Wednesday, April 05, 2006

Why PCs Die - Part III

Upgrading your PC is relatively easy to do yourself, as long as you inform yourself about the task in advance and have an average amount of manual dexterity. Unfortunately sometimes owners will decide to perform an upgrade without having a clear understanding of the pitfalls that can arise in the course of performing it.

So what kind of things can go wrong during an upgrade that can leave you with a dead PC? Number 1 on the pitfalls list is ESD, or electrostatic discharge. This occurs when static electricity builds up on your body and you then touch a component in the computer. As the computer is generally at a lower potential to your body static electricity will jump from your body to the computer and this discharge is sufficient to fry many of the sensitive semiconductors on your motherboard and plug-in cards. While you can feel electrostatic discharges of 3,000 volts, smaller charges are below the threshold of human sensation. Unfortunately, smaller charges can and do damage semiconductor devices. Many of the CMOS technology components used in PCs can be damaged by charges of less than 1,000 volts. Some of the more sophisticated components can be damaged by charges as low as 10 volts. Some common activities that generate static electricity on your body include:

Walking across a carpet, 1,500 to 35,000 volts
Walking over untreated vinyl floor, 250 to 12,000 volts
Worker at a bench, 700 to 6,000 volts
Vinyl envelope used for work instructions, 600 to 7,000 volts
Picking up a common plastic bag from a bench, 1,200 to 20,000 volts.

I had one computer in recently where the owner had decided to upgrade the video card with a newer model. When he changed cards the PC wouldn't POST so he thought that he had a dud video card. He then put back the old card only to find that the PC still wouldn't POST. The problem was that he had no knowledge of the risk of ESD or how to eliminate it which had resulted in him frying his motherboard - an expensive mistake.

An upgrade that many people consider is adding extra memory and, in theory, this is one of the easiest upgrades to perform. However, what many people are suprised to find is that inserting modern memory modules e.g. DDR2 type, requires a heck of a force to get the module into the slot, up to 30 kgs in fact. Many first time upgraders struggle when they come up against the level of force required and can in fact apply too much force in a desperate attempt to get the module seated. The problem with applying excessive force is that the underlying motherboard can flex and, if luck is against you, break a conducting track, resulting in a dead board and a dead PC.

The next upgrade that can go wrong is one that I've had personal experience of and goes to show that even when you (think) you know what you're doing, things can go wrong. This one involves adding a new hard disk to your PC, either replacing an existing one or adding a second. The hard disk is connected to the motherboard with an IDE cable (newer SATA drives use a different cable and what I am about to describe doesn't apply to them) that plugs into a 40-pin connector on the hard disk (see picture). Now the thing about the 40-pin plug on the end of the IDE cable quite often has a solid block of plastic where it mates with the the absent pin 20 in the hard disk connector. If the plug is inserted into the connector wrong way round (pin 1 lined up with pin 40 and pin 39 lined up with pin 2) then the solid block of plastic on the plug crushes pin 19 and you have a dead disk and a PC that cannot boot. Believe me, this is easier to do than it should be and can happen because the connector and plug are not adequately keyed to prevent misalignment and the pins are made of a very soft metal that bends too easily. On the one and only occasion that this happened to me I was able to straighten the crushed pin 19 with some long-nosed pliers and rectify the situation.

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