Lenovo Yoga C940-15IRH No primary Screen

[Noursa]

Hello

I'am a beginner in electronics repair and i got some trouble to find what's goning on a computer. It is a lenovo yoga C940-15IRH laptop and the screen doesn't work anymore, but that work on an external one

the screen seams to be hard to unbuild properly so i want to test it by other way

how can i be sure if the signal is really send to the screen ? i did some check on screen connector on LCD1 got 19v and on MiC1 connector on the other side of the screen (dunno if it's for the screen itself or other thing) got a lot of 3.2v pin

did u got some technics to know if the screen is going well or not ?

Thanx you for reading

ps: excuse my english level

[mcplslg123]

Link schematic, if available . Voltage needs to be probed on edp connector. Look for BKOFF#/LCDVDD/BKL_EN etc.

[Noursa]

hello thx for answer i found one schematics here seams to be the good one
https://www.badcaps.net/forum/troubl...-lc40-18837-sc

i flash the bios with a good version i found

after more test i can say few thing

on eDP_VDD_EN_D on U5501 i got nothing where it's seams to be 3.3v normally

so i got nothing on pin 26 27 for BL_EN LCD_BRIGHTNESS ON LCD1 connector

i got nothing too on pin 30 31 32 for 3D3V_LCDVDD_S0 ON LCD1 connector

i got 3.2 v on pin 15 for eDP_AUX_CPU_N ON LCD1 connector

i got nothing too on PCH1C eDP_VDD_EN maybe the chipset if i understand correctly

it's all i found for the moment thx for help

[Noursa]

Anyone having any idea to check ?

[mon2]

Measure the voltage to ground of LID_CLOSE#.

Repeat with the lid being OPEN and then CLOSED.

[Noursa]

thx for helping

with MB inside the laptop on lid close on tpad1 got 3.2 onlid open and 0v on lid close on pin 1 (i can't find the R6509 on the MB)
With MB oustide the laptop on Rn 2403 got the 3.3 S5 on pin 1 and 2 on pin 3 KBC_NOVO_BTN# got 3.2v and 0v on pin 4 LID_CLOSE#
i cant' find the HALL1 the hall sensor anywhere on MB or other part of the laptop as well as R6701 and C6701 that make me crazy

If i understand correctly that's mean the captor works and cut the signal for TP when laptop is closed

Thx again i wait for next test

[Noursa]

Even if we can't fix it i learn a lot so thx for helping

[reformatt]

Check eDP_VDD_EN when the laptop is first powered on. If there is no communications from the LCD then this line will briefly go high, then low. If no screen is detected, then you won't see backlight enabled etc at all. Most likely you have a faulty screen or cable.

[Noursa]

HEllo thx for helping

so on eDP_VDD_EN_D pin 4 on U5501 got 3.15v like one second thern back to zero

if i understnad what you said this signal didn't detect the screen then shut down the backlight

so it seams that my screen is dead ?

i do some test with other screen (just the same connector not the same model) but that dosen't work (normally that work's when i do that on other laptop but this one seams to be a bit particular

So do you think i have to order a new screen ? everything seams to be fine on the mainboard ?

thx a lot for explaination