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Metal cases and ESD

S

Seraphim974

Gawd
Joined
Nov 7, 2003
Messages
928
So I walked across my bedroom floor the other day and go to take out my headphones from the front connector while my computer is running and hear and faintly feel a shock and my whole computer freezes while making a loud buzz through the speakers until I have to press the reset button.

The computer, which is in signature with aluminum Lian-Li case, seems to work alright still but doesn't it seem odd to design a case that is metal without the metal being grounded or something because it seems like all the static that the case receives goes straight through the entire computer.

Am I missing something?
 
Thanks. That eases my mind. I was just looking at my case a second ago and thought that the PSU should do exactly that. Just kind of odd that my computer reacted in that way.
 
Seraphim974 said:
Thanks. That eases my mind. I was just looking at my case a second ago and thought that the PSU should do exactly that. Just kind of odd that my computer reacted in that way.
Click to expand...

That really is, are you sure that the outlet the the machine is plugged into is grounded? You can check with a cheap tester like this or if you have a meter that will check for continuity handy you can check between the bottom prong on the receptacle (ground) and the larger slot on the outlet (neutral).
 
It's grounded. I'm using a belkin surge protector that will light up an LED when not grounded. I might just re-screw my PSU into the case and not worry about it.
 
I get ridiculous static electricity in Colorado (really dry). I apparently discharged some static and my comp froze as well.

As a precaution, I grounded the chassis in 3 places (mobo tray, HDD area, and top cover) to the PSU and havent had any ESD related issues since. I feel like one would have been fine but 3 is even better, right?
 
right, just because a case is made of metal it doesn't nessacerally mean that all of the parts have good electrical connections to each other. Bonding all the parts together with nice thick wire should reduce the voltages between them when they are hit with the sudden high voltage of a static shock.
 
Well I just shocked and stopped my computer again with a loud buzz coming through the speakers so I turned a rca video cable into a standard wire and loosened an internal screw that appears to contact the front of the computer and looped one end of the wire under the screw and the same thing to a screw on my PSU. I don't want to test it but I haven't felt anything yet so it appears to be working.
 
Seraphim974 said:
Well I just shocked and stopped my computer again with a loud buzz coming through the speakers so I turned a rca video cable into a standard wire and loosened an internal screw that appears to contact the front of the computer and looped one end of the wire under the screw and the same thing to a screw on my PSU. I don't want to test it but I haven't felt anything yet so it appears to be working.
Click to expand...

I tested mine because I didnt believe that the chassis wasn't grounded anywhere. Dragged my feet around for a minute, and touched the case. Sure enough, I got a hard lock while playing music in itunes (skipping and frozen comp).
Grounded the case, and tried it again and it worked like a charm (I think, lol).
 
Probably what happens is that there is not a sufficiently direct path to ground from the case to earth, and the discharge flows through everything connected including the ground plane on the motherboard causing a momentary shift in ground potential and crashing things.
 
My current rig (not the ancient one in my sig) was hit by lightning last summer. Only the motherboard failed, all other parts working and accounted for. In the process of upgrading my case and cooling solutions. Interestingly enough for a short time some of the stuff inside was magnetized. Very strange.
 
Cases are supposed to be mains grounded via contact with the power supply's enclosure.

Many current cases, however, have frames which are painted, and screws are sometimes painted as well. As such, even if the case itself is metal, the case's metal may not have proper contact with the power supply's enclosure. (Black screws may look nice, but they should technically not be used to connect the power supply to the case unless they are something like anodized aluminum screws and not painted.)

Also, even if the case is properly grounded via the power supply's enclosure, this does not mean that every point on a metal chassis will have the same ground. In other words, it is still possible for a ground loop (wherein a small amount of current, due to a slight difference in potential, is present between points A and B on a case) to occur. This is due to a variety of reasons, including high powered devices, such as graphics cards, adding noise to the PCI backplane as well as differences in resistance between various points on the case.
 
I just stopped my computer again by making contact with the front panel after walking to the computer and sitting down and this time my monitor just lost signal and I has to reset the computer to get the monitor back up. I'm using a LIAN LI Black Aluminum PC-C32B item: N82E16811112147 on newegg.com. I've already got the small wire from one channel of an RCA audio cable (and also one polarity of the one channel of the cable) linking the front panel to the power supply by tightening the ends of the wire under the screws of the PSU and case. Also, each side panel is connected in the same way to the front panel internally with the exact same wire.

Seeing as how I am still zapping my computer, what else should I do. Should I do more wiring? Is this wire too thin to disperse the charge through the power supply and into the earth fast enough?

Here is how I have the case wired presently, notice the wires in the top-left and lower-left corners.

(shocked it again 2 hours after this post and froze the computer again. I think I am going to find a cool plastic case on newegg...)

diagramf.png
 
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