One more thing - I attached logic analyzer to PS_ID_R pin of DC1 connector and to PSID_EC line and in both cases all I got was 10 reset signals:
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I tried two different power...

Hi,
PR4205 looks fine (33Ω, 3.31V on both sides), but PR4206 seems to be missing
PQ4201 voltages:
1 (PS_ID_R2) - 3.31V
2 (PSID_DISABLE#_R_C) - 5.15V
3 (PSID) - 3.31V
no significant changes after pressing power button

Regards,
Miłosz

Small update - I did some more software-side testing. I started with bios update, but it didn't change anything. But I also noticed that power supply is detected as 0W power, which cause system to run very very slow. I tried another power supply (both genuine), but issue peristed. Also for unknown reason internal display disappears when Windows starts, there is no way to switch to internal display, I can only use external monitor via HDMI. So internal display works fine in BIOS, but in Windows it's unavailable. I did drivers update with dell tool, but still only external display is visible....

Hi,
So it looks like that jumper (R5222) is missing:

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I traced R5222 pads and it looks like pins are swapped, so it should be like this:

D5202
1 (BKLT_CTRL)...

Hello,
Thank you for your answer

Here are measurements:

D5202
1 (BKLT_CTRL) - 3.17V
2 (eDP_BKLT_CTRL) - 0V
3 (EC_BRIGHTNESS) - 3.37V

D5201
1 (LCDVDD_EN) - 3.2V
2 (EDP_VDD_EN) - 3.37V
3 (LCD_TST_EN) - 0.00V

U5201
1 (EN/LCDVDD_EN) - 3.2V
2 (GND) - 0.00V
3 (VOUT/LCDVDD) - 3.36V
4 (VIN#4) - 3.37V
5 (VIN#5) - 3.37V

LCD connector:
PIN 20 - 3.17V
PIN 21 - 0.00V​

I'm not sure if I mapped correctly pins of D5202/D5201, I assumed that physical...

Hi,
I'm trying to fix friend's Dell, it had liquid damage in the past, but as far as I know it was fixed in professional service. It was working fine for quite some time, except for dead battery, but recently there was blackout in the building and after power was restored, laptop was broken. When I got it, it was posting, but OS didn't boot, also backlight was gone. After some tinkering I switched off secureboot and it started booting normally, but backlight issue persisted. I opened it up and started looking for issues. Checked both fuses on display and all fuses on motherboard which I...