Wooden PC

[kony]

??? They are designed with being grounded to a metal chassis in mind,
not with a wood or plexiglass chassis.

They designed it to be wholey grounded already by the power
connector(s).

The individual ground planes all rely on a low impedance path back
to common ground. The power supply DC return does NOT provide a low
impedance for high frequency noise. Why do you think the MB ground
plane is grounded with metallic screws to the metallic chassis?

Actually, some have been plastic, and some people put fiber
washers on... and it still works fine.

The main reason they're metal is that's the best way to make
a standoff. Same applies for any screw in anything that
doesn't even screw into anything metal.

I don't care if there are 100 ground leads if they all look like a
high impedance to high frequency noise. If you *really* believe that
the PSU DC return path is sufficient, do you use fiber washers between
all standoffs and the MB? Of course not.

There is no impedance lower than the 9 return power leads
needed. This is by design. The board has ground planes
which handle this. Perhaps if it did not, THEN your idea
would have merit.

But with a wooden chassis,
that low impedance ground path is not possible. Hence, the short ground
wire back to the PSU.

Would it interest you to know that some people even use
isolation mats on their PSU mounting so their case isn't
even grounded at all except through those 9 ground return
wires to the PSU? Again their systems work fine.

I suppose you'll just have to stop idealizing and see for
yourself. Plenty of us have already, there simply is no
need and it is easily proven.

Again I ask for specifics of a reproducible problem. If you
have no specifc scenario that can be reproduced, it is an
idea clearly without proof, while on the other hand there
are plenty of systems running right now showing the
opposite.

 

[w_tom]

Absolutely, but my point was that the switches are not grounded at present,
so it won't make any difference if they are moved from a plascic housing to
a wooden one and therefore 'w_tom's point was.. er.. pointless!

You magically know plastic inside surface is not coated with a
conductive material? If that switch is pressed by a long plastic
material, then low conductive plastic would be sufficient to conduct
static elsewhere. But if your finger touches the switch plastic
button, then its body must be mounted on a more conductive surface.
That shorter plastic is sufficiently conductive to discharge into
computer electronics - as was accurately posted previously. Careful
how you just know only because you automatically know.

This static problem also existed in the earliest IBM PC and some
Apples. Keyboard designs were changed by coating inside plastic with
a conductive material. Why the different cable for IBM AT - or did you
never ask such questions - did you always just somehow know? Yes, GT,
a direct challenge to your snide remarks because you just
automatically know?

The point was pointless to those who did not solve those infrequent
problems over many decades; who do not discover why strange problems
occurred. One example of static electric: a wax on a linoleum tile
floor that crashed only some computer when switch was isolated from
conductive materials by epoxy paint. Ground the switch. Then all
computers worked without the rare and infrequent failure.

 

[UCLAN]

They designed it to be wholey grounded already by the power
connector(s).

Really? Seems like a lot of trouble and expense for them to ensure all
necessary layers make contact with the mounting hole, including circuit
etching, if the boards didn't need it. It looks like they wanted better
ground as well. And manuals need not instruct direct contact with the
standoff if only the power connector was needed.

The main reason they're metal is that's the best way to make
a standoff. Same applies for any screw in anything that
doesn't even screw into anything metal.

That doesn't explain the MB ensuring contact with the standoff
via the mounting hole.

There is no impedance lower than the 9 return power leads
needed.

For DC current, yes. For high frequency stuff, no.

Would it interest you to know that some people even use
isolation mats on their PSU mounting so their case isn't
even grounded at all except through those 9 ground return
wires to the PSU? Again their systems work fine.

Right! And I suppose they use special plastic screws to mount their PSU
as well. Get real.

I suppose you'll just have to stop idealizing and see for
yourself. Plenty of us have already, there simply is no
need and it is easily proven.

You've operated a complete computer in a wooden or plexiglass case
for an extended period of time? Really? How long?

I'm not saying it will never work, just that poor high frequency grounding
will cause intermittent "glitches" in some systems where a metal chassis
is not used, or the MB is not mounted on a metallic tray, or a HF ground strap
between MB and PSU is not used. Lots of people smoke and don't get cancer, but
that doesn't mean nobody does.

 

[w_tom]

I'm not saying it will never work, just that poor high frequency grounding
will cause intermittent "glitches" in some systems where a metal chassis
is not used, or the MB is not mounted on a metallic tray, or a HF ground strap
between MB and PSU is not used.

Those high frequency currents are, instead, made completely
irrelevant by what was posted previously:

That wire back to power supply does have higher impedance.
Then we add missing facts. That high wire impedance is made
irrelevant by electrolytic and tantalum capacitors located on the
motherboard that are necessary to create a lower impedance.
Impedance lower than anything provided by a short ground
cable.

Not mentioned are even higher frequency currents. A motherboard is
chock full of ceramic capacitors adjacent to various ICs. Yes
adjacent as in less than one inch; that distance also may be critical.
No significant high frequency currents flow back to the power supply.
In fact, we might put more inductance on those wires just to further
restrict those high frequency currents on that power supply wire - for
reasons that do not apply here.

The hows and whys of grounding motherboard to chassis may involve
something completely different - also involving impedance. For
example (and only one example), put a computer on a glass table. Yes,
glass because other table top materials can be too conductive.
Generate massive static electricity in your body. Shock various parts
of the computer chassis including all eight corners. Those static
discharges should be so strong as to hurt. Computer software must not
crash. If computer does crash, then chassis grounding to motherboard
may be defective. These currents are completely different from
currents into power supply. Those currents are why motherboard ground
is typically different from chassis ground. Yes, both grounds share
an electrical connection - and are electrically different.

 

[GT]

You magically know plastic inside surface is not coated with a
conductive material?

No magic involved - unlike you clearly did, I had a look!

If that switch is pressed by a long plastic
material, then low conductive plastic would be sufficient to conduct
static elsewhere. But if your finger touches the switch plastic
button, then its body must be mounted on a more conductive surface.

Nope - its just a plastic button with a small microswitch connected to the
motherboard via 2 wires. No magic conductive materials, so low conductive
plastic pointers, just a plastic switch that you press with your finger!

That shorter plastic is sufficiently conductive to discharge into
computer electronics - as was accurately posted previously. Careful
how you just know only because you automatically know.

Nothing automatic - just had a look!

[blah blah blah]

 

[kony]

You magically know plastic inside surface is not coated with a
conductive material? If that switch is pressed by a long plastic
material, then low conductive plastic would be sufficient to conduct
static elsewhere. But if your finger touches the switch plastic
button, then its body must be mounted on a more conductive surface.
That shorter plastic is sufficiently conductive to discharge into
computer electronics - as was accurately posted previously. Careful
how you just know only because you automatically know.

Here is a typical, example switch that is used in an OEM or
aftermarket case,
http://www.e-switch.com/pdf/TL2201.pdf

Certainly some systems use different switches than others,
and especially so with this custom build, the OP is free to
choose any switch he desires. Personally, I think a switch
like the following would look rather sharp mounted in wood,
and it's long threaded body would more easily accomdate
that. Since that body is metal, grounding it would be easy.
Unfortunately they are out of stock but I vaguely recall
some other electronics surplus 'site has them too, perhaps
bgmicro.com or allelectronics.com
http://www.mpja.com/prodinfo.asp?number=16093+SW

Yes, upon checking bgmicro has these in both flat and
rounded dome style.
http://www.bgmicro.com/index.asp?PageAction=VIEWPROD&ProdID=9358
http://www.bgmicro.com/index.asp?PageAction=VIEWPROD&ProdID=9359

This static problem also existed in the earliest IBM PC and some
Apples. Keyboard designs were changed by coating inside plastic with
a conductive material.

That was back when things were built to last and cost a bit
more... today most are just made with cheapest method
possible which precludes using conductive coatings or
liners.

 

[kony]

kony wrote:

You've operated a complete computer in a wooden or plexiglass case
for an extended period of time? Really? How long?

I've operated a computer with no case at all hanging on the
wall like a picture for years. I always have some system on
a bench as well. How long? I've been doing it for quite a
few years.

I'm not saying it will never work, just that poor high frequency grounding
will cause intermittent "glitches" in some systems where a metal chassis
is not used, or the MB is not mounted on a metallic tray, or a HF ground strap
between MB and PSU is not used. Lots of people smoke and don't get cancer, but
that doesn't mean nobody does.

I'm still looking for examples. We can find examples of
people who smoke and have cancer, but what about systems
that didn't work properly until placed on/in this grounded
chassis? They do not need it, and you could test this
yourself instead of just a theory with no scientific method
to support resolution of the theory.

 

[w_tom]

Here is a typical, example switch that is used in an OEM or
aftermarket case,http://www.e-switch.com/pdf/TL2201.pdf

This switch is only rated:

Dielectric Strength: 500 VAC

Assuming that is voltage from button to switch conductors (and not
its switching voltage), then static electric discharge could pass from
finger directly into electronics. Some manufacturer solutions include
a long plastic connector between where the switch is pressed and the
switch body. That separation distance provides the 20,000 volt
isolation.

Shielding performs many solutions. That shielding is not always
obvious. Even the conductive material coating inside of a plastic case
(ie keyboard) is not obvious. Other techniques are also used.

Shielding is not for protecting electronics from exterior noise. As
Kony notes, that motherboard must be designed with noise margins so
that exterior noise causes no problems. A chassis connection from
motherboard to mounting plate is not to reduce connection impedance to
the power supply.

Downside of a Wooden PC is that the exterior electrostatic shield may
not exist so that human interface points may put electronics at risk
due to static electric dishcharge and so that excessive RF radiation
exists.

Up side of a wooden PC - good wood (when not painted) can make a
pretty case. A wooden case can be constructed to provide proper
shielding from these rare and unacceptable problems.

 

[UCLAN]

They do not need it, and you could test this
yourself instead of just a theory with no scientific method
to support resolution of the theory.

You want me to run my computer out of its case or in a plexiglass
case for a few months? No thanks. That would only prove it to *me*.
You would still doubt the results. An exercise in futility.

Post your phone number, and the next time I run into someone having
the problem I'll have him give you a call.

 

[kony]

This switch is only rated:
Assuming that is voltage from button to switch conductors (and not
its switching voltage), then static electric discharge could pass from
finger directly into electronics. Some manufacturer solutions include
a long plastic connector between where the switch is pressed and the
switch body. That separation distance provides the 20,000 volt
isolation.

Yes, the above switch always has a button in front of it,
that button usually being significantly longer than the
stock button they sell for the power switch, but perhaps
about the same as their stock buttons for the reset switch.
In some OEM cases the distance is even further as there is a
plastic lever assembly between the outer pushbutton and the
inner switch. These levers or extended length buttons have
become normal now that cases have a fairly deep air cavity
between the front of the bezel and the front metal wall of
the case frame.

 

[kony]

You want me to run my computer out of its case or in a plexiglass
case for a few months? No thanks. That would only prove it to *me*.
You would still doubt the results. An exercise in futility.

Post your phone number, and the next time I run into someone having
the problem I'll have him give you a call.

You claim something with no evidence, while there is ample
evidence of systems running w/o problems having no metal
case ground. Seems you have an argument without any weight
behind it, only an idea which you have not shown has any
_significant_ effect, only that in theory it might have some
tiny effect which is outside of a level which would actually
effect the operation of a system.

Similarly, in theory, having magnets in a hard drive could
create magnetic fields that also interfere with a computer's
operation. In practice, we see through proof of systems
running fine that this also has far too small an effect to
matter.

 

[~misfit~]

Somewhere on teh interweb kony typed:

I've operated a computer with no case at all hanging on the
wall like a picture for years. I always have some system on
a bench as well. How long? I've been doing it for quite a
few years.

LOL! I did that too! ATX board and had the HDD mounted on a (generous-sized)
mobo tray with the PSU on a shelf next to it. It was my firewall/ethernet
switch with all PCI slots populated with NICs. Made a great talking point
with folks that weren't familiar with a computer's insides.

 

[UCLAN]

You claim something with no evidence, while there is ample
evidence of systems running w/o problems having no metal
case ground. Seems you have an argument without any weight
behind it, only an idea which you have not shown has any
_significant_ effect, only that in theory it might have some
tiny effect which is outside of a level which would actually
effect the operation of a system.

As I wrote above, I'll have the owner of the computer having this problem
call you directly next time, but he'll probably simply add the ground
wire first.

 

[kony]

As I wrote above, I'll have the owner of the computer having this problem
call you directly next time, but he'll probably simply add the ground
wire first.

IMO, having the details here would be far more effective...
if there really is some board badly enough designed that it
needs this measure it would be good for others to be able to
find it through a search engine.

Meanwhile, if you insist on grounding yours, go right ahead
since it won't hurt anything, but as already shown time and
time again, neither will not doing it - except for the EMI
that then escapes to potentially effect some other equipment
nearby.

 

[w_tom]

As I wrote above, I'll have the owner of the computer having this problem
call you directly next time, but he'll probably simply add the ground
wire first.

"Doctor. When I bend this elbow, then its hurts."
"Then don't bend the elbow and pay the nurse on your way out."
That is ECLAN's logic. As Kony repeatedly and accurately notes, "You
claim something with no evidence ...". But speculation from UCLAN is
somehow presented as if fact.

This fact does exist and is ignored by UCLAN:

That wire back to power supply does have higher impedance.
Then we add missing facts. That high wire impedance is made
irrelevant by electrolytic and tantalum capacitors located on the
motherboard that are necessary to create a lower impedance.
Impedance lower than anything provided by a short ground
cable.

UCLAN demonstrates that 'speculation promoted as fact' is alive and
still frequent. To keep replying (he never once provides numbers), he
must ignore what he does not understand: those "electrolytic and
tantalum capacitors located on the motherboard that create lower
impedance".

A complaint here is about 'computer experts' who don't even know how
electricity works. To become A+ Certified Computer Tech, one needs no
electrical knowledge. UCLAN demonstrated what gets posted when one
does not have that basic electrical knowledge AND when one cannot
differentiate between speculation and facts.

Any low impedance created by that wire is made completely irrelevant
by something that provides even lower impedance: components on the
motherboard. A+ Certified Techs would not even know why those
components exist or what those components do. But those who do have
electrical knowledge can say confidently and with numerical facts that
his lower impedance connection accomplishes nothing.

Again, what UCLAN ignores because he does not understand it: filters
may be installed on those power supply wires to INCREASE that
reactance. Why do the opposite? Not relevant here. But also done
elsewhere for the same reasons that make UCLAN's solution useless,
ineffective, and an example of 'speculation promoted as fact'.

UCLAN - if your arguments here had merit, then you provided
numbers. You do not provide those numbers for two reasons. First -
that wire impedance is completely irrelevant as demonstrated even by
tantalum capacitors. Second - you don't demonstrate electrical
knowledge to explain the 'whys'. Nowhere do you cite what is solved
by that lower impedance connection. No 'whys' and no numbers; your
claims come from speculation. Kony has repeatedly posted technical
fact. Why, UCLAN, do you keep replying with speculation - and no
numbers? You have a solution to a problem that you cannot even
identify. The problem does not exist which UCLAN would know from
numbers and some fundamental electrical concepts. Do you even know
what a tantalum capacitor is?

"So don't bend the elbow". ECLAN cures a symptom without even
knowing what (or if) a problem exists. ECLAN does not even state what
lower impedance would accomplish. He demonstrates how other computer
'experts' also know without first learning how electricity works.

Mount that motherboard with plastic screws and it works just fine.
Somehow UCLAN knows those metal mounting screws must do something
electrical only because the screws are metal. If the screws are
metal, then an electrical reason must exist? That speculation is his
proof? UCLAN - those mounting holes must be coated in metal for
reasons mechanical. Only one hole - usually one closest to the DC
power connector - makes a necessary electrical connection for
different reasons discussed elsewhere. Reasons that are irrelevant to
anything posted by UCLAN.

Please first identify a problem before recommending a solution.
Your speculation results in a mythical problem and in a solution that
accomplishes nothing. Kony has repeatedly and accurately answered
your posts.

 

[UCLAN]

This fact does exist and is ignored by UCLAN:

A capacitance in series with a high impedance has absolutely no effect
on the high impedance. It would be a different story if the caps were
in parallel with the high impedance, as the caps would act as a low
impedance to the high frequency noise. But, they're NOT. So, they DON'T.

A complaint here is about 'computer experts' who don't even know how
electricity works. To become A+ Certified Computer Tech, one needs no
electrical knowledge. UCLAN demonstrated what gets posted when one
does not have that basic electrical knowledge AND when one cannot
differentiate between speculation and facts.

pot -> kettle -> black

Learn the difference between series and parallel circuits.

 

[kony]

A capacitance in series with a high impedance has absolutely no effect
on the high impedance.

They're not in series, these are decoupling caps.

It would be a different story if the caps were
in parallel with the high impedance, as the caps would act as a low
impedance to the high frequency noise. But, they're NOT. So, they DON'T.

You need to look at a few more chip schematics or bust out a
multimeter and see for yourself, they're parallel,
decoupling. Series caps on a motherboard are a tiny
minority of those present.

 

[UCLAN]

They're not in series, these are decoupling caps.

Doesn't matter *what* you call them. Their electrical position puts them in
series with the PSU power return lines, which are a high impedance return to
chassis ground. They *would* be a low impedance in parallel with those return
lines if the MB ground plane were tied directly to the chassis, which it's not
in a wooden case.

You need to look at a few more chip schematics or bust out a
multimeter and see for yourself, they're parallel,
decoupling. Series caps on a motherboard are a tiny
minority of those present.

*Any* cap to the ground plane on the MB is in series with the PSU ground
return wires. Only if the MB standoffs were directly grounded to the
chassis - which they're not in your scenario of a wooden case - would they
be in parallel. They may be in parallel *on the MB*, but they are in series
with the return lines *from* the MB to the PSU.

Your suggestion of testing this with a multimeter is useless. We are not
discussing DC here. A multimeter will only register resistance, *not*
impedance.

 

[kony]

Doesn't matter *what* you call them. Their electrical position puts them in
series with the PSU power return lines, which are a high impedance return to
chassis ground.

No it does not. Either you have a misunderstanding of the
word series, or you have not done much if any work with
computer electronics.

They *would* be a low impedance in parallel with those return
lines if the MB ground plane were tied directly to the chassis, which it's not
in a wooden case.
Non-applicable




*Any* cap to the ground plane on the MB is in series with the PSU ground
return wires.

No, the cap are generally across a VCC and Gnd. They are
expressly there for power smoothing which includes HF noise
when of a type capable of that frequency like the ceramics
all over the board. This is absolutely manditory circuit
design on everything these days from hard drives to
motherboards, to the processor carrier itself.

Your suggestion of testing this with a multimeter is useless. We are not
discussing DC here. A multimeter will only register resistance, *not*
impedance.

A multimeter would easily determine the parallel or series
placement of the caps in the circuit... if only you knew
where to probe.

This subtopic has reached it's fruitful conclusion. Dance
around a fire swinging a chicken over your head too if you
feel like it, which will of course be similarly unnecessary.

 

[w_tom]

A capacitance in series with a high impedance has absolutely no effect
on the high impedance. It would be a different story if the caps were
in parallel with the high impedance, as the caps would act as a low
impedance to the high frequency noise. But, they're NOT. So, they DON'T.

UCLAN has no electrical knowledge. Accused of posting as so many
computer techs who somehow are experts but do not even know how
electricity works. This is not intended for UCLAN. This post is
intended for others as a warning. Some routinely know; but cannot
bother to first learn even how electricity works.

How does one know UCLAN is posting myths? First, he does not post
numbers for his 'low impedance' solution. Second, he posts a
solution for a problem he cannot even define. Third, he knows only
because he wired something and it worked; as if that is proof that
some problem even existed. Above three are characteristic of those
who proclaim as only a lying politician would; who need not learn
facts, numbers, and reasons 'why'. UCLAN cannot even define the
problem. But he has a solution.

UCLAN tells us those electrolytic and tantalum capacitors are in
series. Of course not. If in series, then no DC power could flow
from power supply to motherboard. UCLAN is that confused.

As Kony accurately notes, those capacitors are in parallel. They
are bypass capacitors. Their function is to create a low impedance
connection. If ULCAN had learned, then he knows what capacitors do,
how those capacitors were connected, what their purpose is, and why
his low impedance connection solves nothing. UCLAN had to be ignorant
on every point to post his reply. It explains why he ignored repeated
referenced to those tantalum, et al capacitors. To make his claims,
UCLAN had to know zero of four above functions. He had to be that
electrically naive.

Nothing posted here will be comprehended by UCLAN. To learn, he
must acknowledge he was wrong. He does not understand how electricity
works and denies electrical facts. UCLAN is too devoted to myths to
acknowledge reality. But again, this is not for UCLAN's benefit.
This post warns others that numerous myths like this are posted by
'self proclaimed' computer experts. This post is a warning to others
about those who are computer experts, but do not even know how
electricity works.

UCLAN does not even understand what a multimeter can measure. But
again, he somehow knows without understanding the significance of
numbers. He does not even understand his solution solves a mythical
problem. And then he overtly denies Kony's electrical facts. Those
capacitor are not in series no matter how voraciously UCLAN denies
electrical concepts.