Unplug the power supply?

H

hdtv guy

I'm confused about something my motherboard manual says.
It says to unplug the power supply when you remove or install
hardware components. Do they mean to just unplug the power cord,
or do they mean you should also disconnect the power supply from
the motherboard?

I noticed that when I wore a wrist strap and I touched the power
supply, it stung because a lot of electricity went through me.
 
N

noway9988

I'm confused about something my motherboard manual says.
It says to unplug the power supply when you remove or install
hardware components. Do they mean to just unplug the power cord,
or do they mean you should also disconnect the power supply from
the motherboard?

I noticed that when I wore a wrist strap and I touched the power
supply, it stung because a lot of electricity went through me.


They mean to unplug the power cord. Yes, static can discharge to the
power supply whether it is plugged in or not. -Dave
 
P

Paul

hdtv said:
I'm confused about something my motherboard manual says.
It says to unplug the power supply when you remove or install
hardware components. Do they mean to just unplug the power cord,
or do they mean you should also disconnect the power supply from
the motherboard?

I noticed that when I wore a wrist strap and I touched the power
supply, it stung because a lot of electricity went through me.

Unplug the power cord. That guarantees that the power supply is
not producing +5VSB, the standby voltage. If +5VSB is present,
then the memory slots will be getting power derived from +5VSB.
Unplugging the computer guarantees that no components get damaged
because of it. (A "hot" memory slot, can damage a DIMM as it is
being plugged in.) You don't need to unplug the one or two
motherboard power connectors.

If you are getting a shock, which is not static electricity,
but the zap of AC current flowing through you, figure out
why. Occasionally, visitors to the USENET groups, have home
wiring that lacks safety ground. A computer power supply, has
a small amount of AC leakage current (it is there by design -
the guy who did it, knew he was doing it - the amount of
leakage is even stated in some documents). The safety ground
(in North America, it is the "third prong") drains that leakage
to ground in the house. If the wall outlet has a safety ground,
then you should not get a shock.

Now, if your AC outlet has no safety ground, there is no place
for the leakage to go. If you then touch the metal chassis of
the computer, you get a mild shock (not enough to stop your
heart or anything, but a shock nonetheless). The home I was born
in, is set up that way, and lacks a safety ground. Which means,
if I returned there, and brought a computer with me, chances are
I would get a 60Hz shock.

To demonstrate where the leakage comes from, this page shows a
design of an RFI filter. They put something similar to this,
inside the power supply, so that switching noise from the power
supply, is not placed on the AC wires. Notice how the datasheet
acknowledges the leakage as no more than 1.2 milliamps. The two
capacitors on the end of the filter, are likely a source of
that current, because as you can see, only those caps have an
electrical path to the other two wires. The design is intended
for the safety ground pin, to go to ground. If there is no ground,
then the leakage waits for someone to touch the chassis.

http://www.corcom.com/pdf/N.pdf

Paul
 
C

Conor

hdtv guy said:
I'm confused about something my motherboard manual says.
It says to unplug the power supply when you remove or install
hardware components. Do they mean to just unplug the power cord,
or do they mean you should also disconnect the power supply from
the motherboard?

I noticed that when I wore a wrist strap and I touched the power
supply, it stung because a lot of electricity went through me.
DO NOT UNPLUG THE POWER CORD UNLESS YOU HAVE ANOTHER WAY OF GROUNDING
YOURSELF as you remove the ability to earth yourself by touching the
chassis.

What you should do is just turn the wallsocket off. Basically, the
manual is warning you that there's still power running through the
board as they only go into standby and never turn fully off.

--
Conor

As a Brit I'd like to thank the Americans for their help in the war
against terror because if they'd not funded the IRA for 30 years, we
wouldn't know how to deal with terrorists.
 
S

spodosaurus

Conor said:
What you should do is just turn the wallsocket off.

If neither the PSU or the wall socket have a switch, buy a powerboard
with one.

Ari


--
spammage trappage: remove the underscores to reply
Many people around the world are waiting for a marrow transplant. Please
volunteer to be a marrow donor and literally save someone's life:
http://www.abmdr.org.au/
http://www.marrow.org/
 
B

Bill

DO NOT UNPLUG THE POWER CORD UNLESS YOU HAVE ANOTHER WAY OF GROUNDING
YOURSELF as you remove the ability to earth yourself by touching the
chassis.

This is wrong. You ground yourself to the chassis to have 0 volts
potential between yourself and any components your working on in the
computer. You always disconnect the computer power cable from the wall
to the computer to eliminate any chance of power being connected to
the computer. You also disconnect the computer from any other
equipment that is plugged into it to eliminate any potential hazards
from them. A separtate ground wire should lead from the computer
chassis to earth ground to eliminate any potential between the
computer and earth.

What you should do is just turn the wallsocket off.

Safe only if you can physically lock out the circuit with a lock, put
a warning tag on the lock, and keep the key in your pocket so no one
can turn the power back on but you.

See:

http://www.ehs.uconn.edu/Word Docs/Electrical Safety Fact%
20Sheet.pdf

as an example.

Basically, the
manual is warning you that there's still power running through the
board as they only go into standby and never turn fully off.

Bill
 
W

w_tom

I'm confused about something my motherboard manual says.
It says to unplug thepower supplywhen you remove or install
hardware components. Do they mean to just unplug the power cord,
or do they mean you should also disconnect thepower supplyfrom
the motherboard?

I noticed that when I wore a wrist strap and I touched thepowersupply, it stung because a lot of electricity went through me.

Noway9 has provided a useful and rather complete reply that implies
a building wiring problem exists.

Meanwhile, never install or remove components with power cord
connected. Never. Otherwise components may be powered even when
computer is off. Switch on a power strip is not sufficient.
Disconnect a power wire completely between wall receptacle and
computer.

For static electric protection, use a static wrist strap that
connects to computer chassis. That wrist strap connected to chassis
is 100% effective with or without power cord connected. Others claim
power cord's safety ground will eliminate damage from static
electricity. It will not. Always disconnect the power cord before
installing or removing components.
 
H

hdtv guy

Okay guys, so how about I do this:

1. I unplug the power cord from the power supply
2. I connect a wire from the chassis to the water pipe in the bathroom
to drain any residual electricity.
3. I connect an anti-static wrist strap from me to the chassis.

Then it will be completely safe to work on the hardware?

By the way, when I said that I got a slight sting from touching the
power supply, I had a wire around my wrist that was connected to the
water pipe. So the electricity was draining from the chassis through
me and into the ground. This was after I had unplugged the power
supply from the wall socket. Does this mean my electrical outlets are
not really grounded?
 
C

Conor

hdtv guy said:
Okay guys, so how about I do this:

1. I unplug the power cord from the power supply
2. I connect a wire from the chassis to the water pipe in the bathroom
to drain any residual electricity.
3. I connect an anti-static wrist strap from me to the chassis.

Then it will be completely safe to work on the hardware?
Or how about:

1. Turn off the wall socket
2. Leave the power cord plugged in.
3. Touch chassis to ground yourself.


--
Conor

As a Brit I'd like to thank the Americans for their help in the war
against terror because if they'd not funded the IRA for 30 years, we
wouldn't know how to deal with terrorists.
 
S

spodosaurus

hdtv said:
Okay guys, so how about I do this:

1. I unplug the power cord from the power supply
2. I connect a wire from the chassis to the water pipe in the bathroom
to drain any residual electricity.
3. I connect an anti-static wrist strap from me to the chassis.

Then it will be completely safe to work on the hardware?

By the way, when I said that I got a slight sting from touching the
power supply, I had a wire around my wrist that was connected to the
water pipe. So the electricity was draining from the chassis through
me and into the ground. This was after I had unplugged the power
supply from the wall socket. Does this mean my electrical outlets are
not really grounded?

Don't touch the chips and keep touching the unplugged metal chasis of
the case while you're working with it. Don't scuff your feet on the
carpet. You'll be fine.

Ari

--
spammage trappage: remove the underscores to reply
Many people around the world are waiting for a marrow transplant. Please
volunteer to be a marrow donor and literally save someone's life:
http://www.abmdr.org.au/
http://www.marrow.org/
 
D

DonC

hdtv guy said:
Okay guys, so how about I do this:

1. I unplug the power cord from the power supply
2. I connect a wire from the chassis to the water pipe in the bathroom
to drain any residual electricity.
3. I connect an anti-static wrist strap from me to the chassis.

Then it will be completely safe to work on the hardware?

By the way, when I said that I got a slight sting from touching the
power supply, I had a wire around my wrist that was connected to the
water pipe. So the electricity was draining from the chassis through
me and into the ground. This was after I had unplugged the power
supply from the wall socket. Does this mean my electrical outlets are
not really grounded?

OK, I'll be contrary :) What you are doing is all OK --- but in my
experience overkill <DUCK!>

Unplugging the power cord and touching the case has been my standard
procedure since opening computer cases began. And I've never had a problem
caused by static discharge or electrical flow*. If you walk across carpet
or anything else that could cause a build up, touch the case. Kept yourself
at the case's voltage potential. It really easy. We used to have a geekie
nerd who used the wrist strap and every other precaution he could think of.
We irreverently joked that he should clip one end of a wire to case and the
other end to his testicles. Sorry if that offends but that's just the facts
:)

* The exception is the power supply. Their are some large capacitors (big
and high capacity) that can give you quite a kick. But it isn't going to
kill you and most often you're not touching a sensitive component while
sticking your finger into the case of the power supply. In general KEEP OUT
OF THE PSU unless you have a damn good reason to be there. I learned this
from replacing CRTs in TVs decades ago. It can knock you into the wall but
you'll survive - kinda like a Taser gun. This is one case where I ended up
always running a wire from the HV connection to ground -- usually the center
prong of a grounded outlet. If I didn't see or hear a zap, I assumed the
system ground wasn't connected. That's another story.


Best of Luck!
 
P

Paul

DonC said:
OK, I'll be contrary :) What you are doing is all OK --- but in my
experience overkill <DUCK!>

Unplugging the power cord and touching the case has been my standard
procedure since opening computer cases began. And I've never had a problem
caused by static discharge or electrical flow*. If you walk across carpet
or anything else that could cause a build up, touch the case. Kept yourself
at the case's voltage potential. It really easy. We used to have a geekie
nerd who used the wrist strap and every other precaution he could think of.
We irreverently joked that he should clip one end of a wire to case and the
other end to his testicles. Sorry if that offends but that's just the facts
:)

* The exception is the power supply. Their are some large capacitors (big
and high capacity) that can give you quite a kick. But it isn't going to
kill you and most often you're not touching a sensitive component while
sticking your finger into the case of the power supply. In general KEEP OUT
OF THE PSU unless you have a damn good reason to be there. I learned this
from replacing CRTs in TVs decades ago. It can knock you into the wall but
you'll survive - kinda like a Taser gun. This is one case where I ended up
always running a wire from the HV connection to ground -- usually the center
prong of a grounded outlet. If I didn't see or hear a zap, I assumed the
system ground wasn't connected. That's another story.


Best of Luck!

What counts, is that all components be brought to the same potential, in
a safe manner. For example, you could unplug the computer, then put the
computer on your lap. Wear a pair of short pants, so your skin is in
contact with the case. Touch the case, to be sure you and the case are
at the same potential.

Open the antistatic bag, with RAM inside. Touch the inside of the bag
first, and not the module. The inside of the bag should have a high
resistance, but still be conducting, and any ESD discharge happens
slowly.

With memory, case, and human at the same potential, you could install
some RAM.

The reason a conducting strap is used, is to guarantee that the things
at the end of the link, are brought to a common potential. Just touching
an item, is not a guarantee it is brought to the same potential. There
is something called an electrophore, which is an insulator with a
charge on it. You can place a conductor (for example, a tin pie plate
with a wax candle as a handle) on top of an electrophore, touch the
tin pie plate, and assume it is grounded. But, if you then lift
the pie plate, and bring it near a ground, such as a cold water pipe
or the screw on a wall socket, a spark jumps over. This is
because, touching the pie plate, while it is sitting on top of
a piece of cat fur, places an "image charge" on it when the plate
is lifted away. And for this reason, you cannot assume, that simply
touching something, is a 100% solution to static. Depending on
the circumstances (such as laying the antistatic bag on top of your
cat), you could in fact pick up the RAM and zap it when it is brought
near the computer.

See page 3 here, for an experiment we did in grade school. It really works.
http://ether.sciences.free.fr/acrobatfiles/electrets/electrophore.pdf

As long as you've used reasonable precautions, to:

1) Bring things to a common potential.
2) Discharge using a high resistance path. The wrist strap provides
such a path (it is not just a piece of wire, but has a resistance).
The antistatic bag has X ohms/square of resistance, and would slow
the discharge. If you want to fast discharge something, such as
you touching the metal chassis, then that should be as safe as
zapping the computer case in real life, while you're using it.
3) Don't lay any components on top of good insulators. Don't situate
yourself in a situation you know throws sparks. For example, if
I put on a certain wool sweater, and rub my back against a wooden
chair, I've been able to throw 25KV static discharges (yes, they hurt).
Such a combination of seating arrangement, and clothing, while working on
a computer, would just be stupid. You can get some idea how bad
your environment is, by how often you're getting zapped by static
when just being in the room and touching a ground. Even taking off
that pair of insulating shoes you wear, is a start.

Connecting the setup to ground, may help if everything in the room
was grounded. For example, in my old lab, the floor was conducting
(you weren't allowed to put liquid wax on the floor, for fear of
insulating the floor), and everything in sight was connected to
ground. Wrist straps were used, and even heel straps in some of
the labs were mandatory. But a typical home scenario, is not
completely decked out in grounds, so the best you can do, is
bring everything to a common potential, as safely as you can
manage.

I've worked with some ESD sensitive components, ones where even
20 volts of static can damage them. They are so bad, that the parts
will die, while sliding down inside an antistatic plastic tube.
Current computer components have better protection than that,
and their sensitivity is probably better than 1KV HBM (human body
model). Intel USB ports, for example, have a 6KV rating, according to
an article I found on the site. Some RS-232 chips have
a 15KV rating, (which is why they don't blow up like the old 1488 and
1489 used to). But the combination of my wool sweater, and a wooden
chair, could blow any of them up.

http://en.wikipedia.org/wiki/Human_body_model

HTH,
Paul
 
W

w_tom

Okay guys, so how about I do this:
1. I unplug the power cord from the power supply
2. I connect a wire from the chassis to the water pipe in the bathroom
to drain any residual electricity.
3. I connect an anti-static wrist strap from me to the chassis.
Then it will be completely safe to work on the hardware?

Do not connect anything to a water pipe. That does nothing for
static electric protection and creates an unsafe condition. Chances
are the table (if not glass) is a good conductor for draining residual
(static) electricity.

A major difference exists between a static wrist strap and a
grounding wire. If using a wire to connect a body to a water pipe,
then death is possible. Static wrist straps contain a component to
eliminate that potential death condition.

Meanwhile, a static wrist strap (not a pipe connection) bleeds off
the currents that are relevant here. Neither pipe nor receptacle
safety ground will bleed those currents.

Any threat from large electrolytic capacitors inside a power supply
is non-existent here for many reasons. 1) Labels say to not open the
supply. Do as the labels say. 2) Nothing inside the power supply is
relevant here. 3) Those electrolytic capacitors are discharged by
circuits inside the power supply. 4) Even if those capacitors do not
discharge, connecting computer to receptacle safety ground or water
pipe does nothing to eliminate the charge.

The only place to safety ground a computer is that wall receptacle
safety ground. Never connect any electrical or electronic appliance
to water pipes. That even includes the incoming cable TV wire. Water
pipes are no longer acceptable for grounding other electrical
devices. Water pipe grounding does nothing useful for this computer
problem.

Again, noway9 in an insightful post, suggests you have another
serious problem with household wiring. A problem separate from the
computer. A separate problem that must not be ignored.

Do not leave power cord connected whenever removing or installing
components. That power cord safety ground does nothing useful for
static electric protection.

I believe it was Paul who noted some components can be damaged even
by 20 volts. Yes. And then when those components are integrated in a
system, that system will withstand thousands of volts. Why do you
need that wrist strap? Because when components are removed, then that
20 volt part is at great risk.
 
P

PeterC

2) Discharge using a high resistance path. The wrist strap provides
such a path (it is not just a piece of wire, but has a resistance).

We used these at work (PCBs worth £20,000 each at the soldering stage!) but
they had to be tested every month. Several were always o/c, so yes, they're
better than just a short to ground but also unreliable.

For home use I've always left the power lead in and off at the socket and
had no problems.
You could have a power lead with no fuse or the live and neutral not
connected.
 
P

PeterC

Do not connect anything to a water pipe.

Many houses have plastic (MDPE or HDPE) to the stopcock so aren't earthed
anyway. The water isn't helpful - I have a paper on earthing of domestic
fittings when all-plastic fittings are used and the resistance in the water
is very high in a short run of pipe.
 
D

DonC

PeterC said:
Many houses have plastic (MDPE or HDPE) to the stopcock so aren't earthed
anyway. The water isn't helpful - I have a paper on earthing of domestic
fittings when all-plastic fittings are used and the resistance in the
water
is very high in a short run of pipe.

"Most houses" where? Probably most NEW houses but for a long time local
building codes refused to catch up with the times.
 
L

Larc

Many houses have plastic (MDPE or HDPE) to the stopcock so aren't earthed
anyway. The water isn't helpful - I have a paper on earthing of domestic
fittings when all-plastic fittings are used and the resistance in the water
is very high in a short run of pipe.

On advice from a tech at a mom and pop computer store near me, I years
ago rigged a grounding setup in the area where I do my computer
building, maintenance, etc. I drove a metal spike into the ground
under my house and attached copper wire removed from electrical cable.
The wire runs up through the wall to a dead twin outlet I've painted
green so I won't confuse it with live outlets in the same area. When
I start to work on a computer, I plug in an old power cord that has a
metal clamp soldered onto the ground wire. The clamp goes on the
computer. Also I can plug the computer power cord into the other
ground outlet.

I've never got a shock nor zapped anything since I started using that
setup. :)

Larc



§§§ - Change planet to earth to reply by email - §§§
 
P

PeterC

"Most houses" where? Probably most NEW houses but for a long time local
building codes refused to catch up with the times.

In my 'corner' of England, most of the houses in the village have plastic
supply pipes. My house's water supply is all plastic throughout (the
central heating is copper).
Basically, a plastic supply won't give ground.
Also the mains 'leccy is earthed through the neutral, so there could be
enough voltage around...!
Yes, equipotential is the answer. At work, about 30 years ago, I developed
a habit of continuous contact with the chassis. When I was using an
opened-up Dell desktop case for bits going to and from another build I just
connected the 2 cases.
 
W

w_tom

Many houses have plastic (MDPE or HDPE) to the stopcock so aren't earthed
anyway.

First the confusion. Why an assumption that grounding of static
electricity is earthing? Earth ground is not relevant to a static
electricity circuit.

To have static electricity, a complete circuit must first exist.
Charges are located on both sides of shoes. What is the electric
circuit? Up leg, out arm, into computer case, down to floor, then
connected to bottom of shoes. A complete circuit required to have
electricity flow. What happens when the arm touches a semiconductor?
Now static electricity is also flowing through that semiconductor.

Are table and floor electrical conductors? Depends on parameters of
that electricity. To static electricity, table and floors are
conductors that complete the circuit path. Nowhere is earth ground
involved. Nowhere does earthing a computer case keep an arm from
discharging through semiconductors.

Second, so that semiconductors are not in that static electric
path, we use a static wrist strap. That wrist strap also is not
considered conductive to computer power (which is necessary for human
safety). But that wrist strap (like the floor and table) is
conductive to static electricity. Using a wrist strap means static
electricity need not conduct to table and floor via semiconductors.
Using earth ground (ie power cord connected to the computer) does
nothing to prevent that destructive ESD.

Do not confuse grounding of static electricity with safety ground
earthing. These are completely different grounds that may only be
interconnected. An earth ground does not solve ESD problems.

Third, other useful solutions include static conductive plastics and
humidifiers.

Bottom line: never leave a computer power cord connected when
servicing a computer. Some have assumed earth ground is a solution to
ESD problems. Obviously not when the electric discharge circuit is
defined.
 
B

Blattus Slafaly £ ¥ 0/00 :)

w_tom said:
First the confusion. Why an assumption that grounding of static
electricity is earthing? Earth ground is not relevant to a static
electricity circuit.

To have static electricity, a complete circuit must first exist.
Charges are located on both sides of shoes. What is the electric
circuit? Up leg, out arm, into computer case, down to floor, then
connected to bottom of shoes. A complete circuit required to have
electricity flow. What happens when the arm touches a semiconductor?
Now static electricity is also flowing through that semiconductor.

Are table and floor electrical conductors? Depends on parameters of
that electricity. To static electricity, table and floors are
conductors that complete the circuit path. Nowhere is earth ground
involved. Nowhere does earthing a computer case keep an arm from
discharging through semiconductors.

Second, so that semiconductors are not in that static electric
path, we use a static wrist strap. That wrist strap also is not
considered conductive to computer power (which is necessary for human
safety). But that wrist strap (like the floor and table) is
conductive to static electricity. Using a wrist strap means static
electricity need not conduct to table and floor via semiconductors.
Using earth ground (ie power cord connected to the computer) does
nothing to prevent that destructive ESD.

Do not confuse grounding of static electricity with safety ground
earthing. These are completely different grounds that may only be
interconnected. An earth ground does not solve ESD problems.

Third, other useful solutions include static conductive plastics and
humidifiers.

Bottom line: never leave a computer power cord connected when
servicing a computer. Some have assumed earth ground is a solution to
ESD problems. Obviously not when the electric discharge circuit is
defined.

You're all wet. Ground is ground is ground. Static electricity is no
different that any other electricity.
If you unplug it you also remove the ground. Leave it plugged into a
power strip and turn off the power strip. To prevent static damage, you
want everything at ground potential including YOU, hence the ground strap.
[Never use a ground strap on powered equipment]. Static electricity will
discharge on ground (Zero potential).
If you just rely on the bench ground where the computer case is sitting
(which is also connected to earth ground by it's outlet power)
you may have insufficient contact and charge your case to 3 to 10 kv or
more by touching it.
 

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