Yoga Slim 7i Carbon 13 power on, no display

[tienlk19]

Hi,
I have this laptop that powers on, all signal LEDs ok, the battery charges,the keyboard light is on, and the fan spins but nothing shows on screen.
I measured the coil voltages and resistance, all seems good. The CPU coil is only 3ohm but this is an 11th gen CPU so I think it's ok. All voltages are present though +1.05VALW line fluctuates a bit from 1.02V to 1.06V.
The CPU gets hot pretty fast after power on (both the CPU and PCH), to the point that without the heatsink, the system turns itself off only after a few seconds.
I backup the BIOS, Clean ME, replace the bios region from extracted Lenovo website bios and reflash the new bios into the system but the screen is still black.
I also tried flashing the extracted Lenovo website bios since it's a full bios however the screen is still black.
One weird thing I notice is that the original bios don't seem to have any DMI info.
This laptop has dual bios chip,onboard RAM, with no discrete VGA. The Schematic is not available. Model: 13ITL5. Board number: NB2608_MB_V4_PCB. The original bios is attached below.
Can anyone suggest me what to do next? I'm stuck.

[SMDFlea]

Re: Yoga Slim 7i Carbon 13 power on, no display

Hi,
The original bios is attached below.
Can anyone suggest me what to do next? I'm stuck.

If you have a bios request please post in the bios requests section https://www.badcaps.net/forum/forumdisplay.php?f=40

By the way,the DMI in your merged bios is at 939000 - 93AFFF .Encrypted.Look for the word LENV

[tienlk19]

Re: Yoga Slim 7i Carbon 13 power on, no display

If you have a bios request please post in the bios requests section https://www.badcaps.net/forum/forumdisplay.php?f=40

By the way,the DMI in your merged bios is at 939000 - 93AFFF .Encrypted.Look for the word LENV

Thanks for your reply and the information about the DMI region.
I think the BIOS is fine. After uploading the Clean ME BIOS, I extracted that BIOS again and realized the BIOS is still in "Configured" state instead of "Initialized" using ME Analyzer.
Then I did some measures while the laptop was powering up. It turns out that the PCH coil voltage while powered on is not 1.05V but 8.7V (the VIN). I guess that explains why the laptop got so hot, the fluctuating S5 1.05V and the "Configured" BIOS .
At this point, I assume the PCH is already killed!
I just wonder why the normal 1.05V would jump to 8.7V after powering up.

[SMDFlea]

Re: Yoga Slim 7i Carbon 13 power on, no display

Yes it hasn`t fully posted if the bios is still in a configured state. It seems like a shorted high side mosfet killed the pch

[tienlk19]

Re: Yoga Slim 7i Carbon 13 power on, no display

Yes it hasn`t fully posted if the bios is still in a configured state. It seems like a shorted high side mosfet killed the pch

I agree partly. If it was always 8.7V, then most likely the high side Mosfet is shorted. However, what I don't understand is why it is only 8.7V after the laptop Power up. When the laptop is off, the PCH voltage is quite normal, fluctuating around 1.05V.

[mcplslg123]

Re: Yoga Slim 7i Carbon 13 power on, no display

Is 8.7v on both sides of the coil??

[tienlk19]

Re: Yoga Slim 7i Carbon 13 power on, no display

Yes, it is. 8.7V on both sides of the coil. And I did some measurements on both high and low side Mosfet in resistance and diode mode. Both seem fine.
Maybe it has something to do with how the driver IC adjusts the output voltage, I myself don't know about this.

[mcplslg123]

Re: Yoga Slim 7i Carbon 13 power on, no display

Whatever may be the reason, SOC is very likely damaged.