mmm yeah not to beat a dead hoss
but think of grounding like this:
every object (including your body) has a static electric charge (positive, or negative) (or zero, which technically isn't a charge) at all times.
So let's use the example of a $20 memory stick you just bought that's sitting in a package on your desk.
I'm just making these numbers up, I have no idea what would be realistic, except that it would be in the thousands of volts. And I might have the direction of current flow backwards too, but whatever. per wikipedia, a typical static electric zap that you can see, feel, or hear is around 30,000 volts.
http://en.wikipedia.org/wiki/Static_electricityso for example:
Your body might have a static charge of +5000 volts.
Lets say the memory stick package has a charge of +1000 volts.
As soon as you pick up the memory stick package, static electricity will flow from the memory stick package to your body. This will cause the charge to equalize between your body and the memory package. The end result might be that now your body has a charge of 4000 volts, and the memory package has a charge of 4000 volts. (Because your body is more massive than the memory package, it can hold more of a charge at a given voltage than the memory package.)
So far, the memory inside the memory package is okay... the memory stick's charge did just change by 3000 volts, but the charge reached the memory stick by flowing through the package. The package is touching the memory stick all over, especially if the memory stick is wrapped in an anti-static bag. (the anti-static bag is electrically conductive.) Because the package is touching the memory stick over a large surface area, the change in static voltage is not isolated to a small part of the stick. The flow of electrons is therefore spread out over the entire memory stick, and so per unit of surface area, there are fewer electrons.
Now let's suppose that the memory stick wasn't in a package, but instead was just sitting on your desk. Maybe you just pulled it out of it's package or you pulled it out of your computer.
If your body is at +5000 volts, and the memory stick is at +1000 volts, when you touch the memory stick with your fingers to pick it up, if the tip of your fingers touches one of the many metal contacts on the stick, that could be bad... what will happen is that a 4000 volt potential will force electrons through that single contact... the entire flow of electrons will be directed into the heart of the memory stick via that electrical contact, and zap, if the static charge is big enough in terms of wattage, you've just fried your memory stick.
Wearing a ground strap on your wrist is helpful because the ground strap will allow the static voltage potential to equalize between your body and whatever the ground strap is clipped to.
(The ground strap contains a high-value resistor in series with the strap, so that low-amperage high-voltage charges (static charges) can pass through it, whereas high-amperage high-voltage charges (dummy jacking a screw driver into his power supply) won't pass through it, thereby protecting the dummy from being electrocuted, at least via the ground strap anyway.)
So let's say your computer chassis is more or less at a neutral charge, and you put on a ground strap and clip it to your computer's chassis. Now your body is also more or less at a neutral charge. But let's say that for whatever reason, the memory stick sitting on your desk is charged with a static charge at -50,000 volts. Ya know, it's a dry environment, maybe the pet cat was batting it around. Whatever. Now you reach over and touch the memory stick. It doesn't matter that you're wearing a ground strap, you just fried your memory stick, because as soon as you touch the memory stick, 50,000 volts will flow from the memory stick into your body. It might even be an audible zap. Okay, this is all hypotetical; I don't know if a memory stick has enough mass to actually hold enough charge to fry it's self. But certainly, if the memory stick is sitting on an ungrounded object that has more mass, that object could have enough charge to fry the stick... that charge would flow between that object and your body via the stick.
so based on the foregoing assumptions of how this all works, here's what I do when I mess with computers:
I touch the metal computer case every 30 seconds or so
I touch stuff like memory chips on the edges before I touch them anywhere else. if an item (such as an expansion card) has any metal pieces attached to it, such as the metal casing of a port, I touch the metal first as the metal is generally connected to the ground tracings on the card, and therefore is electrically common with the greatest amount of surface area of the card.
While I am holding the new item, I touch the metal computer case before I introduce a new item to the computer.
if I have to set down a chip or whatever, I try to set it down on or in the computer case, not on my desk.
But for the most part, if you use common sense, you'll be fine... don't walk around in fuzzy bunny slippers while you're working on your computer. barefoot is best as some shoes are very well insulated and allow static to build up on your body.
The other day I took a laptop __completely__ apart, (except I didn't pull the CPU), I didn't observe any special precautions beyond grounding myself and the laptop components with a common ground (my desktop chassis) before I re-assembled them... and ta da, everything still worked.
computer components have for many years now been less susceptible to static electricity than they once were...
finally, when it comes to memory, run a program like
http://www.memtest86.com/ to make sure that your memory is working correctly. Bad memory is all too common. It might be because it got fried with static electricity, or maybe it's just defective out of the box. Either way, run a program to check the performance of your memory for errors so you can be sure...
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Topic: Help with grounding? (Read 3821 times)