to trust if they are fully charged or not. I am about to just get all new batteries and if the chargers say bad...toss the charger.

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