Power on the CPU fan to spin and then turn off

When the facility on the mainboard is turned on, the fan spins just a few occasions after which turns off, or the CPU fan simply wobbles. These are the instances of touching the facility on the PC mainboard. To repair the issue of triggering the CPU fan to rotate after which flip off, you must comply with the next strategies.

1. Test 12v circuit for CPU

Utterly take away the 12V energy provide jack (4 pin or 8 pin) for the VRM circuit (CPU voltage circuit) and take a look at once more. If the fan is eliminated, the mainboard is being touched by the VRM circuit. Notice that some good sources like Acbel when the facility jack on the mainboard is shorted, then you must utterly take away the 20 pin jack and join the blue and black pins to discharge all the facility after which connect it to the jack to take impact (flip off the facility swap) ).

When eradicating the 4-pin jack of the 12v supply however the machine is regular, you proceed to measure the mosfet on the mainboard to see which one is shorted by. Use an analog clock to regulate the X1 scale and measure on the D – S pins of the mosfet with two measuring instructions (purple rod to D, black rod to S and vice versa, black rod to D, purple to S).

+ If each instructions, measure the resistance from just a few tens to a couple hundred ohms, that mosfet is regular.

+ Quite the opposite, each measurement instructions, or only one course with resistance as much as = 0 ohms, the mosfet has been shorted. You should change the equal mosfet taken from one other primary’s VRM  circuit.

After changing the mosfet, you must also verify if the 12v line for the oscillator circuit is shorted. Through the use of the meter to activate the X1 scale, the purple rod is about to mass, and the black rod is positioned on the  12v pin (the yellow wire has to undergo) of the 20 pin or 24 pin ATX energy jack.

+ If the clock needle solely strikes up a little bit => deduce regular impedance, not touched, quick.

+ If the clock needle is as much as the tip of the size and has an impedance of 0 ohms, the mainboard is shorting the 12V load line. This load line is often equipped to the oscilloscope IC, you need to attempt one other oscillator ic (70% in need of mosfet will kill the oscilloscope ic) the identical or equal. To switch the equal IC, please check with: IC  pinout.

Most CPU fan energy sources rotate after which flip off attributable to quick circuit of CPU voltage regulator. You may measure if there’s a quick by testing by eradicating the 12v jack as above or measuring the 12v impedance equipped to the VRM circuit by utilizing an X1 scale meter, the purple rod is positioned on mass, the black rod is positioned on the 12v pin of jack 4. battery or 8 battery. If the meter has an impedance of 0 ohms, it’s quick, in any other case it’s regular. When eradicating the 12v jack, the supply doesn’t rotate, then we measure the road impedance of 5v and three.3v.

2. Test circuit 3.3v and 5V provide for IC

ATX energy orange connector  = 3.3 V
Yellow connector ATX energy = 5 V

Measure the three.3v and 5v masses by adjusting the meter to the X1 scale, hugging the purple rod to put the mass, the black rod to enter the orange leg (3.3V) then the yellow leg (5v).

+ If the meter solely strikes up a bit, about 500 – 1k ohms, the impedance is regular.

+ If the clock reaches the tip of the needle or is near 0 ohms, the circuit load is shorted.

Shorting 3.3 V, one of many following elements is shorted: IC SIO, male chip, ROM BIOS, IC clock gen, IC LAN onboard.
If you happen to quick circuit 5 V, one of many following elements is shorted:  IC SIO, male chip, ROM BIOS.

Often quick on this load line, most of them have quick circuit of male chip, quick circuit of chipset voltage stabilizer, useless SIO ic, in need of LAN IC. To repair the 3v5 and 5v load quick, you plug within the energy for a second and contact the SIO chip, male chip and onboard LAN to see which one is sizzling, if it is sizzling, 90% of it would die. If there’s a present meter (used to restore the cellphone) then we are able to decide which IC is brief by.

Cut back the voltage of the meter to 0v, put the black rod to floor, the purple rod to the shorted line (3.3x or 5v line). Then modify the voltage steadily till the present reaches 0.8A. Let the present move by way of the mainboard for about 1 minute and contact the above elements. If the kid is sizzling, the kid is shorted, proceed to interchange the opposite one.