Fueling our Schadenfreude is probably not good for our karma (so is mixing metaphors in two languages), but the Designed By Monkeys column would get a big readership boost if a representative from the company in the crosshairs tried to explain design intent. Watching the representative squirm after being subjected to the monkeys would certainly give enjoyment to so many readers.
They don't need to admit liability, but boy, it would be nice to have an answer to "What were they thinking?"
Undersized transistors in this instance are pretty obvious - cost savings by not having fewer unique parts leads to the result in this MbM. However, the lightbulb protected by security torx fasteners should be answerable.
There's no liability in discussing that design choice; the readers in general, and engineers / designers might learn something interesting in the design choices available.
It might be a new quarterly column (figuring that large companies have more inertia and will take time to come up with something). you could call it:
The Monkeys Strike Back
Joking aside, there might be valid reasons for the design choices made; we would all benefit to have a few explained.
I like this idea, TJ. I am always thinking when I read these stories that I can't imagine how the companies and product designers would let something slip through quality assurance like they seem to, so to have them weigh in on what went wrong and how this could have happened is a great idea. I also like the title! Clever. :)
I once worked at a major consumer product company which I will not name because Texas Instruments would get mad.
My project manager insisted on using one RC network to clock TWO micros that had RC-based oscillators using Schmidt trigger inverters. (TMS1000 era..early 1980's).
I explained to him that one of them would have a lower threshold than the other, and thus, only one would clock. Therefore, TWO RC networks were needed. I changed the BOM. Later, I found he changed it back. This made for a funny argument.
To presume that there is a rational decision making process in place for ANY thing is risky. I have made a career out of uncovering the 'why' of problems like this and later, when I ran a contract manufacturing company, my 35 customers and 400 products gave me scores of chances to see how stuff gets into products. I've even done it myself. No one is immune from mistakes. I've found them in dental chair electronics, hospital bed electronics, dog collar electronics, hydraulic presses, missles, test equipment, cryogenic freezer controls, ad infinitum.
This one looks par for the course. Some designs are perfect for some installations. None are perfect for all. This guy found a 'breed weakness' and a questionable feature.
Fauxscot, I agree the breed weakness would never be willingly discussed, but the choice of fastener should be.
It may not even be a questionable feature - we may learn that the product is assembled soley with the one type (and size) of fastener, and that changing the fastener holding the light bulb cover to a different type would greatly increase the fastener assembly time, stocking, etc.
Maybe the designer did evauluate that security torx drivers are not all THAT difficult to acquire. The combination of cost and consumer tool availability makes the design choice not quite so simianly sinister.
These are all my suppositions though, and we won't know unless some manufacturer steps up and tells us. In the right forum (such as right here with Design News), civil questions may be asked and some new understanding gained.
Of course, we could be not so civil, begin throwing the metaphorical poo, and then WE'D look like the monkeys.
Yup. Just as likely was that since there were 50 other torx fasteners, mixing in one that was standard torx added cascading complexity.
that's a very legit tradeoff.
i've found in long experience that few decisions are perfect. some are clever, others efficient, but engineering is almost all about tradeoffs when it comes to building more than one thing. even when building one-off units (like test equipment) the over-riding tradeoff is the impact on NRE.
not flinging poo here, just ruminating in general on a topic of personal interest.
Fauxscot, I did not mean to imply in ANY way that you were flinging.
My goal of the statement was that IF DN could convince a company to willingly sit in the hot seat to explain design intent with civil questions, we should be civil with our questions. Otherwise we ourselves will look like monkeys in the zoo (...flinging).
There was NOTHING wrong with your post and I apologize for even coming close to inferring that.
TJ! While I really appreciate your tongue-in-cheek contribution mostly because it mimics my sarcastic attitudes towards much of current daily life, but I would offer something of more substance as a reason why the TORX screws are used. I can sum it all up in two words: LITIGATION & GREED.
The LITIGATION aspect is from the corporate "bottom-feeders." The lawyers deciced that in order to avoid any possible litigation, they'd insist on security hardware to preclude JOE, Saturday morning mechanic, from repairing his own unit.
The GREED aspect results in the corporate decision to attempt to garner as much of the after-sale service as possible, hoping that people will either return the unit to an "Authorized" service center, or will replace the unit.
I often wonder how many subdivisions in the U.S. could be completely outfitted w/ perfectly working appliances, etal, IF ONLY a defective 10-cent part was replaced? I'd be willing ot bet we'd all be astounded to read the results!!!!
AND, it's precisely because of the "bottom feeders" that you'll NEVER read a response from any current technology person in ANY corporation, either excusing or rationalizing a deficient design. I'm sure that there's literally tons of designers reading these same pages as we are, who are currently employed by these suppliers, and IF they COULD, they WOULD, but they appreciate that paycheck far more than the satisfaction of "ratting out" a dumb design.
@OLD_CURMUDGEON, We also ask if the company logo on the device is counterfeit. I would like to ask Andy Morris to see if a cordless phone works while he stands next to the micorwave oven. They both work on the same 2.4 GHz frequency. If the phone has problems, get away from that oven and trash it.
Yes. The cordless phone whacks out big time when it is close to the working microwave. Even if I'm about 15 ft away, it breaks up and the display goes out. If I recall correctly, the microwave runs at 2.45GHz. According to my owner's manual, the cordless phone ranges in frequency from 2401.056 - 2481.408 MHz.
There is really nothing I can do about it. I'm not going to trash my cordless phone. I just don't use it while the microwave is on. My Wi-Fi enabled Squeezebox internet radio and my RF link between my laptop and my audio system also break up when the microwave is on. All microwaves run at the same frequency, so there is nothing I can do about it. All of these devices have an FCC message printed on them or in the user manual that they must tolerate interference from other devices, and suggests that I relocate it to minimize the interference.
Back in the old days when microwaves used RF gaskets to contain the RF, Radio Shack sold microwave leakage meters. I still have one. I tested my microwave with it a while back. Only at one corner of the door would the needle even move a tiny bit off of the zero pin.
Since the mid 70's (I think) microwaves have used a clever RF choke in the door to contain the energy. Unless the door is damaged, it will not leak. However, you can't completely contain all of the energy and modern RF electronics is extremely sensitive. IMO, it's impossible to stop the interference and I believe that the leakage from the microwave is well below the unsafe level.
We do not use TORX screws as some security feature or fear of litigation. We use them for two reasons: the production line folks can use electric (or air) drivers without stripping and TORX are the only screws that you can get consistant torque.
Every screw inserted into one of our products has a specified torque and all of the drivers are calibrated. Using a driver on Slotted, Philips and POZI screws takes more skill and has way more incidences of damaged screw heads or improperly torqued screws and greatly reduces product robustness.
Another aspect in a large corporation is materials management. If every assembly product has unique screw types and sizes the manufacturing and repair sites would have an infinite variety. It sometimes seems like a no-brainer to add a ten cent screw but when you add in the 10-20 minutes it took some repair tech to search stores for the right screw, at a 2-5 times overhead rate, your warranty cost is, or some customer pays, $60.
BTW, the Torx screws in my microwave are the "security" Torx screws with the center pin in them to prevent a normal Torx screwdriver from working. Still, the security Torx screwdriver bits are commonly available online and at your nearest Harbor Freight store.
But, "Cheers" above claims they don't use the TORX screws for "security" reasons. So, my question then becomes, "why use the security version of the TORX screw instead of the garden variety of the TORX screw, IF NOT for "security" and limited access.
As far as minimizing the inventorying of all sorts of "extra" hardware items, I can speak first hand to that. Many decades ago, when printed circuit boards were becoming more prevalent, and point-to-point wiring was waning, the chief engineer issued a mandate that the minimum wattage for resistors shall remain at the 1/2watt ALLEN BRADLEY composition styles, with higher wattage styles used where deemed appropriate. Even though most of the circuits in our products were low level, and the entire product line COULD HAVE BENEFITTED from smaller p.c. boards by using 1/4w resistors, his reasoning was simple..... we shipped our products all over the free world, and THE MOST COMMON wattage carbon composition resistor was the 1/2watt variety! Every technical repair facility, whether in Houston, TX, or in S. Africa would have a broad assortment of 1/2w carbon comp. resistors on hand!
Designing around parts availability makes perfect sense to me, but Chinese manufacturers nowadays do not want their appliances or gadgets repaired. They want to sell you new ones. I have talked to other engineers online and found out that Chinese manufactures will not manufacture products for you if they contain non-Chinese parts. If they manufacture them, they will redesign them to contain all Chinese-made parts. The Chinese do everything they can to force you to buy from them.
I don't know if my microwave was designed in China or Japan. Even a reputable company like Panasonic can make a mistake once in a while.
Since I'm a retired electrical engineer, now that I fixed the display, I could design and build a timer to keep the fan running for a minute or two after the cooking is complete. Then I'd have a perfect microwave. I have always liked Panasonic products when they were made in Japan.
The entire microwave (inverter, fan, light and turntable) is controlled by one SPST relay on the timer board. That will complicate building a fan timer a bit.
ar: Well I suspect that much of your argument is plausible, but I find it hard to believe that mega-billion $ SONY, PANASONIC, CANON, FORD, GM, VOLKSWAGEN, etal. would tolerate their products being re-engineered by some Chinese engineers. I'm sure that MOST of the products that are exported from China by non-Chinese companies are designed in their laboratories & engineering facilities around the "free" world. China has evolved into a manufacturing magnet because of the overabundance of inexpensive labor, lax environmental statutes, etc. The PLUS for China is that they get a massive infusion of world-wide cash to upgrade their entire infrastructure from military to mundane, AND they get immediate, unfettered access to a lot of technology quickly.
As far as repair is concened, I don't think ANY manufacturers, be they domestic OR foreign, want their products repaired! They want to sell, sell, sell!..... and the ONLY way to do that is to make the item irrepairable in the first place. Even though so many companies have joined the "environmentally righteous" bandwagon, they ignore the obvious...... filling our landfills with their junk!!!!! That's the dirty little "secret" of modern manufacturing. I am of an age where we recycled almost everything from old shirts used as polishing rags to soda & beer bottles, to just about every other item that one could think of which wasn't consumed somehow in the process of being used! We even burned the leaves at the curb in the Fall to eliminate the waist! That's BEFORE someone invented plastic bags for yard waste that the rubbish people pick up, OR the environmentalists decided that a bit of leaf smoke in the air was harmful for the ozone layer.......
I'm sure that what you said is quite correct for large companies, who place huge orders and can take their business elsewhere, but I was referring to products developed by other engineers I've talked to, where the orders are far smaller.
The redesign by the Chinese manufacturers is pretty common. It's pretty common here in the US. I just went through the same BS on my project. To test out this company I sent them solidworks models for two fairly simple plastic plates to make. I should have had the parts back within 24 hours. What I got back first was an email with a pdf drawing of the part and saying they would have it done by tomorrow. What they did was decide the holes threads and recess should be changed regardless of the fact they had zero idea what each were there for. So this drawing showed missing fluid passages, mount holes, holes that were re-sized or moved. I politely sent him my remarks basically telling him to "unfix" it. It's over a week later now and no sign of these. My experience with Chinese manufacturers is you can count on your product being exactly what you want right up to the point you drop off the drawings. Then they go work with cost reduction and resulting quality erosion. This is an on going thing and even if the first units are perfect within a year the quality will worse.
In aerospace we saw this all the damn time which is why we had to have QA almost 100%. In frustration we started putting MIL-TDP-41 as the mandatory manufacturing spec to follow. If someone asked us what that was at least we knew they were looking at the plans. That stood for "Make It Like The Damn Plans For Once". We stopped that when some of our shop drawings made it up to much higher federal types who reside at some cape in Florida. They actually thought it was great and had a good laugh. However our boss had shall we say a royal cow/meltdown and in no uncertain terms said not to do it again. And we never did (sort of, maybe ;-])
Actually, MIL-HDBK-217 (versions B through the current one) point out that using oversized carbon comp resistors degrades reliability. Carbon comp resistors need to run warm to cook off absorbed moisture. If they are oversized their resistance gradually drops as water is absorbed into the carbon, lowering resistance. Bad move on the chief engineer's part.
Larry M: What I related is a policy that was in place from the 1960s through when I left the company in the latter 1970s. So, while the case you made MAY be technically & scientifically correct, it didn't affect our products which were in widespread use from the North Pole atmosphere to the super-saturated S. American rain forests to the deserts of Africa. The product line consisted of mobile & stationary radio communications equipment, and was found wherever one went, from the NY Harbor to the shores of Tripoli to oil rigs in the North Atlantic to wherever humans inhabited the earth and wanted to communicate with each other. And, since many of these products were the assembly of vacuum tubes AND solid state devices, the heat dissipated by the tubes I'm sure served a very valuable secondary purpose....... demoisturizing the chassis.
The chief engineer was directly responsible for many circuit patents that either he and/or the company held, so I'm sure that IF moisture entrapment was a problem, he would have been very concerned with addressing the issue.
Here's another moisture/carbon comp story. Back in the mid '70s, I worked for the "batwing" company in South Florida. I was designing what became the first low-cost "consumer" UHF paging receiver; minimizing power consumption was absolutely critical as all we had room for were a pair of N cells. Thus, the logic (custom IC) was implemented in low-voltage CMOS (a new proprietary technology at the time). To keep power consumption down, we used a watch crystal for the clock, with an internal oscillator circuit. I used a 10 megohm carbon comp for the bias resistor across the crystal. Everything worked quite well, and went into production in very high volumes. After the first few runs, we began to have a significant drop in first-pass EOL test yield. After a lot of head-scratching, we found that the oscillator circuit sometimes wouldn't start. The root cause: unfortunately, the factory floor and the stockroom were not climate-controlled, and in South Florida, that meant the humidity was really high most of the time. It turned out that the carbon comps (especially the high-resistance ones) were absorbing moisture, and the "megohm-plus" ones were becoming either "kilohm-plus" (which just increased the current drain) or were exploding when that moisture was turned into steam duing the wave-soldering process! The ultimate fix was requiring all carbon comps to be stored in a climate-controlled area until they would be pulled for immediate insertion and soldering into the PCBs.
Your exploding components reminded me of an issue we had with our first surface mount lab. In the Summer we suddenly had a soldering problem in the lab and it turned out that moisture inside the circuit boards was rapidly boiling out of the boards during soldering and blowing the little surface mount parts right off the boards. It looked like someone was blowing compressed air across the boards.
TJ, that is a terrific idea. Occasionally a manufacturer will find the posting and begin a conversation with commenters. Sometimes, the person posting the Monkey blog will alert the manufacturer that discussions are proceeding. Sometimes the manufacturer jumps into the discussion, sometimes not.
When someone uses the term "Inverter" when refering to a microwave (μwave) oven they are usually refering to the power conversion circuitry. Originally, most μwave ovens used a simple transformer/bridge rectifier followed by a storage capacitor (Capacitor Input Power Supply). This results in a terible power line current distortion from a sine wave! These power supplies can supply at most about 0.6 of the available power from the AC line to the Magnetron (120V*15A*0.6η = 1080 W input power), due to the large peak currents generated during charging the storage capacitor, only when the input Voltage excedes the capacitors Voltage. Additionally, you have the loses associated with the transformer et cetera.
Newer μwave ovens now use a Power Factor Corrected (PFC) Switched Mode Converter. This consists of the standard bridge rectifier followed by a Boost or "Flyback" Switched Mode converter controlled by the rectifed input Voltage. The resulting current wave from is much closer to the Voltage sine wave, and thus most of the power con be presented to the Magnetron.In a microwave oven, for instance, a 1.1 kilowatt input will generally create about 700 watts of microwave power, an efficiency of around 65%. (http://en.wikipedia.org/wiki/Cavity_magnetron)
To get more power to the magnetron you need to use a PFC converter "Inverter" power supply therefore (120V*15A*0.9η = 1620 W input power) with the magnatron efficency of 65% ≈ 1050 watts in to the oven cavity!
"To get more power to the magnetron you need to use a PFC converter "Inverter" power supply therefore (120V*15A*0.9η = 1620 W input power) with the magnatron efficency of 65% ≈ 1050 watts in to the oven cavity!"
PFC, thanks for the clarification and I think your valuable info may be useful for our community members. Thanks for sharing your knowledge.
The viewing angle of the display is controlled by the polarizing material in front of it, and I prefer the better visibility straight on to lower visibility at some angle. Of course, my Panasonic inverter oven is mounted so that the display is at almost eye level, whyich makes some difference.
If the light were to come on whenever the door were opened it would take more switching, and a bit of logic, since it is also on while cooking. My guess is that at least some of those applications use the light for a snubbing resistance while the magnitron is active, which would make having it on when not cooking even more complex.
As for the lamp being hard to replace, my guess is that the intention is that the unit would be replaced by the time the lamp failed. That is quite common in small appliances currently. Besides that, Panasonic brand electronics has never been easy to work on or service. That goes all the way back to their early cassette recorder days. Those units did not seem to be built with the concept that they would ever be opened again. Som traditions are difficult to change.
See also my posting about the door latch problems on this same product line.
My microwave oven also had a very narrow viewing amgle before I replaced the LEDs. The new generic LEDs are much brighter than the original ones, even though I didn't change the electrical design beyond replacing the transistor in the LED current regulator circuit with a more robust one. The display is so bright now that I can easily read it from almost any angle. From a really wide angle, the display appears to be just a yellow light. BTW, if this microwave didn't belong to somebody handy with electronics, it would probably be in a landfill right now. I wonder how many of this model are in landfills right now as a result of this defect.
I would also prefer the light to be on when I open the door, if I didn't have to leave the door open for an hour to air out after using it. As it is, I'm glad that the light does not stay on when the door is opened.
Other than the LED and the odor issue, it's been a good microwave. I've had it for about 9 years. It was manufactured in China in August of 2003.
The Inverter was a replacement for a Little Litton microwave that I bought in 82 (yes, 31 years ago). It started haveing door interlock problems and was getting to be a real pain. I payed $120 ('82 dollars). The Inverter cost $80 a couple years ago. The irony is that after I put the Litton aside, I must have bounced the junk out of the interlock switch and, naturally, it started working again. It now gets used to warm up the coffee or as a second cooking timer. 31 years, how long with the Inverter last?
The lightbulb one is simple maths. Total product lifetime = 10 years. Total daily usage < 20 min (if it's more than that, you should see a dietician and you should be eating more real food, not warmed up leftovers and TV dinners). Total lightbulb usage over product lifetime = 1000 hours . Lightbulb manufacturers data says lifetime = 2000 hours. So design engineer reckons that the lightbulb should never need replacing. (Thermal cycling is another parameter to consider, though).
Your 20 minutes figure may be good for a single user, but is totally worthless when all my kids were still home or even worse when it is the microwave in the breakroom at work.
I think the idea of lawsuits is much more realistic. Or more likely still, is a company, Panasonic, riding on their reputation and knowing many people will buy brand only, so they can be slipshod and let occasional garbage through.
The LCD visibility is probably a matter of economy. You can obtain a wider viewing angle with less multiplexing, or better yet, a static display, but more pins for less multiplexing means more money. I've worked for a bunch of appliance manufacturers, even the huge stainless steel companies, and rarely is a decision made that favors performance over cost. The conversation with Marketing and Engineering would sound something like a Dilbert script.
Marketing: I can't see the display unless I'm looking right at it, my new smart TV doesn't do that.
Engineering: We can widen the viewing angle with a different display and a micro with more pins.
Marketing: You need pins to fix it? Great, go get some more pins.
Engineering: The new display and larger micro will cost an extra fifty cents on the Bill Of Materials.
Marketing: Fifty cents for more pins? Forget it, nobody will pay that much just to see the clock.
I also have a Panasonic Inverter microwave that is perhaps +8 years old and I like it. Have never had a problem with it. The LEDs issue described does sound like a monkey problem. But the fan doesn't:
The good microwave ovens blow air into the oven. It helps keep the humidity, created by heating/cooking items, from forming too much condensation inside the oven. The condensation can really make a mess of things, just look at the small cheap microwaves. To save money and power, one fan is used to cool the magnetron and blow air into the oven. The problem is that the fan stops when the oven stops. This leaves any condensation still in the oven,... in the oven. Perhaps the fan should run for another minute or two. So I also leave the oven door ajar after using it, to allow the interior to dry out. I also do this for the microwave at work which is not a Panasonic Inverter.
The inverter makes the microwave oven really nice. Rather than duty cycling on/off full power, the inverter continously controls the current through the magnetron(essentially, a diode vacuum tube). Changing the current changes the energy of the microwaves produced not the frequency. I have learned to tweak the microwave instructions on products. If it says high for 3-4 minuets, then I cook it at a lower power for a little bit longer.
After having this inverter oven, will always get an inverter microwave oven until something else better comes along.
I retired from the appliance industry after 20 years. One thing that really bugged me was our design teams constantly repeating mistakes made years before. There existed a requirement stating that before an individual could move into a new position, he or she had to serve in the current position for at least 18 months. This may sound like a long time but in the design world, you are still considered a "new-be" after 5 years. With the exception of a fairly small team of designers, there was constant turnover. I know this contributed to the dumb mistakes made on a fairly continuous basis.
"There existed a requirement stating that before an individual could move into a new position, he or she had to serve in the current position for at least 18 months. This may sound like a long time but in the design world, you are still considered a "new-be" after 5 years. "
Bobengr, you are right. Every day new technologies and design methodologies are developing, so one should have to be updated it frequently. That's the one reason an engineer seems to be "new be" throughout his career.
Is it possible that the author has overlooked another way to access the lamp? Perhaps the cover snaps off from inside the oven, but takes more force than he has applied?
We had another Made For Monkeys article about two years ago where that author complained about how difficult it was to clean the filter in his washing machine and boasted about how he had cut a hole in the side of the cover to facilitate its reinstallation.
Another posted pointed out that had he removed the access panel plainly visible at the base of the front panel he would have had easy access to the filter.
No, I'm sure that removing the outer jacket is the only way to replace the bulb. Besides being a retired electrical engineer, I repaired TVs and later, VCRs for most of my adult life, in addition to my day job, until they got too cheap to repair. I know what I'm talking about.
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