HP 240 G3 turns on for 5 seconds then off. No boot, no display

[anandvsalunke]

Hi everybody,

Motherboard ZSO40 LA-A995P came in with short circuit KB9012QF A4. A magic smoke has escaped this chip..

Removed KB chip and checked the LDO 3.3V output from RT8243 was OK. Then replaced with new KB chip and programmed the EC BIOS. Now, upon power button press, we get 5Valw and 3Valw, but only for fee seconds and then it power off. Isn't the ALW voltage supposed to be present even before pressing the power button?

To diagnose further, we find no voltage at pin 8 of BIOS IC, which is powered from 1.8VALW. This is derived from an LDO, which is enabled using SPOk from RT8243 pin PGOOD. We find that the SPOK line is pulled low during powerup and remains low.

Upon reading the datasheet of RT8243, it is understood that the PGOOD is open drain output, which is pulled low in case of faults like over/under volts, current. Since the power rails are not shut down by RT8243, it is suspect that SPOk is pulled low by other chip.

Quickly the suspect is new KB chip, where the SPOk is connected to pin 72 of KB chip. Lifting pin 72 of KB now releases SPOk and now we also see 1.8VALW and 1.0VALW. bit still no power up. This confirms the suspision.

[ Post made via Android ]

[anandvsalunke]

Problem is identified. The SPOK signal is input to pin 72 of KB chip. Reading the data sheet of KB9012, it appears that this pin can be configured as either output of DAC or General purpose IO pin. Since, KB is pulling down this pin, its a suspect that the pin configuration is not correctly done immediately after reset.

Since the KB chip is a microcontroller, the pin config is done through the firmware. At this point, it was obvious that the firmware uploaded was not correct. So, we got firmware from another website and flashed it. And voilla..it works. Problem solved.

[ Post made via Android ]

[PINTUSINGH]

thanks for sharing this.

[anandvsalunke]

Attached is the EC Bios that is working

[ganeshcell]

thanks for sharing this wonderfull info