Laptop LCD becomes dim when plugged to power supply

[Guest]

The LCD of my Dell was broken and replaced in a local laptop repair shop. Now, when I plug my it to power supply, the LCD becomes dim. When use unplugged (on battery), the brightness become normal. I've checked in both modes (AC supply and battery), the brightness settings are at 100%.
What's going wrong and what should I do?

 

[r_manic]

Return it to the shop; obviously there's something the technician missed, and you shouldn't waste any time or money on something that should've been resolved.