John, I will bet you that the time you spent diagnosing the problem was longer than the time you spent fixing it. This is the problem with many automotive systems. With the advent of very inexpensive microcontrollers, this should be the next wave of automotive improvements.
Isn't that always the case-? Diagnostics taking longer than the corrective action-? Makes me think of a recent issue I had on the product I was designing. I had hand-assembled the very first (10) working prototypes, but every time I tightened down the outer housing screws, the display blanked-out. I spent literally 2 solid weeks of assembly evaluations and diagnostic trouble shooting before I narrowed the cause to the lack of insulated solder-resist on the PCB top layer. Tightening the housing screws simply squeezed the metal modem casing onto exposed circuitry which should have been insulated during the PCB fabrication process. Corrective action was a 1c piece of Kapton tape under the module. Two week investigation; 10 second fix. Of course that is a natural part of development and this type of issue must be completely resolved months before production. I hate to see silly issues like this affect the consumer end-user.
Speaking for the people that two years from now that have to figure out why your product suddenly stopped working, you should never rely on soldermask for insulation (been there done that). Or are you giving someone else an opportunity for a future 'Sherlock Ohms' submission.
The specific occurrence was a small array of plated thru via's (to the main LCD flex ZIF) anchored through the board with annular rings. The annular rings were <.015" O.D. but completely exposed. Meanwhile, the transceiver module had a die cast zinc outer casing and laid directly over those via's, flush to the PCB surface.
There are nearby areas of other printed circuit traces also under the zinc casing, but they are under the layer of solder resist. (I don't get why those traces were covered but the ZIF vias were not; oversight by the PCB designer, I guess) But that's a moot point if your concern is true (which I do believe you).
Solder resist/mask is not a mechanically robust component and is not designed to provide any mechanical isolation. As its name implies, it's designed to prevent solder from going places you don't want (e.g. wicking from pads).
If you cannot confine your enclosure's contact with the PWB to purpose designed areas of the board (e.g. a mounting pad), you need a mechanical component like an insulated washer or a coverlayer of kapton or equivalent.
On a tangent, for higher reliability, you should avoid via's (or plated holes) under mounting pressure anyways since the thru hole barrels tend to crack under the compression.
Mounting a PCB directly against a metal housing, with only solder mask as insulaiton is a bad, bad idea from a reliability perspective. All it takes is a pinhole or crack in the solder mask, and a little corrosion (or a little whisker/dendrite), and a short will develop. Thermal expansion/contraction could also eventually scuff through the solder mask. Space the board off the housing or use robust insulation.
More than one person has tried to mount a computer motherboard directly into a computer case with no standoffs. Guess what happens!
That's reasonable and sound advice; but I think you are picturing something entirely different than the actual application I was troubleshooting. It wasn't mounting a motherboard on a chassis (i.e. like a computer tower or cabinet card rack); the situation was a mini transceiver with a diecast under casing, designed by the OEM for direct PCB mounting. The host PCB is intended to be handheld portable size, about 3 inches in length typically. So you might imagine why the detecting the failure mode was so elusive; because the design was in complete conformance with the developer's kit recommendations. (which now, is quite clear, illustrates its a potential failure mode waiting to happen).
Putting the bad switch back IN was a waste of time except as confirmation that it was mechanically bad. The failure was in a very small bounding box containing only the switch and its connector and the vehicle's harness side. Going to the dealer for a $20 replacement was also suboptimal since almost every vehicle has $8 aftermarket replacements available at any parts store.
I'm a volunteer tech specialist on a Chevy Trailblazer / GMC Envoy forum, and we get these sorts of questions monthly. Brake lights and ignition switches are well-known high failure rate items.
But I have to comment on the microcontrollers changing automotive manufacturer's design goals any time soon. The capability is there for plug and play peripherals on everything except vehicles. Install a new intelligent driver's door switch module (that dies over time because the switches are horizontal where rain and snow falls right on them with every time you open the door), or a 4WD transfer case control module, and you THEN must go the dealer, who has the "magic" Tech II tool, to download the personality firmware into the module. Minimum charge for this 5 minute process? $75-200!
GM and the like will NEVER do something to decrease the revenue stream for their dealer network for outyear support by assisting the DIY repair owners. I get more and more bitter when I see design decision made that thwart DIYers in order to drive the owners back into the clutches of often-abusive dealers. I know it's not the designer's fault - they are under management orders. But it's an economically-driven cycle, not technical, and therefore not open to the usual rational discussion we would have about other products and systems.
Just LOOK at the insane number of Delco/Delphi connectors and ESPECIALLY the little safety catch/latch mechanisms that thwart mechanics and diagnosticians at every turn. Irrational.
Inexpensive micro controllers will not ever, at any time, under any condition, improve automobile anything! BUT they will certainly increse the profits gained from replacing the failed parts, since the code will be unavailable to anybody except the auto companies repair parts makers. While emissions and economy have been improved through electronic controls, all of the other car functions have been rendered less reliable and nonrepairable by the use of them.
Recall that a few years back it was predicted that automotive electrical systems would go to a seriel buss and just a pair of power wires, in order to reduce the weight and cost of all those wires. BUT what we have now is a few central modules and huge bundles of wires. We also have a few accessory modules for those extra-priced expensive options, which only become more expensive each year.
An unfortunate number of things that sort of sound like good ideas are actually some vendors idea in search of acceptance, instead of something that actual customers would have any desire to implement.
William K: I have to disagree with you there. For one thing, there are at least 50 microcontrollers in a car today. It is often much simpler to put in another microcontroller than trying to integrate software within a central processing unit. Since many of the components come from other manufacurers, or even other divisions of a car company, this makes sense. As for cost, even simple electromechanical are very expensive. My wife and I recently replaced the automatic door lock actuators in a minivan. I think they were between $50 and $100 apiece. And we installed them outselves. I was a fun project. On the other hand, these were simple relays. There are many reasons for the high cost of automotive parts, but not having access to the code is not one of them.
It is almost always "easier" to stick in a micro controller and put in some code than to do any actual engineering. No question about that. BUT the unintended consequences of code that it is unable to handle exceptions, or does not handle the way some users think, and is generally not exactly the best choice. That is the fundamental flw that I see in using software to implement many functions. Primarily code is only written to handle what the programmer believes will happen, which is usually a very small subset of the real world.
Here's a counter to your proposal for using inexpensive microcontrollers....
We were driving our 2000 Pontiac Montana minivan one day when somebody started flashing their lights at us from behind. We asked what was the matter and they said our brake lights were out. That was strange...in 40 years of working on cars, I had never had BOTH lights go out at the same time. Funny thing is that the high-mounted center brake light still worked.
I replaced the bulb on the right side and...NOTHING!!! Same on the left. We called the dealer and they laughed saying, "Oh that must be the controller board." Funny thing that, for over 50 years, a switch was good enough for controlling brake lights, but NOW you need a controller.
Back in the 1990's (I think) Chrysler wired their stereo's into the vehicle's CAN bus. Problem with that was that when the radio failed, the whole vehicle shut down and needed a tow back to the dealer. Seemed like a good idea at the time.
Not only is it harder for DIY auto repair because of the proprietary nature of the components, but because these components interact in complicated ways.
Only legislation requiring manufactures to publish technical spec's on their components (and their component's intended/expected behavior) will improve the situation for the consumer. Thankfully we have the internet and youtube.
As a closet libertarian it pains me to say, but yes Virginia, we need more legislation to protect the consumer. Car companies do the things they do to maximize profits for their shareholders and stakeholders (dealerships). Then they worry about the labor unions. Customers come last. In a cut-throat environment like the auto industry, there are NO new cars that I know of that are easily/cheaply servicable any more. Certainly such creatures (even if they did exist) wouldn't inspire a blog post here (an example of what you won't read here: "I changed my spark plugs last week, I could reach them all w/o lifting the engine or contorting my body, and it took 15 minutes", yawn.) I would interested to hear any examples of cars that are easy/cheap to service.
But, as an example of "good" legislation: look at the OBD ports in ALL modern cars. Such a thing would NEVER have existed without that legislation. In any case, legislation evens the playing field and allows/forces car companies to do the right thing without going bankrupt.
3drob--publishing the technical specs and code for components will be a sure advantage to consumers. I don't think the average Joe will need them, while us DIYers will become more adaptable at working on these formerly "unfixable" problems.
Publishing the explanations for those fault codes could be quite useful. I sold a car with the caveat "No guarrantee that it will get you home" because it would periodically die, often while running at 25 or 35MPH. No cough or sputter, just all at once no engine power. The new owner, a friend who purchased it understanding that it had a problem, eventually found that the "processor reset" code message was brought about by a very intermittent short circuit to ground of the power supply feed terminal, inside one of the fuel injectors. But how was that cryptic statement going to be traced to a short circuit leading to the reset?
On a tangent; I once was asked to help when a car would not shift out of Park when the brake pedal was pressed. And also, the brake lights were not lighting when the brake pedal was pressed. It turned out to be a loose wire at the switch. The brake lights turned out to be a troubleshooting test.
I had a minivan that I put many miles on doing field service work. Got to where the cruise control would not stay engaged one 11 hour trip. When I got back home (another 11 hours without the cruise control) I started poking around. Wiggled the brake switch and things behaved for about 2 weeks. Then I had a problem with intermitent brake lights. Finally replaced the switch. Turns out it was a few years of accumulation of crud and minor arcing that finally led to switch failure.
I was a comfirmed DIY for years. Points & plugs every 12,000 miles. Oil every 3 and filter every other change. Air filter at 12,000 when the plugs got changed, etc. We do not have to do that junk nearly as often any more. So the brake light switch went bad, big deal. Both mechanical and elecrical parts fail on occasion, and need replacing.
Autos are so much more dependable than years past that when something does go wrong it is worthy of a magazine article. It wasn't that terribly long ago that a vehicle with 75,000 miles on it was almost always ready for the salvage yard. I have fond memories of my first decent car, 1962 Buick with a 401 cubic inch engine,and AFB carb. I would love to have it back. But, I would not want it as my primary mode of transportation, because I am no longer willing to spend every other weekend working on a car. Or at least that is what it seemed like.
I agree. What's the big deal? Finding and replacing a bad brake-light switch doesn't require too much diagnostic effort.
On the other hand, it did get us all started writing these silly messages that we enjoy so much! Thanks, John.
One thing that puzzles me is why a Volvo engineer would write about replacing a bad switch. Certainly there must be something more interesting in his work that would be more interesting to readers as well, but maybe Volvo won't let him publish.
Critic: You are correct and seldom do all the comments pertain directly to the original post. I learn things from some of the splinters and that makes these forums enjoyable. I guess my gripe was that when something fails it is not always a mistake. Sometimes things just wear out from repeated use and few of us would be willing to pay the price of a vehicle in which everything is built to last through eternity, even if that was possible.
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