Top of the screen is much darker than rest

I am in the process of repairing a Samsung ln40b530p7n with similar issues as you are experiencing. After testing voltages with a multimeter I found the gamma IC on the t-con board has incorrect voltage readings in a few areas. On the board I'm repairing there are 22 test points on the t-con board to check the gamma IC voltages. They are labeled on the t-con board as VGMA1-VGMA22. When checking the voltages they should decrease in voltage in one direction. So for example:

VGMA1: 15.23v

VGMA2: 14.97v

VGMA3: 14.83v

VGMA4: 12.61v

VGMA5: 11.77v

VGMA6: 10.79v

VGMA7: 10.06v

VGMA8: 9.72v

VGMA9: 8.38v

VGMA10: 8.23v

VGMA11: 7.78v

VGMA12: 6.99v

VGMA13: 6.79v

VGMA14: 6.60v

VGMA15: 5.25v

VGMA16: 4.82v

VGMA17: 4.60v

VGMA18: 3.59v

VGMA19: 2.65v

VGMA20: 0.65v

VGMA21: 0.51v

VGMA22: 0.29v

I found the voltages for VGMA14 @ 7.37v, VGMA15 @ 12.45v, and VGMA16 @ 9.92v. So the increase in voltages there signal a failing gamma ic. The gamma IC is a AS15 F on the t-con board I'm repairing. I believe your t-con board also has an AS15 gamma IC. It seems that these ICs are known to fail. So if you or someone you know can check the voltages in the area I have mentioned with a multimeter than you may be able to determine if the gamma IC is indeed the issue. If so you can find a replacement t-con board or for a harder but far cheaper repair you can just replace the bad IC. I recommend www.shopjimmy.com for TV replacement parts. Hope this is helpful and let me know if you have any questions.