Liquid spill results in extremely dim screen, how to fix?

Someone spilled tea on it and saw the screen short out. After using Windex to clean up the logic board almost everything works, memory, power, etc. except that the screen is so dim I need to use a flashlight to see it. Output to external monitor is just fine. Can this dim screen output be fixed?

Repair shop tried soldering something on the logic board they thought would affect screen brightness but to no avail. They said that the controller for screen brightness was not working, not sending the correct voltage out to make the screen brighter.

I can press every key on the keyboard and they all work, but the screen brightness keys (although showing the brightness icon and filling more bars as I press longer) do not affect screen brightness in any way. It is still dim. So close and yet so far-- what can I do to fix this?