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Sherlock Ohms

The New Controller Just Wasn’t Cool

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Rob Spiegel
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Blogger
A simple solution
Rob Spiegel   11/20/2013 11:38:53 AM
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Here's yet another beautiful example of a Sherlock Ohms solution that is incredibly simple. 

Charles Murray
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Re: A simple solution
Charles Murray   11/20/2013 7:00:58 PM
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This is the kind of problem that causes engineers to search for weeks and examine every possibility, no matter how complex. Only an experienced engineer would have thought of something as simple as vent holes.

Nancy Golden
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Platinum
Re: A simple solution
Nancy Golden   11/24/2013 7:01:52 PM
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"This is the kind of problem that causes engineers to search for weeks and examine every possibility, no matter how complex. Only an experienced engineer would have thought of something as simple as vent holes."

Until it happens once - then you never forget and overheating comes to the top of your list...I can't tell you how many times I have had to tell my son to quit covering the vents on any of the numerous electronic boxes that are common to any household from TVs to stereos etc. or to not use his laptop on the carpeting. Air circulation is your friend and covering vents with books or DVD cases is not a friendly act...


Freon was also standard on every tech bench in the old days. When I worked in product engineering - we also tested chips across temp. We were either forcing them cold with liquid nitrogen or burning them in. Spec sheets will tell you a chip's operating temperature tolerances but it's harder at the system level for the reasons stated in various comments. Keeping electronics cool is definately an issue that needs to be considered in every design from chip to chassis...


OLD_CURMUDGEON
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Platinum
Aaaaaaaaaaaaaaaaaah, YES! ... HEAT!
OLD_CURMUDGEON   11/21/2013 8:48:29 AM
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When ICs were becoming MORE popular in the late 60s, onward, one of the essential pieces of "test equipment" at all our engineering lab benches was at least one aerosol can of "cold".  The equipment designed was high-end, commercial grade radio communications gear.  It had to function from the environs of the Arctic cold to the sub-Saharan hot.  We could not risk heat prostration failures, since these chassis were a combination of solid-state & vacuum tube technology.  Additionally, since much of this equipment had to pass FCC certification, it was subjected to extensive environmental chamber testing while in full operation mode, whether receiving or transmitting signals.  Even w/ directed forced-air cooling, provisions were made for proper operation at the full specified operating temperature range.

tekochip
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Platinum
Re: Aaaaaaaaaaaaaaaaaah, YES! ... HEAT!
tekochip   11/21/2013 9:25:37 AM
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Freeze Mist.  I hate to say how much of that stuff we used to go through, and how much of it was used to defeat locked thermostats on a drafty factory floor, attempt cryogenics on insects or propel test tube stoppers.  At least the components were better by the time the EPA killed Freon in a can.
 
Really, think about how many component failures we had back then.  The fallout was so large that we used to burn-in components and systems.


OLD_CURMUDGEON
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Platinum
Re: Aaaaaaaaaaaaaaaaaah, YES! ... HEAT!
OLD_CURMUDGEON   11/21/2013 9:36:21 AM
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"Bathing" p.c. boards and simultaneously watching signals change drastically on the o-scopses!  Aaah! What fun!  Most of the ICs we used were plastic, commercial-grade devices, although in some critical applications we did use the more reliable ceramic DIP variant.  And, it was especially important to us since frequency drift was restricted to about 20 cycles / Mc. 

Cabe Atwell
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Re: Aaaaaaaaaaaaaaaaaah, YES! ... HEAT!
Cabe Atwell   1/20/2014 5:42:46 PM
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Just goes to show that drilling holes in things can sometimes help and in this case, it did just that!

3drob
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Platinum
Re: Aaaaaaaaaaaaaaaaaah, YES! ... HEAT!
3drob   11/21/2013 9:50:54 AM
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The old style Freon freeze spray was awesome stuff.  The new spray's just don't cut it (stupid O'zone hole).  But don't forget pulling out the heat gun to "encourage"  problems to reveal themselves.

In the recent past, I've also used a FLIR (borrowed from another program) to actually see the parts that were running too hot.  Much faster and easier to get a quick snap-shot right after pulling a lid than instrumenting with a bank of thermocouples.

A good story, (but surprising because I was expecting the solution to start with "and then I had to hop on the next flight ..." ).

TRCSr
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Silver
Re: Aaaaaaaaaaaaaaaaaah, YES! ... HEAT!
TRCSr   11/21/2013 8:27:18 PM
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Yes, I used a lot of the spray Freon over the years of my carrer. In this case I just failed to give thought to heat being the source of the problem, mainly since both controllers were mounted in what I thought were nearly identical environments. It turned out that there was leakage nearer to the one that allowed the cooling air to be concentrated on that controller. Lesson learned!

Larry M
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Platinum
Re: Aaaaaaaaaaaaaaaaaah, YES! ... HEAT!
Larry M   12/3/2013 8:42:19 PM
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The freeze-spray posts remind me of a problem I had to trouble-shoot in the mid-1990s. We were working with an embedded modem assembled from a pair of vendor parts and our surrounding analog components. The modems would start and run properly sometimes, but most of the times they would hang. I puzzled over this for two weeks, not making much progress. After six hours of no success in the lab one day I retired to my office to try to get some distance from the problem.

My manager found me there and demanded to know why I wasn't heads-down in the lab. And by the way, he asked, "What is this problem, anyway?" So I walked him to the lab and started the product. It started correctly. I stated that this was the rare, successful case as I quickly shut the device off and restarted it--and it started into a hang state I had never before seen. Suspecting something, I quickly turned it off and on again--and it hung in the all-too-familiar hanging state.

I told my boss to stay right there--not to move--and walked to the chemical storage cabinet in the next room and returned with a can of freeze-spray. "Watch," I said. "I will now make it boot successfully several times. I laid down what was probably 1/16" of frost on the two modem parts and sure enough it started successfully several times in a row. As the frost began to melt and the water droplets warmed, eventually it hung again.

I had changed the problem from "It hangs most of the time." to "It hangs except when cold." This was a real breakthrough, since it indicated a race condition that changed winners as temperature increased, and was now isolated to the modem chips. (Incidentally I was only able to make this discovery because I had taken a break, allowing the system to cool. I never pointed this out to the manager--realized it just now--but had I not left the lab for a break I would not have made this breakthrough.)

Ultimately the problem had to be fixed by the modem chip vendor. The circuit included an unused three-state input/output register pin where proprietary internal software carried out these steps:
  1. Enable register output
  2. Read input  <--Hangs here on unexpected value being returned
  3. Initialize register which was being read

instead of
  1. Enable register output
  2. Initialize register which was being read
  3. Read input <--Now reads the properly initialized value

Had we not found the thermal sensitivity we would never have been able to get the modem vendor's attention.

taimoortariq
User Rank
Gold
DebuggingI
taimoortariq   11/30/2013 11:02:28 PM
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I actually have had similar problems with the motor controllers, specially for the motors that have high current ratings and run on high load. The heating problem is the worst of them all. Ultimately, I ended up using huge heat sinks to solve my problem.

johnr
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Iron
A universal debugging axiom?
johnr   12/2/2013 4:32:27 PM
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In the software debugging world there's a saying:  "My computer is not the same as your computer."  The idea is the same as in the article:  you need to test under the same conditions as the end user.  In our lab our technical computing people have spend a lot of time and effort to make sure everyone's computer is the "same" so that our DA tools work (or fail!) the same way for every engineer!


OLD_CURMUDGEON
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Platinum
Re: A universal debugging axiom?
OLD_CURMUDGEON   12/4/2013 7:54:16 AM
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I applaud you for this position.  And, you MUST have a very dedicated support staff in MIS that can keep these PCs running on an EXACTLY equivalent level.

I have 3 PCs in my charge, ALL running WINDOWS XP PRO S/P 3.  All are "legit", registered w/ MICROSOFT, so they all receive timely updates.  One is a DELL "tower-style" unit, the other, a H-P laptop (wide screen style), & the third, an ACER laptop.  Besides the individual vendors' customizations & preloaded applications, ALL have the SAME applications software loaded, essentially CAD programs & software editors (VISUAL BASIC, VISUAL C, PLC LADDER editors, Servomotor editors, WORD, etc.)

In spite of all this "sameness", each PC boots differently, displays differently & reacts differently.  It has been far easier over the years to live with these anomalies than to waste a lot of time delving into the complexion of WINDOWS!!!!

johnr
User Rank
Iron
Re: A universal debugging axiom?
johnr   12/6/2013 6:11:11 PM
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Oh yeah, our technical computing people are the best and a huge contribution to our productivity.  Part of what makes their job easier is that all design work is done on Linux systems, which seem to be easier to keep in lock-step with respect to the OS and applications that are installed.  We also have a very large farm of compute systems, that are kept absolutely identical, where most of the heavy lifting is done.  Things are good now, but I remember the bad old days from 15 or 20 years ago when things weren't so good!  I don't want to go back!

William K.
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Platinum
Returned without finding the problem???
William K.   12/2/2013 9:06:39 PM
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I presume that your customer was fairly competent and that they had some credibility when they said that the product failed. If the fault was as well defined as one motor ceasing to run, why in the world would you return it until you understood why? A complaint about a malfunction that is so obvious as a motor not running would certainly merit a much more intense investigation, such as running the machine all night. Every machine thatr I have delivered or repaired gets that 24 hours constant run after being "completed" and otherwise ready to ship. The 24 hour run would have spotted the fault before it was shipped initially. 

The only time to ship a product back and claim "no trouble found" is when the flaw that is repaired is such a dumb thing that you are embarassed to tell anyone. But if the machine does not fail again they will probably not complaintoo much.

William K.
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Platinum
An interesting comparison
William K.   1/6/2014 5:57:33 PM
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The original posting finally brought to mind what I learned from my very best technician, who had been a service person for jet fighter avionics and systems on an aircraft carrier. Those repairs were taken a lot more seriously, since both lives and expensive aircraft depended on repairs being correct the first time. When one outcome could be a court-marshal there is a very serious attitude about verifying the fault, finding the failure, and then producing the repair. It was a good method and certainly produced good results, although there were times when a plane might be out of service until the failure was found. NOT what the CO wanted to hear, but a lot better than losing one.

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Sherlock Ohms highlights stories told by engineers who have used their deductive reasoning and technical prowess to troubleshoot and solve the most perplexing engineering mysteries.
Sherlock Ohms highlights stories told by engineers who have used their deductive reasoning and technical prowess to troubleshoot and solve the most perplexing engineering mysteries.
Sherlock Ohms highlights stories told by engineers who have used their deductive reasoning and technical prowess to troubleshoot and solve the most perplexing engineering mysteries.
Sherlock Ohms highlights stories told by engineers who have used their deductive reasoning and technical prowess to troubleshoot and solve the most perplexing engineering mysteries.
Sherlock Ohms highlights stories told by engineers who have used their deductive reasoning and technical prowess to troubleshoot and solve the most perplexing engineering mysteries.
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