Lenovo X240 - motherboard replacement for X250, no image.

[andrhouseolly]

Friends. I beg you to help me in this situation.
Lenovo X240 with a video problem. Native Intel drivers are not installed,
after installation, a black screen. It works with the standard Microsoft driver.
Understanding that there are problems with the video core,
I ordered a motherboard from Lenovo X250.
The laptop turns on, starts up, there is no image on the internal display.
The image is output to the external monitor.
I ordered another motherboard from Lenovo X250.
The laptop turns on, starts up, there is no image on the internal display.
The image is output to the external monitor.
All motherboards are the same by marking VIUX1 NM-A091 Rev: 1.0,
they differ only in FRU.

On LCD CONNECTOR (J10):
VBL20 - 20v
VCC3P (VCC3LCD) -3.3v
PANEL_BKLT_CTR - N/A
BACKLIGHT_ON - N/A

Information from BIOS:

Native board:
Does not display matrix on external display when cable is connected
On Lenovo website: X240 Laptop (ThinkPad) - Type 20AL
Intel Corei5-4210U
UEFI BIOS Version: GIFT99W (2.49)
UEFI BIOS Date: 2020-03-17
Embedded Controller Version: GIHT33W (1.18)
ME Firmware Version: 9.5.65.3000
Machine Type Model: 20AL00ETGE
System Unit Serial Number: PC02XDDP
System Board Serial Number: L1HF4BV06KE
VIUX1 NM-A091 Rev:1.0
FRU: 00HM952
-------------------------------------------------------------------------------------------
First X250:
Outputs to external display when matrix cable is connected
On Lenovo website: X250 Laptop (ThinkPad) - Type 20CL
Intel Corei5-5300U
UEFI BIOS Version: N10ET54W (1.33)
UEFI BIOS Date: 2018-09-18
Embedded Controller Version: N10HT17W (1.16)
ME Firmware Version: 10.0.60.3000
Machine Type Model: 20CLS08G00
System Unit Serial Number: PC08ZQ2X
System Board Serial Number: L1HF5AZ079J
VIUX1 NM-A091 Rev:1.0
FRU: 00HT385
---------------------------------------------------------------------------------------------
Second X250:
Outputs to external display when matrix cable is connected
On Lenovo website: by Machine Type Model is not on Lenovo website
Intel Corei5-5300U
UEFI BIOS Version: N10ET57W (1.36)
UEFI BIOS Date: 2019-05-10
Embedded Controller Version: N10HT17W (1.16)
ME Firmware Version: 10.0.57.3000
Machine Type Model: 20OPTOORIT
System Unit Serial Number: 89043544
System Board Serial Number: L1HF63C031M
VIUX1 NM-A091 Rev:1.0
FRU:00HT381

Please tell me what the problem is.
Thank you.

[rogfanther]

First, have you tested this display panel in another ( working ) laptop ?

Then, do you have a cable for the x250 display ? Chances are good that the cables from the 240 & 250 are different. ( well, supposing your display is good ) .

[andrhouseolly]

This matrix is new, works (displays) with the original X240 motherboard (flex cable from X240).
I thought about the flex cable, but there is no flex cable for X250, besides, the schematic diagrams for X240 and X250 are the same (VIUX1 NM-A091 Rev:1.0 platform).
The LCD CONNECTOR connector (J10) has no modifications according to the schematic diagram. I checked the complete set (matrix flex cable) on the Lenovo website in the "Details" section
on X240 Laptop (ThinkPad) - Type 20AL (original board) and on X250 Laptop (ThinkPad) - Type 20CL (one of the purchased boards),
they have flex cables with the same Part Numbers "eDP, FHD, LUX - Part No 00HM135" in their factory configuration catalog.
Just in case, I connected the FHD matrix (original - HD), it did not help.
It is interesting that on the native X240 board the image is output to the matrix, but is not output to the external monitor,
until you disconnect the matrix, i.e. when the board does not see the matrix - it outputs to the external.
And in X250 boards, the image is output to the external immediately, even with the matrix connected, but is not output to the matrix.
It seems that these boards do not see the matrix. But I do not understand where the identification of the presence of the matrix is made.
I thought on pin18 J10 (EDP_HPD), but I do not see any signal on it (even on a working board).

[andrhouseolly]

The problem is solved by replacing the loop. The situation is very confusing due to the fact that with the old loop, the native board (X240) works and displays the image normally, and the two boards (X250) do not display anything on the matrix, although the platforms are identical (VIUX1 NM-A091 Rev:1.0). In addition, on the Lenovo website, in the catalog of factory components, absolutely identical cables (identical part numbers) are specified for all three laptops (by serial numbers). Thanks to rogfanther for the suggestion to replace the loop, I listened and got the right result.
Thank you all.

[rogfanther]

Nice, one more solved. Thanks for informing of the results.