This is the first part in what will be an ongoing and occasional series looking at the factors that can cause your PC to die or, at best, become fatally wounded.
Despite what you might think, modern PCs are incredibly reliable, at least at the electrical and electronic level. Reliability at the operating system and application software level is another matter entirely, which we'll deal with in coming weeks.
Today I want to talk about the number 1 cause of system failure in a PC, which is faulty power supply units (PSU). For most PC users the PSU is not something that you are likely to be aware of or give any consideration to. Unlike some of the other components, like the CPU or the RAM, there is very little hype about the PSU in the marketing brochures. Let's face it, a piece of metal and wire the size of a brick that converts 230 volts AC into 12, 5 and 3.3 volts DC is not something most of us would cross the road to find out more about. However, its the first part of the computer that the electricity hits when you press the big round button on the front panel so you're right in thinkng that if this component isn't working then the rest of the machine is going to find it tough to get going! In essence, the PSU is a big transformer (or more correctly a series of transformers) that converts the input AC voltage into different output DC voltages. The 3.3- and 5-volt supplies are typically used by digital circuits on the motherboard, while the 12-volt supply is used to run motors in disk drives and fans.
The most common cause of power supply failures is overheating. Once power supplies get to very high temperatures, the components inside of them fail resulting in unacceptable or no voltage being supplied to the computer components. Power supplies generally overheat due to improper airflow through the unit. This typically is the result of either a failing or failed cooling fan or a blocked air intake. One is fairly easy to detect, but the other is more difficult. As a fan's bearings tend to wear out (a precursor to their failure), they produce a greater amount of noise. Often this will be a scraping or high pitched tone. If your power supply is showing these audible signs, its best to take the time and money to replace the power supply. If the fan fails completely, the power supply will likely overheat which can result in greater damage to your components.
As I said at the outset, modern computers are extremely reliable. However, PC Medic can confirm that the most common hardware failure we see is due to defective PSUs. More about PSUs again.