CPU fan

By gulabg
Dec 27, 2009
  1. My CPU fan is not working. Also my e-machines computer does not boot and
    display does not show on the monitor. I checked the electrical input to the fan.
    It is getting 5v. Does the fan not coming on affect the boot up?

    Best regards,
  2. Ritwik7

    Ritwik7 TechSpot Chancellor Posts: 1,672   +9

    It shouldn't affect boot up as such but usually should give an error message. Have you tried replacing the CPU fan?
  3. red1776

    red1776 Omnipotent Ruler of the Universe Posts: 5,219   +157

    with most machines, i think almost all. during POST the system will check for a functioning cpu fan. if it does not find one it will not allow the machine to boot. this is one of the reasons that the cpu fan is connected to the motherboard directly. 1) for the RPM control as it senses the current temperature and 2) to make sure the cpu cooling is functioning correctly to prevent thermal damage.
  4. captaincranky

    captaincranky TechSpot Addict Posts: 11,462   +1,760

    First, all CPU and case fans are designed to run on the 12V tap of the PSU. So, if it's only being delivered 5 volts then you could have a bad PSU. some fans will run at 5V, some may not

    Generally, the CPU fan voltage is variable and set by the computer's BIOS so as not run excessively fast (loud) when it isn't needed. This matches the cooling potential to the task or tasks being performed.

    Take the fan out of the computer and try testing it with a 12V source. Believe it or not, and although it seems like overkill, a car battery is a competent 12v source. (red wire = positive, black = negative, ignore the yellow and blue wires (if present)).

    Depending on the age and model of your particular Emachine, more likely causes of boot (or "POST" failure, which is actually closer to what you're describing), could be a bad PSU or a bad motherboard, the fan not running being more of a symptom than a root cause. (as Ritwik has stated).

    The best approach here is, after testing the fan, is to sub the PSU with a known good one to see what happens.
  5. gulabg

    gulabg TS Enthusiast Topic Starter Posts: 49

    Many thanks.

    It appears that PSU is not operating properly.

    The computer is fairly old, so I will try and get one on ebay. I hope that will help.

    Best regards,
  6. captaincranky

    captaincranky TechSpot Addict Posts: 11,462   +1,760

    Wait, Not so Fast.......

    I recommend purchasing a decent, quality, PSU such as Antec, Corsair, OCZ, or a couple other brands. Just because the computer is old, that's not really a good reason to risk destroying it with a "Saturday Night Special" of a unit from Ebay. The bottom line is that with a quality unit, even if your computer should give up the ghost, it never hurts to have a PSU as a backup. The PSU is probably the number one part failure in a PC. Followed by optical drives and memory.
  7. gulabg

    gulabg TS Enthusiast Topic Starter Posts: 49

    I noticed that CPU fan has 3 wires, Yellow, black and red. Do they carry different
    voltages? If so, any reason for that?
    Also for drives, there are 4 wires, yellow, 2 black and red. Are they for different
    voltages? Do different drives need different voltages?

    I will appreciate the information. Incidently the CPU fan is working. The 20 pin
    connector was not seated properly.

    Many thanks.
    Best regards,
  8. captaincranky

    captaincranky TechSpot Addict Posts: 11,462   +1,760

    Yes, The wires are as follows;

    Red; 12 volts +

    Black Ground

    Yellow; Tachometer

    Blue (if present) PWM (pulse width modulation) control wire.

    Note; Older BIOS(s) control the speed of the CPU fan (or don't) by varying the voltage delivered to the fan.

    Newer BIOS (Intel especially) control the fan by the duration of time that full voltage is applied to the fan motor. Hence "pulse width". It's simply a full voltage, time on, time off strategy.

    Three wire fans will work on 4 wire PWM motherboards, and accurately report fan RPMs, but, to actually vary the fan's speed, a fan controller must be in the fan circuit.

    In 4 wire "Molex" type connectors, the Red wire is 5 volts +, the Yellow wire is 12 volts +, and the 2 black wires are a ground for each voltage.

    No, generally speaking, different drives don't need DIFFERENT voltages, they need BOTH voltages, for different purposes.

    Oh, we're glad you're up and running, and you're quite welcome.
  9. Technochicken

    Technochicken TechSpot Paladin Posts: 729

  10. captaincranky

    captaincranky TechSpot Addict Posts: 11,462   +1,760

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