testing mobo outside of a case?

[okeefe58]

hi

i cant even think of how to word this question to do a search , so maybe someone here can help -i want to test a couple open box mobos i bought by just hooking up to a power supply and monitor (put in a mem stick of course) and see if they post -is this ok to do? is a mobo supposed to be mounted inside a case for reasons other than the obvious? are the screwholes grounds? and case for grounding everything together?

dennis
okeefe58@yahoo.com

 

[PottedMeat]

yes thats fine, many people test components by setting the motherboard on a table and hooking up the cards/cables and turning it on.

the case is just to protect the components and provide shielding/grounding.

 

[Mark R]

The mobo will be adequately grounded through the big ATX connector.

 

[Rastus]

As a matter of fact, you do not want to supply a seperate ground to your mobo. You will create a ground loop if the two grounds are even slightly different.

 

[CycloWizard]

One of my old roommates ran a gaming server out of a desk drawer for a couple years - just a motherboard/CPU/RAM/HDD sitting in a drawer.

 

[zylander]

Originally posted by: CycloWizard
One of my old roommates ran a gaming server out of a desk drawer for a couple years - just a motherboard/CPU/RAM/HDD sitting in a drawer.

heh, my friend did the same thing, except he had all the components stretched across a shelf.

 

[MrDudeMan]

I put together a computer in a plexiglass box on a piece of wood. It ran quite well as an MP3 server for over a year. It had 16 xbox hard drives in it connected to PCI controller cards for a total of 125gb, lol. The point of the story is that the motherboard can be just about anywhere other than a giant piece of metal and it will be fine.

 

[mindless1]

Originally posted by: Rastus
As a matter of fact, you do not want to supply a seperate ground to your mobo. You will create a ground loop if the two grounds are even slightly different.

Untrue, many (most?) parts in metal cases have multiple ground paths.
Ground loops are not significant when there are so many grounds that none have particularly large differences in current if no alternate grounding path.

 

[MrDudeMan]

Originally posted by: mindless1

Originally posted by: Rastus
As a matter of fact, you do not want to supply a seperate ground to your mobo. You will create a ground loop if the two grounds are even slightly different.

Untrue, many (most?) parts in metal cases have multiple ground paths.
Ground loops are not significant when there are so many grounds that none have particularly large differences in current if no alternate grounding path.

There may be multiple paths in a case, but I think he meant simply connecting a single, alternate ground to the motherboard in some way. If that were the case, then it could be a significant issue. I'm not familiar with the grouding inside of a computer case, but I was under the impression that most of the grounding was done through the ATX connector, making a "single" ground connection.

 

[mindless1]

Originally posted by: MrDudeManThere may be multiple paths in a case, but I think he meant simply connecting a single, alternate ground to the motherboard in some way. If that were the case, then it could be a significant issue. I'm not familiar with the grouding inside of a computer case, but I was under the impression that most of the grounding was done through the ATX connector, making a "single" ground connection.

Alternate paths to the motherboard in a case include the standoffs the board is mounted on, card brackets that are ground and touching or screwed to the case (ground), drive/other peripherals with grounded metal cases screwed to the system case.

Alternate paths regardless of case, may include video card with power connector, drives, sound cards with cables connected, video or capture/tuner cards with cables connected, other cards.

It would be a very unusual system to not have several ground loops. Sometimes the loops DO cause issues, like when it's not a digital signal but rather analog on integrated sound you may get noise on the output depending on system load. Sensitive amps->speakers are more likely to reveal that noise.

Yes the only "required" ground is through the board (or other parts' connector) pins/leads, but if there were a single alternate ground to the board, it should still work fine.

 

[MrDudeMan]

Originally posted by: mindless1

Originally posted by: MrDudeManThere may be multiple paths in a case, but I think he meant simply connecting a single, alternate ground to the motherboard in some way. If that were the case, then it could be a significant issue. I'm not familiar with the grouding inside of a computer case, but I was under the impression that most of the grounding was done through the ATX connector, making a "single" ground connection.

Alternate paths to the motherboard in a case include the standoffs the board is mounted on, card brackets that are ground and touching or screwed to the case (ground), drive/other peripherals with grounded metal cases screwed to the system case.

Alternate paths regardless of case, may include video card with power connector, drives, sound cards with cables connected, video or capture/tuner cards with cables connected, other cards.

It would be a very unusual system to not have several ground loops. Sometimes the loops DO cause issues, like when it's not a digital signal but rather analog on integrated sound you may get noise on the output depending on system load. Sensitive amps->speakers are more likely to reveal that noise.

Yes the only "required" ground is through the board (or other parts' connector) pins/leads, but if there were a single alternate ground to the board, it should still work fine.

I wouldn't really count hard drives, floppies, etc. as ground paths since they are on the same ground line as the ATX connector. It all meets in one physical location, or at least on every PSU I've ever dissected. Also, I've tested multiple motherboards laying around for ground planes around the support screws and I've never had it beep on the multi-meter for continuity. The grounding pads can also be connected to non-metal stand-offs, which removes them as a grounding loop source. The shielding around the motherboard peripherals is not a true ground source - it is a shield ground with very little or no current running through it. Lastly, the power from an external video card connection will be at the same ground potential as the ATX connecter ground potential because they are the same physical line. I have a sound card in front of me that is not registering the mounting bracket as part of the ground circuit.

 

[mindless1]

Originally posted by: MrDudeManI wouldn't really count hard drives, floppies, etc. as ground paths since they are on the same ground line as the ATX connector. It all meets in one physical location, or at least on every PSU I've ever dissected.

No, there are grounds through the data cables, and grounding of the drive/etc frame as well. Several ground paths.

Also, I've tested multiple motherboards laying around for ground planes around the support screws and I've never had it beep on the multi-meter for continuity.

That's a curious thing you're reporting, since I've found continuity as the norm, and just to double-check I checked continuity on two boards in front of me and both (are).

The grounding pads can also be connected to non-metal stand-offs, which removes them as a grounding loop source.

I don't think anybody claimed a board "had" to be grounded through them, but that IS the intention, why board manufacturers deliberately connect them to ground plane instead of the alternative that would be as easy for them - a break in the copper before the hole.

The shielding around the motherboard peripherals is not a true ground source - it is a shield ground with very little or no current running through it.

It is deliberately ground on the parts I'd mentioned it is a "true ground source". If you mean it is not intended as the primary ground return for supply current or signaling purposes, you are right - but it doesn't in any way change that it IS a ground source by intentional design. To say it doesn't have much current through it is beside the point, we were not talking about fitness for any given load, rather that there ARE multiple ground paths and in the end, if you didn't have the primary ground wire delivery from the PSU, it would then be a higher current ground path.

Lastly, the power from an external video card connection will be at the same ground potential as the ATX connecter ground potential because they are the same physical line.

Wrong. Having an electrical connection is not the same thing as same potential. That's the whole point of our distinctions between multiple grounds. When you have impedance and/or loops, particularly higher current to some devices like a CPU or video card, your ground return currents will result in it being a different gnd potential than another ground line.

Maybe I didn't word the above very well. Take a PSU - forget about the system, just a PSU. Connect a 1 Ohm load to the CPU connector. That's 12A through it. Leave a drive plug empty. You now have different GND potential at the CPU plug than at the empty drive plug. "Ideally" there wouldn't be, in a hypothetical system where there were no constraints like wire size, cost, flexiblity, etc. In a real system there is.

I have a sound card in front of me that is not registering the mounting bracket as part of the ground circuit.

Ok, but I didn't claim it was necessary. The vast majority of sound cards do though, there is typically a ground plane over (most of) the back of the card and (again as with a motherboard) deliberate exposed and tinned copper where the bracket screws to it. It is a curious thing that your parts are so oddly made, the odds are against having more than one that is in a limited # of tests. What makes and models are these? I'm wondering if your multimeter has some problem, either that or at least with the sound card you are measuring a part of the bracket that has coating over the metal. On a non-bare metal surface I put a needle tip on the meter probe so it can pierce the surface layer.

 

[Matthias99]

Wrong. Having an electrical connection is not the same thing as same potential. That's the whole point of our distinctions between multiple grounds. When you have impedance and/or loops, particularly higher current to some devices like a CPU or video card, your ground return currents will result in it being a different gnd potential than another ground line.

Maybe I didn't word the above very well. Take a PSU - forget about the system, just a PSU. Connect a 1 Ohm load to the CPU connector. That's 12A through it. Leave a drive plug empty. You now have different GND potential at the CPU plug than at the empty drive plug. "Ideally" there wouldn't be, in a hypothetical system where there were no constraints like wire size, cost, flexiblity, etc. In a real system there is.

I may have to pull out my meter and look at the connectors on my PSU -- but I would expect the voltage differences at different points in the ground returns to be very small. There should be, ignoring small local voltage fluctuations due to current flow, one consistent electrical ground for the entire system. Generally everything is grounded either to the PSU or case (or both), and the case should be grounded to the PSU through its metal casing. You can definitely run an ATX system with no ground other than the one provided through the PSU; the assumption is that this is the "definitive" electrical ground.

Alternate paths to the motherboard in a case include the standoffs the board is mounted on, card brackets that are ground and touching or screwed to the case (ground), drive/other peripherals with grounded metal cases screwed to the system case.

Alternate paths regardless of case, may include video card with power connector, drives, sound cards with cables connected, video or capture/tuner cards with cables connected, other cards.

These should all be the same ground -- the only significant current return for the system should be back through the PSU to the wall outlet. Any voltage differences between "different" grounds in the system should be very small -- and if they are not you might have problems, since it will change the apparent voltage being seen by the various components.

 

[mindless1]

Originally posted by: Matthias99These should all be the same ground -- the only significant current return for the system should be back through the PSU to the wall outlet. Any voltage differences between "different" grounds in the system should be very small -- and if they are not you might have problems, since it will change the apparent voltage being seen by the various components.

Yes, I didn't mean to imply they weren't the same ground but they are multiple ground paths or loops present in practically all systems. It is true the voltage difference is small, the point is that they are there and yet it is no problem.

 

[Matthias99]

Originally posted by: mindless1

Originally posted by: Matthias99These should all be the same ground -- the only significant current return for the system should be back through the PSU to the wall outlet. Any voltage differences between "different" grounds in the system should be very small -- and if they are not you might have problems, since it will change the apparent voltage being seen by the various components.

Yes, I didn't mean to imply they weren't the same ground but they are multiple ground paths or loops present in practically all systems. It is true the voltage difference is small, the point is that they are there and yet it is no problem.

Usually when people refer to a "ground loop" they mean an electrical circuit that is (usually by mistake) connected to two truly distinct grounds, not a circuit or part of a circuit that has two paths to the same ground. This leads to things like getting 60Hz hum in analog audio equipment.

Multiple unintended ground paths can also be significant, but generally not at this scale.

 

[mindless1]

Originally posted by: Matthias99Usually when people refer to a "ground loop" they mean an electrical circuit that is (usually by mistake) connected to two truly distinct grounds, not a circuit or part of a circuit that has two paths to the same ground. This leads to things like getting 60Hz hum in analog audio equipment.

Multiple unintended ground paths can also be significant, but generally not at this scale.

Funny you mention audio equipment because I build my own amps. There is no difference, in audio as well a ground loop is merely two paths to the same ground. That ground is a potential, which will have different voltages due to impedance and current changes. The same is true in a PC! It "could" be as you described, where there are two truely distinct grounds but it is not at all reserved to that scenario in audio, or computers. They can't really be considered two distinct ground though, if there is a wire connecting them it is roughly same situation as in a computer with a power ground lead. It is then the loop when a second path is involved - also like in a computer.

The distinction is when you have low level signals, levels low enough that the changes in ground potential are a significant % of the signal level. This is important in audio because the whole point is precise signal levels. While the same situation in computers, the result is not so important because it is digital and only has to fall above or below a threshold value - there is some immunity to the noise.

The grounds and loops scenario between them are the same, the only difference is whether the ground loop effects the intended result. In a computer it still can in limited ways like motherboard integral audio output noise.

 

[Matthias99]

Originally posted by: mindless1

Originally posted by: Matthias99Usually when people refer to a "ground loop" they mean an electrical circuit that is (usually by mistake) connected to two truly distinct grounds, not a circuit or part of a circuit that has two paths to the same ground. This leads to things like getting 60Hz hum in analog audio equipment.

Multiple unintended ground paths can also be significant, but generally not at this scale.

Funny you mention audio equipment because I build my own amps. There is no difference, in audio as well a ground loop is merely two paths to the same ground. That ground is a potential, which will have different voltages due to impedance and current changes. The same is true in a PC! It "could" be as you described, where there are two truely distinct grounds but it is not at all reserved to that scenario in audio, or computers. They can't really be considered two distinct ground though, if there is a wire connecting them it is roughly same situation as in a computer with a power ground lead. It is then the loop when a second path is involved - also like in a computer.

The distinction is when you have low level signals, levels low enough that the changes in ground potential are a significant % of the signal level. This is important in audio because the whole point is precise signal levels. While the same situation in computers, the result is not so important because it is digital and only has to fall above or below a threshold value - there is some immunity to the noise.

The grounds and loops scenario between them are the same, the only difference is whether the ground loop effects the intended result. In a computer it still can in limited ways like motherboard integral audio output noise.

I suppose it's mostly a matter of perspective -- most "grounds" eventually go to an earth ground, so at some level they're all the same.

I'm just saying that when someone talks about a "ground loop", I usually think of situations like having two pieces of audio equipment plugged into different A/C circuits (which can have significantly different voltages, be out of phase, etc.) As compared to having, within a single device, two slightly different paths to a single definitive ground. Although yes, depending on scale and severity, they can both cause the same problems and can be seen as the same.

 

[jagec]

Originally posted by: mindless1
Funny you mention audio equipment because I build my own amps. There is no difference, in audio as well a ground loop is merely two paths to the same ground. That ground is a potential, which will have different voltages due to impedance and current changes.

How can "the same ground" have a potential? Obviously it's NOT the same ground.

 

[Matthias99]

Originally posted by: jagec

Originally posted by: mindless1
Funny you mention audio equipment because I build my own amps. There is no difference, in audio as well a ground loop is merely two paths to the same ground. That ground is a potential, which will have different voltages due to impedance and current changes.

How can "the same ground" have a potential? Obviously it's NOT the same ground.

In an abstract modelling sort of way, no, it can't, unless you really have two grounds.

In practice, circuits aren't perfect (and everything is analog if you break it down far enough.) Consider one of the leads coming off your PC's power supply. Let's say you have two devices plugged into it -- one at the end and one in the middle.

Current flows down the lead, into each of the devices (in parallel), and then back through the ground (black) wire to the PSU. In theory, this wire is always at 0V relative to the wall/PSU ground. If you hooked up a voltmeter to the ground wire right next to the PSU and measured its voltage relative to the wall/PSU ground, you'd get very very close to 0V (so close that a standard household voltmeter would probably say it's exactly 0V, though if you had sensitive enough gear you'd see some tiny difference). But out at the end of the lead you'd have a slightly higher voltage, since the electrons being dumped into the ground wire take a little bit of time to actually work their way down to the PSU, producing a higher voltage locally as they pass through. Probably, on the scale of your PSU, you'd be talking millivolts at most.

In general, unless a circuit is either badly flawed or hooked up to two truly different grounds, any such differences will be extremely small and thus not a problem. If something is wrong with the circuit, especially if it's a sensitive analog circuit like an amplifier, tiny voltage differences like that can get magnified and cause real problems.

 

[Check]

I always thought the point of putting the motherboard on posts (or whatever you want to call those things we screw the mobo into) was to keep the solder points on the back of the board from getting shorted from touching the metal case. I find it hard to believe that they are to ground the mother board in different places since there is no way for a voltage to get to ground (via the ground on the three pronged outlet), unless of course you are going to tell me that the metal casing on the PSU leads to the ground...

Same thing when talking hard drives and other things in the computer being grounded because they are connected to the metal case, I think the only grounding they have is in the power connector.

I dunno something just doesn't add up here with the whole being grounded in different places, or whatever.

Maybe I should take apart the broken PSU I have sitting in my closet to see if it actually has the metal case grounded or not.

 

[Navid]

Originally posted by: check
I always thought the point of putting the motherboard on posts (or whatever you want to call those things we screw the mobo into) was to keep the solder points on the back of the board from getting shorted from touching the metal case. I find it hard to believe that they are to ground the mother board in different places since there is no way for a voltage to get to ground (via the ground on the three pronged outlet), unless of course you are going to tell me that the metal casing on the PSU leads to the ground...

Same thing when talking hard drives and other things in the computer being grounded because they are connected to the metal case, I think the only grounding they have is in the power connector.

I dunno something just doesn't add up here with the whole being grounded in different places, or whatever.

Maybe I should take apart the broken PSU I have sitting in my closet to see if it actually has the metal case grounded or not.

The power supply case is electrically connected to the third prong power connector of the PSU. This is the same as any electrical utility, to protect you if there is an accidental short from the hot power line to the metallic (conductive) body of the unit, and you touch the unit.

The power supply case is also electrically connected to the black wires (common return path) on the PSU connectors (Molex) being connected to the motherboard, hard drives, fans, etc.
This is to establish a known ground plane potential on the motherboard and other PC components.

 

[Check]

I should have known that anything with a metal case that gets plugged into a wall is generally grounded (duh).

The only question I have is, what about acrylic cases? There is no ground plane potential since the case is non conductive, wouldn't charges be able to build up on the casings of the devices?

 

[Navid]

Originally posted by: check
The only question I have is, what about acrylic cases? There is no ground plane potential since the case is non conductive, wouldn't charges be able to build up on the casings of the devices?

I have trouble understanding your question!

The motherboard ground plane is connected to the third prong of the power outlet (if it exists). So, the motherboard (and all the cards and components attached to it) is grounded as soon as you connect the 20 or 24-pin connector to the motherboard and plug in the power, in a metallic case, acrylic case, or even with no case.

 

[Check]

I was referring to before when they (whoever those posters were) were talking about the case acting as a ground as well so all of the devices are grounded via being connected to the case as well through the molex or ATX power.

It doesn't really matter, just wondering if a significant voltage can build up on the casing to a hard drive or cdrom in an acrylic case since there is electricity flowing inside of the hard drive (creating a small field) and the outside case to the drive is isolated and there would be no path to ground if a voltage was created.

I'm probably not explaining it properly considering the amount of physics and electrical I have taken. Oh well.

 

[Navid]

Originally posted by: check
I was referring to before when they (whoever those posters were) were talking about the case acting as a ground as well so all of the devices are grounded via being connected to the case as well through the molex or ATX power.

It doesn't really matter, just wondering if a significant voltage can build up on the casing to a hard drive or cdrom in an acrylic case since there is electricity flowing inside of the hard drive (creating a small field) and the outside case to the drive is isolated and there would be no path to ground if a voltage was created.

I'm probably not explaining it properly considering the amount of physics and electrical I have taken. Oh well.

You are explaining it fine.

The ground connection on an electric utility (washing machine, refrigerator, TV, PC, ...) through the third connector of the power outlet is there to protect the user. It does not provide any protection for the equipment itself.

You could power electronic equipment with battery. They are not connected to ground and they do not need to be.