MacBook Pro 2020 A2251 (820-01949) No Backlight

[pcmacdoctors]

Hello, I have an A2251 MacBook Pro logic board (820-01949) with an unknown history and no signs of liquid damage. I'm trying to make use of it. The computer boots up and works normally, except there is no backlight on the screen and the camera is not working. An external display works fine.

I swapped the display and display cable with known working ones, but there was no change.

Upon inspecting the board, I found that L8504 was blown. I replaced it and the adjacent components (C8504, CC727). Now the camera works. I also replaced C8440 near U8400, as it looked like it might have been knocked. It seems okay, with a reading of ~5V from pin 1.

While the camera now works, the backlight is still not functioning. There is no short to ground on PPVOUT_LCDBKLT. All those capacitors look fine, they are not getting hot, but no voltage seems to be going through them either. The F8400 fuse works, with a continuity test showing a voltage reading of ~12.6V on both sides, which I believe is correct.
no voltage on either side of L8410 and I've replaced that also.

I can't detect any short to ground on the EDP lines of the display connector.

R8442 has no voltage on pin 1 or 2. According to Repair.wiki, this suggests a problem with U8400 and/or the CPU.

I swapped over U8400 also and still doesn't work.
I found that really tough to do and although it looks pretty good I might have failed to swap it properly.

I suspect it's U8400 as the computer works fine otherwise. Is there anything else I should try?

Thanks

[mon2]

Do you see graphics on the LCD display? Test with a phone torch from the front of the LCD.

Measure the voltage to ground of IPD_LID_OPEN.

[pcmacdoctors]

Hah I should have checked that. It actually doesn't look like it does, I cant see Apple logo under the torch.
IPD_LID_OPEN reads as 1.79v.