Author Topic: Be careful with those teardowns, kids!  (Read 20415 times)

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Offline vk6zgo

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Re: Be careful with those teardowns, kids!
« Reply #25 on: October 10, 2012, 12:08:51 pm »
My bet is on it being plugged in, or he was particularly lucky to have bridged the cap across his heart with both hands. Probably the former, as the amount of stored energy isn't what would cause the burns described.

Quote from: vk6zgo
Actually picture tubes are highly overrated when it comes to danger from them remaining charged.
The EHT voltage is quite high,& they do retain charge for quite a while,but their capacitance is too low to supply a lethal shock.
The danger of those is not from the shock itself, but from the surprise making you do something else, like drop the set or smash your hand against the neck. I've gotten static shocks on dry days, those can be tens of kV and the secondary effects are what really makes you do something stupid, not the shock itself.

Back in the very early days of picture tubes,they were quite dangerous if dropped,but almost anything from the early 1960s on is very unlikely to implode catastrophically.

If you smash your hand against the neck,you may break that part of the tube & give yourself a dangerous cut,but it won't implode.

Back when I used to fix TV Picture  Monitors & TVs,if we junked a CRT,we were supposed to knock the end off the neck to render them "safe".
 We were also supposed to stand back & do this when the dumped tube was already in the dumpster.
It was incredibly hard to do,even with direct hits on the neck with lengths of galvanised pipe or star pickets.
No implosion if you did,just a gentle sigh.

On one occasion ,we had some tubes from very old 1950's 12" monitors--they did go bang when we chucked them in the dumpster.
 

Offline vk6zgo

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Re: Be careful with those teardowns, kids!
« Reply #26 on: October 10, 2012, 12:32:03 pm »
@BoredAtWork: You seem bitter at people?

No, I am not bitter at people. I am annoyed by these fruitcakes who think they are an engineer just because then can rip off the latest Lady Gaga abomination and load it as a cell phone ring tone, or who glue Arduino to everything. And I am annoyed by those companies like Make who encourage them and rip them off.

Just read this thread. It didn't take long and you have a bunch of fruitcakes coming out of the closest telling you that the primary cap in a SMPS can't kill you. Because, wait for it, they survived it. Hint, those who didn't survive it can't talk any more. Hint 2, if you get zapped you failed, nothing to be proud of. They should sit in a corner, being ashamed of themselves, think about how to avoid it in the future, instead of proudly announcing that this is all harmless. And it does not matter if the boy in the current case was killed by it or something else. That doesn't change the fact that it is dangerous.

I would pretty much say "Bravo" to the sentiments in both your postings.

I'm just a bit concerned I might be included among the "fruitcakes",as I was a bit doubtful about the lethality of such a capacitor.
I did "hedge my bets" though,as I said:-
"I would have thought,nasty,maybe life-threatening,but electrical burns seems a 'bridge too far".

There are documented cases of fatalities by getting across the big oil filled caps in Broadcast Transmitters.
Many years back,I got a nasty belt from one of these.
Luckily,it wasn't fully charged,& the"zap"was through a big filter choke,the reactance of which limited the current.
Obviously,those things have lower capacitance,but are charged to a lot higher voltage than a switchmode primary cap.
 

Offline Mechatrommer

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Re: Be careful with those teardowns, kids!
« Reply #27 on: October 10, 2012, 12:39:29 pm »
i smell religion thread.... people died while they are asleep... sleeping is dangerous!
if something can select, how cant it be intelligent? if something is intelligent, how cant it exist?
 

Offline N2IXK

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Re: Be careful with those teardowns, kids!
« Reply #28 on: October 10, 2012, 12:42:51 pm »
Quote
Still, though many teens now fancy themselves as technological experts, it's as well to consider whether it's worth it, especially as some replacement parts can be cheap.

As computer repair expert Dave Bradshaw told KCTV-5: "It's a $20 power supply. Why tear into it?

He added: "You're taking your life into your own hands."

You heard the "expert"--don't try to FIX anything, or take the risk of LEARNING ---your duty is to CONSUME!  ::)
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Offline David_AVD

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Re: Be careful with those teardowns, kids!
« Reply #29 on: October 10, 2012, 12:47:56 pm »
Back in the very early days of picture tubes,they were quite dangerous if dropped,but almost anything from the early 1960s on is very unlikely to implode catastrophically.

When I was a kid (about 1975 I think), I pulled apart a couple of dead TVs that I got from the local appliance retailer.  I had stored the CRTs underneath a table in a downstairs room.

One evening, we heard an almighty bang and went down to find glass spread all over the room.  One of the tubes had imploded (I guess) but the other was still perfectly intact!  What a mess to clean up.
 

Offline tom66

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Re: Be careful with those teardowns, kids!
« Reply #30 on: October 10, 2012, 12:50:36 pm »
No, I am not bitter at people. I am annoyed by these fruitcakes who think they are an engineer just because then can rip off the latest Lady Gaga abomination and load it as a cell phone ring tone, or who glue Arduino to everything. And I am annoyed by those companies like Make who encourage them and rip them off.

Just read this thread. It didn't take long and you have a bunch of fruitcakes coming out of the closest telling you that the primary cap in a SMPS can't kill you. Because, wait for it, they survived it. Hint, those who didn't survive it can't talk any more. Hint 2, if you get zapped you failed, nothing to be proud of. They should sit in a corner, being ashamed of themselves, think about how to avoid it in the future, instead of proudly announcing that this is all harmless. And it does not matter if the boy in the current case was killed by it or something else. That doesn't change the fact that it is dangerous.

I wouldn't call those people engineers either. Still, I have no problem with makers/hackers/tweakers/what-ever-else'ers, as long as they keep it to themselves. Creativity is good. About half the students in my ELEC1130 class have never touched a soldering iron. They don't know ohms law or how to use an opamp. I wonder how long they'll last. They are MME students though - music multimedia electronics - not sure what horrible combination that is!

I wouldn't call a primary cap safe by any means. I have been stupid before. Shocked myself on a cap on a big LCD TV. I had assumed, after the fuse had quite spectacularly blown across the room (which in itself was a danger) that the cap would be discharged, so when one hour later I went to remove it, it would be safe. Nope! Got a 160V shock - turns out the TV discharges it down to 160V then dies - and it sits like that for a very long time. Maybe I got lucky - it was only 160V. It definitely hurt. (It also turned out that it had a separate standby bridge rectifier, and that part shorting out is what made the fuse go but it didn't discharge the main cap.)

However, you learn from your mistakes. I learnt my lesson. Maybe I'm lucky. I think they're mostly survivable, but it's kind of like a car accident: sure, you can survive it if you're lucky (and if it's not too violent), but you'll do you best to avoid it. Yet, we still don't do the #1 thing that avoids it: not driving a car, because it brings so much advantage for the risk of being seriously injured or even killd.
« Last Edit: October 10, 2012, 12:52:10 pm by tom66 »
 

Offline Ed.Kloonk

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Re: Be careful with those teardowns, kids!
« Reply #31 on: October 10, 2012, 12:58:02 pm »
There is a lot of bogative stuff in this story. A $20 psu? A pic in the orig quoted article of a Corsair 650. I own a few of them and I know I didn't pay $20 for them.

Coincidently, I started buying the corsair psu's because I got tired of the twenty dollar cheapys with crap noisey fans that rattle. Added up the cost of putting in jaycar replacement fans a few times and I could have bought the better psu with a nice, quiet fan.

I've now got an army of these monsters. I don't think about psu's anymore.

 8)

The kid just pharked up. No one's fault. They should just say that. I can understand that it is good for selling newspapers though...


 

Online SeanB

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Re: Be careful with those teardowns, kids!
« Reply #32 on: October 10, 2012, 03:23:27 pm »
Built in UPS? If he touched one lead while at the same time had the other hand on the heatsink connected to the other terminal then bye. It might leave a burn mark on the finger that touched the cap, and you find that discharge resistors in power supplies often quietly fail open circuit.
 

Offline G7PSK

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Re: Be careful with those teardowns, kids!
« Reply #33 on: October 10, 2012, 03:41:14 pm »
The most dangerous place to be has to be the cemetery. There are more dead people there than any where else, ergo it must be hazardous to one health.
I do know of one kid that was killed by a TV tube imploding, it was in the mid sixty's he climbed into the yard of the local TV. repair man (whose name was Collin Crisp and ran the radio club at the school I was attending) and started to throw bricks at the old tubes stacked there, one of them imploded and a piece of glass cut his femoral artery, the kid bled to death before any one could help him. 
 

Offline free_electron

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Re: Be careful with those teardowns, kids!
« Reply #34 on: October 10, 2012, 05:40:13 pm »
Guess I need to post a sign over my bench... "When Working on Mains Stuff, Sit On Your Left Hand!"
add this to it :

- lift feet off ground
- make sure no other part of body comes in contact with any object that can close an electric loop with the right hand
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Any comments, or points of view expressed, are my own and not endorsed , induced or compensated by my employer(s).
 

Offline tom66

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Re: Be careful with those teardowns, kids!
« Reply #35 on: October 10, 2012, 05:43:54 pm »
Installing a solid RCD is also a very good idea.

Many household installations now require it, but older houses don't always have them.

It's a lifesaving bit of kit, but you must understand its limitations.
 

Offline free_electron

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Re: Be careful with those teardowns, kids!
« Reply #36 on: October 10, 2012, 05:44:21 pm »
i smell religion thread.... people died while they are asleep... sleeping is dangerous!
Life is defined as a medical condition to which 100% of the patients finally succumb...
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Any comments, or points of view expressed, are my own and not endorsed , induced or compensated by my employer(s).
 

Online Monkeh

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Re: Be careful with those teardowns, kids!
« Reply #37 on: October 10, 2012, 05:51:15 pm »
All household installations now require it, but older houses don't always have them.

Fixed that for you.
 

Offline XynxNet

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Re: Be careful with those teardowns, kids!
« Reply #38 on: October 10, 2012, 06:14:21 pm »
The kid needn't be electrocuted. Going into shock or having a heart attack because of the unexpected electric discharge can be enough.
 

Offline tom66

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Re: Be careful with those teardowns, kids!
« Reply #39 on: October 10, 2012, 07:02:04 pm »
All household installations now require it, but older houses don't always have them.

Fixed that for you.

In the UK, sure - but it's not necessarily a requirement in other countries.
 

Offline Pentium100

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Re: Be careful with those teardowns, kids!
« Reply #40 on: October 10, 2012, 07:35:53 pm »
Caps can store the voltage for a long time. My tube headphone amp has two big caps (470uF and 330uF) for the anode supply and they are big enough so that when I switch off the amp, the tubes cool down faster than the caps discharge. That is why I put a bleeder resistor and also a little neon lamp - when the lamp turns off there is less than 50V on the cap. When I need to repair it or whatever, I always wait for the lamp to turn off before doing anything (and even then I measure the voltage with a meter, the lamp is just a convenience so I don't have to continually measure the voltage waiting for the cap to discharge).

Somebody should have taught the kid about safety - charge a small capacitor (so the shock is not lethal, but still pretty painful) and let him touch it - after that he would have learned to not touch capacitors that could be charged.
 

Offline Mediarocker

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Re: Be careful with those teardowns, kids!
« Reply #41 on: October 10, 2012, 07:47:19 pm »
Honestly I was kinda expecting it. Kids these days DON'T respect power. They aren't taught to respect and be careful around electricity.

I mean, you gotta start somewhere... but I gotta call darwinism on this. I was 7 years old and did the same thing. How am I still alive? I made sure my tools didn't touch the caps. I used insulated tools, and when I started tinkering with the PSU I discharged the caps beforehand using a resistor.
 

Offline tom66

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Re: Be careful with those teardowns, kids!
« Reply #42 on: October 10, 2012, 07:51:24 pm »
That reminds me of one very nice feature Panasonic include in their plasma TVs. Plasma TVs use 200V to make the panel light up with typically over 2000µF on the bus for this voltage (50A peak currents at 200kHz... and older sets had at least double, if not more.) There's a little LED tied in series with the voltage detect divider. It stays lit until the caps discharge below about 30V, at which point you risk only a minor shock if anything.

Repairing stuff is good. Just have a safe respect for electricity. It can kill you. Maybe you'll get lucky. Maybe that's why we're only allowed to use 30V in the labs, max (though the teachers don't realise the power supplies have a button for selecting series configuration. I accidentally had the output at ~50V into a logic IC, and I smoked it - I was running it at the maximum 20V but had the other supply set to 30V when I bumped the switch which is very sensitive.)
 

Offline asbokid

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Re: Be careful with those teardowns, kids!
« Reply #43 on: October 10, 2012, 09:15:51 pm »
Teen electrocuted while working on unplugged computer

Quote
A 16-year-old is stripping down a family computer, which is unplugged. He dies. An autopsy reveals electrocution burns.

Apparently this happened when he took the PC's power supply apart.  I'm guessing there was still a lethal charge on the mains cap(s).

Probably just made up.  The meeja at its worst.  Or if the poor sod really did die, what probably killed him was some deadly heart disorder that he knew nothing about.

 

Offline grumpydoc

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Re: Be careful with those teardowns, kids!
« Reply #44 on: October 10, 2012, 09:32:38 pm »
Quote
what probably killed him was some deadly heart disorder that he knew nothing about.

It's always possible -  some will be obvious at Post Mortem eg HOCM (hypertrophic obstructive cardiomyopathy) others don't show up on gross pathology eg Brugada.

However the "electrical burns" bit still doesn't _quite_ add up.

It's all speculation and guesswork though - the fact remains that anything with a high voltage capacitor can yield a nasty surprise even with the power off and anything connected to the mains can readily supply a fatal shock. If you don't realise this you're playing with your life.
 

Offline LaurenceW

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Re: Be careful with those teardowns, kids!
« Reply #45 on: October 10, 2012, 09:56:17 pm »
I have had three THUMPING GOOD electric shocks in my life - all from direct AC mains and all when I was much younger. I musta learned, 'cos I'm still alive and no shocks for a couple of decades. Except... I did have the minor embarrassment of posing as a discharge path to a large cap in a cheap (no bleed resistor) electronic flashgun, a few weeks back. THAT woke me up.

But - could a kid (even a standard issue, 21st century stupid kid) REALLY kill themselves just from the energy stored in a partial charged PSU cap?? I'd put money on "no"

It is just possible, I suppose, that the mee-dee-yah have cocked up their facts.

Anyone with medical experience care to suggest how much current (and importantly, for how long) it really takes to STOP a heart? Once we've got that the maths should be easy enough.


$20 dollar PSU?? Remind me not to buy spare parts from THAT guy!
If you don't measure, you don't get.
 

Offline asbokid

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Re: Be careful with those teardowns, kids!
« Reply #46 on: October 10, 2012, 09:59:14 pm »
anything with a high voltage capacitor can yield a nasty surprise even with the power off and anything connected to the mains can readily supply a fatal shock. If you don't realise this you're playing with your life.

Sure. I got a bolt from a PC PSU weeks after its last use. Certainly woke me up!  no need for a perm that week :)

cheers, a
 

Offline TerminalJack505

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Re: Be careful with those teardowns, kids!
« Reply #47 on: October 10, 2012, 10:37:41 pm »
If this individual did, in fact, have an outstanding health issue then it could be a big factor in his death.  Supposedly (and I don't necessarily subscribe to this) outstanding health problems are frequently the cause of death in taser-related fatalities.
« Last Edit: October 11, 2012, 01:24:32 am by TerminalJack505 »
 

Offline meanpc

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Re: Be careful with those teardowns, kids!
« Reply #48 on: October 10, 2012, 10:52:02 pm »
Fruitcake checking in.  I'll strap an Arduino to almost anything.

Offline Psi

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Re: Be careful with those teardowns, kids!
« Reply #49 on: October 11, 2012, 01:02:58 am »
It's perfectly plausible that he went to short out the cap with a screwdriver but touched both sides of the cap as he did. The current flowed through his heart for a fraction of a second, killing him. Then the screwdriver made contact with both sides of the cap which covered his fingers in carbon and metal from the vaporized screwdriver tip.

Anyone viewing the body would see he died while working on something electrical and would notice charring on his fingers and assume they're electrical burns.
« Last Edit: October 11, 2012, 01:05:14 am by Psi »
Greek letter 'Psi' (not Pounds per Square Inch)
 


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