w550s/t550 LCD screen replacement - brightness set at max.

Hello,
I replaced the horrible TN panel of the w550s (1080p) with a compatible model (lp156wf4) and now the brightness is stuck on max with no control over brightness levels (fn keys do not work for brightness). Updated video drivers... Anyone know what could be the issue? Thinkpad LCD monitor driver and generic PNP monitor driver do not help fix.

Any help would be great. Thanks!