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Sherlock Ohms

Don’t Like the Problem? Don’t Believe It

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tekochip
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Finding Believers
tekochip   10/1/2013 9:58:37 AM
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I had a similar issue with an instrumentation amplifier in a scale.  This was back in the days when you had to roll your own amplifier and offset drift was a major issue.  This design had a chopper amplifier which seemed to work very well, built then would suddenly become wildly unstable, possibly from solar flares, gravitational storms, or spirit orbs.  Same story; it worked great for six years, now suddenly YOU think there's something wrong with the design.
 
It turned out that the chopper frequency would sometimes drift a little with temperature and if the frequency wound up being an odd harmonic of 60Hz, the hum that is everywhere, the hum would no longer be common mode (maybe 10 ripples on the + input but only 9 on the – input).  When I found the cause, I was able to demonstrate the problem and redesign the scale with a modern, monolithic instrumentation amplifier.


Rob Spiegel
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Blogger
Re: Finding Believers
Rob Spiegel   10/1/2013 10:40:38 AM
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Thanks Tekpochip. I would guess there are a lot of stories like this -- communication problems between the engineer and others in the organization. If you have one, please send it along as a comment.

RogueMoon
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Platinum
using the last resort
RogueMoon   10/2/2013 9:06:42 AM
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Despite the motivation, I'm sure the decision to leave wasn't easy.  Sometimes a situation like this leaves you with few choices.  Rather than have your skills impugned by a manager clearly unqualified to judge these matters, it's perfectly reasonable to take your skills elsewhere.  I'm glad you found something better.

TJ McDermott
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Do it anyway
TJ McDermott   10/1/2013 10:52:42 AM
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If quitting was in your mind, did you consider unlacing all the wire bundles to make a rat's nest before leaving?  Maybe see if you could make that former sargeant eat some crow?

bob from maine
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Re: Do it anyway
bob from maine   10/1/2013 4:34:33 PM
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While in the Navy, I had opportunity to operate and repair a famous 1960s era VHF radio. These radios were multi frequency tube type and quite robust. The biggest downfall was the wiring, which looked exactly like a rat's nest but was very precisely set so interelement conductance was exactly balanced and made it possible for these things to work. You could move one wire to replace a resistor and if you didn't put it back exactly right, the radio would either be off frequency or have low output. Unsoldering a tube socket frequently condemned the entire set to the scrap pile. They were frequently used as 'learning tools' for bosses with more knowledge than common sense.

ratkinsonjr
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Gold
Re: Do it anyway
ratkinsonjr   10/2/2013 9:35:08 AM
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I know it can be hard working for the boss from hell, and the hardest part must have been waiting until you could afford to leave.

My question is: How come the boards were wire-wrapped?! That may be okay for a prototype, but for production hardware you always transition to a printed circuit board for improved reliability and easier maunfacturability. I can just imagine the nightmares trying to troubleshoot a board if a wire broke off or fell off of a post. The only reason I can think of for not using a PCB was if this was a low volume product. Low volume, fast-turn PCB houses are commonplace now, but were unheard of back in the 1980's when I started my career. How many sims did they actually build? 

armorris
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Platinum
Re: Do it anyway
armorris   10/2/2013 11:21:29 AM
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ratkinsonjr,

Yes, this was very low volume. Wire-wrap was very reliable when done properly. Also, it can be done semi-automatically, but I don't think this particular panel was. The semi-automatic system would have routed the wires in ratsnest style (unless that is a selectable option). The semi-automatic system moves the panel around so that the operator only has to operate the actual wire-wrap gun. It greatly speeds up the process and greatly reduces wiring errors. The simulator I was working on was serial number 4or 5.

The wires are wrapped tightly around square pins, whose corners bite into the wires, providing an excellent electrical connection. The wires are automatically sripped first, of course.

tekochip
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Platinum
Re: Do it anyway
tekochip   10/2/2013 11:27:11 AM
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Wire wrap cards were very popular back in the late Seventies and early Eighties when you had rows and rows of logic gates on cards.  The machines that wrapped the crads were easily programmed and servicing the crads wasn't awfull as long as you didn't have to unwrap anything. 

Thankfully microcontrollers got to be cheaper.

bobl
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Iron
Re: Do it anyway
bobl   10/2/2013 11:49:43 AM
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re: wire wrap panels

 

Digital Equipment Co (DEC) made most of their computers using wire wrap panels.  If I remember correctly, they were rats-nest type wiring.  They built "millions" of PDP-11 computers and peripherals this way.  They must have thought it cost-effective to use wire wrap.

ndgraybeard
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Iron
Re: Do it anyway
ndgraybeard   10/6/2013 12:05:16 PM
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There were two kinds of wire-wrapped boards in use in low-volume flight simulators, at least at Evans & Sutherland, where I worked in the early '80's.  The type that allowed rats-nest routing was the type where the wire-wrap was on the opposite side of the board from the 7400-series components.  All components were socketed, with the wire-wrap posts forming part of the socket.  As has been mentioned, power and ground connections were sometimes problematic in this stye of wire-wrap board.

To save space in the rack and pack the boards on tigher pitches, and to get more reliable power and ground connections, the second type of wire-wrap board put the wire-wrap posts on the same side as the 7400-series components, which were soldered into the board.  In this style of board, routing was not rats-nest; instead, the wires were routed in channels between the components.  Cross-talk _was_ a problem in this style of wire-wrap board.  The operator who wrapped the wires had a choice, whether to route from point A to B.  The wire could be routed vertically and then horizontally, or horizontally and then vertically. So two critical signals which would cross-talk if they were in close proximity, _would_ be in proximity in boards built by some operators, and would not be in close proximity in other boards. 

Usually the engineer didn't know, before the fact, which signals would interact, so these problems would usually only be found by de-bugging and re-wiring.

 

William K.
User Rank
Platinum
Re: Do it anyway
William K.   10/2/2013 6:00:49 PM
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Why weren't the boards wirewrapped? The answer is simple and logical. In that era mostly circuit boards were at most double sided, and in addition, most of the circuit board layouts were not done by computers, but by skilled layout designers. And my guess is that these were fairly large boards with forty to eighty  14 and 16 pin chips, and a whole lot of discreat logic. Today that could be economical with an autorouter and six or eight layers. Back then it would not have happened. Besides that, the systems were all really prototypes, or very limited production runs, at best. How many flight simulators are sold every year? Not at all like cell phones where millions are sold. THAT is why the boards were wire-wrapped..

One classic fix for wirewrapped boards that were intermittant was to very carefully solder the wires to the posts, starting with the grounds, followed by the V+ pins. And one source of a great deal of greif was the occasional poor ground connection that had been soldered, but not well, prior to the start of wrapping.

ratkinsonjr
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Gold
Re: Do it anyway
ratkinsonjr   10/2/2013 6:25:29 PM
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Ah, yes, the days of mylar sheet with black layout tape and an X-Acto knife, followed by making a copy at 2:1 scale. This so you could trace the layout by hand with colored markers on paper with the clear layout sheets underneath on a light table, to check for routing errors and safety spacings.

You were lucky if you had the luxury of a double-sided board though. My first board (for a CRT monochome display computer terminal) had to be single-sided for cost reasons, which meant that we had over a dozen zero-ohm jumpers on the board, to allow traces to cross over each other.

Almost makes you nostalgic, doesn't it? :-)

William K.
User Rank
Platinum
Re: Do it anyway
William K.   10/2/2013 8:01:58 PM
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Sometimes it is handy to think things out on paper, at least for the initial component location stage of a design. Or if not paper, in a cad program in conjunction with other drawings.

tekochip
User Rank
Platinum
Re: Do it anyway
tekochip   10/3/2013 8:57:30 AM
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Nostalgic.
 
At first I was going to say "no", but then I remembered being hunched over a light board with spools of different sized tape slipped over my wrists like bracelets.  The back of my left hand was decorated with various scraps of tape for filling in land areas and laying out a simple one-sided board for an automotive switch could take a couple days, not including sending the artwork off to the photographer to be reduced.  Making a board was labor intensive, expensive, and there was no guarantee that the board you laid out would match the schematic.  Now, just imagine if you had to make a change.
 
We are so spoiled now.


dbell5
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Platinum
Re: Do it anyway
dbell5   10/22/2013 4:48:43 PM
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"Why were the boards wire-wrapped?" Because that was the technology of choice!

I encountered the same (technical, thankfully, not administrative) problem, I'm guessing 5-10 years before Mr. Morris. We didn't have 74xx devices; these were 0.5" square modules, each with a single TO5 can DTL device, plugged onto wire-wrap panels a rack wide and about 4 feet tall.

Control Bay #1 came out of Engineering, rat's nest style, and after considerable debugging and re-wiring, worked to spec.

That was the cue for the next 10 identical racks to be built in Manufacturing. Except they weren't identical; they were "neat". And didn't work.

Interestingly, this was also a contrct with the Navy...

 

armorris
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Platinum
Re: Do it anyway
armorris   10/1/2013 7:52:42 PM
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TJ,

I am not a quitter. That was just the last straw. That guy was probably a former US Army drill sargent. He managed by intimidation. All the other young engineers that hired in at the same time as I did, quit. I stuck it out for a year, because I didn't have the moving money to pay back. Because I was on the night shift, I didn't have easy access to the personnel department, where I could lodge a complaint. And yes, I was intimidated by him. When I was in the Army and the drill sargents were screaming at me, I could do something about it. I could run harder, or do whatever I was being ordered to do, but, there was nothing I could do about this guy. Also, I couldn't repair the problem myself because it was a union shop. The wires weren't laced. They were just pressed into the gaps between the long wire-wrap pins. I would have had to rip the wires out and rewire them.

This employer believed that young engineers had to "pay their dues" in the shop area for a year before being alowed into the design area. That was a horrible place to work. I didn't want to work in the design area for such an employer. Exactly one year after I hired into that place, a headhunter lined me up with my next job and I got out of there. The rest of my career was good.

Ann R. Thryft
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Blogger
Re: Do it anyway
Ann R. Thryft   10/1/2013 8:43:24 PM
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There must have been a lot of former sergeants in industry back when I was in marketing in the 70s and 80s. Andrew's ex-boss sounds just like a few I had, but they managed to acquire college degrees. The 'tude was similar: if I didn't personally see it break, it can't really be broken so shut up; if it was good enough for your predecessor why are you complaining even if we could save time/money/sanity/all-of-the-above; if we could buy XYZ goods or services 10 years ago for $100, why should it cost $300 now?, etc.

TJ McDermott
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Blogger
Re: Do it anyway
TJ McDermott   10/2/2013 2:09:06 AM
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Mr. Morris, please forgive my poor choice of words.  I did not mean to imply you were a quitter.

armorris
User Rank
Platinum
Re: Do it anyway
armorris   10/2/2013 11:24:41 AM
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TJ,

Thanks. Please forgive my misinterpretation of your meaning.

Zippy
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Platinum
Military intelligence?
Zippy   10/2/2013 8:14:42 AM
Remember, every problem has three approaches: the right way, the wrong way, and the Army way!   :)

Battar
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Platinum
Re: Military intelligence?
Battar   10/2/2013 10:13:57 AM
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Zippy,

         Having worn a uniform (never mind which - thats classified) for many years, I resent your remark about military technical incompetence. I worked with a bunch of professionals, it was the rare commander who thought he knew better than us when in fact he didn't.

armorris
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Platinum
Re: Military intelligence?
armorris   10/2/2013 11:36:17 AM
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Battar,

I'm sure Zippy meant that as humor (note the ":)" at the end of his comment). I have met a lot of highly competent people in the military, but I've met some idiots, too. The military are just people, like the rest of us.

I was drafted into the Army. When you draft people, you get all kinds.

Zippy
User Rank
Platinum
Re: Military intelligence?
Zippy   10/2/2013 5:15:33 PM
Battar, thank you for your service. You find my humorous comment offensive, for which I apologize.  I will point out two things, however;

1.  This story is in fact about just such an incident.  That's not an indictment of the whole organization, but these things do happen.

2.  My quote was a favorite of my father, who served in WWII and Korea, and retired as a colonel after 30 years.  A well-developed sense of humor can get you through a lot in life.

 

Respectfully,

Zippy

Battar
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Platinum
Re: Military intelligence?
Battar   10/3/2013 2:10:28 AM
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Zippy,

        I understand that your remark was made in jest, but it wasn't really funny. I served in a US-allied organization which is internationally recognized for its' competence and is generally held in high regard. We had our share of fools, but not in the technical units. And yes, a sense of humor is indispendible.

Watashi
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Platinum
Re: Military intelligence?
Watashi   10/4/2013 5:19:24 PM
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It sounds funny but you are also correct that it is not.  It is actually a statement of fact that acknowledges the things that drive decisions in the military are not always obvious to civilians. 

A civilian engineer generally looks at a problem based on a specific requirement set.  A military technician must be cognizant of a much larger requirement set including wide ranging considerations based on how, where, when, how often, etc... the system will be employed.

Watashi
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Platinum
Re: Military intelligence?
Watashi   10/4/2013 5:02:11 PM
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I found it humorous, although dated.

As a former US Navy Fire Controlman (weapon system technician) I can attest to the fact that you get a variety of technical competencies in the service.  Generally, I noticed that guys who liked the work (like me) were left to work on the system(s) while the lesser technicians caught our collateral duties.

However, it was a double edged sword – the competent were recognized at the division level for being key personnel, but the less competent were more active with the rest of the ship and oftentimes got recognition from the higher levels.

It is similar in industry – the smart guys are in the lab doing great things and usually don't get any visibility, while others handle reporting up the line and reap the praise from on high.

James Patterson
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Silver
Re: Military intelligence?
James Patterson   10/4/2013 6:27:23 PM
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I have worked with a large number of military (and ex) people. Those with a sense of humor get ahead and get promoted. Those with out that, are usually not very successful.

If your boss accuses you of incompetence then you need to leave. His mind is made up and he is not supplying you with either the motivation or the resources to succeed in your current position.

Humor is good. Hubris is not. Glad you moved on to a sucessful career!

Battar
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Platinum
E and S
Battar   10/2/2013 10:17:56 AM
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I worked with Evans and Sutherland display systems in the 80's (that was a military installation, too), they also had hand wire-wrapped backplanes. We never had crosstalk problems but we did get the occasional fault due to poor or loose wiring. Our solution was to "comb" the wire-wrap pins with a credit card or something similar (at my pay level at the time, it had to be "something similar"). That worked most of the time.

William K.
User Rank
Platinum
BUT it was a sergeant
William K.   10/2/2013 6:07:16 PM
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The other point that I would make is that the boss was an ex-sergeant. Of course there are quite a few very competent sergeants in the service, but usually the good ones get promoted before they leave. And I can vouch that there are a few of the other kind. 

Being able to give orders and follow orders by the book does not make one a good engineer.

wbswenberg
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Gold
Head Strong
wbswenberg   10/5/2013 11:39:15 AM
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When at the E company I worked on a Digital Interface Unit.  It bridged the gap from old micros in test equipment to fast in production equipment.  It had mutiple ports, direct and multiplxed addressing and data buses.  The problem was mostly that the power supply had lost some EMI protection and certain chip were sensitive to it - both conductive and radiated.  I could not get a replacement that should have been a linear and not a switcher.  Luckily there was software trouble shooting using mild coruption of verification code.  I would run walking 1s and 0s and other patterns.  Using a logic analyzer I would check the input and output of chips.  The big labor was pinning out the clamp-ons cause every chip is different.  Some of the fixes were added caps.  No decoupleing caps at all in the design.  In another case I used copper tape.  It would work with the lid off but not on.  Radiated EMI from the power supply.  I talked to the guy that ended up as a super Tech.  I did not relaize he was the designer and builder. And he was very good rose to the max and rightfully so.  But he was unhappy with my fixes and pulled them out.  So I got to redo them.  After I guess the fixes were left as we needed the equipment.  

oldtimer8080
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Gold
Sometime the REMFs ARE the problem!
oldtimer8080   10/5/2013 5:12:52 PM
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Seriously, some military officials think they can change a physical law by ordering it. Many become cops and try to do the same thing which becomes an epic FAIL, especially when it gets caught on video and broadcast on YouTube..

But I digress

My first ATE job was manually fixing and calibrating the  Pin Electronics cards in the ATE built by different mfgs for AMD. Remember MIL-SPEC 883 required traceability to NIST and that was why MIL-SPEC parts cost 10x more than the civilian product.

Everyone hated to repair those damn cards. The good techs ( like me ) got the regular Test floor running properly and were " rewarded " with fixing and testing spare PE and power cards in that extra time we had.

This problem followed me all over my jobs in Silicon Valley and I rose to the top of my field and was a Senior Calibration Technician. The Test Engineer Degree was not available and that became the sole reason I wasn't made an Engineer by the HR people in Silicon Valley.

When Cray Research hired me to create a way to test ICs from their brand new $5M wafer fab, I created a test system out of an older Genrad PCB tester they had. The next step was to build a Parametric Analyzer out of some Keithley equipment they had at Cray.

Now, Keithley has a whole division dedicated to test; we never patented the concept because we needed a test solution for our fab area.

I finally made Test Engineer at Cray.

I also was able to solve the unwanted job of calibrating PE cards by having my fellow test engineer develop software that calibrated the ATE we finally bought design the progrm that just needed a " gold " device inserted into the socket on the test head.

Then I went on to better things at Cray, like " inventing the Internet "...

 

 

 

 

 

 

 

 

 

 

AnandY
User Rank
Gold
RE: Do it anyway
AnandY   10/8/2013 8:06:57 AM
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It's devastating how graduates venturing into their job professions are viewed as juniors and are often looked down upon. Yah, experience is important but whether the equipment you are using is in shape or not, your failure is always viewed as incompetence by your seniors. It's high time we gave the fresh blood in the professions a chance to mature by listening to them and nurturing them.

bobjengr
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Platinum
DON'T BELIEVE IT
bobjengr   10/10/2013 5:39:47 PM
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I had a very similar situation some years ago working for one of the "majors" in the appliance industry.  I was new to the company and an ME.  (Those two facts are important.)  Wiring harnesses were designed to carry low voltage control circuits and high voltage; i.e. 240 volt A.C. supplying the bake and broil elements in the oven cavity.  We had huge issues with interference confounding the ERC (electric range controller).  This was in the days when bit generators were used and long long before capacitive touch equipment became available.   I mentioned to my supervisor the fact that low and high voltage conductors should not be in the same wire bundle.  He blew me off indicating that I had attended a public university while he had attended MIT.  My concern was "noted" but not taken seriously.  I was really POed but carried on like a good soldier.  I found out later he called one of his EE professors at MIT and received the same advice as I had given.  He never came back and apologized for being somewhat condescending. NEVER.  Believe it or not, that actually allowed me to score one small point with the guy. 

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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.
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