Your stupidest mistakes

[peteb2]

Here's another, not directly my stupid mistake but a reminder to stay across work and projects around you when part of a team under the same employer.

ON this day everyone was really busy with their current tasks at the bench. It was the 1990s and urgency was a Broadcast TV News Camera (shoulder job) that had finally had so many pixel failures on all its 3 sensors it produced pictures more akin the Milky Way. The firm decided they'd spring the almost $20,000 for a new optical block which consists of a bayonet lens mount, dichroic red, green and blue prism, filter wheel, timing PCB and 2/3" CCD sensors and amplifiers bonded to the prism such that the red and blue channel devices are half a pixel offset to the green, ( latter done to reduce aliasing in the video).

The part arrived in the country and that morning there was only one person in the team of techs who'd a spare moment to swap the block out.

OK, so he was the new guy who'd come to work with us recently. We all assumed he'd be familiar with the basics of a 3-sensor camera so. He was asked to just pull the old optical block and put the new one in.

About an hour passed when one of the other guys asked if the camera was done because the department that used it needed it by noon. New guy said nothing so a quick look see over a shoulder was made...

That's when a bit of fright set in.... there was a carefully denuded of its CCD sensors prism sitting in its shipping container and the same kind of thing in the camera! 

It was impossible to remount the CCD sensors for registration and the half pixel offset without the special alignment jig used in the factory in Japan and to make sure there was zero dust. The best would be a 3 image red, green, blue noisy picture.

Normally it would have been unplug a few cables and unscrew a few front screws, pull the front casting and swap over!

So in short we had a $20,000 paperweight and a dead camera...

The firm must have done some excellent bean-counting to buy another spare but there was that long shipping delay that could not be sped up. CCDs for cameras could fail if sent by air and so had to travel by sea....

We learned a lot that day how important it was to communicate with a fellow worker and perhaps to have a chat about how to knock a repair off including the proper procedure and how to check their experience or ever done it before!

[karoru]

As I have a spare 9V battery clip at hand, I thought it would make a much better connection than using just the crocodile clips alone. I connected the red lead of the spare battery clip to positive and black lead to negative of DC supply output. Finally, the spare clip was mated with the battery clip in the device.

Whooops, yes, that can be easy to happen with those 9V connectors.

That's how I learned the hard way there are two kinds of these connectors with different polarities. At least most 9V batteries have awful internal resistance and it's hard to make too much smoke with them.

[eblc1388]

That's how I learned the hard way there are two kinds of these connectors with different polarities.

No, the polarity of the spare battery clip is absolutely correct.

The fact that one mated two such clips together effectively transposed the polarity. I strongly advise anyone whose have two such battery clips would try mate them together as I did and satisfy yourself that the red lead on one is now connected to the black lead on the other.


 

[Assafl]

Ahh - step down autotransformer. 220v input: 110v output. Pretty simple. NOT.

Turned out the Chinese Manufacturer wired the plug in reverse (actually randomly). So the 110v was actually hooked to the 220v line and the "neutral" was at 110v.

So still 110v? Yup - except the input protection varistors on a 110v power strip (probably 140-150V) dumped the 220v to earth.

All dumped through ground - and by the time the fuse popped dispatched the magic smoke from a $700 HDMI card, the TV controller card and a 50:60Hz HDMI frame rate converter. Luckily a 10m cable protected the projector... 

(Oh and another 220:110v transformer decided to be pass through and fried the Roomba charger).

Since then I double measure all transformer wiring.

[senso]

I have a load of stories I can tell about my quadcopter project(s) as well!
...
more recently, I was rewiring the quadcopter and my hands slipped and well same as before 12V got connected to ground, causing a whole bunch of wires to go up in smoke.

You do realize they make these things called fuses, right?   

What my quadcopter really needs is a complete re-wiring, and making a PCB with all the parts on one board. Maybe a ruggeduino too. 

What you need is to remember to disconnect the battery before tinkering or one day you will blow up one battery and the learn the lesson the hard way..

[moffy]

When I was 13 or 14 with no real understanding of Ohms law I decided I would try to make a heater element. I got a solid steel bed spring (because to me it looked like a heater coil) then I got some flex with a plug on it and wrapped the wire to the coil ends. I then placed the coil on a breadboard in the lounge room and switched it on. Some minutes later when I could see again after a section of the cable vaporised I noticed tiny little spheres of copper that had burnt their way through my mothers lace table cloth. When I removed the copper spheres you couldn't notice the extra holes because the lace disguised them. Mum never knew.

[basinstreetdesign]

When I went home for Christmas break in 3rd year university I left a few things in a locker on campus.  Amongst some inconsequential stuff I left a 1942 copy of the Royal Air Force Signal Manual.  It was loose leaf about 4 inches thick and bound with string and was called by one educator as "about as authoritative as you can get" on the subject of signals and electronics as of then.  I got it from a friend of my dads who retired after many years working for the Canadian government writing and editing training manuals for the military.  I forgot that the lockers would be emptied by the school by new years day and everything in them would be discarded.  I searched, inquired,  ranted trying to find it but never found where it went.  I still get misty thinking about what a fool move that was.

[Circlotron]

Almost 40 years ago had an old Pontiac with a very sloppy column shift gear linkage. Went to start it one day and absolutely nothing. Gear was in R but selector showed PK and so the inhibit switch was preventing it doing anything. Popped the bonnet and put a screwdriver across the starter motor solenoid terminals. Engine springs to life at at a fast idle and a second or two later I heard the unmistakable sound of the old Powerglide auto tranny getting up hydraulic pressure and engaging... Car flew backwards across the yard and through the fence into next door's back yard. 

[karoru]

No, the polarity of the spare battery clip is absolutely correct.

The fact that one mated two such clips together effectively transposed the polarity. I strongly advise anyone whose have two such battery clips would try mate them together as I did and satisfy yourself that the red lead on one is now connected to the black lead on the other.

There are some with wire colours marked backwards - for use in power supplies, so the "color-polarity" matches one on battery, not one on the usual clip. That's what I meant:)

[jeroen79]

A non-electronic but stupid mistake:
I was putting up some rollup curtain and took careful measurements. I then calculated that the curtain and rollbar had to be shorted by 30mm and double checked this.
Then I proceeded to carefully mark off 30cm and sawed it off.
I was greatly surprised when I held it up to the window.

When I was 13 or 14 with no real understanding of Ohms law I decided I would try to make a heater element. I got a solid steel bed spring (because to me it looked like a heater coil) then I got some flex with a plug on it and wrapped the wire to the coil ends. I then placed the coil on a breadboard in the lounge room and switched it on. Some minutes later when I could see again after a section of the cable vaporised I noticed tiny little spheres of copper that had burnt their way through my mothers lace table cloth. When I removed the copper spheres you couldn't notice the extra holes because the lace disguised them. Mum never knew.

As a kid I wanted to build an electromagnet I saw in a book.
So I wound some wire around a nail and hooked this up to a transforer for an electric blanket. This made the magic smoke escape from the carpet in my room!
I tried to conceal the mark by putting a wastebin over it. Unfortunately this did not fool my dad.

[Cupcakus]

I designed a pcb boost converter recently with a battery connector on one side for the low voltage, and the same connector on the other side for the high voltage.  I placed the high voltage connector first, then flipped it for the battery connector but forgot to flip the silkscreen polarity marks on the part.  So the boards arrived and I connected the battery backwards and it's amazing how much magic smoke one little battery can cause.

[vealmike]

Many years ago as a young product quality engineer (yup, many years) I was asked to run a burn in cycle on a new product. The test was due to run over a weekend, the kit was somewhat expensive.

Somewhat? Well it was a prototype disk enclosure, a 19" rack box with a bunch of spinning hard disks in the front and power cooling / RAID controller in the back. The first and only proto.
It was loaded with a brand new drives from Seagate. From memory they were the first of that model of Barracudas in Europe. They were pre production drives, purchased at a great uplift over their already expensive planned ship cost. So, we're talking about £75,000 ish UK Sterling in the early/mid 1990s.

So muggins loads the kit into the thermal chamber. The thermal chamber had its own mains outlet for powering the DUT, limited to 2KW, at 2.5KW my kit was too much for this so I plugged the kit into the mains, set the chamber to ramp rapidly from 10C to 40C and back. I connected a host PC and started random IO running to thrash the disks. Happy in the knowledge that I'd done an excellent job, I headed home for an average 20 something's weekend of alcohol and loud music.

Anyone spotted the mistake yet?

Monday morning, I turn up for work a little late. Its Monday, its normal. First person I see looks at me and shakes his head. Second one tells me to brace myself. When the third told me to start clearing my desk, I started to wonder if I might have cocked something up...

Over the weekend, the thermal chamber had tripped. Both the heater and the chiller had cut out. Had I plugged the DUT into the chamber's dedicated power out, the DUT would have had its power cut too. But I didn't do that, all 2.5KW of DUT was powered from the mains, and kept going.

Those of you who have used thermal chambers will have noticed how thick the walls of the chamber are.It turns out that there is a lot of thermal insulation in those walls. I guess you don't want heat from your lab warming the inside of the cold chamber, or heat from the chamber escaping to the lab. The latter kind of explained why the plastics on the DUT were emulating Dahli's clock.

I discovered that a 2.5KW heater sealed in a thermos and left going for ~60  hours gets bloody hot.
Hot enough to melt all the plastics. Hot enough for half the drives to stop working. Too hot to handle any of the parts for a good half hour after it was switched off. Chamber temperature was 115C. The DUT had fan cooling, typically we see a 50C rise between inlet (chamber temperature) and air flowing over our PSU/Controllers.

I'm sure its not the dumbest thing I've done, but it is the most expensive mistake I've made.

[Circlotron]

A non-electronic but stupid mistake:
I was putting up some rollup curtain and took careful measurements. I then calculated that the curtain and rollbar had to be shorted by 30mm and double checked this.
Then I proceeded to carefully mark off 30cm and sawed it off.
I was greatly surprised when I held it up to the window.

That bring back memories of my adventures with a curtain rail. It was 300mm too long so I went and cut off 330mm. D'oh! Off to the shop and get a new rail, measure it and then cut off 330mm a second time... 

[FrankenPC]

13 years old. 

My Commodore 64 monitor dies.  Hey, I have a screwdriver...I wonder if I can fix it?  What's that weird  suction cup on the tube?  I think I'll try to pry it off with my screw driver. The ensuing discharge damaged my hearing for two days and blew a quarter sized hole in my parents carpet. 

Well, I'm still alive at least.

[SeanB]

    And let's here the rest of the story. 

Please to report that was the only disaster for the night, everything else was a greater success

18 years ago now, still have the pocket knife as a reminder.

Still have the sidecutters, with the now built in wire stripper. both of them..........

[Inflex]

Still have the sidecutters, with the now built in wire stripper. both of them..........

That's the stuff!

[Planobilly]

I "ASSUMED" and that was all it took, followed by a liteiny of unwanted outcomes.  LOL

Billy

[David Hess]

Still have the sidecutters, with the now built in wire stripper. both of them..........

A friend made a comment to me that one room in his house had a light switch that did not work after refurbishing.  I immediately suspected that the problem was likely caused by the wall socket having been replaced without removing the shorting bar on the hot side so we pulled the cover plate off and removed the socket from the wall.

The only tool I had was my Swiss army knife which included pliers and while I was messing with the socket my friend asked, "Shouldn't we flip the breaker to turn the power off?" *zap* "Nope, I have taken care of it."

It took a nice divot out of one of the teeth on my Swiss army pliers.

[Codebird]

Many years ago, I was playing with bodged-up device. It involved a step-down transformer off the mains, a rectifier, and a bloody huge capacitor bank - I was trying to spot-weld something, I think. Somehow I managed to mis-wire the thing. I'm still not sure how, but I took out all the power. To the street.

I think I discharged the bank into the transformer secondary, and created a very high-voltage pulse on the mains - enough to trip a safety shutdown at the substation. Fortunately it came back up a minute later, so there must have been an automatic reset.

Others:
- Building a buck converter, buying a nice low-drop diode, but just assuming it was a schottky. It wasn't. It went pop. High frequency operation is not something regular rectifier diodes are made for.
- Connecting a 10KV voltmeter to a 4KV capacitor bank, thinking it had an internal resistor. It did not. It went pop.
- Crashing mobile phones with an EMP. Several times, before I got a camera with a zoom.
- Using a 12V car headlamp bulb as a test load. Placing said test load on a wooden surface.
- Not using proper eye protection when trying to make a laser lawnmower. This doesn't work, anyway - you need to evaporate the water from the grass before the laser will cut through it. I had visions of putting the laser on a turntable and sweeping it slowly across the lawn.

Some friends and I dabble in high energy physics as a hobby. Our safety considerations mostly involve being in another room from the business end of things, and operating the zappy gear via a fiber-optic cable. I had to design all the electronics to be hardened against EM some of our machines can generate when firing, as it tends to crash anything too delicate.

[Inflex]

- Not using proper eye protection when trying to make a laser lawnmower. This doesn't work, anyway - you need to evaporate the water from the grass before the laser will cut through it. I had visions of putting the laser on a turntable and sweeping it slowly across the lawn.

Ignoring the obvious undulations of the land, all you need is a bigger laser... yes, thought about it myself too

[SeanB]

- Not using proper eye protection when trying to make a laser lawnmower. This doesn't work, anyway - you need to evaporate the water from the grass before the laser will cut through it. I had visions of putting the laser on a turntable and sweeping it slowly across the lawn.

Ignoring the obvious undulations of the land, all you need is a bigger laser... yes, thought about it myself too

How about that big one Mike'selectricstuff was showing on his channel recently. might trim the lawn nicely, though the neighbours could be upset with the large holes that appear in the walls, and your electric bill would suddenly show a 3 orders of magnitude increase.

[Inflex]

How about that big one Mike'selectricstuff was showing on his channel recently. might trim the lawn nicely, though the neighbours could be upset with the large holes that appear in the walls, and your electric bill would suddenly show a 3 orders of magnitude increase.

Would explain the power problems in ZA in the last 12 months (hope that's been sorted out now for you guys)

[Christopher]

My biggest mistake?

Getting a job in Electronics.

[baltersice]

I just dropped my phone in ferric chloride
https://www.youtube.com/watch?v=GYIiOkr6x9o#t=10m9s

[ZeTeX]

I just dropped my phone in ferric chloride
https://www.youtube.com/watch?v=GYIiOkr6x9o#t=10m9s

By your video I thought you dropped your dick in ferric chloride