Break the law by being a daredevil? (Curiosity questions only.)

"mike3" wrote in message
...
On Feb 15, 9:11 pm, richard wrote:
On Sat, 16 Feb 2008 01:32:07 -0000, (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.

Exactly. In my highschool electronics class, one of my friends
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).

Precisely. That's what the coil does. It increases the voltage to like
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?

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."

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.

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

On Feb 18, 5:59 pm, mike3 wrote:
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.

On Feb 19, 10:11*am, richard wrote:
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.

On Feb 18, 7:17 pm, Paul wrote:
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?

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.


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.

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.

"w_tom" wrote in message
...
..

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.

mike3 wrote:
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.
How many people do you know who are in prison for removing the tag from
a mattress?

In message ProfGene
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.