Help Asus X421EAYB Rev 2.0 PROCHOT# pulled to 0volts

[Carlos Simbaña]

Hello, I need help with this laptop, which powers on and shows video, but it’s extremely slow and the fan spins at maximum speed from the very first second.
When measuring PROCHOT#, it reads 0 volts, which limits the processor speed. I’ve been checking the charging circuit and everything seems to be fine. Additionally, I’ve already reprogrammed the main BIOS and the EC BIOS. If someone could give me a hand with whether I should replace the EC, or which signal I should measure to determine the fault, I would really appreciate it. Regards.

[mon2]

Which charger ic is onboard?

Be sure to use the official OEM power rated adapter.

Review each sensor that is most likely smbus (scl/sda) interfaced. If a sensor is missing, CPU speed will be throttled.

[Carlos Simbaña]

Which charger ic is onboard?

Be sure to use the official OEM power rated adapter.

Review each sensor that is most likely smbus (scl/sda) interfaced. If a sensor is missing, CPU speed will be throttled.

The charger IC is a BQ24780S

[mon2]

Remove all power. Meter in resistance mode. Measure the resistance between the srn and the srp pins.

What is the full path resistance?

[Carlos Simbaña]

The resistance between SRN and SRP is 20 ohms.
The impedance of SRN and SRP is around 1.6 megaohms

[mon2]

Path resistance matches the TI datasheet / reference design.

What is the voltage on ILIM pin?

[Carlos Simbaña]

Path resistance matches the TI datasheet / reference design.

What is the voltage on ILIM pin?

The voltage of the ILIM pin is 1.16v

[Carlos Simbaña]

Hello, I’ve made some additional measurements. The EC IT5125VG-128 BGA has pin B1 (PECI), and the voltage on this pin is 0 V. I also measured the VR_HOT# pin and it has 0.33 V. I lifted resistor PR8007, and on the VRM side I have 0.33 V, while on the side that goes to the CPU I get around 0.22 V.
I did the same with the PECI line, and on the EC side I have 0 V, while on the side that goes to the CPU I have 0.5 V.
Anyone of the rails have low resistance.
Maybe the CPU is bad? Any opinion?

[mon2]

The board is booting but is slow so do not believe it is a defective CPU. Only that this same signal is throttling the CPU speed to be dog slow. Can be linked to a dead battery - saw this case with a macbook earlier this week. Using a fresh battery pack and the speed is restored back to normal boot times. Or can be a missing sensor on the board which is resulting in the same condition.

[Carlos Simbaña]

The board is booting but is slow so do not believe it is a defective CPU. Only that this same signal is throttling the CPU speed to be dog slow. Can be linked to a dead battery - saw this case with a macbook earlier this week. Using a fresh battery pack and the speed is restored back to normal boot times. Or can be a missing sensor on the board which is resulting in the same condition.

The battery is indeed dead; I’m going to try with a new one and see what happens.