X390 possible WQHD display upgrade?

[DrathVader]

I've been a ThinkPad owner since the X220 era but this is my first post here, so hello everyone.

Has anyone tried hacking the X390 with a higher res screen? These never came with anything higher than 1080p from Lenovo, but the motherboard is the exact same as T490s, which did have a QHD option. Checking the motherboard visually I can see four pairs of traces coming to the LCD connector, indicating that there are indeed 4 DP lanes wired up. There's also 4 lanes shown in the schematic.
That means that - in theory - you could connect a 40-pin cable from a QHD T490s to an X390 motherboard and that should make it possible to use QHD (and beyond, maybe even 4K?) displays in the X390.

Has anyone tried that yet? I'm seriously tempted to do it. Would be nice to run Linux without scaling issues.

[TPFanatic]

Both laptops (T490s, X390) use the same BIOS as well. I think this could work.

[DrathVader]

Even the FRU is the same for X390 and T490s motherboards, so it has to be physically the same part. I really see no reason this wouldn't work, other than maybe slightly different cable length, but it anything it should be longer on the T490s so it shouldn't be an issue.

I'll order the LCD flex and see if I can procure a cheap QHD panel for testing. I'll update the thread once they arrive.

UPDATE 1:
First lesson learned is to be careful with cheap aliexpress LCD cables. The one I ordered plugged in fine, but it was wired completely back to front, ie. pin 1 was wired to pin 40 and pin 40 to 1.
The result was a short to ground in the backlight circuit and a blown fuse - I had no image even with original display + cable. The fuse in question is F5102, located on the bottom side of the motherboard, near the SIM/uSD card slot. After replacing it I got an image again.

My test QHD display should still be good. I'll source another T490s WQHD cable and update the post again.

UPDATE 2:
I got the cable and can confirm X390 does indeed work with QHD displays and there's no reason to assume it wouldn't work with 4K as well. The problem I found is tracing a display that would actually fit.
The display in my (touchscreen) unit is 300mm wide, most of the QHD displays I find are wider and won't fit without cutting into the cover. Maybe non-touch covers are more roomy. For now I've put the experiment on hold until I can figure out how to actually mount the new screen.