Asus X512D (Mobo: X512DK Rev.2.1) - Laptop Does Not Start

Hello Everyone,
I am looking for fault confirmation before I will order new component.
Laptop does not start due to the problem with KBC, I think.
On pin 11 (IT8225E-128) should be voltage of 3.3V (VCC) but I measure 2,7V only.
When I measure resistance on pin 11 to ground it looks OK to me (40kΩ).
Has anyone come across the same problem please and can confirm KBC problem ?
Thanking you in advance.
Regards,
Rafal S.

RafiManch napisał(a):I am looking for fault confirmation (...) problem with KBC

Cannot confirm KBC fault. The voltage on pin 11 is most likely taken from the MOSFET switch (+3VA => +3VS), which is driven by a higher voltage (12-15V). If this voltage is incorrect or, the MOSFET is faulty, the output +3VS voltage may be lower than normal or not present at all. First you have to locate all the components that pin 11 of KBC is connected to (especially search for 8-pin and 6-pin MOSFETs). Then please measure the voltages to ground on all pins of those components.

Hello Vogelek23,
Thank you for your reply and help. I can't find board view anywhere so your help is much appreciated. I have found MOSFET as advised:

Low voltage 4.65V on the gate must the reason of 3.3V being pulled to 2.7V.
I have removed MOSFET and has tested good. I have re-measured gate when is removed and voltage was 4.5V. As you have said voltage should be around 13V.
I know I have to find power IC supplying 4.5V instead of 13V.
From your experience should I expect one close to MOSFET or could be anywhere on motherboard ?
Thank you.
Regards,
Rafal

Please, post a clear picture of marked area of the board.

Hello Matic,
Please see attached photo.

Thank you.
Regards,
Rafal

Measure the resistances and voltages to ground on pins 1, 2, 5 of marked component.

Hi Matic,
I have measured required values:
PIN 1 - 4.6kΩ and 5V
PIN 2 - 4.6kΩ and 5V
PIN 5 - 4.8kΩ and 4.96V
I can't find any datasheet for this IC.
Do you think this one is faulty and is not producing required 13V ?
Thank you.
Regards,
Rafal

- Measure the resistance between pin 1 and pin 2 of this component.

RafiManch napisał(a):I can't find any datasheet for this IC.

It's a diode BAT54BRW.

RafiManch napisał(a):Do you think this one is faulty and is not producing required 13V ?

We don't know that yet.

Hi Matic,
Resistance between pin 1 and pin 2 is 30Ω.

Should I expect value of few MΩ's when pins are not making any connection inside of diode ?
Thank you.

RafiManch napisał(a):Resistance between pin 1 and pin 2 is 30Ω.

If I'm not mistaken, this resistance should be in kΩ range or greater.

RafiManch napisał(a):Should I expect value of few MΩ's when pins are not making any connection inside of diode ?

If I determined the circuit correctly, the pin 1 and pin 4 of this diode are connected together on the board, so there is actually connection inside the diode, but the resistance should still be high.

Remove this diode from the board and remeasure the resistance between pad 1 and pad 2 on the place of this diode. If the resistance will be high (in kΩ or greater), the diode is damaged and needs to be replaced.

Thank you for your continuous help.
After removing diode I measure 1.5MΩ between pin 1 and pin 2.
I will order new diode.
Thank you again.