Need help to set PWM frequency to 25kHz on pin 8 of Arduino Mega to control speed of a 4-wire cpu fan

Question

This question is not same as the other one and this is more about employing the pwm signal to drive a CPU fan;

I am trying to follow the answer by Edgar Bonet on the question Need help to set PWM frequency to 25kHz and generate the same 25khz on pin 8 of arduino mega which is controlled by TIMER 4 and use this pwm signal to control the speed of a 4-wire cpu fan(with black, yellow, green and blue wires);

Following is my updated code for generating the pwm signal on timer 4

void analogWrite25k(int value)
{
    OCR4C = value;
}

void setup()
{    
    TCCR4A = 0;
    TCCR4B = 0;
    TCNT4  = 0;        
    TCCR4A = _BV(COM4C1)  // non-inverted PWM on ch. C
          | _BV(WGM41);  // mode 10: phase correct PWM, TOP = ICR4
    TCCR4B = _BV(WGM43)   
         | _BV(CS40);   // prescaler = 1
    ICR4   = 320;      // TOP = 320

    // Set the PWM pin as output.
    pinMode( 8, OUTPUT);
}

void loop()
{
    analogWrite25k(10);
    for (;;) ;  // infinite loop
}

I have connected pin 8 on the mega to the pwm input on the fan(blue wire) but I dont see any variation in fan speed and fan seems to run at full speed;

I dont really have any means or tools to verify if its really generating a 25khz pwm signal but fan speed is not changing or if its not generating a 25khz pwm signal because of which there is no change in the speed of fan;

I am stuck at this point and any help on this would he highly appreciated;

Answer 1

I've just tested your setting with older "Alpine 64 GT" CPU Fan and it works as expected. I've just added parsing integers sent from serial monitor, so I don't have to change code anymore.

void analogWrite25k(int value)
{
    OCR4C = value;
}

void setup()
{    
    TCCR4A = 0;
    TCCR4B = 0;
    TCNT4  = 0;

    // Mode 10: phase correct PWM with ICR4 as Top (= F_CPU/2/25000)
    // OC4C as Non-Inverted PWM output
    ICR4   = (F_CPU/25000)/2;
    OCR4C  = ICR4/2;                    // default: about 50:50
    TCCR4A = _BV(COM4C1) | _BV(WGM41);
    TCCR4B = _BV(WGM43) | _BV(CS40);

    Serial.begin(115200);

    // Set the PWM pin as output.
    pinMode( 8, OUTPUT);
}

void loop()
{
    int w = Serial.parseInt();
    if (w>0) {
      analogWrite25k(w);
      Serial.println(w);
    }
}