Break the law by being a daredevil? (Curiosity questions only.)
mike3
Although I would not probably ever do this in reality at all due to
the danger, I'd be curious as to know what would happen if one opened
up a computer power supply unit. I've heard that one can get in
trouble with the law doing this (unless one has the proper
qualifications?). Is that right, and does this mean that even if I
didn't get zapped, and did this enough times (say 10 counts of illegal
opening of a power supply unit), I could spend the rest of my life in
prison (maximum security prisons, too???)? And furthermore, would just
1 count have _lifelong_ consequences, even if I made it through the
jail term? Are these worse or better than getting electrocuted?
Just curiosity questions: I wasn't really planning on doing something
dumb.
SteveH
Assuming for a minute you are being serious, I should be locked up for life
probably then!
SteveH
pcbldrNinetyEight
news:UHntj.7919$XI....@text.news.virginmedia.com:
Me too. Just call me Sparky.
--
pcbldrNinetyEight
RIAA
"mike3" <mike...@yahoo.com> wrote in message
news:21fbf7db-9f69-4538...@d21g2000prf.googlegroups.com...
I hope there is no death sentence involved. ;<)
DaveW
The power capacitors inside store a lethal quantity of electricity in them
long after the PSU is unplugged, and so you can kill yourself. (I suppose
killing yourself could be viewed as illegal...)
--
--DaveW
"mike3" <mike...@yahoo.com> wrote in message
news:21fbf7db-9f69-4538...@d21g2000prf.googlegroups.com...
philo
"mike3" <mike...@yahoo.com> wrote in message
news:21fbf7db-9f69-4538...@d21g2000prf.googlegroups.com...
I always open the supplies when the fan dies.
I have a whole box full of spare fans and cannot see tossing a PS just
because the fan dies.
The reason the caution label is on the supply is to keep people who do not
know what they are
doing from fooling around inside.
It's possible the capacitors could hold a charge and give someone a shock
DonC
"DaveW" <radi...@nuclear.org> wrote in message
news:ZKKdnYc6nrR1gyva...@comcast.com...
> It is not ILLEGAL to open a PSU, at least not in the USA. But it is
> UNWISE. The power capacitors inside store a lethal quantity of electricity
> in them long after the PSU is unplugged, and so you can kill yourself. (I
> suppose killing yourself could be viewed as illegal...)
Lethal? Maybe if you're wearing a ring and hanging onto a grounded point
with your other hand. Otherwise I have to disagree. The voltage may be high
but the total energy is unliikely to kill you unless you work hard at it.
Gordon Burditt
>> UNWISE. The power capacitors inside store a lethal quantity of electricity
>> in them long after the PSU is unplugged, and so you can kill yourself. (I
>> suppose killing yourself could be viewed as illegal...)
>
>Lethal? Maybe if you're wearing a ring and hanging onto a grounded point
>with your other hand. Otherwise I have to disagree. The voltage may be high
>but the total energy is unliikely to kill you unless you work hard at it.
If you open up the power supply for a CRT-based monitor or TV, the
high voltages (can be over a thousand volts) on some pretty hefty
capacitors can kill you even if it's unplugged. You still might
need to be fairly stupid to get killed, like grounding yourself.
But I think it is possible and has happened numerous times that
someone can kill themselves by accident.
And yes, I've survived getting zapped, not only with it unplugged,
but with it plugged in and operating and sticking in probes to
measure voltages. In older TVs, the power supply is not a separate
part sealed in a metal box. The high voltages aren't all in the
power supply, either. Use *one* hand and don't ground yourself.
If you don't need it to have power while you are working on it,
unplug it and let it sit for a while. Watch what you touch. And
if you don't know what you are doing, don't try it.
If you open up the power supply for a computer (motherboard, not
CRT monitor), which typically outputs voltages like 5 and 12 volts,
you're a lot safer. The *input* voltages are higher, but since
they are AC, any capacitors on the input side won't have much stored
charge after you unplug them. With it plugged in, there will be
higher voltages present. It's not a real good idea to stick your
fingers in a light socket, either. You don't worry about touching
both ends of a battery when picking it up, do you? The voltages are
low enough to not present a danger.
Sticking your tongue on a 9-volt battery may be unpleasant, but it
won't kill you. Connecting myself to a 12V car battery via jumper
cables in the process of jump-starting another car doesn't even
tingle if you have dry hands. (Warning: the ignition system has
much higher voltages. Do not hold on to spark plug wires while
cranking the engine).
DonC
"Gordon Burditt" <gordon...@burditt.org> wrote in message
news:13rcf8n...@corp.supernews.com...
>>> It is not ILLEGAL to open a PSU, at least not in the USA. But it is
>>> UNWISE. The power capacitors inside store a lethal quantity of
>>> electricity
>>> in them long after the PSU is unplugged, and so you can kill yourself.
>>> (I
>>> suppose killing yourself could be viewed as illegal...)
>>
>>Lethal? Maybe if you're wearing a ring and hanging onto a grounded point
>>with your other hand. Otherwise I have to disagree. The voltage may be
>>high
>>but the total energy is unliikely to kill you unless you work hard at it.
>
> If you open up the power supply for a CRT-based monitor or TV, the
> high voltages (can be over a thousand volts) on some pretty hefty
> capacitors can kill you even if it's unplugged. You still might
> need to be fairly stupid to get killed, like grounding yourself.
> But I think it is possible and has happened numerous times that
> someone can kill themselves by accident.
Over the past 45+ years I have replaced many dozens of TV picture tubes
i.e., CRTs, and have been zapped more than a couple of times (more in the
beginning, fewer in the mid-years and none in the latter stages : ) It
kicks like hell but far from killed me. I always removed my rings, etc. The
voltages IIRC are in the range of 15,000 volts but the amperage is quite
low. I wouldn't recommend that anybody mess around with such voltages but
I've yet to hear of anybody being killed although under extreme
circumstances I imagine one could -- ring on hand, bare feet in water, etc.
Think TASER gun; I suspect the voltages and amperages are on the same order.
Also the capacitors in a computer PSU are nowhere near the size of those in
TV high voltage supplies.
mike3
> It is not ILLEGAL to open a PSU, at least not in the USA. But it is UNWISE.
> The power capacitors inside store a lethal quantity of electricity in them
> long after the PSU is unplugged, and so you can kill yourself. (I suppose
> killing yourself could be viewed as illegal...)
>
Yeah, that's what I guessed, but I glanced over this, which was why I
asked:
http://groups.google.com/group/alt.comp.hardware.pc-homebuilt/msg/cb4d109b7145ddcc?dmode=source
" Working on high voltage equipment is always dangerous due to the
possibility
of fire and or electrocution. That's why its sealed with a warning and
that's why only those with the proper training should work on such
devices.
************* There's also a criminal and financial responsibility
involved. *************
So even if it doesn't seem like much the consequences can be
*tremendous*."
(emphases mine. Do the "tremendous" consequences include this alleged
"criminal" responsibility,
(not very tremendous compared to, well...) or are they referring to
the possibility of death (...that.)?)
Should've mentioned that in the post. Also, I heard that PSUs are
simply not meant to be
repaired, period, not even by a computer repair professional:
http://pcsupport.about.com/od/safetyconsiderations/qt/safety_tips.htm
"Never Service the Non-Serviceable
When you come across labels that say "No serviceable components
inside" don't take it as a challenge.
Some parts of a computer are just not meant to be repaired,
********* even by most professional computer repair persons
********* .
You will usually see this warning on power supply units but you may
also see them on monitors, hard
drives, optical drives and other dangerous or highly sensitive
components."
(emphasis mine also.)
How accurate is any of this information I've been accruing?
(PS. I suppose the warning about hard drives only applies if you care
about the data on the drive, not,
for example, experimenting with an old junker that was acquired
specifically for that purpose.)
Paul
> There's also a criminal and financial responsibility involved.
This refers to what happens if you repair an ATX PSU for your
friend. Your friend goes home, plugs in the computer, and
goes to bed. Later in the night, the supply catches fire.
Much later, the fire marshall and the insurance company, want to know
who modified/played with the supply.
Your friend's mom decides to sue, to help get money to rebuild the
house or pay for medical treatments for your friend. She has to
do something, after all, because the insurance was cancelled.
Even if you do stuff to your own power supply, you still
might run the risk of invalidating a fire insurance claim,
if the insurance company investigates and decides a change
to the PSU caused the fire.
Anything in the computer which is less likely to
catch fire, and burn down your house, has a lesser
risk associated with it. (For example, changing
sticks of RAM.)
Note that getting advice from USENET, you're going to
get lots of goofy, slightly off answers. Respondents
don't really care what happens to you. Remember
that, before you reach for that screwdriver...
Paul
naug...@netscape.net
Ahhhhhhhhh...
...gottabeatrollgottabeatrollgottabeatroll...
Yes... It's Every Bit as ILLegal as Removing Tags From Pillows...
Naughtius "Do Not Remove Tag Under Penalty Of Law" Maximus
Gordon Burditt
>> The power capacitors inside store a lethal quantity of electricity in them
>> long after the PSU is unplugged, and so you can kill yourself. (I suppose
>> killing yourself could be viewed as illegal...)
>>
>
>Yeah, that's what I guessed, but I glanced over this, which was why I
>asked:
>
>http://groups.google.com/group/alt.comp.hardware.pc-homebuilt/msg/cb4d109b7145ddcc?dmode=source
>" Working on high voltage equipment is always dangerous due to the
>possibility
>of fire and or electrocution. That's why its sealed with a warning and
>that's why only those with the proper training should work on such
>devices.
>************* There's also a criminal and financial responsibility
>involved. *************
If you represent yourself as qualified to fix something, and you
do it improperly for pay for someone else, and it catches fire or
electrocutes someone because of the incompetent job you did, there
may be financial or criminal responsibilities. If you screw yourself
in this manner, fewer people will be complaining. You may still
be in trouble if you burn down the apartment building you live in.
On the other hand, if you try to send it back to the manufacturer
for repair, package it up, and set it down on a range where you're
cooking lunch, then go look for some stamps, you have a bigger
chance of causing a fire.
The manufacturer's notice should put YOU on notice that if you kill
yourself trying to fix it, your heirs have no business suing them
for it.
>So even if it doesn't seem like much the consequences can be
>*tremendous*."
How much does an apartment building and all of its contents cost?
How about a few dozen dead former residents of said building?
>(emphases mine. Do the "tremendous" consequences include this alleged
>"criminal" responsibility,
>(not very tremendous compared to, well...) or are they referring to
>the possibility of death (...that.)?)
>
>Should've mentioned that in the post. Also, I heard that PSUs are
>simply not meant to be
>repaired, period, not even by a computer repair professional:
If I buy a power supply, I can reintend it to whatever purpose I
want to, including smashing cockroaches with it, and the manufacturer
has no business trying to reintend it back to what *he* intended.
This does not mean, however, that when it does a poor job of smashing
cockroaches, that I can claim it was defective under the warranty.
>http://pcsupport.about.com/od/safetyconsiderations/qt/safety_tips.htm
>
>"Never Service the Non-Serviceable
>When you come across labels that say "No serviceable components
>inside" don't take it as a challenge.
>Some parts of a computer are just not meant to be repaired,
>********* even by most professional computer repair persons
>********* .
I have had a power brick for a laptop end up making arcing noises
when you plugged it in, and it quit working. Turned out to be a
couple of bad solder joints. I opened it up, fixed this, sealed
it up again with duct tape, and it's been working fine. It's now
safer than it was, because the arcing generated a lot of heat but
didn't suck enough power to blow a fuse, so it might possibly have
caused a fire.
On the other hand, I probably wouldn't have tried to identify the
main power transistors in the PSU and replace them, because it's
too much trouble, not guaranteed to fix the problem, costs a lot
in shipping of tiny parts, and without a schematic which is never
included these days, I don't know the specs needed for the replacement.
Manufacturers, of course, want me to buy a new one. Manufacturers
also want you to buy a new CD and CD player after you've listened
to a CD once, as that gets them more sales.
>You will usually see this warning on power supply units but you may
>also see them on monitors, hard
>drives, optical drives and other dangerous or highly sensitive
>components."
>(emphasis mine also.)
Power supplies for CRT monitors have *very* high voltages in them
(and the monitor circuitry and CRT also do). (I'm not sure about
LCD or plasma displays.) Power supplies or anything else that you
plug directly into the wall have high voltages in them. These can
injure or kill people, or start fires. If you don't know what you
are doing, don't try to repair them.
And remember, crossing the street is dangerous, and can kill you
(I am sure there are plenty of documented cases), but there are
plenty of people who are going to claim they've survived crossing
the street. Don't let these people convince you that you CAN'T get
killed crossing the street. But being forced to cross the street
isn't a death sentence.
Hard drives and optical drives do not have dangerous voltages in
them. (unless it's an external drive that includes a power supply
that plugs into the wall. External drives that plug only into USB
ports don't have high voltages). YOU may have dangerous voltages
in YOU (static electricity) that are sufficient to zap the electronics
(but will only give you a mild shock from touching a doorknob), but
if they are already broken, and you're about to void the warranty
anyway, who cares? Also, dust and dirt contaminating a hard or
optical drive can cause a head crash or otherwise kill the drive
and your data. If you don't have a clean room and open up the hard
drive platter enclosure, don't expect it to work reliably again.
You might possibly get lucky. Data-recovery specialists may have
setups to do this properly, if you're desparate to get your data
back.
I don't know of any reason why it's unsafe to open up a dead (and
unplugged) hard drive, take out the platters, have something printed
on them, and hand them out to employees as awards for a job well
done. A former employer did exactly that. The employees then spent
some time joking around trying to identify the bad tracks with a
magnifying glass or the naked eye.
larry moe 'n curly
richard wrote:
> In order for a capacitor to store 1 amp of power,
...one "amp" of power? That's a new one because power = volts x amps
> that capacitor would have to be about five times the size of your computer. At the least.
Only if your computer is the size of a pea.
larry moe 'n curly
mike3 wrote:
> http://groups.google.com/group/alt.comp.hardware.pc-homebuilt/msg/cb4d109b7145ddcc?dmode=source
> " Working on high voltage equipment is always dangerous due to the
> possibility
> of fire and or electrocution. That's why its sealed with a warning and
> that's why only those with the proper training should work on such
> devices.
> ************* There's also a criminal and financial responsibility
> involved. *************
> So even if it doesn't seem like much the consequences can be
> *tremendous*."
Check www.repairfaq.org for information about electronics repair and
safety. It's great.
The danger of shock isn't that bad if the PSU is unplugged from the AC
cord. High voltage capacitors can remain charged if the PSU has
failed, because the failure may have blown a component or copper
trace, removing any path to discharge the capacitors. But a normal
working PSU will discharge in 30 seconds or less due to its circuitry
loading down the high voltage capacitors, but even if that doesn't
happen, there are almost always bleeder resistors that will discharge
them in 30 minutes.
Never open a PSU unless it's unplugged from the AC.
Never touch anything inside a PSU without first measuring the voltage
on it because any exposed metal can be at high voltage, including the
heatsinks. I've measured 170V DC on PSU heatsinks. Discharge all
voltage to the case by connecting a wire or resistor between the case
and the device, being sure to make the first connection to the case.
Never plug a PSU to the AC unless its cover is securely installed
(tighten all screws). The cover provides protection against electric
shock and exploding capacitors.
Never plug a PSU into an AC outlet that isn't grounded or protected by
a GFCI, and don't assume that an outlet is grounded just because it
has 3-prong sockets because some people replace broken 2-prong sockets
with 3-prong ones, as they're easier to find. The only situation
where it's acceptable to use an ungrounded outlet is when it's
protected by a GFCI, but beware that GFCIs can go bad without any
indication (IOW press the GFCI's test button, and verify that the wall
outlet has no voltage.
> Also, I heard that PSUs are simply not meant to be
> repaired, period, not even by a computer repair professional:
>
> http://pcsupport.about.com/od/safetyconsiderations/qt/safety_tips.htm
It's just not economical to have a computer shop repair a PSU because
the typical minimum labor rate is $60-100,.or more than the cost of a
typical brand new PSU. Also the average person working in computer
repair doesn't know how to do many actual repairs and just replaces
whole assemblies (PSUs, motherboards, cards, etc.). But it's silly to
say PSUs aren't meant to be repaired because I've repaired several,
and I'm certainly no technician. In fact a PSU may be the easiest
computer device to fix because so many of its components are generic
and are soldered in conventionally, not surface mount soldered.
Typical PSU failures are from bad fans, shorted transistors or diodes,
bad solder connections, and rotted capacitors (almost always the low
voltage ones, but sometimes a high voltage one in the +5Vstandby
circuit). The power supply forum at www.badcaps.net has detailed
information about the latter and how to fix it.
mike3
> mike3 wrote:
> > There's also a criminal and financial responsibility involved.
>
> This refers to what happens if you repair an ATX PSU for your
> friend. Your friend goes home, plugs in the computer, and
> goes to bed. Later in the night, the supply catches fire.
>
> Much later, the fire marshall and the insurance company, want to know
> who modified/played with the supply.
>
> Your friend's mom decides to sue, to help get money to rebuild the
> house or pay for medical treatments for your friend. She has to
> do something, after all, because the insurance was cancelled.
>
> Even if you do stuff to your own power supply, you still
> might run the risk of invalidating a fire insurance claim,
> if the insurance company investigates and decides a change
> to the PSU caused the fire.
>
Ah. This makes more sense.
> Anything in the computer which is less likely to
> catch fire, and burn down your house, has a lesser
> risk associated with it. (For example, changing
> sticks of RAM.)
>
> Note that getting advice from USENET, you're going to
> get lots of goofy, slightly off answers. Respondents
> don't really care what happens to you. Remember
> that, before you reach for that screwdriver...
>
Well, I wasn't planning on messing around with a PSU
like that anyway: like I said, these are curiosity questions.
Furthermore do you know of a source other than USENET
that is more accurate and is affordable to someone who
has less than $15000/year income?
> Paul
mike3
<snip>
Thank you for the good answer.
mike3
> On Sat, 16 Feb 2008 01:32:07 -0000, gordonb.0e...@burditt.org (Gordon
>
>
>
> Burditt) wrote:
> >>> It is not ILLEGAL to open a PSU, at least not in the USA. But it is
> >>> UNWISE. The power capacitors inside store a lethal quantity of electricity
> >>> in them long after the PSU is unplugged, and so you can kill yourself. (I
> >>> suppose killing yourself could be viewed as illegal...)
>
> >>Lethal? Maybe if you're wearing a ring and hanging onto a grounded point
> >>with your other hand. Otherwise I have to disagree. The voltage may be high
> >>but the total energy is unliikely to kill you unless you work hard at it.
>
> >If you open up the power supply for a CRT-based monitor or TV, the
> >high voltages (can be over a thousand volts) on some pretty hefty
> >capacitors can kill you even if it's unplugged. You still might
> >need to be fairly stupid to get killed, like grounding yourself.
> >But I think it is possible and has happened numerous times that
> >someone can kill themselves by accident.
>
> >And yes, I've survived getting zapped, not only with it unplugged,
> >but with it plugged in and operating and sticking in probes to
> >measure voltages. In older TVs, the power supply is not a separate
> >part sealed in a metal box. The high voltages aren't all in the
> >power supply, either. Use *one* hand and don't ground yourself.
> >If you don't need it to have power while you are working on it,
> >unplug it and let it sit for a while. Watch what you touch. And
> >if you don't know what you are doing, don't try it.
>
> accidentally touched the coil of a crt, which was unplugged, and it
> took about five minutes for the juice to drain through his body. He
> was ok.
>
>
>
>
>
> >If you open up the power supply for a computer (motherboard, not
> >CRT monitor), which typically outputs voltages like 5 and 12 volts,
> >you're a lot safer. The *input* voltages are higher, but since
> >they are AC, any capacitors on the input side won't have much stored
> >charge after you unplug them. With it plugged in, there will be
> >higher voltages present. It's not a real good idea to stick your
> >fingers in a light socket, either. You don't worry about touching
> >both ends of a battery when picking it up, do you? The voltages are
> >low enough to not present a danger.
>
> >Sticking your tongue on a 9-volt battery may be unpleasant, but it
> >won't kill you. Connecting myself to a 12V car battery via jumper
> >cables in the process of jump-starting another car doesn't even
> >tingle if you have dry hands. (Warning: the ignition system has
> >much higher voltages. Do not hold on to spark plug wires while
> >cranking the engine).
>
> around 50,000 volts (5,000?) which makes the current less than a 1/10
> of an amp. It's the voltage arcing across the spark plugs points that
> ignite the fuel. Not the current.
>
How come a monitor has so much more juice in it than a desktop's
PSU? Is it because of that electron gun?
DonC
Sort of. It's because of the extremely high voltage necessary to thrust
electrons into the phosphor coating the screen. That's why it's called an
"electron gun."
Paul
>
> Well, I wasn't planning on messing around with a PSU
> like that anyway: like I said, these are curiosity questions.
> Furthermore do you know of a source other than USENET
> that is more accurate and is affordable to someone who
> has less than $15000/year income?
>
As you'd guess, "free" and "accurate" don't always go hand
in hand. I've worked with a number of people, who in their
daily lives, feel that they should not share their knowledge,
unless someone is paying them. And certainly, there are people
who do repair work during their working day, and don't want
to continue to do repair work, by answering questions on USENET
in the evening.
Inside the computer, there are a lot of items which are
modular, replaceable, and operate at a low voltage. The
existence of such, allows the average home user, to
make changes, or do simple maintenance. For example,
adding a hard drive to the computer, or adding a
stick of RAM.
Anything involving the AC power line, should be treated with
more care. A number of devices in the household, do store a
considerable amount of energy. They also have protection
features, to protect against the most common failure
conditions. Opening up such an item, is not really smart,
if you don't know anything about what is inside them.
I can give you an example of something that happened to me.
At work, we had a number of microwave ovens, located so that
employees could heat up their lunch, at lunch time. The
microwave ovens were not cheap ones - they were the so-called
"commercial grade" ones, the same kind you used to see next to
sandwich vending machines, years ago. They still have roughly
the same power rating as a home machine, but are more solidly
built (fewer plastic bits that can break off, and the door
could take more abuse).
Now, there were a few individuals at work, who used to make
buttered popcorn, virtually every day, in the afternoon.
When buttered popcorn cooks, steam is released, and the steam
contains water, butter, and *salt*. Over time, this mixture
coats parts inside the microwave.
OK, so it is the evening and I'm working late. I take something
up to the microwave, push the button. BAM! The most loud explosion
you can imagine happens. Just like a firecracker going off right
next to you. I couldn't hear for about ten minutes after it
happened, that is how loud the sound was.
Now, what happened there ? Inside the microwave, there is a
transformer, a high voltage diode, and what could be an oil
filled high voltage capacitor. The capacitor is rated for
5000V. It holds a significant amount of energy. If the path
between the (+) and (-) terminals happens to conduct (such
as if there was a coating of salt, grease, and moisture
on the PCB), the cap can arc over. What I heard, was the sound
of a lot of energy being discharged at one instant.
The funny part of all this, is the microwave wasn't damaged at
all. It still operated afterwards (but not by me!). I still
phoned maintenance the next day and had it taken away, so it
could be properly (and safely) cleaned by someone qualified to
do it. The 5000V in that capacitor could easily kill someone, if
connected to them by accident, so shouldn't be cleaned by an
amateur.
So while you might assume your microwave oven is a benign beast,
it isn't necessarily so, as I got to learn first hand.
The ATX power supply has a main capacitor in it as well. If you
do the calculation, it holds a significant amount of energy.
It has a couple features, which help drain the energy. The capacitor
has a bleeder resistor across it, which could take a minute or
two to drain all the juice. The +5VSB standby rail of the supply,
and its associated circuit, also tend to drain the cap, and on
my current computer, that takes about 30 seconds, for the loading
of the +5VSB rail on the motherboard, to take the stored energy
out of the main cap. But now, consider a theoretical scenario.
The bleeder resistor is broken. There is no indicator, to say it
is working or not. The power supply doesn't monitor it. Now,
further say, that the +5VSB rail is not drawing any energy.
(Say the +5VSB circuit is broken somehow as well.) Now, the energy
in the main capacitor is still there. Not a problem, unless the
amateur working on it, happens to touch the terminals.
C5 and C6 are high voltage. R2 and R3 are bleeder resistors.
"Second power supply", bottom left, is the +5VSB circuit, and
draws energy from the main caps.
http://www.pavouk.org/hw/en_atxps.html (ATX schematic)
Professionals make no assumptions about the state of any
capacitors inside a powered device. If there is a possibility
they contain significant energy, then a discharge method may
be applied, to make them safe. Due to the noise issue, you
don't just jam an insulated screwdriver in there - depending
on the thing being discharged, you'd want to use a resistor of
some sort, to discharge the energy a bit slower. Note that capacitors
don't drain all their energy, when discharged just the once.
Some capacitors can show a residual charge (still enough to
kick you on your ass), even after being discharged. They
may require repeated attempts, or even leaving the discharge
device connected to the capacitor, while working on it.
Now, people who work with this stuff every day, probably
don't do a lot of risk analysis, and think through the
possible range of things that could happen. For example,
I worked on a project involving high voltage, and my
first reaction to my boss, is I wanted no part of the
project. I found out, from another company we were working
with, that their star designer "got shocks all the time in
the lab". That is not where I wanted to be (as careless
as that guy) :-)
I've only been knocked on my ass just the once by high
voltage. I was in my basement, as a kid, and playing with
an ignition coil. One minute, I'm standing next to the
work bench. The next, I'm on the floor, a few feet from
the bench, and don't really remember how I got there. In
all the high voltage stuff I've done since then, I've never
had that happen again. But I do think through, all the
things that could happen, before I reach for the
screwdriver.
HTH,
Paul
w_tom
> How come a monitor has so much more juice in it than a desktop's
> PSU? Is it because of that electron gun
Voltage in a TV is something between 10,000 and 20,000 volts.
Computer power supply voltages as much as 350 volts. Both are
dangerous. However one can open and fix their TV - but not the
computer power supply? Nonsense. Some here have posted myths based
in fear.
We routinely opened TVs to find failed vacuum tubes. I was doing it
even at the age of 12. So what makes it dangerous? Ignorance. We
did not blindly fix things as so many now do with TVs. For example,
so called 'computer experts' typically don't even know how electricity
works. They may also claim opening a power supply is a legal
violation.
The danger inside a TV, a computer, and also a microwave oven is
eliminated by a discharge resistor. But sometimes that resistor
fails. Then the power supply is a major and unexpected threat. The
informed simply discharge capacitors everytime after completely
removing power cord from the wall using a screw driver. No
exceptions. Then no risk.
Furthermore, when working on any part of a computer, always
completely disconnect that power cord.
You are encouraged to learn how power supplies work. But also
encouraged to take routine precautions - always. Learn the dangers
before sticking a hand inside.
Find a capacitor that did not discharge, short it with a screw
driver, then appreciate why that charge is so dangerous. It's one
thing to be told. Experience (the discharge) puts knowledge into a
whole new perspective.
What makes that voltage so dangerous? A discharge circuit that
passes through the heart. Informed and cautious techs may also keep
one hand in a pocket. Then dangerous voltages will not discharge arm
to arm - through the heart. Electrical tape around tool handles is
another routine precaution. Drier skin conducts less electricity. If
that 'much less' 300 volts inside a power supply does discharge
through you, then better appreciate why we do these routine
precautions.
Most dangerous are microwave ovens. Voltages inside TVs are almost
as dangerous. Computer power supplies are trivial by comparison.
It's not the power as much as voltage that creates danger.
Appreciate that computer techs need not even have electrical
knowledge to obtain A+ Certification. Their answers to your questions
are more often based in myths. This post intended as a supplement to
multiple replies from DonC.
w_tom
> I know the old school of electronics. I don't know a damn thing about
> this new microchip technology. But like you say, the so called techies
> of today, don't know jack squat about electronics. What they know is
> theory and how to interpret the data presented to them.
>
> Ask an A+ guy how to build a radio, he can't tell you.
When a tech could not explain why the computer would run diagnostics
all night; crash only when he was not there. Superstition then took
hold. He would loudly announce he was leaving for coffee, stomp out
of the room, then sneak back to spy on that machine behind a doorway.
And still that computer would crash only when he left the building.
Things always occur for good science reasons. Somebody foolishly
grounded that computer to an elevator. Computer only crashed when the
tech used that elevator to get coffee. A problem solved when one with
basic electrical knowledge could then follow the evidence.
A+ Certified computer tech need not know how electricity works to be
declared 'computer literate'. Shotgunning then becomes the solution.
Unlike replacing a light bulb, one first needed respect a TV's
dangerous parts. To understand some basic electrical principles. Some
principles that are routinely unknown by A+ Certified computer techs.
Explains why some here post fear of insides to a power supply.
mike3
> mike3 wrote:
>
> > Well, I wasn't planning on messing around with a PSU
> > like that anyway: like I said, these are curiosity questions.
> > Furthermore do you know of a source other than USENET
> > that is more accurate and is affordable to someone who
> > has less than $15000/year income?
>
> As you'd guess, "free" and "accurate" don't always go hand
> in hand. I've worked with a number of people, who in their
> daily lives, feel that they should not share their knowledge,
> unless someone is paying them. And certainly, there are people
> who do repair work during their working day, and don't want
> to continue to do repair work, by answering questions on USENET
> in the evening.
>
Well, If I was going to do this, I'd want to really know how to do
it right, ie. I'd want accuracy, and if that costs a lot of money,
then
I'd like to know how to be able to get it. Can most people get the
required money if they work enough? And can one do it with a
minimum of starting capital?
> Inside the computer, there are a lot of items which are
> modular, replaceable, and operate at a low voltage. The
> existence of such, allows the average home user, to
> make changes, or do simple maintenance. For example,
> adding a hard drive to the computer, or adding a
> stick of RAM.
>
> Anything involving the AC power line, should be treated with
> more care.
That's what I'd think.
> A number of devices in the household, do store a
> considerable amount of energy. They also have protection
> features, to protect against the most common failure
> conditions. Opening up such an item, is not really smart,
> if you don't know anything about what is inside them.
>
So then how can you learn about that first?
Was it as loud as shooting off a rifle without any hearing protection?
> The funny part of all this, is the microwave wasn't damaged at
> all. It still operated afterwards (but not by me!). I still
> phoned maintenance the next day and had it taken away, so it
> could be properly (and safely) cleaned by someone qualified to
> do it. The 5000V in that capacitor could easily kill someone, if
> connected to them by accident, so shouldn't be cleaned by an
> amateur.
>
Why do you need to be getting paid in order to handle the
capacitor properly? (You said shouldnt be done by an "amateur".
I suppose you mean someone who isn't experienced with this
type of thing.)
> So while you might assume your microwave oven is a benign beast,
> it isn't necessarily so, as I got to learn first hand.
>
> The ATX power supply has a main capacitor in it as well. If you
> do the calculation, it holds a significant amount of energy.
> It has a couple features, which help drain the energy. The capacitor
> has a bleeder resistor across it, which could take a minute or
> two to drain all the juice. The +5VSB standby rail of the supply,
> and its associated circuit, also tend to drain the cap, and on
> my current computer, that takes about 30 seconds, for the loading
> of the +5VSB rail on the motherboard, to take the stored energy
> out of the main cap. But now, consider a theoretical scenario.
> The bleeder resistor is broken. There is no indicator, to say it
> is working or not. The power supply doesn't monitor it. Now,
> further say, that the +5VSB rail is not drawing any energy.
> (Say the +5VSB circuit is broken somehow as well.) Now, the energy
> in the main capacitor is still there. Not a problem, unless the
> amateur working on it, happens to touch the terminals.
>
ZAP.
> C5 and C6 are high voltage. R2 and R3 are bleeder resistors.
> "Second power supply", bottom left, is the +5VSB circuit, and
> draws energy from the main caps.
>
> http://www.pavouk.org/hw/en_atxps.html (ATX schematic)
>
> Professionals make no assumptions about the state of any
> capacitors inside a powered device. If there is a possibility
> they contain significant energy, then a discharge method may
> be applied, to make them safe. Due to the noise issue, you
> don't just jam an insulated screwdriver in there - depending
> on the thing being discharged, you'd want to use a resistor of
> some sort, to discharge the energy a bit slower. Note that capacitors
> don't drain all their energy, when discharged just the once.
> Some capacitors can show a residual charge (still enough to
> kick you on your ass), even after being discharged. They
> may require repeated attempts, or even leaving the discharge
> device connected to the capacitor, while working on it.
>
So then it takes a bit of paranoia as well. I guess this is one
of those things where the more paranoid one is, the better. :)
Shadow36
"w_tom" <w_t...@usa.net> wrote in message
news:1b0c69ce-bb96-453c...@c33g2000hsd.googlegroups.com...
.
A+ Certified computer tech need not know how electricity works to be
declared 'computer literate'. Shotgunning then becomes the solution.
Unlike replacing a light bulb, one first needed respect a TV's
dangerous parts. To understand some basic electrical principles. Some
principles that are routinely unknown by A+ Certified computer techs.
Explains why some here post fear of insides to a power supply.
----------------------------------------------------------------
People generally don't like to get shocked, regardless of how little It Is
or even If someone else guarantees It won't kill you.
ProfGene
> Hi.
>
> Although I would not probably ever do this in reality at all due to
> the danger, I'd be curious as to know what would happen if one opened
> up a computer power supply unit. I've heard that one can get in
> trouble with the law doing this (unless one has the proper
> qualifications?). Is that right, and does this mean that even if I
> didn't get zapped, and did this enough times (say 10 counts of illegal
> opening of a power supply unit), I could spend the rest of my life in
> prison (maximum security prisons, too???)? And furthermore, would just
> 1 count have _lifelong_ consequences, even if I made it through the
> jail term? Are these worse or better than getting electrocuted?
>
> Just curiosity questions: I wasn't really planning on doing something
> dumb.
a mattress?
DevilsPGD
wrote:
>How many people do you know who are in prison for removing the tag from
>a mattress?
I'd guess none, since that's not actually illegal.