ASUS g731 fan control not working

[asustuf]

Hello,
laptop: ASUS g731gw-ev212t
CPU fan is not faulty (works when connected to GPU fan header, or directly to PSU), but does not work when connected to CPU fan header. In BIOS there is no information about CPU fan RPM. Laptop works completely fine otherwise.

Voltages when laptop is running on the CPU fan header are constantly the following:
red wire: 10.15V
blue wire: 0.02V
black wire: 0V
yellow wire: 3.35V

on the GPU fan, which is working, voltages were at one moment the following:
red wire: 10.15V
blue wire: 0.95V
black: 0V
yellow: 1.69V

All fuses near CPU fan header are OK, nothing visually to see burnt or discoloured.

I would appreciate the idea how to debug the issue. I will ask for schematics in another forum section.

[asustuf]

Re: ASUS g731 fan control not working

read the forum rules, searched few topics and found a schematic here -> https://www.badcaps.net/forum/showth...highlight=G531

mainboards for G731 and G531 are the same

[ResoluteHawk]

Re: ASUS g731 fan control not working

Please reply to this post if you find a fix for this.

I have the exact same issue with a G14. I think the issue might be related to the EC/SIO FAN TACH pin but I'm not 100% sure.

[mon2]

Re: ASUS g731 fan control not working

Review this to see if it helps:

https://www.asus.com/support/FAQ/1034000

[asustuf]

Re: ASUS g731 fan control not working

I tried in armoury crate to change fan speed, but nothing happens. AI suite seems to be incompatible with laptops.

I checked schematic and see that pwm pin comes from IT8225VG-128/CX and will be short to ground if cap C5008 or C5013 (both 100PF/50V) are broken. Tacho feedback is dependent on C5007, C5012 and R5002, R5003 (pull-up resistors 10KOhm). No idea how to identify those, so will try to check all caps I see on the board.

[mon2]

Re: ASUS g731 fan control not working

Plan B is to create a simple circuit to mimic the PWM to drive this fan.

[asustuf]

Re: ASUS g731 fan control not working

How about connecting PWM from working fan header with thin wire/probes to the non-working fan header?

On the working fan header (GPU) I measured 3.3V on tacho pin (yellow wire) when fan is disconnected and then when it is connected and doesn't spin (stopped by hand) also 3.3V, but when spins around 1.7V. That also makes sense when checking the schematics.
However, when I spinned the fan on the non-working side (with help of electric screwdriver) tacho pin still was measuring 3.3V. Checked also with oscilloscope and there is no pulse. How does that make sense? VCC and GND are on the header. GPU fan also doesn't work on the CPU header, so it is definitely not the faulty fan.

[asustuf]

Re: ASUS g731 fan control not working

disconnected GPU fan just in case and shorted PWM from GPU header to CPU header -> CPU fan works. Therefore, problem is in PWM signal.
From the schematic I see two options:
1) C5008/5013 is shorted
2) IT8225VG-128/CX pin for CPU PWM is faulty

If someone has an idea where to find those caps please say so

edit: actually the board I have is G531GW rev 1.6 and there is a boardview https://www.badcaps.net/forum/showthread.php?p=1146196
edit2: C5008 is missing on my mainboard , so it is definitely not shorted. C5013 is for GPU fan
edit3: measured 315 ohm of resistance between CPU PWM pin and ground. Between GPU PWM pin and GND is open line. Any ideas?

[Sephir0th]

Re: ASUS g731 fan control not working

I have a similar board on my bench which repeatedly burned the EC via the FAN0_PWM line. I traced the issue back to the physical Fan connector, which has shorted +12VS to FAN0_PWM.

So visual inspection first!

[asustuf]

Re: ASUS g731 fan control not working

I checked again and there is no short between any of the pins. But there is only 315 ohm of resistance between CPU PWM pin and ground. Between GPU PWM pin and GND is open line. This is measured without fans connected, so the problem is related to the mainboard.

Because i found nothing else in the schematic, I am suspecting the IT8225VG-128/CX chip.

Visually I inspected the board with magnifying glass and did not find anything suspicious.

[ResoluteHawk]

Re: ASUS g731 fan control not working

I have a similar board on my bench which repeatedly burned the EC via the FAN0_PWM line. I traced the issue back to the physical Fan connector, which has shorted +12VS to FAN0_PWM.

So visual inspection first!

So I have this exact same issue on a G14 and I saw this post and went to measure those two lines. Straight short between both of them. Interesting.

About 10 minutes later I measured it again and there is no short. Back to the drawing board.

[asustuf]

Re: ASUS g731 fan control not working

I am thinking about buying a new IT8225VG-128/CX chip, but can't find any datasheet for it. Does it need to be flashed before soldering it to the mainboard? I assume no, but better safe than sorry.

[ResoluteHawk]

Re: ASUS g731 fan control not working

Typically, if an EC/SIO chip is BGA, it will receive its programming from the BIOS chip.

Just make sure that you order a blank chip.

[asustuf]

Re: ASUS g731 fan control not working

after I lifted the IT8225VG-128/CX chip, there was open line between ground and PWM (instead of 315 ohm as before), so it seems problem was the chip itself.
I soldered the new blank chip, balls on the sides look OK, nothing stupid happened (all small components are still on the mainboard), but now laptop doesn't turn on and also status LEDs are not working (not showing battery is charging etc.)

Is there any special procedure how blank chips get its programming from the BIOS chip?

[asustuf]

Re: ASUS g731 fan control not working

in this topic I found some information, but my laptop doesn't start.

https://www.badcaps.net/forum/showthread.php?t=98712

[paulfish]

have you found a solution? i have inserted my fan connector yo the header j5001 upside down by force. The cpu fan stopped working or recognised by the system, of course . however when i realised my mistake and flipped the connector which went in easily, the system do o not power on, no led nothing, no smoke no smell.. i checked the j5001 header, apparently i have shorted pwm with ground and my c5008 is missing too..

Now i removed the j5001 and cleaned, but i get a near short on pwm with 2.1 Ohms only, compared to the j5002 which is open infinite! now i assumed from boardview that c5008 was shirted, but it does not exist! so where is this pwm going to? what could have possibly happened?

p.s: power supply to battery is ok i get 15v on battery... but system completely dead no led.. I have also checked mofset no short.

[pc_okay]

Hello guys,

Same problem a few months ago one guy short the fan connector, and laptop won't start after that no led....

You just have to change IT8225VG-128.
First time it's does'nt work like asustuf just led no power on. (i thought i soldier it properly too.... but no)
Then i desoldier the chip, reball it, clean the board properly and resoldier the chip, after that laptop working fine!
No need to flash this chip, maybe try with another one.

https://www.badcaps.net/forum/troubl...on-gl504gs-2-1

Good luck.