My power supply fan starts to spin really really fast. I'm not sure why it does this. Most of the time, its running at normal speed. It only does it a few times a day randomly, and i dont think its because it is hot because it happens sometimes within the first few minutes after i just turn it on. Any help is appreciated. Thanks

It does no harm if it does spin faster, but are you sure it's the power supply fan? If your think you HEAR it spinning faster.... - CD/DVD drives can make noise while spinning if there is a CD in them, the led on the drive doesn't always come on when it does, and it can sound similar to fan noise. Windows will spin the CD/DVD drive if there is a CD in it while booting and shortly after, and at various times, and the led on the drive doesn't always come on when it does. ".....it happens sometimes within the first few minutes after i just turn it on." points to that source as likely. The solution to that is simple - remove your CD's when you aren't using them. - you may have other fans, such as case fans, that are temperture controlled, or that come on periodically.

I am sure it is the power supply because i am keeping it open these days so i can check it out when the fan starts spinning faster. I've inspected it closely when i hear the sound of a fan and i am sure it is the power supply fan. And although there is no harm if the fan is spinning faster, i am worried because i highly doubt it is supposed to spin faster for no reason, so there must be a reason as to why it is doing this. Maybe its in the early stages of malfunction? Perhaps someone knows something about this, maybe the sensor is messed up? Thanks for the suggestion though =)

If you have a motherboard with an Intel chipset, check for the latest BIOS upgrade. Search Engines Are Your Friends Morpheus: There is a difference between knowing the path and walking the path. "The Matrix"

Some power supplies have an external connection to the motherboard for the fan. If yours is that way you may have some control over it in cmos/bios setup. That connection may be for a sensor, which may be faulty as you mention, and not the sole source of power for the fan. In that case, if you disconnect it I think the fan will spin normally.

If you have a power supply that is supposed to regulate the fan speed according to the temp of the PS, it has a sensor and a circuit inside the PS that control that - that could be malfunctioning. Check the PS for evidence of excessive dust and lint - if you find that, blow it away, with something such as the exhausy from a vacuum cleaner it you can do that. That may allow the sensor and circuit to work normally again. Sometimes a better PS has a pair of small wires (or possibly 3 but I haven't seen that) that come out of the PS that can be connected to the 3 pin fan headers on the mboard, on a PS or System or Case fan header, to monitor the rpm of the fan in the PS. If it has only 2 wires, it can only provide the rpm reading to the mboard, it doesn't matter whether it is connected to the mboard or not because the power to the fan is provided inside the PS, and the mboard cannot control its speed. If it has three wires it is possible the mboard can control its speed if the bios has settings for that, but that's not likely, because it would have to be plugged into the mboard in order to work (I haven't seen 3 wire ones for that). Usually if it has external fan wires the PS has two fans - does yours? However, if the PS does NOT have a temperature controlled fan, the higher speed may be it's normal speed and the slower speed is the abnormal situation. It is very common for PS fans, especially if one or both bearings on it is a sleeve bearing rather than a ball bearing, to develop problems with their bearings over time, and for the fan to spin slower than it should off and on for a while, and then for the fan bearings to seize and the fan not spin at all, making the PS overheat and eventually fail. Try looking up your model of PS to see whether it has a temperature controlled fan. ...... "If you have a motherboard with an Intel chipset, check for the latest BIOS upgrade." That's probably completely uncalled for. If it has the external wires that can be connected to the mboard for a fan and that has only 2 wires, or if there is no external wires for a fan from the PS, there's no bloody way updating the bios would have any effect. Even if the PS has an external three wires to a fan connector that can go to the mboard, if there is nothing in bios about controlling fan speeds, there's no bloody way updating the bios would have any effect.

Fan automatically speeds up as temperature rises to maintain proper cooling temperature inside the power supply unit. When the temperature is lowered, fan automatically slows down to reduce wear and provide quieter operation. Thermal sensor built in the power supply.Just like a thermostat. Maybe you need to clean your computer inside including the power supply and the PSU fan won't constantly run so fast. Have you gave it a good cleaning lately? I still believe the fan speedup is a safe guard built into your power supply.