CPU Cooling Fan Replacement

CPU Cooling Fan

A replacement fan is often required when the existing one starts making excessive noises. As the bearings wear out it will make so much noise that, it might become impossible to work with. Sometimes the fan stops working altogether and will not spin at all.

Manufacturers often provide a small aluminium heatsink, because they are expensive to manufacture, and compensate for its lower heat drawing capacity by using a high-speed fan. These fans can be very noisy sometimes due to the high speed.

Obviously, it would be nicer if manufacturers provided a larger heatsink, with a slower quieter fan. However, you get what you pay for. If you have a noisy fan that is driving you mad then the best option is to replace it with a quieter one.

Unfortunately, with an old computer it is sometimes not cost-effective to take it to a computer repair shop. I sometimes come across old machines such as the Dell Inspiron 1545 that require a replacement fan.

I had an old machine with a noisy fan that sounded like a jet engine! It had a stock fan and heatsink that came fitted to a Socket-A motherboard.


Dimensions60 mm × 60 mm × 10 mm
Voltage12 V
Speed4800 rpm
Air Flow22.21 cfm
Current0.17 A
Noise Level30 dBA
BearingBall
ConnectorTX3, 3 pin Molex
Reliability50,666 hours

Fitting A Replacement Fan

Fitting the fan to the motherboard - Socket A.

As you can see there is not much to changing the Socket-A motherboard fan. Typically, the microprocessor fits into a Zero Insertion Force (ZIF) Socket. There is a lever on the socket for locking the pins.

First, install the microprocessor chip. The metal heat sink assembly typically clips onto the plastic tabs on the top and bottom sides of the ZIF socket. The CPU cooling fan fits on top of the meal heatsink held in place by four self-tapered screws.

Tachometer Compatibility Issues

Sometimes there is a compatibility issue concerning the tachometer signal. There are two main standards currently in use, and you can tell if the fan provides a tachometer signal by the number of wires on the socket. Three wires usually indicate the presence of a tachometer signal.

If the tachometer signal is not compatible, it may result in the motherboard receiving incorrect rpm signals. As a safety measure, to protect the processor from over-heating, the self-test checks the operation of the fan, and a warning occurs during boot accompanied with a by-pass option.

I was able to take apart the noisy fan to determine the tachometer signal standard, and its electronic interfacing requirements. This information is in the CPU Cooling Fan Tachometer Standards article.

Many fans follow the same three-wire colour scheme. The red wire tends to be +12 V, black 0 V, and yellow the tachometer signal. The positioning of the pins has not been standardised, hence one must make sure they are correct for the motherboard.

It is generally better to test the fan by powering it with an external power supply, just in case the manufacturer used a non-standard colour scheme. A digital meter could also identify the +12 V and 0 V pins on the motherboard.

Cheap Replacement Fan

Many repair shops sell cooling fans, and the price can range from as little as £1.07 to over £100. Therefore, it is worth shopping around to see what one can find. I often use the Cooler Master Fan, or Arctic CPU Cooling Fan and Heatsink Kit as a replacement, however this time I decided to experiment with changing the fan alone.

Electronics stores also sell cooling fans; therefore, it is worth seeing if they have the size of fan that you require. The airflow direction is such that it sucks air away from the heatsink and blows it outward. Hence, providing you fit it the right way round it has a chance of working!

I managed to find the cheapest 60 mm fan that would fit in place of the original one. It was from an eBay seller in China. It cost £1.07 including postage, and I bought it for experimental purposes.

Dimensions60 mm × 60 mm × 10 mm
Voltage12 V
Speed3000 rpm
Air Flow17.3 cfm
Current0.04 A / 0.48 W
Noise Level17.3 dBA
BearingBall
ConnectorTX3, 3 pin Molex
Reliability50,666 hours

The 3-pin connector was identical to the original fan with the same colours and wiring sequence, hence it plugged into the motherboard straight away.

Comparing the above specification with that of the original fan, one can see that the noise level in dB is significantly less. However, the speed in rpm is also much less. These types of fans are for the PC case. However, this was an experiment and I just wanted to see if it was possible to make my old PC quieter on a shoestring budget.

Benchmark Study of Temperature

Baseline study using BIOS parameters.

I decided to perform a baseline study of the original fan. The idea was to compare the figures obtained with the new cheap fan.

Modern motherboards provide all sorts of information regarding their operation and health status. The BIOS will provide you with real-time values of the voltages, fan rpm, and even the CPU core temperature.

The two main parameters of interest are CPU Temperature and Fan Speed. I decided to record these values, so that I could compare them with new values when the fan was changed.

Since the new fan had a lower rpm, it was obvious that it would not be as effective as the old one. However, providing it maintained the temperature within normal operating parameters, it should work.

A 1.6 GHz AMD Duron stabilises to 44 °C / 111 °F with the original stock cooling fan. With the new fan, that was slower, and but considerably less noisy, it stabilised to 48 °C. Result! I decided to use that instead.


Changing the Thermal Compound

Since the new fan was keeping the CPU core temperature 4 °C above that of the original fan, I decided to see if I could claw back some of that lost performance, by improving the heatsink compound.

The original compound was an excessively large blob that had dried up and probably now acting as an insulator!

I had some Thermal Gold compound, normally used by overclockers. I removed the dried-up compound and applied a very fine, thin layer of thermal gold. With this new compound, I found that the core temperature was remaining steady at 46 °C, which was an improvement by 2 °C.

So far, it has been working fine and I have not had any problems with it since last year.