Dumbest failure modes you've seen - Page 1
Forum section: electronics / general

author: AndyC_772
author_rank: Super Contributor
timestamp: July 24, 2013, 08:27:41 am
content: Here in the UK we're enjoying some unusually warm weather right now, and a couple of days ago my TV fell apart.The particular TV in question has a glass front panel, complete with LEDs and capacitive touch 'buttons', stuck over the front of the LCD using some double sided sticky foam tape. The glue on the tape had softened in the heat, allowing the glass panel to fall to the floor, and ripping the connector and several PCB traces off the LED board.Amazingly, the glass itself survived, but repairing the PCB was a fiddly job. If I weren't able to do surface mount rework myself, the TV would have been uneconomic to repair... scrap for the sake of a few pence worth of sticky foam tape.Has anyone come across a dumber, more unneccesary failure mode in an electronic product?

author: Alana
author_rank: Frequent Contributor
timestamp: July 24, 2013, 08:43:17 am
content: All i can think of is dumb users who trash perfectly good laptop PSU because power cord has broken conductor near the plug and buying crappy Chinese replacements for like 25e or more.

author: tom66
author_rank: Super Contributor
timestamp: July 24, 2013, 09:14:49 am
content: Quote from: AndyC_772 on July 24, 2013, 08:27:41 amSamsung LExxAxxx series? The one I got faulty (and fixed) is doing the same. Cheap plastic, cheap glue, but that's Samsung for you... I need to secure it at some point but it's already started sagging. Very common issue on these TVs.

author: Psi
author_rank: Super Contributor
timestamp: July 24, 2013, 10:00:32 am
content: So what you're saying is that the 'front fell off' ?That's happened before...

author: amyk
author_rank: Super Contributor
timestamp: July 24, 2013, 10:56:07 am
content: Quote from: Psi on July 24, 2013, 10:00:32 amI've never liked the "let's rid all the screws and glue/snap everything together" style.

author: Rerouter
author_rank: Super Contributor
timestamp: July 24, 2013, 10:58:31 am
content: On an asus monitor they have a line of buttons down the bottom, i was lucky enough to find out if the button is not installed correctly in the factory it will break loose and float inside the monitor upon the first press,as far as on the more technical side of things, usb hub being killed by static due to no protection to the asic,

author: Skimask
author_rank: Super Contributor
timestamp: July 24, 2013, 12:03:34 pm
content: Sitting at the desk of my old shop, firing off a few emails... (my old shop = a shop where we fixed "stuff", didn't matter what it was, we'd try to fix it, electronic or mechanical or whatever)Guy comes in carrying a high end stereo receiver, lots of dials and a big display on the front, lots of connections on the rear panel.Guy starts rambling on and on about how expensive this receiver was, how high end it is, talking himself up at how much money he can throw at audio/visual equipment and impress everybody...Guy continues to ramble on and on about how this unit worked just fine at his last place before he had it shipped and that when he plugged it in, it wouldn't power up, wouldn't show anything on the front panel, nothing.Guy's old place of employment was in the U.K.Guy's new place of employment is in the U.S.A.I reach up to the back panel after this Guy gives me about 5 seconds to talk, flip the switch from one side to the other, tell him it's fixed, go back to emailing.Guy stands there with stupid look on face, doesn't say anything else as he picks up his expensive receiver and walks out the door.What a dipshit...

author: AndyC_772
author_rank: Super Contributor
timestamp: July 24, 2013, 12:08:52 pm
content: What a terrible shame it wasn't the other way around...

author: ptricks
author_rank: Frequent Contributor
timestamp: July 24, 2013, 12:20:11 pm
content: Quote from: Skimask on July 24, 2013, 12:03:34 pmYou missed an opportunity to sell him some of your audiophile speaker wire !

author: _Sin
author_rank: Regular Contributor
timestamp: July 24, 2013, 12:34:40 pm
content: I had a wireless mouse a few years ago, came with a little USB dongle to communicate with the PC.The dongle PCB was neatly designed with a perfectly straight row of small vias running right across the board, just between the USB connector and the plastic case. In other words, they'd perforated the board at the perfect point to snap off if the slightest pressure was applied.

author: c4757p
author_rank: Super Contributor
timestamp: July 24, 2013, 12:43:34 pm
content: That may be intentional. Better to break off the dongle than the entire USB port. I cannot even guess how many ports of various types I have repaired for my sister because she insists on leaving her laptop with shit plugged in...

author: Psi
author_rank: Super Contributor
timestamp: July 24, 2013, 02:02:53 pm
content: We bought one of those electric mulchers (im not sure if they're called that in other countries).Its one of those things you push tree branches into a slot at the top and you get wood chips out the bottom.Anyway, it came with a plastic rod with a handle on one end for using to push branches into the machine in case they got stuck halfway.The first time we used it the machine chewed off the end. It was about 3cm too long!

author: Skimask
author_rank: Super Contributor
timestamp: July 24, 2013, 04:50:02 pm
content: Quote from: AndyC_772 on July 24, 2013, 12:08:52 pmI forgot to mention that "Guy" was a Yank, not a Brit.I would expect a Brit to know better.

author: Phaedrus
author_rank: Frequent Contributor
timestamp: July 24, 2013, 04:58:02 pm
content: ATX power supplies have an odd design fault; the 8-pin EPS12V connector for the CPU and the 8-pin PCIe connector for graphics cards are both 2x4 pin minifit jr. connectors. They both carry +12V. But they have slightly different pinouts, so they're keyed to prevent you from mixing them up.Except if you rotate the connector 180 degrees and force it, the PCIe connector will fit in the EPS12V socket, and you get 3 +12V pins shorted directly to ground. Turn on the computer, and...I can't tell you how many RMAs this nonsense has caused.

author: c4757p
author_rank: Super Contributor
timestamp: July 24, 2013, 05:05:58 pm
content: RMA? I'm not a PC person and I've certainly never shorted out an ATX PSU, but don't they have some sort of short-circuit protection so they don't damage themselves? Three pins straight to a solid ground ought to give a low enough impedance for some sort of foldback current limit to detect a dead short...

author: smashedProton
author_rank: Frequent Contributor
timestamp: July 24, 2013, 05:19:13 pm
content: If you have to force a connector you are not qualified to be working on it...

author: c4757p
author_rank: Super Contributor
timestamp: July 24, 2013, 05:21:13 pm
content: I've seen people try to cut off connector keys to fit them in...

author: Phaedrus
author_rank: Frequent Contributor
timestamp: July 24, 2013, 05:29:48 pm
content: The ground through the motherboard is generally high-enough impedance that the short circuit protection (normally implemented on the primary side in ATX PSUs) doesn't catch it, or at least not quickly enough to prevent motherboard damage. Most PSUs have over current protection on the secondary, which also doubles as short circuit protection. However when you have a really high-wattage PSU with a single +12V rail that's spec'd to deliver 60, 80, even 120A... The OCP trip point is usually set at least 10A higher than that. So if you've got an impedance of 0.2R (which is reasonable for this scenario due to cable resistance, connector resistance, and the motherboard's own impedance), that PSU is going to deliver 60As through that connector and the OCP will do nothing, and the primary will take several milliseconds to detect the partial short. In the end your motherboard looks like you ran it through the toaster.I prefer multi-rail PSUs, which (usually) really only have a single +12V output, but divide the output cables between different OCP circuits, so that instead of having one 100A circuit, you have three 40A circuits. This prevents motherboard damage in most cases when a PSU is plugged in incorrectly, or when a MOSFET on the motherboard or graphics card VRMs fails shorted. Unfortunately "multiple rail" is horrible marketing since most people like the sound of the "single massive, powerful, throbbing +12V rail".

author: smashedProton
author_rank: Frequent Contributor
timestamp: July 24, 2013, 05:38:32 pm
content: Quote from: EEVblog on July 24, 2013, 11:08:37 amWas the the product with the pressure transducer a sonobouy?

author: c4757p
author_rank: Super Contributor
timestamp: July 24, 2013, 05:43:11 pm
content: Quote from: Phaedrus on July 24, 2013, 05:29:48 pmThese people deserve exactly what they get.

author: Phaedrus
author_rank: Frequent Contributor
timestamp: July 24, 2013, 05:57:27 pm
content: It's actually the industry's fault. When the multi-rail "suggestion" was added to the EPS12V spec, most consumer PSU makers followed the guidelines... which were intended for server units.So they'd have a 20A rail dedicated to the CPU (a 4-8A load) and a 20A rail dedicated to the motherboard, graphics card, hard drives, optical drives, and fans (a 10-30A load). So multi-rail PSUs would often shut down if the user used a high-end graphics card. So multi-rail units became associated with instability. A company called PC Power & Cooling switched to single rail by removing OCP entirely (saving a buck in the process) and made a massive marketing push involving the "Single Powerful Rail" and a bunch of FUD about multi-rail units. Everyone ate it up, and the industry followed.And so even today, the majority of enthusiast PSUs are single rail. However, people are (slowly) starting to realize that having what amounts to no short circuit protection on a 1000W+ power supply with an 83A or 100A or 114A +12V rail is what we in the industry like to call a "Bad Idea". So more and more 1kW+ units are implementing 4 to 8 rail OCP. Which is a good thing for everyone who doesn't intend to use their computer PSU as an arc welder.

author: Unknown
author_rank: Unknown
timestamp: July 24, 2013, 06:08:18 pm
content: It also used to be common a couple of years ago that supplies sold as 'split rail' would actually have all 12V1/12V2/12V3 wires soldered to the same pad, which obviously makes separate OCP impossible. Do the various split rails supplies actually have split rails these days?

author: Phaedrus
author_rank: Frequent Contributor
timestamp: July 24, 2013, 06:12:40 pm
content: They may or may not. It also goes the other way; many SeaSonic units claim to be single rail, but implement two or three OCP rails. It's basically a mess, and the only way to tell is to look at the PCB.There are also weird units like the Channel Well PUC platform (not as common anymore) which actually has not just split +12V rails, not just two transformers, but actually has two separate primaries. Basically two PSUs on one PCB. One handling +12V and +5V, the other handling +12V and +3.3V. There was also a weird unit I saw ages ago that had two transformer taps for +12V, each with their own rectifier and inductor.99.9% of the time though, multiple rail mains multiple OCP rails. Except when it doesn't. Or when it does. Or something like that.

author: madires
author_rank: Super Contributor
timestamp: July 24, 2013, 06:20:16 pm
content: Quote from: c4757p on July 24, 2013, 05:21:13 pmThere's a telephone connector called TAE available in two versions. TAE-F is for telephones and TAE-N is for fax machines/modems. The difference is a pair of small protrusions at different pin positions while the pinout is exactly the same. Murphy makes sure that when you got a TAE-F socket the only cable you got is a TAE-N or vice versa. Instead of buying a cable with the matching plug you simply cut off the protrusions and the plug will fit in any TAE socket. Problem solved :-)

author: c4757p
author_rank: Super Contributor
timestamp: July 24, 2013, 06:22:08 pm
content: At least Murphy took the day off when they chose the pinouts. I wouldn't be surprised to see it different on each plug...

author: Andy Watson
author_rank: Super Contributor
timestamp: July 24, 2013, 06:45:27 pm
content: Quote from: c4757p on July 24, 2013, 06:22:08 pmThat would be the day that Murphy popped over to sort out the numbering system on the British telephone jacks. The plugs are labelled 1 to 6, the corresponding connections in the socket are labelled 6 to 1.

author: AndyC_772
author_rank: Super Contributor
timestamp: July 24, 2013, 07:05:40 pm
content: At least phones are, for the most part, reversible... notwithstanding the equally ridiculous 3rd wire for carrying the ringing signal.DIN41612 connectors can't claim the same get-out. They're sometimes - though not always - connected 1-to-32, 2-to-31 and so on.

author: nctnico
author_rank: Super Contributor
timestamp: July 24, 2013, 08:55:29 pm
content: Quote from: Andy Watson on July 24, 2013, 06:45:27 pmMotorola always reversed the numbering on their modular jack (like RJ11, RJ45 etc) connections. Very annoying!

author: amyk
author_rank: Super Contributor
timestamp: July 24, 2013, 09:21:46 pm
content: Quote from: Psi on July 24, 2013, 02:02:53 pmThat's what's called a self-fitting part.

author: grumpydoc
author_rank: Super Contributor
timestamp: July 24, 2013, 10:06:36 pm
content: QuoteThat dates back to the days of pulse dialling when it had a reason. The dial has a pair of contacts which short out the bell otherwise it would tinkle as you dialled (and so would the bells on any extension phones). Having the ringing signal on a separate wire allows any phone to suppress the bells on all the extensions.

author: TimNJ
author_rank: Super Contributor
timestamp: July 25, 2013, 03:52:46 am
content: Quote from: Phaedrus on July 24, 2013, 06:12:40 pmOff topic...but Phaedrus! I remember you from OCN. I think my name was TheLaw. I lived on the PSU section for a solid 2 years. Good to see you've made it over to EEVBlog.

author: Phaedrus
author_rank: Frequent Contributor
timestamp: July 25, 2013, 03:54:54 am
content: Quote from: TimNJ on July 25, 2013, 03:52:46 amHowdy mate! I remember you.What's going on man?I actually work for Cooler Master now! Just got hired a couple months ago. I'm working to improve their PSU line-up. It's hard workbut I'm doing my best!

author: TimNJ
author_rank: Super Contributor
timestamp: July 25, 2013, 04:09:03 am
content: Quote from: Phaedrus on July 25, 2013, 03:54:54 amWow that's awesome! Best of luck. Maybe I'll actually consider buying a CM PSU in the future. eXtreme Power *cough*

author: vk6zgo
author_rank: Super Contributor
timestamp: July 25, 2013, 06:19:48 am
content: Quote from: EEVblog on July 24, 2013, 11:08:37 amAt my second last job,the local "guru" discovered that one of the newly assembled units on test did not meet specifications.The most likely suspect was a 15kOhm resistor which was tucked down right near the front panel & hard to get at.He grabbed one of the UNI-T meters which we had been equipped with,measured the resistor,which read around 14 kOhms.Allowing for parallel components,that sounded OK,so he went of in search of other possibilities.After a while,I happened to pass by & "stuck my nose in where it wasn't wanted".I grabbed a light & peered at the resistor's colour code,which looked like 27k Ohm,but I wasn't sure,so I got my private Fluke 77,hung across it & saw around 22kOhm!It turns out that the wrong resistor was fitted,& that when these early model UNI-T meters had a battery which was dying,their resistance range read low.The thing was fixed,the "guru" was embarrassed,& another black mark went against my name!

author: IanJ
author_rank: Unknown
timestamp: July 25, 2013, 11:14:35 am
content: 1980's we used to build paper chart recorders for offshore. The electronics was a rack type arrangement.The rig reported the recorder wasn't working. Had a power light but no functions. Rig sparky couldn't fix.......didn't want to discuss over the phone, they wanted it fixed NOW.We sent one of our technicians offshore, his first ever trip, and when he came back next morning he reported that he walked up to the unit, pulled the cover off, re-seated the card that had jumped loose, closed the cover and went to wait for his chopper back to the beach. Time to fix, about 15 seconds.An expensive trip.Ian.

author: SeanB
author_rank: Super Contributor
timestamp: July 26, 2013, 05:45:49 pm
content: Quote from: amyk on July 24, 2013, 09:21:46 pmFunny enough a lot of engine crankshaft position sensors do the same when you install them, they are a little long and then when you fit them they touch the flywheel teeth, and when you first start with the new part it grinds off a little of the tip till it has clearance.Then again I get called because the computer is not working, and to go there and fix it ****NOW**** ( so she can play solitaire most likely, skills are barely above that and the odd email which might or might not go to the right recipient, or get sent at all) so go there, and the night before there was a power failure that outlasted the UPS batteries, and the box was turned off. Press power button and all lights come on.

author: peter.mitchell
author_rank: Super Contributor
timestamp: July 28, 2013, 04:48:20 pm
content: mobile phones that have the micro usb port break off the pcb, bringing the pads with them.so many solutions....

author: John Coloccia
author_rank: Super Contributor
timestamp: July 28, 2013, 05:58:26 pm
content: Some years ago, I was working on a series of rather complex automated alignment, assembly and test stations for some telecomm stuff...putting together tunable VCSELS, actually. Anyhow, we had these alignment stages with steppers, piezos, etc, and they were driven by a rack mount chassis filled with discrete components...a controller, stepper drivers, piezo drivers, etc.So one day the thing starts acting up. Very odd behavior. Clearly there was something wrong, we couldn't figure out what. So what do you do? You start replacing things one at a time until you find the culprit. Well, NOTHING could bring this thing back to life. We where taking known good components and we couldn't get them to work. We couldn't get the components out of the failed unit to work in a known good chassis.I wish I could remember the details now, but what had happened is that there was some failure mode in the components, and some common circuitry. One failed in such a way...a short, I think....that whatever else happened to be plugged into the backplane was induced to also fail...in the same way. Something must have been shorting out and melting, or blowing up or whatever...maybe solder reflow. I forget. Anyhow, it didn't matter WHAT we replaced since if there was even one bad component left in the chassis it would immediately blow up the new component that we plugged in. Now understand, we weren't willy nilly about this....this is expensive stuff and we were very careful, but it was insidious and by the time we figured it out we had a nice little pile of blown up components. I don't know...$50,000 worth...maybe more.

author: Corporate666
author_rank: Unknown
timestamp: July 28, 2013, 06:20:24 pm
content: We used to make a sort of lighting system with an array of high powered LED's. It was quite carefully designed, with lots of thought put into the type of LED, driving them at the correct level, and also the thermal design. Of course, white boards reflect light better, and we have found that white soldermask is whiter and glossier and more reflective than white silkscreen, so we always spec white boards, black silkscreen on the back (non-LED) side.We had a guy call and plead and beg us to look at his light that was way out of warranty... he loved it and needed it badly but it just didn't work. So we told him to send it in.When it showed up, everyone had a good laugh. He smothered the front of the board with wood glue... then dumped about a cup full of *glitter* on the board. Not sure what it's called worldwide (probably still glitter), but it's tiny little flakes of highly reflective metal or metallized plastic. He figured this would be more reflective than plain white. Of course he shorted out every LED... and the board no longer sat flush against the housing.We actually did end up fixing it amazingly... the unit had been out of production for years and we had no parts, but after a short bath soaking in acetone, his DIY glitter applique came off without much trouble, and the shorted out parts were replaced.I still laugh at that one.

author: Chalky
author_rank: Regular Contributor
timestamp: July 29, 2013, 10:11:15 am
content: My wife's Audi A3 (and other Audis, VWs etc) - speedo needle is mounted on small electric motor. Motor kind of sits on tiny fragile 5mm long brittle PLASTIC spindle. Spindle snaps, coz it's plastic. No speedo = no WOF (= no MOT for the poms?) Smallest replacement part from Audi? The whole instrument cluster. Cost upwards of NZ$1300 / US$1000. Or, get replacement plastic bits for £10 from some guy in Europe.http://www.akspeedo.com/audi-vw-speedometer-repair-shop.php. I spent the rest on a Fluke 196C!

author: madires
author_rank: Super Contributor
timestamp: July 29, 2013, 10:44:06 am
content: Even if the product is bullet proof there is always a "smart" idiot capable of destroying it. Some years ago I worked for a tier1 carrier and we deployed a lot of Cisco 6500 switches around all data centers. It's a big box with a backplane, redundant PSUs and several slots for cards (management & switch fabric, interfaces and so on). Box and cards are designed to mechanically prevent any misalignment but quite often cards don't just slide in smothly and require some force. Some technician mounted the switch into the rack and inserted all cards in the desired slots. After he powered on the switch a lot of the magic smoke was released and the fuses prevented a melt-down. He called an engineer who quickly saw that one card was inserted upside down. The technician told him that the card required a little bit more force to be pushed it in and since it wasn't unusual he assumed everything was alright.

author: deephaven
author_rank: Frequent Contributor
timestamp: July 29, 2013, 11:02:38 am
content: Many years ago when I was still at school I had a Saturday job at the local TV/Radio shop. We had a call from a local church asking if we could have a look at their audio system which appeared to have stopped working. There was quite a lot of installed wiring, so we had a go at tracing it all through. We then discovered that they had used audio XLR connectors for mains outlets and identical ones for the audioNeed I say more?

author: SArepairman
author_rank: Frequent Contributor
timestamp: July 29, 2013, 11:02:57 am
content: jammed printer in the andromeda strain.