BOOT CAMP 553 (03/12/08)

Make Do and Mend, part 5


Back in the 1980s Amstrad launched a PC with no cooling fans. It didn’t need any as all of the parts that got hot – principally the power supply – were built into the monitor, which was able to safely dissipate the heat through convection. However, this didn’t stop a scare campaign, which eventually forced Amstrad into fitting one, which served no purpose whatsoever other than to reassure worried consumers.


These days fans are a necessary evil, more so now thanks to our unquenchable thirst for speed and power but it still seems slightly incongruous that for all of their technical sophistication, most desktop and laptop computers are wholly dependant upon crude mechanical fans to blow air around the case to stop the chips from cooking.


In fact totally silent, fanless PCs are available and it’s even possible to modify existing models with elaborate cooling systems but the vast majority of desktop PCs rely on a pair of cooling fans, one inside the power supply unit (PSU) and another sitting on top of the CPU chip. What’s more these fans are often cheaply made and prone to failure, in some cases lasting only a couple of years. Most PC cooling fans can be expected to fail after 4 or 5 years of continuous use but this didn’t used to be an issue. Most users tend to retire their computers before the fans give out, however, in these fiscally uncertain times many of us are delaying replacement and dead or dying fans can become a problem.


The first sign that a cooling fan is about to pop its clogs may be a change in the noise level. The bearings become noisy and emit a high-pitched whine or rattling sound, though it may die down once it has warmed up. Sometimes there’s no audible warning and if the CPU fan slows down or stops you may experience unexpected shutdowns, as thermal sensors inside the CPU and on the motherboard cut out to protect the microchips. When this happens Windows or the open program usually get the blame. The PC often restarts and operates normally, sometimes for several hours if the fan is only on a go-slow, which can make fault finding quite difficult; see also this week’s Top Tip.


Failure of the PSU fan is usually fairly easy to diagnose though, the deathly silence and the fact that the PC is completely inert is usually a good clue… PSU fans can be replaced but I really don’t recommend it unless you know what you are doing. Large capacitors inside the PSU case can retain a hefty charge for several days and give you a nasty jolt if your fingers stray into places they shouldn’t go.


Apart from anything else standard PC PSUs are not that expensive and you can expect to pay from around £15 upwards. They are not difficult to replace either. Most are held in place by only 4 screws and the size and case fitting is fairly standard. The only points to watch out for are the connector plugs and power rating. The latter will be clearly printed on the side of the PSU and is typically in 250 to 500 watt range. It doesn’t hurt to err on the side of caution and get a higher rated PSU than the one you are replacing.  The type of power connector depends on the motherboard and case form factor (usually ATX or Micro ATX); nowadays most PCs use a standard 20/24-pin plug and interchangeable IDE/SATA disc drive power connectors but if you are in any doubt don’t take any chances and seek expert help.


CPU cooling fans, coolers and heatsinks come in a bewildering array of shapes, styles and designs so it is important to get the right one for your machine. The key factors are CPU make and type, and the socket it uses. You should be able to find this information from your user manual and examples of PCs made within the past 5 years include Socket 423, 478 and 775 (or Socket T), which are mainly used by Intel chips. AMD processors use Socket 7, 939, 940 AM2 and AM2+ sockets. Cooling fan prices vary enormously but to give you an idea, a bog standard replacement fan for an Intel P4 processor (Socket 478) should cost you no more than £10 - £15, less if you buy online. Nevertheless, you can easily spend ten times as much if you want to install a fancy fanless, heatpipe or liquid-cooled system, but make sure it’s compatible with your CPU, motherboard and case as some of the more elaborate ones can be quite large and may require some plumbing skills to fit…


Replacing a CPU fan is the sort of job an averagely component DIYer can tackle, but be warned; there is the potential to wreak expensive damage. Most CPU cooling fans are help in place by spring clips or twist and lock screw fittings and they can be quite tight or fiendishly difficult to get at in the confines of the case. One slip of the screwdriver and you can wreck dozens of tiny and very delicate components mounted close to the CPU socket so again, seek ask an expert if you are in any doubt.


Next Week – Make-do and Mend. Part 6





Motherboard layout standard, defined by Intel, covering the physical size (305 x 244mm), position of sockets, expansion slots and mounting holes



Central Processor Unit - the main microprocessor chip in a PC



Advanced and space-saving cooling systems used on many recent PCs and laptops, employing gas or fluid filled pipes to transfer heat away from electronic components to fan-cooled radiators or finned heatsinks



Don’t wait for your cooling fans to fail. At the very least you could end up losing your work if the CPU overheats and the computer shuts down unexpectedly. At worst you could fry the motherboard and CPU. A small freeware utility called Motherboard Monitor ( will alert you if the fans fail or the CPU temperature rises above a preset limit, giving you time to save your work and shut down the PC before any damage occurs.


Don't forget, there's a full archive of previous Boot Camp Top Tips at



© R. Maybury 2008, 1211


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